1 AMT 109B Aircraft Power Plant Ignition...

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1 AMT 109BAircraft Power Plant Ignition Systems

2 Course Outline• Introduction to ignition concepts• Powerplant ignition needs• Types of ignition systems

– Battery powered ignition– Magneto powered ignition

3 Course Outline• Theory of magneto operation• Lenz’ Law• Magnetic circuit• Electrical circuit

– Primary– Secondary

4 Course Outline• High tension systems• Low tension systems• Voltage distribution• Sparking/firing order

5 Course Outline• Ignition switches• Starting circuits• Ignition starting devices

– Couplers– Powered igniters

6 Course Outline• Internal magneto timing• External magneto timing• Bendix single & dual magnetos• Compensating cam magnetos• Ignition harnesses & shielding• Spark plugs

7 Course Outline

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• Inspection and overhaul of magnetos• Inspection and overhaul of ignition harnesses• Inspection and overhaul of sparkplugs

8 Introduction to Ignition Concepts• All internal combustion engines need some source of ignition

to cause combustion.• The type, duration and source of ignition depend on the engine,

and the type of fuel being ignited.

9 Introduction to Ignition Concepts• Most fuels ignite at different temperatures (flash point-point of

rapid evaporation).• Temperature is a measure of molecular activity.• Heat is a measure of the capacity to do work.

10 Introduction to Ignition Concepts• Fuel’s have different heat requirements to create sustained

combustion.• Temperature will have to be higher and there will have to be enough

heat energy to maintain evaporation of the fuel. (flame point)

11 Introduction to Ignition Concepts• Additionally when the combustion process is happening

rapidly the ignition duration is also a factor.

12 Introduction to Ignition Concepts• Three factors effecting fuel ignition

– Temperature of ignition– Heat energy produced by ignition source– Duration of ignition

13 Powerplant ignition needs• Internal combustion engines typically need an ignition source.• This is always from some heat generating device or system.• The most common is an electric spark.

14 Powerplant ignition needs• The process of power generation in an engine is to compress a

mixture of air and fuel.• In a reciprocating engine this occurs as the result of a piston

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moving up and down in a cylinder.

15 Powerplant ignition needs• In a two stroke engine the piston moves down for power and exhaust

and then draws in air and fuel.• It then moves up to compress it• The mixture is spark ignited and the piston moves down producing

power• The piston then repeats itself ventilating air, fuel and exhaust.

16 Powerplant ignition needs• This engine needs to have a spark generated in the combustion

chamber at a very specific time each crankshaft rotation.

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18 Powerplant ignition needs• In a four stroke the piston goes up and down twice for each

power stroke.• Down to intake• up to compress and ignite• down for power• and up for exhaust, then repeat.

19 Powerplant ignition needs• This engine needs a timed spark generated in the combustion

chamber every other crankshaft rotation.• If the engine has more than one cylinder it needs to have the

spark “distributed to each cylinder in the appropriate order.

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21 Powerplant ignition needs• In the other type of four stroke reciprocating engine the air is

highly compressed by the piston moving up.• Then the fuel is sprayed directly into the hot pressurized air.• This directly ignites the fuel into an explosion rather than a

burn

22 Powerplant ignition needs• This process works because the fuel type used has a very low

flame point of 300° - 400° (Diesel/Jet A)

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23 Powerplant ignition needs• In a turbine engine it is done with a spinning compressor

“pumping” air into a chamber where fuel is introduced.• The fuel is always spraying like a blow torch, so once ignited it

will self sustain the flame front.

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25 Powerplant ignition needs• In every aircraft engine the spark must spark consistently every

time, when needed.• Even when the spark occurs perfectly it is common to have a

cylinder misfire partly for many reasons.

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27 Powerplant ignition needs• The engine also needs sparking to occur differently at different

times.• RPM is the most significant factor on when to spark the fuel air.• Load, air/fuel ratio, intake air density, and temperature are also

factors.

28 Powerplant ignition needs• The rate of fuel burning stays fairly constant at about 200 ft per

second.• Any reciprocating engine needs to have the maximum average

pressure occur at 15° ATDC.• Powell’s magic angle

29 PowellPowell’’s Magic Angles Magic Angle







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37 PowellPowell’’s Magic Angles Magic Angle• This relationship is what determines all timing criteria for

reciprocating engines.

38 Powerplant ignition needs• Depending on the RPM the spark will have to occur some time

before this so the fuel will be completely burned.• At 2500 RPM with a 5” dia. piston this will be about 40° before

Powell’s angle• Or 25° BTDC

39 Powerplant ignition needs• Any engine that is directly coupled to the thrusting medium like

a car will need to vary the spark “timing” to produce optimum power at different RPMs.

40 Powerplant ignition needs• Fluid coupled engines like and aircraft really only produce most

of their power in the last few hundred RPM. (2400-2700)• Therefore they are fixed timing set to be optimum at those

RPMs

41 Powerplant ignition needs• As load, air density, and temperature increase there is a

tendency for the fuel charge to explode rather than burn.• The heat and pressure cause the fuel to ignite at the speed of

sound in multiple flame fronts.

42 Powerplant ignition needs• The resultant rapid rise shocks the up rising piston.• It occurs way before TDC and Powell’s angle.• It breaks things, including pilot serenity.• This is detonation.

43 Powerplant ignition needs• Another condition is called preignition.• It occurs as a result of an alternative ignition source.• Such as feathered valve edges, glowing carbon flakes, etc.

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44 Powerplant ignition needs• Detonation and preignition can be related, but they are not the

same.

45 Powerplant ignition needs• Lean air/fuel ratios will increase temperatures but heat energy will

remain fairly constant. • This is due to less evaporation and slower burning.• This can also cause detonation but is more likely to just melt things.

46 Powerplant ignition needs• Rich air/fuel ratios will reduce temperatures and heat energy

due to the added vaporization.

47 Powerplant ignition needs• During starting the engine will need extra sparking power due

to the cold temps, and slow RPM.• Timing will need to be very retarded (spark occurs late) to avoid

damage to the starter.

48 Powerplant ignition needs• During off periods the sparking will need to be disabled.• This eliminates inadvertent starting when propeller is moved by

hand.

49 Powerplant ignition needs• It will need to be able to spark at any altitude, attitude and

humidity.• This includes completely wet and or frozen with ice.• It will need to be reliable and predictable.

50 Powerplant ignition needs• For aircraft they need to be self contained.• They are usually run in pairs for redundancy and to improve

overall ignition.• Dual ignition impact is more significant with large bore

engines.

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54 Battery powered ignition• A typical battery powered ignition uses a transformer, a several

switching devices, and a power source.• The power source is the battery.

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56 Battery powered ignition• The first switch allows battery voltage to the primary coil.• Voltage from the primary coil then goes to a second switch in

the engine, then to ground.• This switch is “timed” to open when spark is desired.

57 Battery powered ignition• The opening, causes the current to stop in the primary.• This collapses the magnetic field around both coils.• For every one primary turn there are 2,000 secondary turns in

this coil pack.

58 Battery powered ignition• The resultant exchange causes 12 volts to become a 24,000 volt

surge.• The 2 amps becomes 1 milliamp

59 Battery powered ignition• This high voltage is enough to break down the dielectric air gap

between the spark plug electrodes and produce a spark.

60 Battery powered ignition• Once the spark starts it will continue conducting current at a

lower voltage value• This will happen until the magnetic field is “drained” from the

coil.

61 Battery powered ignition• Shortly after this the switch will need to close to give the magnetic field

time to rebuild in the coil, for the next spark event.• The points are often mounted on a moveable(rotating) plate to provide

variable timing options

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• This allows good engine operation at all RPM ranges.

62 Battery powered ignition• The secondary voltage is carried to the spark plug via a rotary

switch called the distributor.• Then it travels through “high tension” wires to the plugs.• They are sequenced to the firing order needs of the engine.

63 Battery powered ignition• These extremely high surges in the coils cause rapid oscillations of

voltage and current.• This can damage the “engine switch” (points or contact points)• A condenser is installed as a parallel path to ground.

64 Battery powered ignition• This drains the A/C oscillations to ground preventing high current

arcing of the points.• A condenser is a large capacitor.• It is imperative that the capacitor be balanced with the inductor(coil)

and the supply voltage.

65 Battery powered ignition• Summary:• The off/on switch is between the battery and the coil.• The engine switch is between the coil and ground.• Current is supplied from a battery, which is charged by an engine

driven generator.

66 Battery powered ignition• To defeat the system the circuit is broken stopping voltage to the coil.• If the battery fails the systems fails.• But the battery can produce great spark at any engine speed, including

cold or hot starts.

67 Magneto powered ignition• Magneto operation differs primarily because it does not use

battery current.• It incorporates its own rotating permanent magnet generator.

68 Magneto powered ignition• The rest of the components are similar, but the theory of

operation is somewhat different.• Its primary advantage is that it can be completely self

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contained in a small engine driven package.

69 Magneto powered ignition• Multiple units can be installed for redundancy and improved

flame propagation.

70 Magneto powered ignition• Two main disadvantages are that they need moderate engine

RPM to function.• They do not provide a means to vary the timing during

operations other than start.

71 Theory of Mag Operation• Internal circuits include:• Magnetic• Primary-electrical• Secondary-electrical

72 Theory of Mag Operation• Magnetic circuit includes:• Rotating four (or more) pole magnet• Pole shoes w/extentions• Coil core

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74 Theory of Mag Operation• Primary circuit includes:• Primary coil winding• Points• Condenser• Connecting wire• Grounding “P” lead and switch

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76 Theory of Mag Operation• Secondary circuit includes:• Secondary coil winding• Distributor• High tension leads

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• Spark plugs

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78 Theory of Mag Operation• The magnetic circuit allows the lines of flux in the rotor to

oscillate.• At neutral the poles are not lined up with the shoes.• There is no flux concentrating in the poles and coil core.

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80 Theory of Mag Operation• At all other times flux is varying in the coil core and poles.• The flux reverses each cycle, or one time for each rotor pole.• Due to hysterisis the plot of this is a flattened circular shape.

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82 Lenz’ Law• States that current inducted in a circuit will produce counter

magnetic lines of flux that oppose the original induction flux.

83 Lenz’ Law• This means if the flux in the pole shoes and coil core is allowed

to pass through a complete circuit, the resultant current will create flux that opposes the rotor flux.

84 Lenz’ Law• No coil the flux will concentrate on the core.

85 Lenz’ Law• As the core moves close the lines bend to fit it.

86 Lenz’ Law• They finally concentrate in it.

87 Lenz’ Law• With a coil as the core moves close counter current will cause

88 Lenz’ Law• opposite polarity magnetism, resisting a build up of flux.

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89 Lenz’ Law

90 Lenz’ Law• As the core moves away the current and resultant field

switches

91 Lenz’ Law• The magnetic polarity is the same and the fields

92 Lenz’ Law• resist any decreases

93 Lenz’ Law• Thus the addition of a coil circuit to the core will create an

inductive lag in the magnetic flux.

94 Lenz’ Law• This lag allows us to maximize the field buildup and minimize

the collapse time when the current is cut off.

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96 Theory of Mag Operation• So as a result of Lenz’ law the flux lags and stays “built”

around the coil until something after the rotor gets back to neutral.

97 Theory of Mag Operation• At this time the points open, the current disappears• the time between when the rotor passes neutral and when the

points open is called E-gap, or efficiency gap.

98 Theory of Mag Operation• At this point if there had been no coil the magnetic circuit

would already have been reversed.• So rate of field collapse when the points open is enhanced

some by the reversed field.

99 Theory of Mag Operation• Enhancing too much (E-Gap) then interferes with the buildup of

the next field cycle.

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• In a sense the primary circuit and the magnetic circuit are constantly working against each other, and the secondary is auxiliary to them.

100 Theory of Mag Operation• But what we desire from this system is the field collapse

around the secondary.• The secondary is identical to a battery operated system.• A distributor switches each spark to the next cylinder inline for

firing.

101 Theory of Mag Operation• The magneto is disabled by adding another circuit parallel to

the primary points. • This causes the primary circuit to stay active causing constant

magnetic flux lag, that never rapidly collapses around the secondary.

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103 Theory of Mag Operation• These devices have no means to alter when the spark fires for each

cylinder like other timing devices do.• Primarily because the most of the power of a propellered engine is

produced between 300-400 RPM.

104 Theory of Mag Operation• But they may have devices that do alter timing during starting.

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106 Magneto Timing• The two areas of timing a magneto are internal, and external.• A number of things must occur at the same time, or in a well

orchestrated sequence for the engine to function.

107 Magneto Timing• Within the magneto the magnetic rotor must be just past

neutral axis (E-Gap).• The points must be just opening.• And the distribution rotor must be pointed at the correct

cylinder.

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110 Magneto Timing• Within the engine the intake and exhaust valve must be closed. • The piston/cylinder that is to fire must be close to the top of its

compression stroke.• It must have a fresh air/fuel charge.

111 Magneto Timing• The selected wire(s) from the magneto(s) distributor must be

connected to this cylinder.• And the crankshaft/magneto must be spinning.

112 Magneto Timing• If all of these conditions are met, the cylinder will fire.

113 Magneto Timing• Timing is initially set internally in the magneto.• It is then set to the engine.• Both “setting procedures” may call for initial gross settings,

followed by some means for fine adjustment.

114 Magneto Timing• The first step is to install the magnetic rotor/points cam. On

some this can be indexed infinitely, and others it will be one or two positions depending on rotation.

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116 Magneto Timing• Then for most magnetos, set the rotor at the points opening

position (E-Gap)• Adjust the points to just open.• Move rotor to maximum opening to verify the points range of

operation.

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118 Magneto Timing

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• If the points don’t have the correct range of operation, even though they are in time, the coil will not charge correctly.

• Or the points will wear out prematurely.• This happens when the cam is indexed wrong but the points are se t to

make up for it.

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120 Magneto Timing• Once E-Gap and range are within limits, auxiliary points may be

adjusted.• Adjustment of points will require the use of a feeler gauge, a

screw driver and a degrees of rotation indicator.

121 Magneto Timing• The points are secured with two screws, where one attachment

is slotted. By carefully moving the slotted end with the other screw snug it can be set, and secured.

122 Magneto Timing• Usually the last thing to be set is the distributor/rotor

alignment.• Depending on the magneto, the distributor will be indexed to

the rotor shaft during initial assembly of the magneto upper and lower housing.

123 Magneto Timing• This calls for correct alignment of the drive and driven gears.• There are indicator marks for this alignment.• Most can be set for either left (CCW) or right (CW) hand

rotation.

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125 Magneto Inspection & Repair• Magneto exterior inspection is to determine general security of

fasteners & wiring, attachment to engine, leaks or obvious damage.

• Inspection includes checking/ adjusting magneto to engine timing.

126 Magneto Inspection & Repair

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• In general internal inspection is done during overhaul.• AD/SBs do call for interior inspection on some models at

specific intervals.

127 Magneto Inspection & Repair• Overhaul constitutes replacement of primary wear items and

cleaning.• Additional requirement to measure rotor flux for loss of

magnetism.

128 Magneto Inspection & Repair• Magneto overhaul usually done through a MRO (Maintenance

Repair Operator).• Units returned or exchanged w/FAA 8130 release tag.

129 Magneto Inspection & Repair• The points in a magnetos are the primary wear item.• Bearings are the next likely to fail.• Coils may fail due to heat, particularly from large spark plug

gaps.

130 Magneto Inspection & Repair• Points typically wear in several ways, almost always leaving

some pitting peaks.

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135 Magneto Inspection & Repair• The magneto ignition harnesses do degrade over time.• This is due to both use and exposure to heat, contaminants,

mechanical damage and time.• Typical failure is for spark to leak to the exterior shielding.

136 Magneto Inspection & Repair• Once the spark begins a trail it will create a carbon track that

makes it easier to allow more leakage.• Leaking harnesses can only be replaced.

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137 Magneto Inspection & Repair• Wires can be made up but most common field repair is to

replace entire harness as one assembly.• Harness can be tested using equipment that supplies high

voltage A/C to leads.

138 Magneto Inspection & Repair• Magnetos and harnesses can be pressurized.• Pressurization reduces tendency to leak.• Inspection includes ensuring integrity of pressurization.

139 Aircraft Magneto Operation• Critical Safety Note:• Treat all aircraft engines as if they were a loaded Gun• MAGNETO grounding systems fail commonly• Stay clear of the Propeller Arc

140 Aircraft Magneto Operation• Aircraft magnetos are attached to the engine case with

adjustable hold down clamps or fasteners• Aircraft engines use two independent magnetos

141 Aircraft Magneto Operation• The gear drive must be correctly aligned to the engine gears • They have a spark lead for each cylinder• To maintain proper timing each lead must be attached to the

correct cylinder

142 Aircraft Magneto Operation• Each magneto must be set so that they spark simultaneously• They must do this when the crankshaft and camshaft are in the

correct position

143 Installation and Adjustment• Upon initial installation they must inserted with the drive gears

correctly meshed to the engine• This is done by rotating the propeller to No.1 cyl on compression

stroke• A timing mark on the crankshaft or ring gear is aligned with the case

split

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144 Installation and Adjustment

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146 Installation and Adjustment• The magneto is then set to No. 1 spark lead just firing

– This can be done by locating either a chamfered internal tooth, or some use an alignment pin inserted into the housing

147 Installation and Adjustment

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151 Installation and Adjustment• Do not rotate the crankshaft or the magneto until all

alignment jigs have been removed

152 Installation and Adjustment• Each magneto is now installed carefully maintaining alignment• Once they are both clamped snugly in place a buzz box can be use d to

“fine tune” the setting• The buzzer will change tone when the internal switch just opens

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154 Installation and Adjustment• The buzzer has three leads, one for each mag, and one for

ground• The buzzer leads are attached to the P-leads outputs on the

mag• Lightly tap the magneto housing with a knuckle for fine

movements.

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156 Installation and Adjustment• Be sure to rotate the magneto in a fashion that eliminates any gear or

impulse coupling freeplay

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• Set the second magneto identical to the first unless otherwise specified• Clamp each unit down and rotate propeller to verify accuracy

157 Installation and Adjustment• Often tightening magnetos will change their setting• Make sure P-leads are attached and functional• Once this is done attach spark plug leads in the correct

locations

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159 Spark Plug Firing Order• Engine firing order is the sequence of spark events that must

occur for all cylinders to produce power.• It is established by the engine’s crank & camshaft.

160 Spark Plug Firing Order• Magneto firing order is always 1, 2, 3, 4, ? Etc.• #1 mag will always go to #1 cylinder, then #2 mag goes to #3 or

#4 depending on the manufacturer.

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162 Spark Plug Firing Order• Cylinder numbering is set by the manufacturer.• Lycoming is with #1 in front odds on the right.• Continental is #1 rear odds on the right

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164 Spark Plug Firing Order• Radials put #1 on top, rear bank if twin bank.• Odds to the rear and evens to the front in direction of

crankshaft rotation.

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167 Spark Plug Firing Order• For all Lycoming and Continental 4 and 6 cyl engines the firing

order of the engines are the same.

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• This is due to the difference in numbering and firing order.

168 Spark Plug Firing Order• Lycoming 4 Cyl

2 14 3

• Firing order = 1, 3, 2, 4• Continental 4 Cyl

4 32 1

• Firing order = 1, 4, 2, 3

169 Spark Plug Firing Order• Lycoming Continental

2 1 6 54 3 4 36 5 2 1

• 1, 4, 5, 2, 3, 6 1, 6, 3, 2, 5, 4

170 Spark Plug Firing Order• Five, seven, and nine cylinder radials fire odds the evens.• Twin banks fire opposite side/opposite bank, roughly.

171 High Voltage Distribution• Generally most ignition systems develop high voltage in the

magneto then distribute it via high tension wires.• These wires are positively mechanically attached.

172 High Voltage Distribution• They will have an inner core of stranded wire.• An outer core of shielded wire.• The attachments should ground the shielding on both ends.• The high voltage shielding is provided by a 4mm thick layer of

insulation.

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175 High Voltage Distribution• The leads going from the magneto points to the kill switch will

also be shielded but not of the high tension variety.

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• The problem with high tension voltage is it produces large amounts of EMF energy.

176 Low Voltage Distribution• This system is used for engines operated at high altitude.• The coils are suspended on the end of the spark plugs.

177 Low Voltage Distribution• The mag has a primary coil that feeds a second primary coil at

the plug end. It is wound with the secondary coil.• The high voltage tends to easily leak at low atmospheric

pressures

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180 Starting Devices• There are several types of units designed to assist engine

starting.• The magneto is not setup very well for the low RPM situation

found during start.

181 Starting Devices• The most common is a impulse coupler.• This device works by having fly weights that catch stop pins at

slow RPM.

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183 Starting Devices• The pin stops the mag for about 20° then lets it fly back to

original timing.• This gives it retarded timing and faster mag speed.

184 Starting Devices


186 Starting Devices• One problem these have is the new generation of starters and

light weight high current wiring.

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• This allows the starter to spin the engine faster than the coupler is designed to work.

187 Starting Devices• They are typically installed on the left mag only.• The ignition switch should account for this and disable the

right one during start.

188 Starting Devices• Another type is the induction vibrator.• It provides a rapid firing battery powered spark during the

timing event.

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193 Starting Devices• The Bendix S-200 series use an additional “retard” breaker

assembly.• This actuates an additional battery powered ignition circuit

timing to fire very late.


195 Starting Devices• The vibrator section will only operate when the starter circuit is

on, the retard points are open and the main points are open.• Power comes from the starter circuit, and the other two points

will ground the vibrator.

196 Combined Ign/strt sw

197 Spark plugs• Primary purpose of a Spark Plug is to start the ignition process.• Secondarily it can regulate the temperature in the cylinder

some.

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198 Spark plugs• Composed of three main sections: Shell, ceramic insulator, and

core/electrodes• Can be insulated or non-insulated• May have internal resistor to reduce current in secondary

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201 Spark plugs• This prevents rapid deterioration of plug, rotor and block• Shell contains insulator and core electrode, ground electrode

fused to tip of shell

202 Spark plugs• Electrodes can be copper core with steel gnd, or silver core

with iridium gnd• The former uses massive electrodes, the latter uses fine wire

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204 Spark plugs• The upper portion of the shell will provide shielding for the

connector• It will be ceramic lined as well• Connector and ceramic must be spotless and sterile

205 Spark plugs• Can use 5/8-24 connector nut or ¾-20 nut (most common)• Sparkplugs attachment can be 14mm long or short reach, or 18mm long

or short reach.• Reach is a measure of how deep the plug penetrates into the cylinder.

(3/8”-13/16”)

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207 Spark plugs• Sparkplug temperatures need to range from 800°f to 1630°f to

operate correctly. • Too hot causes pre-ignition, too low causes lead fouling.

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209 Spark plugs• The temperature is adjusted by designing the ceramic and core

to fit “tighter” in colder plugs.• More ceramic contact with the shell produces a colder plug.

210 Spark plugs

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212 Spark plugs• Basic numbering for Champion includes:• R H M 40 E• R = Resistor type• H=3/4 Shielded, E=5/8 shielded, blank= un-shielded

213 Spark plugs• R H M 40 E• Bore x Reach, M=18mm x ½”, L=14mm x ½”, B=18mm x 13/16”,

J=14mm 3/8”, U=18mm x1 1/8”• 40= heat range, higher is hotter• Electrode design, E=2 prong massive, W=fine wire iridium

214 Spark plugs• Prior to installation of the plug set the gap.• This must be done with the proper tools. (Clamp type device)

215 Spark plugs• Checking gap is done with rod type feeler gauge• Flat one will give inaccurate readings.

216 Spark plugs

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218 Spark plugsAdjusting either type of electrode without the proper tool will damage the electrodes and destroy the sparkplug.

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219 Spark plugs• Installation includes torque of 360-420 inch lbs for Lycomings,

300-360 for all others.• Use 7/8 deep sparkplug socket only, with torque wrench.• Use new gasket unless gasket is CHT probe.

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221 Spark plugs• Champion 2612 anti-seize on 2nd & 3rd threads. Do not get on

electrodes or in connector well.

222 Spark plugs• Connector well must be sterile.• Do not let anything including wire termination spring come in

contact with ceramic bore.

223 Spark plugs• Pull straight out

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225 Spark plugs• If you let the spring drag it will leave a mark that will become a

track for current to follow.• Carbon will build up there and allow more current to go this

way rather then across the gap.

226 Spark plugs

227 Spark Plug Inspection & Repair• Engine conditions can be determined by examining the spark

plugs.• Proper conditions will leave a light grey or brown dusty

coating.

228 Spark Plug Inspection & Repair• Electrode erosion is normal and all but fine wire can be

adjusted.• Ground lug is bent back to gap specification after spark plugs

are cleaned.

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234 Spark Plug Inspection & Repair• Rotating spark plugs extends their life.• Typical pattern calls for each plug to fire one way, + >>> -, or

- >>> +• They also should be rotated top to bottom in the cylinders.

235 Spark Plug Inspection & Repair• Use a service tray as spark plugs are removed.• Rotate tray 180° for reinstallation.• This moves them from top to bottom and moves them from

odds to evens, reversing polarity.

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• DO NOT OVER TORQUE

238 Turbine Igniters• Typically has four parts• Off/On control• Ignition exciter• Leads• Igniter

239 Turbine Igniters• Off/On control is likely to be integrated into the aircraft

systems.• Computerized controls will handle the entire starting sequence

including ignition.• Pilot control will be available.

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1 AMT 109B Aircraft Power Plant Ignition...

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