Engine Operation and Malfunctions

7/27/2019 Engine Operation and Malfunctions

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Airplane Turbofan Engine Operation and MalfunctionsBasic Familiarization for Flight Crews

Chapter 1

General Principles

Introduction

Today's modern airplanes are powered by turbofan engines. These engines arequite reliable, providing years of trouble-free service. However, because of therarity of turbofan engine malfunctions,and the limitations of simulating thosemalfunctions, many flight crews havefelt unprepared to diagnose enginemalfunctions that have occurred.

The purpose of this text is to providestraightforward material to give flightcrews the basics of airplane engineoperational theory. This text will also

provide pertinent information aboutmalfunctions that may be encounteredduring the operation of turbofan-

powered airplanes, especially thosemalfunctions that cannot be simulatedwell and may thus cause confusion.

While simulators have greatly improved pilot training, many may not have been programmed to simulate the actual noise,vibration and aerodynamic forces thatcertain malfunctions cause. In addition,it appears that the greater the sensations,the greater the startle factor, along with

greater likelihood the flight crew will tryto diagnose the problem immediatelyinstead of flying the airplane.

It is not the purpose of this text tosupersede or replace more detailedinstructional texts or to suggest limiting

the flight crew's understanding andworking knowledge of airplane turbineengine operation and malfunctions to thetopics and depth covered here. Uponcompleting this material, flight crewsshould understand that some enginemalfunctions can feel and sound moresevere than anything they have ever experienced; however, the airplane isstill flyable, and the first priority of theflight crew should remain "fly theairplane."

Propulsion

Fig 1 showing balloon with no escape path for the air inside. All forces are balanced.

Propulsion is the net force that resultsfrom unequal pressures. Gas (air) under pressure in a sealed container exertsequal pressure on all surfaces of thecontainer; therefore, all the forces are

balanced and there are no forces to makethe container move.


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Fig 2 showing balloon with released stem. Arrow showing forward force has no opposing arrow.

If there is a hole in the container, gas(air) cannot push against that hole andthus the gas escapes. While the air isescaping and there is still pressure insidethe container, the side of the container

opposite the hole has pressure against it.Therefore, the net pressures are not

balanced and there is a net forceavailable to move the container. Thisforce is called thrust.

The simplest example of the propulsion principle is an inflated balloon(container) where the stem is not closedoff. The pressure of the air inside the

balloon exerts forces everywhere inside

the balloon. For every force, there is anopposite force, on the other side of the

balloon, except on the surface of the balloon opposite the stem. This surfacehas no opposing force since air isescaping out the stem. This results in anet force that propels the balloon awayfrom the stem. The balloon is propelled

by the air pushing on the FRONT of the balloon.

The simplest propulsion engine

The simplest propulsion engine would be a container of air (gas) under pressurethat is open at one end. A divingSCUBA tank would be such an engine if it fell and the valve was knocked off thetop. The practical problem with such an

engine is that, as the air escapes out theopen end, the pressure inside thecontainer would rapidly drop. Thisengine would deliver propulsion for onlya limited time.

The turbine engine

A turbine engine is a container with ahole in the back end (tailpipe or nozzle)to let air inside the container escape, andthus provide propulsion. Inside thecontainer is turbomachinery to keep thecontainer full of air under constant

pressure.

Fig 3 showing our balloon with machinery in front to keep it full as air escapes out the back for continuous thrust.

Fig 4 showing turbine engine as a cylinder of turbomachinery with unbalanced forces pushing

forward.

Components of a turbine engine

The turbomachinery in the engine usesenergy stored chemically as fuel. The

basic principle of the airplane turbineengine is identical to any and all enginesthat extract energy from chemical fuel.


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The basic 4 steps for any internalcombustion engine are:

1) Intake of air (and possibly fuel).2) Compression of the air (and possiblyfuel).

3) Combustion, where fuel is injected (if it was not drawn in with the intake air)and burned to convert the stored energy.4) Expansion and exhaust, where theconverted energy is put to use.

These principles are exactly the sameones that make a lawn mower or automobile engine go.

In the case of a piston engine such as the

engine in a car or lawn mower, theintake, compression, combustion, andexhaust steps occur in the same place(cylinder head) at different times as the

piston goes up and down.

In the turbine engine, however, thesesame four steps occur at the same time

but in different places. As a result of this fundamental difference, the turbinehas engine sections called:

1) The inlet section2) The compressor section3) The combustion section4) The exhaust section.

The practical axial flow turbineengine

The turbine engine in an airplane has thevarious sections stacked in a line from

front to back. As a result, the engine body presents less drag to the airplane asit is flying. The air enters the front of the engine and passes essentially straightthrough from front to back. On its wayto the back, the air is compressed by thecompressor section. Fuel is added and

burned in the combustion section, then

the air is exhausted through the exitnozzle.

The laws of nature will not let us getsomething for nothing. The compressor needs to be driven by something in order

to work. Just after the burner and beforethe exhaust nozzle, there is a turbine thatuses some of the energy in thedischarging air to drive the compressor.There is a long shaft connecting theturbine to the compressor ahead of it.

Compressor combustor turbine nozzle

Fig 5 showing basic layout of jet propulsion system.

Machinery details

From an outsider's view, the flight crewand passengers rarely see the actualengine. What is seen is a largeelliptically-shaped pod hanging from thewing or attached to the airplane fuselagetoward the back of the airplane. This

pod structure is called the nacelle or cowling. The engine is inside thisnacelle.

The first nacelle component thatincoming air encounters on its waythrough an airplane turbine engine is theinlet cowl. The purpose of the inlet cowlis to direct the incoming air evenlyacross the inlet of the engine. The shapeof the interior of the inlet cowl is verycarefully designed to guide this air.


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The compressor of an airplane turbineengine has quite a job to do. Thecompressor has to take in an enormousvolume of air and compress it to 1/10 th or 1/15 th of the volume it had outside theengine. This volume of air must be

supplied continuously, not in pulses or periodic bursts.

The compression of this volume of air isaccomplished by a rotating disk containing many airfoils, called blades,set at an angle to the disk rim. Each

blade is close to the shape of a miniature propeller blade, and the angle at which itis set on the disk rim is called the angleof attack. This angle of attack is similar

to the pitch of a propeller blade or anairplane wing in flight. As the disk with

blades is forced to rotate by the turbine,each blade accelerates the air, thus

pumping the air behind it. The effect issimilar to a household window fan.

Fig 6 showing compressor rotor disk.

After the air passes through the bladeson a disk, the air will be acceleratedrearward and also forced circumferen-tially around in the direction of therotating disk. Any tendency for the air to go around in circles iscounterproductive, so this tendency iscorrected by putting another row of

airfoils behind the rotating disk. Thisrow is stationary and its airfoils are at anopposing angle.

What has just been described is a singlestage of compression. Each stage

consists of a rotating disk with many blades on the rim, called a rotor stage,and, behind it, another row of airfoilsthat is not rotating, called a stator. Air on the backside of this rotor/stator pair isaccelerated rearward, and any tendencyfor the air to go around circumferentiallyis corrected.

Fig 7 showing 9 stages of a compressor rotor assembly.

A single stage of compression canachieve perhaps 1.5:1 or 2.5:1 decreasein the air's volume. Compression of theair increases the energy that can beextracted from the air during combustionand exhaust (which provides the thrust).In order to achieve the 10:1 to 15:1 totalcompression needed for the engine todevelop adequate power, the engine is

built with many stages of compressorsstacked in a line. Depending upon the

engine design, there may be as many as10 to 15 stages in the total compressor.

As the air is compressed through thecompressor, the air increases in velocity,temperature, and pressure. Air does not

behave the same at elevatedtemperatures, pressures, and velocities as


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it does in the front of the engine before itis compressed. In particular, this meansthat the speed that the compressor rotorsmust have at the back of the compressor is different than at the front of thecompressor. If we had only a few

stages, this difference could be ignored; but, for 10 to 15 compressor stages, itwould not be efficient to have all thestages rotate at the same speed.

The most common solution to this problem is to break the compressor intwo. This way, the front 4 or 5 stagescan rotate at one speed, while the rear 6or 7 stages can rotate at a different,higher, speed. To accomplish this, we

also need two separate turbines and twoseparate shafts.

Fig 8 showing layout of a dual rotor airplaneturbine engine.

Most of today's turbine engines are dual-rotor engines, meaning there are twodistinct sets of rotating components.The rear compressor, or high-pressurecompressor, is connected by a hollowshaft to a high-pressure turbine. This isthe high rotor. The rotors are sometimescalled spools, such as the "high spool."In this text, we will use the term rotor.The high rotor is often referred to as N2for short.

The front compressor, or low-pressurecompressor, is in front of the high-

pressure compressor. The turbine thatdrives the low-pressure compressor is

behind the turbine that drives the high- pressure compressor. The low-pressurecompressor is connected to the low-

pressure turbine by a shaft that goesthrough the hollow shaft of the highrotor. The low-pressure rotor is called

N1 for short.

The N1 and N2 rotors are not connectedmechanically in any way. There is nogearing between them. As the air flowsthrough the engine, each rotor is free tooperate at its own efficient speed. Thesespeeds are all quite precise and arecarefully calculated by the engineerswho designed the engine. The speed inRPM of each rotor is often displayed on

the engine flight deck and identified bygages or readouts labeled N1 RPM and

N2 RPM. Both rotors have their ownredline limits.

In some engine designs, the N1 and N2rotors may rotate in opposite directions,or there may be three rotors instead of two. Whether or not these conditionsexist in any particular engine areengineering decisions and are of no

consequence to the pilot.

The turbofan engine

A turbofan engine is simply a turbineengine where the first stage compressor rotor is larger in diameter than the rest of the engine. This larger stage is calledthe fan. The air that passes through thefan near its inner diameter also passesthrough the remaining compressor stages

in the core of the engine and is further compressed and processed through theengine cycle. The air that passesthrough the outer diameter of the fanrotor does not pass through the core of the engine, but instead passes along theoutside of the engine. This air is called


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bypass air, and the ratio of bypass air tocore air is called the bypass ratio.

Fig 9 showing schematic of fan jet engine. Inthis sketch, the fan is the low-pressure

compressor. In some engine designs, there will be a few stages of low-pressure compressor withthe fan. These may be called booster stages.

The air accelerated by the fan in aturbofan engine contributes significantlyto the thrust produced by the engine,

particularly at low forward speeds andlow altitudes. In large engines, such asthe engines that power the B747, B757,B767, A300, A310, etc., as much asthree-quarters of the thrust delivered bythe engine is developed by the fan.

The fan is not like a propeller. On a propeller, each blade acts like anairplane wing, developing lift as itrotates. The "lift" on a propeller blade

pulls the engine and airplane forwardthrough the air.

In a turbofan engine, thrust is developed by the fan rotor system, which includesthe static structure (fan exit guide vanes)around it. The fan system acts like theopen balloon in our example at the startof this discussion, and thus pushes theengine, and the airplane along with it,through the air from the unbalancedforces.

Fig 10 showing schematic of a turboprop. Inthis configuration, there are two stages of turbine with a shaft that goes through the engineto a gearbox which reduces the rotor speed of the propeller.

What the fan and the propeller do havein common is that the core engine drivesthem both.

LESSON SUMMARY

So far we have learned:

1) Propulsion is created by the

unbalance of forces.2) A pressure vessel with an open end

delivers propulsion due to theunbalance of forces.

3) An airplane propulsion system is a pressure vessel with an open end inthe back.

4) An airplane engine provides aconstant supply of air for the

pressure vessel.5) An airplane turbine engine operates

with the same 4 basic steps as alawnmower or automobile engine.6) An airplane turbine engine has

sections that perform each of the 4 basic steps of intake, compression,combustion, and exhaust.


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7) Compression is accomplished bysuccessive stages of rotor/stator

pairs.8) The compressor stages are usually

split into low-pressure and high- pressure compressor sections.

9) The low-pressure section can bereferred to as N1 and the high-

pressure section can be referred to as N2.

10) A fan is the first stage of compression where the rotor and itsmating stator are larger in diameter than the rest of the engine.


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Chapter 2Engine systems

From an engineer's point of view, theturbofan engine is a finely-tuned piece of mechanical equipment. In order for theengine to provide adequate power to theairplane at a weight that the airplane canaccommodate, the engine must operateat the limit of technical feasibility. Atthe same time, the engine must providereliable, safe and economical operation.

Within the engine, there are systems thatkeep everything functioning properly.Most of these systems are transparent tothe pilot. For that reason, this text willnot go into deep technical detail. Whilesuch discussion would be appropriate for mechanics training to take care of theengine, it is the purpose of this text to

provide information that pilots can use inunderstanding the nature of some enginemalfunctions that may be encounteredduring flight.

The systems often found associated withthe operation of the engine are:

1) The accessory drive gearbox2) The fuel system3) The lubrication system4) The ignition system5) The bleed system6) The start system7) The anti-ice system.

In addition, there are airplane systemsthat are powered or driven by the engine.These systems may include:

1) The electrical system2) The pneumatic system3) The hydraulic system4) The air conditioning system.

These airplane systems are notassociated with continued function of theengine or any engine malfunctions, sothey will not be discussed in this text.The airplane systems may provide cuesfor engine malfunctions that will bediscussed in the chapter on enginemalfunctions.

Accessory drive gearbox

The accessory drive gearbox is mostoften attached directly to the outsidecases of the engine at or near the bottom.The accessory drive gearbox is driven bya shaft that extends directly into theengine and it is geared to one of thecompressor rotors of the engine. It isusually driven by the high-pressurecompressor.

Fig 11 showing typical accessory drive gearbox.

The gearbox has attachment pads on itfor accessories that need to bemechanically driven. These accessoriesinclude airplane systems, such asgenerators for airplane and necessaryengine electrical power, and thehydraulic pump for airplane hydraulicsystems. Also attached to the gearbox


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are the starter and the fuel pump/fuelcontrol.

Fuel system

The fuel system associated directly with

the propulsion system consists of:

1) A fuel pump2) A fuel control3) Fuel manifolds4) Fuel nozzles5) A fuel filter 6) Heat exchangers7) Drains8) A pressurizing and dump valve.

All are external to the engine except thefuel nozzles.

The airplane fuel system supplies pressurized fuel from the main tanks.The fuel is pressurized by electrically-driven boost pumps in the tanks and thenflows through the spar valve or low

pressure (LP) shut-off valve to theengine LP fuel pump inlet.

The fuel pump is physically mounted onthe gearbox. Most engine fuel pumpshave two stages, or, in some engines,there may actually be two separate

pumps. There is an LP stage thatincreases fuel pressure so that fuel can

be used for servos. At this stage, thefuel is filtered to remove any debris fromthe airplane tanks. Following the LPstage, there is an HP (high-pressure)stage that increases fuel pressure above

the combustor pressure. The HP pumpalways provides more fuel than theengine needs to the fuel control, and thefuel control meters the required amountto the engine and bypasses the rest back to the pump inlet.

The fuel delivered from the pump isgenerally used to cool the engine oil andintegral drive generator (IDG) oil on theway to the fuel control. Some fuelsystems also incorporate fuel heaters to

prevent ice crystals accumulating in the

fuel control during low-temperatureoperation and valves to bypass thoseheat exchangers depending on ambienttemperatures.

The fuel control is installed on theengine on the accessory gearbox,directly to the fuel pump, or, if there isan electronic control, to the engine case.The purpose of the fuel control is to

provide the required amount of fuel to

the fuel nozzles at the requested time.The rate at which fuel is supplied to thenozzles determines the acceleration or deceleration of the engine.

Fig 12 characterizing that the fuel control is an"intelligent" component that does the work oncethe flight crew "tells it what to do."

The flight crew sets the power requirements by moving a thrust lever inthe flight deck. When the flight crew

adjusts the thrust lever, however, theyare actually "telling the control" what

power is desired. The fuel controlsenses what the engine is doing andautomatically meters the fuel to the fuelnozzles within the engine at the requiredrate to achieve the power requested by


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the flight crew. A fuel flow meter measures the fuel flow sent to theengines by the control.

In older engines, the fuel control ishydromechanical, which means that it

operates directly from pressure andmechanical speed physically input intothe control unit.

On newer airplanes, control of the fuelmetering is done electronically by acomputer device called by names such as"EEC" or "FADEC." EEC stands for Electronic Engine Control, and FADECstands for Full Authority Digital EngineControl. The net result is the same.

Electronic controls have the capability of more precisely metering the fuel andsensing more engine operating

parameters to adjust fuel metering. Thisresults in greater fuel economy and morereliable service.

The fuel nozzles are deep within theengine in the combustion section rightafter the compressor. The fuel nozzles

provide a precisely-defined spray pattern

of fuel mist into the combustor for rapid, powerful, and complete combustion. Itis easiest to visualize the fuel nozzlespray pattern as being similar to that of ashowerhead.

The fuel system also includes drains tosafely dispose of the fuel in themanifolds when the engine is shut down,and, in some engines, to conduct leakedfuel overboard.

Lubrication system

An airplane turbine engine, like anyengine, must be lubricated in order for the rotors to turn easily withoutgenerating excessive heat. Each rotor system in the engine has, as a minimum,

a rear and front bearing to support therotor. That means that the N1 rotor hastwo bearings and the N2 rotor has two

bearings for a total of 4 main bearings inthe engine. There are some engines thathave intermediate and/or special

bearings; however, the number of bearings in a given engine is usually of little direct interest to a basicunderstanding of the engine.

The lubrication system of a turbineengine includes:

1) An oil pump.2) An oil storage tank.3) A delivery system to the bearing

compartments (oil lines).4) Lubricating oil jets within the bearingcompartments.5) Seals to keep the oil in and air out of the compartments.6) A scavenge system to remove oilfrom the bearing compartment after theoil has done its job. After the oil isscavenged, it is cooled by heatexchangers, and filtered.7) Oil quantity, pressure, temperature,

gages and filter bypass indications on theflight deck for monitoring of the oilsystem.8) Oil filters.9) Heat exchangers. Often, oneexchanger serves as both a fuel heater and an oil cooler.10) Chip detectors, usually magnetic, tocollect bearing compartment particles asan indication of bearing compartmentdistress. Chip detectors may trigger a

flight deck indication or be visuallyexamined during line maintenance.11) Drains to safely dispose of leaked oiloverboard.

The gages in item 7 are the window thatthe flight crew has to monitor the healthof the lubrication system.


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Ignition system

The ignition system is a relativelystraightforward system. Its purpose is to

provide the spark within the combustionsection of the engine so that, when fuel

is delivered to the fuel nozzles, theatomized fuel mist will ignite and thecombustion process will start.

Since all 4 steps of the engine cycle in aturbine engine are continuous, once thefuel is ignited the combustion processnormally continues until the fuel flow isdiscontinued during engine shutdown.This is unlike the situation in a pistonengine, where there must be an ignition

spark each time the combustion stepoccurs in the piston chamber.

Turbine engines are provided with a provision on the flight deck for "continuous ignition." When this settingis selected, the ignitor will produce aspark every few seconds. This provisionis included for those operations or flight

phases where, if the combustion processwere to stop for any reason, the loss of

power could be serious. Withcontinuous ignition, combustion willrestart automatically, often without the

pilot even noticing that there was aninterruption in power.

Some engines, instead of havingcontinuous ignition, monitor thecombustion process and turn the igniterson as required, thus avoiding the needfor continuous ignition.

The ignition system includes:

1) Igniter boxes which transform low-voltage Alternating Current (AC) fromeither a gearbox-mounted alternator or from the airplane into high-voltageDirect Current (DC).

2) Cables to connect the igniter boxes tothe igniter plugs.3) Ignitor plugs.

For redundancy, the ignition system hastwo igniter boxes and two igniter plugs

per engine. Only one igniter in eachengine is required to light the fuel in thecombustor. Some airplanes allow the

pilot to select which igniter is to be used;others use the engine control to make theselection.

Bleed system

Stabil i ty bleeds

The compressors of airplane turbineengines are designed to operate mostefficiently at cruise. Without help, thesecompressors may operate very poorly or not at all during starting, at very low

power, or during rapid transient power changes, which are conditions when theyare not as efficient. To reduce theworkload on the compressor duringthese conditions, engines are equippedwith bleeds to discharge large volumes

of air from the compressor before it isfully compressed.

The bleed system usually consists of:

1) Bleed valves.2) Solenoids or actuators to open andclose the bleed valves.3) A control device to signal the valveswhen to open and close.4) Lines to connect the control device to

the actuators.

In older engines, a control devicemeasures the pressure across one of theengine compressors, compares it to theinlet pressure of the engine, and directshigher-pressure, high-compressor air toan air piston-driven actuator at the bleed


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valve to directly close the valve. Innewer engines, the electronic fuelcontrol determines when the bleedvalves open and close.

Generally, all the compressor bleed

valves are open during engine start.Some of the valves close after start andsome remain open. Those that remainopen then close during engineacceleration to full power for takeoff.These valves then remain closed for theduration of the flight.

If, during in-flight operation, the fuelcontrol senses instability in thecompressors, the control may open some

of the bleed valves momentarily. Thiswill most often be completely unnoticed

by the flight crew except for an advisorymessage on the flight deck display insome airplane models.

Coolin g/clearance control bleeds

Air is also extracted from thecompressor, or the fan airflow, for cooling engine components and for

accessory cooling in the nacelle. Insome engines, air extracted from thecompressor is ducted and directed ontothe engine cases to control the clearance

between the rotor blade tips and the casewall. Cooling the case in this wayshrinks the case closer to the blade tips,improving compression efficiency.

Service bleeds

The engines are the primary source of pressurized air to the airplane for cabin pressurization. In some airplanes,engine bleed air can be used as anauxiliary power source for back-uphydraulic power air-motors. Air is takenfrom the high compressor, before anyfuel is burned in it, so that it is as clean

as the outside air. The air is cooled andfiltered before it is delivered to thecabins or used for auxiliary power.

Start system

When the engine is stationary on theground, it needs an external source of

power to start the compressor rotating sothat it can compress enough air to getenergy from the fuel. If fuel were lit inthe combustor of a completely non-rotating engine, the fuel would puddleand burn without producing anysignificant rearward airflow.

A pneumatic starter is mounted on the

accessory gearbox, and is powered by air originating from another engine, fromthe auxiliary power unit (APU), or froma ground cart. A start valve controls theinput selection. The starter drives theaccessory gearbox, which drives thehigh-compressor rotor via the same driveshaft normally used to deliver power TOthe gearbox.

Fuel flow during starting is carefully

scheduled to allow for the compressor's poor efficiency at very low RPM, and bleeds are used to unload the compressor until it can reach a self-sustaining speed.During some points in a normal enginestart, it may even look as if the engine isnot accelerating at all. After the enginereaches the self-sustaining speed, thestarter de-clutches from the accessorygearbox. This is important, as starterscan be damaged with exposure to

extended, high-speed operation. Theengine is able to accelerate up to idlethrust without further assistance from thestarter.

The starter can also be used to assistduring in-flight restart, if an engine must

be restarted. At higher airspeeds, the


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engine windmill RPM may be enough toallow engine starting without use of the

pneumatic starter. The specific AirplaneFlight Manual (AFM) should beconsulted regarding the conditions inwhich to perform an in-flight restart.

Anti-ice system

An airplane turbine engine needs to havesome protection against the formation of ice in the inlet and some method toremove ice if it does form. The engine isequipped with the capability to takesome compressor air, via a bleed, andduct it to the engine inlet or any other

place where anti-ice protection is

necessary. Because the compressor bleed air is quite hot, it prevents theformation of ice and/or removes already-formed ice.

On the flight deck, the flight crew hasthe capability to turn anti-ice on or off.There is generally no capability tocontrol the amount of anti-ice delivered;for example, "high," "medium" or "low."Such control is not necessary.


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Chapter 3Engine instrumentation in the flight deck

Airplanes in service today are equippedwith devices available to the flight crewthat provide feedback information aboutthe engine to set engine power andmonitor the condition of the engine. Inolder airplanes, these devices were gageson the panel. In newer airplanes, theairplane is equipped with electronicscreens which produce computer-generated displays that resemble thegages that used to be on the panel.Whether gages or electronic displays areused, the information given to the flightcrew is the same.

The gages are most useful whenconsidered in context with each other,rather than considering one gage inisolation.

What follows is a brief description of thegages and what information they

provide.

Engine Pressure Ratio or EPR.Engine pressure ratio is a measure of thrust provided by the engine. EPR indicators provide the ratio of the

pressure of the air as it comes out of theturbine to the pressure of the air as itenters the compressor. EPR is a certifiedthrust-setting parameter. Some enginemanufacturers recommend that engine

power management be performed byreference to EPR.

A low EPR reading may be caused byengine rollback or flameout, or internaldamage such as an LP turbine failure.Rapid EPR fluctuations may be caused

by engine operational instability, such assurge, or rapidly-changing externalconditions, such as inclement weather or

bird ingestion. Unexpectedly high EPR may indicate a fuel control malfunction,or malfunction or clogging of the inletair pressure probes.

Rotor RPM . On an airplane equippedwith a multiple-rotor turbine engine,there will be a rotor speed indication for each rotor. The N1 gage will providethe rotor speed of the low-pressure rotor and the N2 (or N3 for a 3-rotor engine)gage will provide the rotor speed of thehigh-pressure rotor. N1 is a certifiedthrust-setting parameter.

The units of rotor speed are RevolutionsPer Minute or RPM, but rotor speed isindicated as a non-dimensional ratio that of engine rotor speed as comparedto some nominal 100% speedrepresenting a high-power condition(which is not necessarily the maximum

permissible speed). Engine operatingmanuals specify a maximum operationallimit RPM or redline RPM that willgenerally be greater than 100 percent.

Low N1 may indicate engine rollback or flameout, or severe damage such as LPturbine failure. Rapid N1 fluctuations


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may be caused by engine operationalinstability such as surge. Higher rotor speeds will be required at high altitudesto achieve takeoff-rated thrust.Unexpectedly high N1 may indicate afuel control malfunction.

N2 is used for limit monitoring andcondition monitoring. On older engines,it is also used to monitor the progress of engine starting and to select theappropriate time to start fuel flow to theengine.

Exhaust Gas Temperature or EGT.Exhaust gas temperature is a measure of the temperature of the gas exiting therear of the engine. It is measured atsome location in the turbine. Since theexact location varies according to enginemodel, EGT should not be compared

between engine models. Often, there aremany sensors at the exit of the turbine to

monitor EGT. The indicator on theflight deck displays the average of all thesensors.

High EGT can be an indication of degraded engine performance.Deteriorated engines will be especiallylikely to have high EGT during takeoff.

EGT is also used to monitor enginehealth and mechanical integrity.

Excessive EGT is a key indicator of engine stall, of difficulty in enginestarting, of a major bleed air leak, and of any other situation where the turbine isnot extracting enough work from the air as it moves aft (such as severe enginedamage).

There is an operational limit for EGT,since excessive EGT will result inturbine damage. Operational limits for EGT are often classified as time-at-temperature.

Fuel Flow indicator. The fuel flowindicator shows the fuel flow in pounds(or kilograms) per hour as supplied tothe fuel nozzles. Fuel flow is of fundamental interest for monitoring in-

flight fuel consumption, for checkingengine performance, and for in-flightcruise control.

High fuel flow may indicate a significantleak between the fuel control and fuelnozzles, particularly if rotor speeds or EPR appear normal or low.

Oil Pressure Indicator. The oil pressure indicator shows the pressure of the oil as it comes out of the oil pump.In some cases, the oil pressure readingsystem takes the bearing compartment

background pressure, called breather pressure, into account so that the gagereading reflects the actual pressure of the

oil as it is delivered to the bearingcompartments. Oil system parametershistorically give false indications of a

problem as frequently as the oil systemhas a genuine problem, so crosscheckingwith the other oil system indications isadvisable.


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Low oil pressure may result from pumpfailure, from a leak allowing the oilsystem to run dry, from a bearing or gearbox failure, or from an indicationsystem failure. High oil pressure may beobserved during extremely low

temperature operations, when oilviscosity is at a maximum.

Low Oil Pressure Caution. Generally,if the oil pressure falls below a giventhreshold level, an indication light or message is provided to draw attention tothe situation.

Oil Temperature Indicator. The Oiltemperature indicator shows the oiltemperature at some location in thelubrication circuit, although this locationdiffers between engine models.

Elevated oil temperatures indicate some

unwanted source of heat in the system,such as a bearing failure, sump fire or unintended leakage of high temperatureair into the scavenge system. High oiltemperature may also result from amalfunction of the engine oil cooler, or of the valves scheduling fluid flowthrough the cooler.

Oil Quantity Indicator. The oilquantity indication monitors the amount

of oil in the tank. This can be expectedto vary with power setting, since theamount of oil in the sumps is a functionof rotor speed.

A steady decrease in oil quantity mayindicate an oil leak. There is likely tostill be some usable oil in the tank even

after the oil quantity gage reads zero, butthe oil supply will be near exhaustionand a low pressure indication will soon

be seen. A large increase in the oilquantity may be due to fuel leaking intothe oil system, and should be

investigated before the next flight.Flight crews should be especiallyvigilant to check other oil systemindications before taking action on anengine in-flight solely on the basis of low oil quantity.

Oil Filter Bypass Indication. If the oilfilter becomes clogged with debris(either from contamination by foreignmaterial or debris from a bearing

failure), the pressure drop across thefilter will rise to the point where the oil

bypasses the filter. This is announced tothe pilot via the oil filter impending

bypass indication. This indication maygo away if thrust is reduced (because oilflow through the filter and pressure dropacross the filter are reduced).

Fuel Filter Impending Bypass. If thefuel filter at the engine fuel inlet

becomes clogged, an impending bypassindication will alert the crew for a shortwhile before the filter actually goes into

bypass.

Fuel Heat Indication. The fuel heatindicator registers when the fuel heat ison. Fuel heat indicators are not neededfor engines where fuel heating is

passively combined with oil cooling, andno valves or controls are involved.

Engine Starter Indication. Duringassisted starting, the start valve will beindicated open until starter disconnect.The position of the start switch showsthe starter status (running or disconnected). If the starter does notdisconnect once the engine reaches idle,


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Chapter 4Engine Malfunctions

To provide effective understanding of and preparation for the correct responsesto engine in-flight malfunctions, thischapter will describe turbofan enginemalfunctions and their consequences in amanner that is applicable to almost allmodern turbofan-powered airplanes.These descriptions, however, do notsupersede or replace the specificinstructions that are provided in theAirplane Flight Manual and appropriatechecklists.

Compressor surge

It is most important to provide anunderstanding of compressor surge. Inmodern turbofan engines, compressor surge is a rare event. If a compressor surge (sometimes called a compressor stall) occurs during high power attakeoff, the flight crew will hear a veryloud bang, which will be accompanied

by yaw and vibration. The bang willlikely be far beyond any engine noise, or other sound, the crew may have

previously experienced in service.

Compressor surge has been mistaken for blown tires or a bomb in the airplane.The flight crew may be quite startled bythe bang, and, in many cases, this has ledto a rejected takeoff above V1. Thesehigh-speed rejected takeoffs havesometimes resulted in injuries, loss of the airplane, and even passenger fatalities.

The actual cause of the loud bang shouldmake no difference to the flight crews

first response, which should be tomaintain control of the airplane and, in

particular, continue the takeoff if theevent occurs after V1. Continuing thetakeoff is the proper response to a tirefailure occurring after V1, and historyhas shown that bombs are not a threatduring the takeoff roll they aregenerally set to detonate at altitude.

A surge from a turbofan engine is theresult of instability of the engine'soperating cycle. Compressor surge may

be caused by engine deterioration, it may be the result of ingestion of birds or ice,or it may be the final sound from asevere engine damage type of failure.As we learned in Chapter 1, theoperating cycle of the turbine engineconsists of intake, compression, ignition,and exhaust, which occur simultaneouslyin different places in the engine. The

part of the cycle susceptible to instabilityis the compression phase.

In a turbine engine, compression isaccomplished aerodynamically as the air

passes through the stages of thecompressor, rather than by confinement,as is the case in a piston engine. The air flowing over the compressor airfoils canstall just as the air over the wing of anairplane can. When this airfoil stalloccurs, the passage of air through thecompressor becomes unstable and thecompressor can no longer compress theincoming air. The high-pressure air

behind the stall further back in theengine escapes forward through thecompressor and out the inlet.


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This escape is sudden, rapid and oftenquite audible as a loud bang similar to anexplosion. Engine surge can beaccompanied by visible flames forwardout the inlet and rearward out thetailpipe. Instruments may show highEGT and EPR or rotor speed changes,

but, in many stalls, the event is over soquickly that the instruments do not havetime to respond.

Once the air from within the engineescapes, the reason (reasons) for theinstability may self-correct and thecompression process may re-establishitself. A single surge and recovery willoccur quite rapidly, usually withinfractions of a second. Depending on thereason for the cause of the compressor instability, an engine might experience:

1) A single self-recovering surge2) Multiple surges prior to self-recovery3) Multiple surges requiring pilot actionin order to recover 4) A non-recoverable surge.

For complete, detailed procedures, flightcrews must follow the appropriatechecklists and emergency proceduresdetailed in their specific Airplane FlightManual. In general, however, during asingle self-recovering surge, the cockpitengine indications may fluctuate slightlyand briefly. The flight crew may not

notice the fluctuation. (Some of themore recent engines may even have fuel-flow logic that helps the engine self-recover from a surge without crewintervention. The stall may gocompletely unnoticed, or it may be

annunciated to the crew for information only via EICASmessages.) Alternatively, the enginemay surge two or three times before fullself-recovery. When this happens, thereis likely to be cockpit engineinstrumentation shifts of sufficientmagnitude and duration to be noticed bythe flight crew. If the engine does notrecover automatically from the surge, itmay surge continually until the pilot

takes action to stop the process. Thedesired pilot action is to retard the thrustlever until the engine recovers. Theflight crew should then SLOWLY re-advance the thrust lever. Occasionally,an engine may surge only once but stillnot self-recover.

The actual cause for the compressor surge is often complex and may or maynot result from severe engine damage.

Rarely does a single compressor surgeCAUSE severe engine damage, butsustained surging will eventually over-heat the turbine, as too much fuel is

being provided for the volume of air thatis reaching the combustor. Compressor

blades may also be damaged and fail as aresult of repeated violent surges; thiswill rapidly result in an engine whichcannot run at any power setting.

Additional information is provided below regarding single recoverablesurge, self-recoverable after multiplesurges, surge requiring flight crewaction, and non-recoverable surge. Insevere cases, the noise, vibration andaerodynamic forces can be verydistracting. It may be difficult for the


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flight crew to remember that their mostimportant task is to fly the airplane.

Single self-recoverable sur ge

The flight crew hears a very loud bang

or double bang. The instruments willfluctuate quickly, but, unless someonewas looking at the engine gage at thetime of the surge, the fluctuation mightnot be noticed.

For example: During the surge event,Engine Pressure Ratio (EPR) can dropfrom takeoff (T/O) to 1.05 in 0.2seconds. EPR can then vary from 1.1 to1.05 at 0.2-second intervals two or three

times. The low rotor speed (N1) candrop 16% in the first 0.2 seconds, thenanother 15% in the next 0.3 seconds.After recovery, EPR and N1 shouldreturn to pre-surge values along thenormal acceleration schedule for theengine.

M ul tipl e sur ge fol lowed by self -recovery

Depending on the cause and conditions,

the engine may surge multiple times,with each bang being separated by acouple of seconds. Since each bangusually represents a surge event asdescribed above, the flight crew maydetect the "single surge" described abovefor two seconds, then the engine willreturn to 98% of the pre-surge power for a few seconds. This cycle may repeattwo or three times. During the surge andrecovery process, there will likely be

some rise in EGT.

For example: EPR may fluctuate between 1.6 and 1.3, Exhaust GasTemperature (EGT) may rise 5 degreesC/second, N1 may fluctuate between103% and 95%, and fuel flow may drop2% with no change in thrust lever

position. After 10 seconds, the enginegages should return to pre-surge values.

Surge recoverable after flight crew action

When surges occur as described in the previous paragraph, but do not stop,flight crew action is required to stabilizethe engine. The flight crew will noticethe fluctuations described inrecoverable after two or three bangs,

but the fluctuations and bangs willcontinue until the flight crew retards thethrust lever to idle. After the flight crewretards the thrust lever to idle, the engine

parameters should decay to match thrust

lever position. After the engine reachesidle, it may be re-accelerated back to

power. If, upon re-advancing to high power, the engine surges again, theengine may be left at idle, or left at someintermediate power, or shutdown,according to the checklists applicable for the airplane. If the flight crew takes noaction to stabilize the engine under thesecircumstances, the engine will continueto surge and may experience progressive

secondary damage to the point where itfails completely.

Non -recoverable sur ge

When a compressor surge is notrecoverable, there will be a single bangand the engine will decelerate to zero

power as if the fuel had been chopped.This type of compressor surge canaccompany a severe engine damage

malfunction. It can also occur withoutany engine damage at all.

EPR can drop at a rate of .34/sec andEGT rise at a rate of 15 degrees C/sec,continuing for 8 seconds (peaking) after the thrust lever is pulled back to idle.

N1 and N2 should decay at a rate


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consistent with shutting off the fuel, withfuel flow dropping to 25% of its pre-surge value in 2 seconds, tapering to10% over the next 6 seconds.

Flameout

A flameout is a condition where thecombustion process within the burner has stopped. A flameout will beaccompanied by a drop in EGT, inengine core speed and in engine pressureratio. Once the engine speed drops

below idle, there may be other symptoms, such as low oil pressurewarnings and electrical generatorsdropping off line in fact, many

flameouts from low initial power settings are first noticed when thegenerators drop off line and may beinitially mistaken for electrical

problems. The flameout may result fromthe engine running out of fuel, severeinclement weather, a volcanic ashencounter, a control system malfunction,or unstable engine operation (such as acompressor stall). Multiple engineflameouts may result in a wide variety of

flight deck symptoms as engine inputsare lost from electrical, pneumatic andhydraulic systems. These situationshave resulted in pilots troubleshootingthe airplane systems without recognizingand fixing the root cause no engine

power. Some airplanes have dedicatedEICAS/ECAM messages to alert theflight crew to an engine rolling back

below idle speed in flight; generally, anENG FAIL or ENG THRUST message.

A flameout at take-off power is unusual only about 10% of flameouts are attakeoff power. Flameouts occur mostfrequently from intermediate or low

power settings, such as cruise anddescent. During these flight regimes, itis likely that the autopilot is in use. The

autopilot will compensate for theasymmetrical thrust up to its limits andmay then disconnect. Autopilotdisconnect must then be accompanied by

prompt, appropriate control inputs fromthe flight crew if the airplane is to

maintain a normal attitude. If noexternal visual references are available,such as when flying over the ocean atnight or in IMC, the likelihood of anupset increases. This condition of low-

power engine loss with the autopilot onhas caused several aircraft upsets, someof which were not recoverable. Flightcontrol displacement may be the onlyobvious indication. Vigilance isrequired to detect these stealthy engine

failures and to maintain a safe flightattitude while the situation is stillrecoverable.

Once the fuel supply has been restoredto the engine, the engine may berestarted in the manner prescribed by theapplicable Airplane Flight or OperatingManual. Satisfactory engine restartshould be confirmed by reference to all

primary parameters using only N1, for

instance, has led to confusion duringsome in-flight restarts. At some flightconditions, N1 may be very similar for awindmilling engine and an enginerunning at flight idle.


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Fire

Engine fire almost always refers to a fireoutside the engine but within the nacelle.A fire in the vicinity of the engineshould be annunciated to the flight crew

by a fire warning in the flight deck. It isunlikely that the flight crew will see,hear, or immediately smell an enginefire. Sometimes, flight crews areadvised of a fire by communication withthe control tower.

It is important to know that, given a firein the nacelle, there is adequate time tomake the first priority "fly the airplane"

before attending to the fire. It has beenshown that, even in incidents of fireindication immediately after takeoff,there is adequate time to continue climbto a safe altitude before attending to theengine. There may be economic damageto the nacelle, but the first priority of theflight crew should be to ensure theairplane continues in safe flight.

Flight crews should regard any firewarning as a fire, even if the indicationgoes away when the thrust lever isretarded to idle. The indication might bethe result of pneumatic leaks of hot air into the nacelle. The fire indication

could also be from a fire that is small or sheltered from the detector so that thefire is not apparent at low power. Fireindications may also result from faultydetection systems. Some fire detectorsallow identification of a false indication(testing the fire loops), which may avoidthe need for an IFSD. There have been

times when the control tower hasmistakenly reported the flamesassociated with a compressor surge as anengine "fire."

In the event of a fire warning

annunciation, the flight crew must refer to the checklists and procedures specificto the airplane being flown. In general,once the decision is made that a fireexists and the aircraft is stabilized,engine shutdown should be immediatelyaccomplished by shutting off fuel to theengine, both at the engine fuel controlshutoff and the wing/pylon spar valve.All bleed air, electrical, and hydraulicsfrom the affected engine will be

disconnected or isolated from theairplane systems to prevent any fire fromspreading to or contaminating associatedairplane systems. This is accomplished

by one common engine "fire handle."This controls the fire by greatly reducingthe fuel available for combustion, byreducing the availability of pressurizedair to any sump fire, by temporarilydenying air to the fire through thedischarge of fire extinguishant, and by

removing sources of re-ignition, such aslive electrical wiring and hot casings. Itshould be noted that some of thesecontrol measures may be less effective if the fire is the result of severe damage the fire may take slightly longer to beextinguished in these circumstances. Inthe event of a shut down after an in-flight engine fire, there should be noattempt to restart the engine unless it iscritical for continued safe flight, as the

fire is likely to re-ignite once the engineis restarted.

Tailpipe Fires

One of the most alarming events for passengers, flight attendants, ground personnel and even air traffic control


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(ATC) to witness is a tailpipe fire. Fuelmay puddle in the turbine casings andexhaust during start-up or shutdown, andthen ignite. This can result in a highly-visible jet of flame out of the back of theengine, which may be tens of feet long.

Passengers have initiated emergencyevacuations in these instances, leading toserious injuries.

There may be no indication of ananomaly to the flight crew until thecabin crew or control tower drawsattention to the problem. They are likelyto describe it as an Engine Fire, but atailpipe fire will NOT result in a firewarning on the flight deck.

If notified of an engine fire without anyindications in the cockpit, the flight crewshould accomplish the tailpipe fire

procedure. It will include motoring theengine to help extinguish the flames,while most other engine abnormal

procedures will not.

Since the fire is burning within theturbine casing and exhaust nozzle,

pulling the fire handle to dischargeextinguishant to the space betweencasings and cowls will be ineffective.Pulling the fire handle may also make itimpossible to dry motor the engine,which is the quickest way of extinguishing most tailpipe fires.

Hot starts

During engine start, the compressor is

very inefficient, as already discussed. If the engine experiences more than theusual difficulty accelerating (due to such

problems as early starter cut-out, fuelmis-scheduling, or strong tailwinds), theengine may spend a considerable time atvery low RPM (sub-idle). Normalengine cooling flows will not be

effective during sub-idle operation, andturbine temperatures may appear relatively high. This is known as a hotstart (or, if the engine completely stopsaccelerating toward idle, a hung start).The AFM indicates acceptable

time/temperature limits for EGT duringa hot start. More recent, FADEC-controlled engines may incorporate auto-start logic to detect and manage a hotstart.

Bird ingestion/FOD

Airplane engines ingest birds most oftenin the vicinity of airports, either duringtakeoff or during landing. Encounters

with birds occur during both daytimeand nighttime flights.

By far, most bird encounters do notaffect the safe outcome of a flight. Inmore than half of the bird ingestions intoengines, the flight crew is not evenaware that the ingestion took place.

When an ingestion involves a large bird,the flight crew may notice a thud, bang

or vibration. If the bird enters the enginecore, there may be a smell of burnt fleshin the flight deck or passenger cabinfrom the bleed air.

Bird strikes can damage an engine. The photo on the next page shows fan blades bent due to the ingestion of a bird. Theengine continued to produce thrust withthis level of damage. Foreign ObjectDamage (FOD) from other sources, such

as tire fragments, runway debris or animals, may also be encountered, withsimilar results.

Bird ingestion can also result in anengine surge. The surge may have anyof the characteristics listed in the surgesection. The engine may surge once and


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recover; it may surge continuously untilthe flight crew takes action; or it maysurge once and not recover, resulting inthe loss of power from that engine. Birdingestion can result in the fracture of oneor more fan blades, in which case, the

engine will likely surge once and notrecover.

Fig 13 showing fan blades bent by encounter with a bird.

Regardless of the fact that a birdingestion has resulted in an engine surge,the first priority task of the flight crew isto "fly the airplane." Once the airplaneis in stable flight at a safe altitude, theappropriate procedures in the applicableAirplane Flight Manual can beaccomplished.

In rare cases, multiple engines can ingestmedium or large birds. In the event of suspected multiple-engine damage,taking action to stabilize the engines

becomes a much higher priority than if only one engine is involved but it isstill essential to control the airplane first.

Severe engine damage

Severe engine damage may be difficultto define. From the viewpoint of theflight crew, severe engine damage is

mechanical damage to the engine thatlooks "bad and ugly." To themanufacturers of the engine and theairplane, severe engine damage mayinvolve symptoms as obvious as large

holes in the engine cases and nacelle or as subtle as the non-response of theengine to thrust lever movement.

It is important for flight crews to knowthat severe engine damage may beaccompanied by symptoms such as firewarning (from leaked hot air) or enginesurge because the compressor stages thathold back the pressure may not be intactor in working order due to the engine

damage.

In this case, the symptoms of severeengine damage will be the same as asurge without recovery. There will be aloud noise. EPR will drop quickly; N1,

N2 and fuel flow will drop. EGT mayrise momentarily. There will be a loss of

power to the airplane as a result of thesevere engine damage. It is notimportant to initially distinguish between

a non-recoverable surge with or withoutsevere engine damage, or between a fireand a fire warning with severe enginedamage. The priority of the flight crewstill remains "fly the airplane." Once theairplane is stabilized, the flight crew candiagnose the situation.


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Engine Seizure

Engine seizure describes a situationwhere the engine rotors stop turning inflight, perhaps very suddenly. The staticand rotating parts lock up against each

other, bringing the rotor to a halt. In practice, this is only likely to occur atlow rotor RPM after an engineshutdown, and virtually never occurs for the fan of a large engine the fan hastoo much inertia, and the rotor is being

pushed around by ram air too forcefullyto be stopped by the static structure. TheHP rotor is more likely to seize after anin-flight shutdown if the nature of theengine malfunction is mechanical

damage within the HP system. Shouldthe LP rotor seize, there will be some

perceptible drag for which the flightcrew must compensate; however, if theHP rotor seizes, there will be negligibleeffect upon airplane handling.

Seizure cannot occur without beingcaused by very severe engine damage, tothe point where the vanes and blades of the compressor and turbine are mostly

destroyed. This is not an instantaneous process there is a great deal of inertiain the turning rotor compared to theenergy needed to break interlockingrotating and static components.

Once the airplane has landed, and therotor is no longer being driven by ramair, seizure is frequently observed after severe damage.

Symptoms of engine seizure in flightmay include vibration, zero rotor speed,mild airplane yaw, and possibly unusualnoises (in the event of fan seizure).There may be an increased fuel flow inthe remaining engines due to aircraftautomatic compensations; no specialaction is needed other than that which is

appropriate to the severe engine damagetype failure.

Engine Separation

Engine separation is an extremely rare

event. It will be accompanied by loss of all primary and secondary parameters for the affected engine, noises, and airplaneyaw (especially at high power settings).Separation is most likely to occur duringtake-off/climb-out or the landing roll.Airplane handling may be affected. It isimportant to use the fire handle to closethe spar valve and prevent a massiveoverboard fuel leak; refer to the airplaneflight or operations manual for specific

procedures.

Fuel System Problems

Leaks

Major leaks in the fuel system are aconcern to the flight crew because theymay result in engine fire, or, eventually,in fuel exhaustion. A very large leak can

produce engine flameout.

Engine instruments will only indicate aleak if it is downstream of the fuelflowmeter. A leak between the tanksand the fuel flowmeter can only berecognized by comparing fuel usage

between engines, by comparing actualusage to planned usage, or by visualinspection for fuel flowing out of the

pylon or cowlings. Eventually, the leak may result in tank imbalance.

In the event of a major leak, the crewshould consider whether the leak needsto be isolated to prevent fuel exhaustion.

It should be noted that the likelihood of fire resulting from such a leak is greater at low altitude or when the airplane is


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stationary; even if no fire is observed inflight, it is advisable for emergencyservices to be available upon landing.

I nabili ty to shutdown Engine

If the engine fuel shut-off valvemalfunctions, it may not be possible toshut the engine down by the normal

procedure, since the engine continues torun after the fuel switch is moved to thecutoff position. Closing the spar valve

by pulling the fire handle will ensurethat the engine shuts down as soon as ithas used up the fuel in the line from thespar valve to the fuel pump inlet. Thismay take a couple of minutes.

F uel fi lter Clogging

Fuel filter clogging can result from thefailure of one of the fuel tank boost

pumps (the pump generates debris whichis swept downstream to the fuel filter),from severe contamination of the fueltanks during maintenance (scraps of rag,sealant, etc., that are swept downstreamto the fuel filter), or, more seriously,

from gross contamination of the fuel.Fuel filter clogging will usually be seenat high power settings, when the fuelflow through the filter (and the sensed

pressure drop across the filter) isgreatest. If multiple fuel filter bypassindications are seen, the fuel may beheavily contaminated with water, rust,algae, etc. Once the filters bypass andthe contaminant goes straight into theengine fuel system, the engine fuel

control may no longer operate asintended. There is potential for multiple-engine flameout. The AirplaneFlight or Operating Manual provides thenecessary guidance.

Oil System Problems

The engine oil system has a relativelylarge number of indicated parametersrequired by the regulations (pressure,temperature, quantity, filter clogging).

Many of the sensors used are subject togiving false indications, especially onearlier engine models. Multipleabnormal system indications confirm agenuine failure; a single abnormalindication may or may not be a validindication of failure.

There is considerable variation betweenfailure progressions in the oil system, sothe symptoms given below may vary

from case to case.

Oil system problems may appear at anyflight phase, and generally progressgradually. They may eventually lead tosevere engine damage if the engine isnot shut down.

Leaks

Leaks will produce a sustained reduction

in oil quantity, down to zero (thoughthere will still be some usable oil in thesystem at this point). Once the oil iscompletely exhausted, oil pressure willdrop to zero, followed by the low oil

pressure light. There have been caseswhere maintenance error caused leaks onmultiple engines; it is thereforeadvisable to monitor oil quantitycarefully on the good engines as well.Rapid change in the oil quantity after

thrust lever movement may not indicatea leak it may be due to oil gulping or hiding as more oil flows into thesumps.


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Bearing failu res

Bearing failures will be accompanied byan increase in oil temperature andindicated vibration. Audible noises andfilter clog messages may follow; if the

failure progresses to severe enginedamage, it may be accompanied by lowoil quantity and pressure indications.

Oil pump failur es

Oil pump failure will be accompanied bylow indicated oil pressure and a low oil

pressure light, or by an oil filter clogmessage.

Contamination

Contamination of the oil system bycarbon deposits, cotton waste, improper fluids, etc. will generally lead to an oilfilter clog indication or an impending

bypass indication. This indication maydisappear if thrust is reduced, since theoil flow and pressure drop across thefilter will also drop.

No Thrust Lever Response

A No Thrust Lever Response type of malfunction is more subtle than the other malfunctions previously discussed, sosubtle that it can be completelyoverlooked, with potentially seriousconsequences to the airplane.

If an engine slowly loses power or if,when the thrust lever is moved, the

engine does not respond the airplanewill experience asymmetric thrust. Thismay be partly concealed by theautopilots efforts to maintain therequired flight condition.

As is the case with flameout, if noexternal visual references are available,

such as when flying over the ocean atnight or in IMC, asymmetric thrust may

persist for some time without the flightcrew recognizing or correcting it. Inseveral cases, this has led to airplaneupset, which was not always

recoverable. As stated, this condition issubtle and not easy to detect.

Symptoms may include:

Multiple system problems such asgenerators dropping off-line or lowengine oil pressure.

Unexplained airplane attitudechanges.

Large unexplained flight controlsurface deflections (autopilot on) or the need for large flight controlinputs without apparent cause(autopilot off).

Significant differences between primary parameters from one engineto the next.

If asymmetric thrust is suspected, thefirst response must be to make theappropriate trim or rudder input.Disconnecting the autopilot without first

performing the appropriate control inputor trim may result in a rapid rollmaneuver.

Reverser malfunctions

Generally, thrust reverser malfunctionsare limited to failure conditions wherethe reverser system fails to deploy whencommanded and fails to stow whencommanded. Failure to deploy or tostow during the landing roll will result insignificant asymmetric thrust, and mayrequire a rapid response to maintaindirectional control of the airplane.

Uncommanded deployments of modernthrust reverser systems have occurred


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and have led to Airworthiness Directivesto add additional locking systems to thereverser. As a consequence of thisaction, the probability of inadvertentdeployment is extremely low. Theairplane flight or operations manual

provides the necessary systeminformation and type of annunciations

provided by the airplane type.

No Starter Cutout

Generally, this condition exists when thestart selector remains in the start positionor the engine start valve is open whencommanded closed. Since the starter isintended only to operate at low speeds

for a few minutes at a time, the starter may fail completely (burst) and causefurther engine damage if the starter doesnot cut out.

Vibration

Vibration is a symptom of a wide varietyof engine conditions, ranging from very

benign to serious. The following aresome causes of tactile or indicated

vibration:

Fan unbalance at assembly Fan blade friction or shingling Water accumulation in the fan rotor Blade icing Bird ingestion/FOD Bearing failure Blade distortion or failure Excessive fan rotor system tip

clearances.

It is not easy to identify the cause of thevibration in the absence of other unusualindications. Although the vibration fromsome failures may feel very severe onthe flight deck, it will not damage theairplane. There is no need to take action

based on vibration indication alone, butit can be very valuable in confirming a

problem identified by other means.

Engine vibration may be caused by fanunbalance (ice buildup, fan bladematerial loss due to ingested material, or fan blade distortion due to foreign objectdamage) or by an internal engine failure.Reference to other engine parameterswill help to establish whether a failure

exists.

Vibration felt on the flight deck may not be indicated on instruments. For someengine failures, severe vibration may beexperienced on the flight deck either during an engine failure or possibly after the engine has been shut down, makinginstruments difficult to read. This largeamplitude vibration is caused by theunbalanced fan windmilling close to the

airframe natural frequency, which mayamplify the vibration. Changingairspeed and/or altitude will change thefan windmill speed, and an airplanespeed may be found where there will bemuch less vibration. Meanwhile, there isno risk of airplane structural failure dueto vibratory engine loads.


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Wrap-upThe tabulation of engine conditions and their symptoms below shows that many failureshave similar symptoms and that it may not be practicable to diagnose the nature of theengine problem from flight deck instrumentation. However, it is not necessary to

understand exactly what is wrong with the engine selecting the wrong checklist maycause some further economic damage to the engine, but, provided action is taken with thecorrect engine, and airplane control is kept as the first priority, the airplane will still besafe.

E n g

i n e s e p a r a t

i o n

S e v e r e

d a m a g e

S u r g e

B i r d i n g e s

t i o n

/ F O D

S e i z u r e

F l a m e o u t

F u e

l c o n t r o

l p r o b

l e m s

F i r e

T a i

l p i p e

f i r e s

H o

t s t a r

t

I c i n g

R e v e r s e r i n a d v e r

t e n t

d e p

l o y

F u e

l l e a k

Bang O X X O O OFire Warning O O O XVisible flame O O O O O X OVibration X O X O X XYaw O O O O O O O XHigh EGT X X O O X O X O

N1 change X X O O X X X X N2 change X X O O X X X XFuel flow change X O O O X O O XOil indication change X O O O X OVisible cowl damage X X O XSmoke/odor in cabin

bleed air O O O

EPR change X X X O X X X X

X = Symptom very likelyO = Symptom possible

Note: blank fields mean that the symptom is unlikely


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Engine Stall/SurgeEvent Descri ption Engine Stall or Surge is a momentary reversal of thecompressor airflow such that high-pressure air escapes

out of the engine inlet. Corr ective action After stabilizing airplane flight path, observe engineinstruments for anomalies. Stall/surge may be self-correcting, may require the engine to be throttled back,or may require engine shutdown, if the engine can bepositively identified and the stall will not clear.

Symptoms High power: Loudbang and yaw(may berepetitive).Flames from inletand tailpipe.Vibration. HighEGT/TGT.Parameter fluctuation

Low power: Quietbang/pop or rumble.

N1

EPR

EGT

N2

POSSIBLE MESSAGES

ENG STALL

EGT OVERLIMIT

ENG FAIL

FLUX


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Flameout Event Descri ption Engine Flameout is a condition where the combustor isno longer burning fuel. Corr ective action

After stabilizing airplane flight path, verify fuel supply toengine. Re-start engine according to AFM.

Symptoms Single engine:Core speed, EGT,EPR all decay.Electricalgenerator dropsoff line; low oilpressure warningas core speeddrops below idle.Multiple engines:

As above, butalso hydraulic,pneumatic andelectrical systemproblems.

N1

EPR

EGT

N2

POSSIBLE MESSAGES

ENG FAIL

OIL LO PR GEN OFF

BLD OFF

ALL ENG FLAMEOUT

LOW


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Fire Event Descri ption Engine fire is a fuel, oil or hydraulic fluid fire betweenthe engine casing and the cowlings (or occasionally a

metal fire). It could result from severe damage. Hot air leaks can also give a fire warning. Corr ective action

After stabilizing airplane flight path, shut the enginedown and discharge extinguishant. Avoid restarting theengine.

Symptoms Fire warning.Flame or smokemay be observed.

N1

EPR

EGT

N2

POSSIBLE MESSAGES

ENG FIRE

PARAMETERS MAY LOOK NORMAL

NORMAL


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Tailpipe fire Event Descri ption Fuel puddles in the tailpipe and ignites on hot surfaces. Corr ective action

Shut off fuel to the engine and dry motor it.

Symptoms Observed flamesand smoke. N ofire warning.

N1

EPR

EGT

N2

POSSIBLE MESSAGES

START FAULT

LOW


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Bird Ingestion Event Descri ption

A bird (or other creature) is sucked into the engine inlet.Note: ingestion of ice slabs, blown tires, etc., will

produce similar, but more severe, symptoms. Corr ective action After stabilizing airplane flight path, watch engineinstruments for anomalies. If the engine surges, throttleback or shut down as necessary. If multiple engines areaffected, operate engines free of surge/stall to maintaindesired flight profile.

Symptoms Thud, bang,vibration. Odor incabin. Surge mayresult from birdingestion.

N1

EPR

EGT

N2

POSSIBLE MESSAGES

ENG STALL

EGT OVERLIMIT

VIB

PARAMETERS MAY LOOK NORMAL

NORMAL


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Severe Engine Damage Event Descri ption The engine hardware is damaged to the point where theengine is in no condition to run such as bearing

failure, major fan damage from ingestion of foreignobjects, blade or rotor disk failures, etc. Corr ective action

After stabilizing airplane flight path, observe engineinstruments for anomalies. Shut down engine.

Symptoms Depending onnature of damage

surge/stall,vibration, firewarning, highEGT, oil systemparameters out of limits, rotor speedand EPR decay,yaw.

N1

EPR

EGT

N2

POSSIBLE MESSAGES

ENG FAIL

EGT OVERLIMIT

ENG STALL

VIB

OIL LO PR

LOW


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Engine Separation Event Descri ption Engine Separation is the departure of the engine fromthe airplane due to mount or pylon failure. Corr ective action

After stabilizing airplane flight path, observe engineinstruments for anomalies. Turn off fuel to appropriateengine.

Symptoms Loss of all engineparameters.Hydraulic,pneumatic andelectrical systemproblems

N1

EPR

EGT

N2

POSSIBLE MESSAGES

ENG FIRE

HYD OFF

GEN OFF

BLD OFF

ZERO

Engine Operation and Malfunctions

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Transcript of Engine Operation and Malfunctions