Post on 14-Apr-2018
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Unreliable speed indications
Operational Liaison Meeting
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2Unreliable speed indications
Background
Two recent fatal accidents on non-Airbusaircraft and several reports of incidents
attributed to erroneous airspeed and/or altitude
indications have prompted the need to improve
flight crew awareness to identify and tacklesuch a failure.
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Content
Architecture display architecture interface with flight controls
interface with flight guidance
conclusion about architecture Probes: what may happen?
Recommendations
Procedure
Conclusions
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Display architecture - A300/A300-600/A310
ADC 1 ADC 2
Normal display
Reconfigurations
STBY
probes
STBYPFD 2
(Airspeed
indicatoron A300)
PFD 1
(Airspeed
indicatoron A300)
CAPT
probes
F/O
probes
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Display architecture - Fly by wire A/CPFD 1 PFD 2
ADC 1 ADC 3 ADC 2
Normal display
Reconfigurations
STBY
CAPT
probes
STBY
probes
F/O
probes
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Effect on flight controlsA300 / A300-600 / A310:
Erroneous airspeed / altitude does not affect
the flight controls (conventional aircraft ).
Fly by wire aircraft: Depending of the failure, erroneous airspeed /
altitude may affect the flight control of fly by
wire aircraft. In the worst case, the aircraft
reverts to a conventional aircraft.
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Effect on flight controls fly by wire A/C)Each flight control computer (PRIM on A340/A330, ELAC
on A320) receives the speed from the three ADC.
ADC 1
ADC 3
ADC 2
speed PRIM ELAC
speed
speed
COMPARISON/
SELECTION
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Effect on flight controls fly by wire A/C)
it is eliminated, without any caution.
Normal operations continue.
If one has deviated:
ADC 1
ADC 3
ADC 2
speed
COMPARISON/
SELECTION
speed
speed
PRIM ELAC
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Effect on flight controls fly by wire A/C)
ADR DISAGREE caution is triggered.the flight controls revert to alternate law (without protections).
SPD LIM flag is shown on both PFD ( no Vls, no Vsw).
This situation is latched ( PRIM/ELAC reset has no effect).
If the two remaining values are no longer in agreement:
ADC 1
ADC 3
ADC 2
speed
speed
speed
.
DISAGREE
PRIM ELAC
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Effect on flight guidance
AP / ATS are affected if ADC 1 or 2 are affected.
Possible AP /ATS disconnection depending on speed
inaccuracy.
A300/ A300-600 /A310
ADC 2 speed/altitude
ATS 2
AP 2
ADC 1speed/altitude ATS 1
AP 1
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Effect on flight guidanceFly by wire aircraft:Each flight envelope computer (FE)on A340/A330 or flight
augmentation computer (FAC) on A320 receives the speed
and the altitude from the three ADC.
ADC 1
ADC 3
ADC 2
FE FAC
COMPARISON/
SELECTION
speed/altitude
speed/altitude
speed/altitude
On A320, same check is performed by the FMGC on the
speed and the altitude.
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Effect on flight guidance
the related ADC is eliminated without any caution.
Normal operations continue (except that CAT 3 is no more
available).
If one speed deviates:
ADC 1
ADC 3
ADC 2
speed/altitude
speed/altitude
speed/altitude
COMPARISON/
SELECTION
FE FAC
Fly by wire aircraft:
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Effect on flight guidance
autopilot and autothrust disengage.
If the two remaining ADC are no longer in agreement:
ADC 1
ADC 3
ADC 2
speed/altitude
speed/altitude
speed/altitude .DISAGREEFE FAC
Fly by wire aircraft:
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Effect on flight guidance
When the disagree disappears:
the autopilot and the autothrust may be used again
on the A330 / A340.
Fly by wire aircraft:
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Conclusion about architecture Single failure (one probe affected):
A300 / A300-600 / A310:
One display is wrong.
AP and ATS are affected with possible automatic
deactivation.
Fly by wire aircraft:
One display is wrong but,
no effect on flight control and guidance.
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Conclusion about architecture Dual failure - Two probes affected, giving
different wrong values:A300 / A300-600 / A310:
Autopilot and autothrust are affected with possible
automatic deactivation.
Fly by wire aircraft:
flight control normal law and protections, autopilot,
autothrust are lost; on A330/A340, FD/AP/ATHR are
again available if disagree disappears.
The crew is aware of the anomaly (ADR DISAGREE
ECAM caution).
The aircraft reverts to a conventional aircraft, in
manual flight.
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Conclusion about architecture Dual failure - Two probes affected, giving
identical wrong values:
This may not be detected by the systems
which may eliminate the correct value and usethe erroneous ones (only fly by wire aircraft).
The crews must be aware of thesymptoms in order to recognize such a
situation.
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Pitot probes
Total
pressure
ADM
Drain hole
Heatingresistor
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Pitot probes - heavy rain
speed indication is too
low or fluctuating
It returns to normalwhen water drains.
ADM
Total pressure
Measured pressure is
lower than total
pressure:
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Pitot probes - icingPitot icing may be due to:
severe icing condition (in this case the anomaly is
transient)
or, pitot heat failure.
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Pitot probes - icingADM
Total
pressure
with free
drain hole
speed indication
decreases.
If icing is transient, speed
fluctuations and erratic
A/THR are observed.
Measured pressure
gradually decreases :
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Total
pressure with
obstructed
drain hole
Measured pressure
remains constant
Pitot probes - icingADM
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Pitot probes-foreign objectaccumulation
ADM
Total
pressure
Measured pressure
remains constant:
Abnormal AP/FD behavior to
hold the speed:
pitch up in OPEN CL pitch down in OPEN DES( SPEED MODE A300/A310).
Speed is constant in level flight.
It increases in climb.
It decreases in descent.
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Pitot probes obstructedOther consequences:
The Mach number will vary in the same way as
IAS.
The altitude and V/S information remains
correct. The FPV remains correct.
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Static probes - total obstruction ongroundStatic pressure constant at airfield value.
Lift-off
speeddecreases
speedincreases
altitude remains constant
Normalindications
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Static probes - total obstruction onground Altitude is wrong
Speed and Mach are wrong
Flight Path Vector is unreliable
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RecommendationsPilots should suspect erroneous speed/altitude
information when they observe:
Fluctuations of indicated speed.
Abnormal correlation of the basic flight parameters
(speed, pitch attitude, thrust, climb rate).
Abnormal AP/FD/ATHR behavior.
Undue stall warning or overspeed warning.
Reduction of aerodynamic noise with increasing speed.
Increase of aerodynamic noise with decreasing speed.
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Crosscheck all three ADR outputs and
stand-by instruments.
Recommendations When erroneous speed/altitude information is
suspected:
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Crosscheck all three ADR outputs and
stand-by instruments.
Recommendations When erroneous speed/altitude information is
suspected:
Detecting an unreliable airspeed indication presents
some traps:
all indications may be consistent but equally
unreliable. indications may differ but attempting to assess the
correct indication may be hazardous.
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RecommendationsWhen erroneous speed/altitude information is
suspected:
Disconnect AP, FD and A/THR.
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RecommendationsWhen erroneous speed/altitude information is
suspected:
Pitch and thrust memory items have been
established for short term flight path control:
Intended to provide short term protectionagainstVls and Vmax until the QRH is accessed.
Fly target pitch attitude and thrust setting.
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Procedureto ensure safe flight before referring to QRH
AP/FD....................................................................OFFA/THR....................................................................OFF
FLAPS.......................MAINTAIN CURRENT CONFIG
SPEEDBRAKES.......................CHECK RETRACTED
L/G...........................................UP WHEN AIRBORNE
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Procedureto ensure safe flight before referring to QRHINITIAL PITCH ATTITUDE AND THRUST GUIDANCE:
A300 / A300-600 / A310:
To climb:
PITCH...with slats extended: 12.5
with slats retracted: below FL
100: 7.5
above FL 100: 5
THRUST................................................100% N1
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INITIAL PITCH ATTITUDE AND THRUST GUIDANCE:
A300 / A300-600 / A310:
to level off / maintain level flight (at safe altitude) :
PITCH ................................2.5
THRUST.......................... below FL 100: 72 % N1
FL 100 - FL 250: 82
% N1
above FL 250: 92
% N1
To descend:
PITCH ..............................- 2.5(nose down)
THRUST........................ IDLE
Procedureto ensure safe flight before referring to QRH
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INITIAL PITCH ATTITUDE AND THRUST GUIDANCE:
Fly by wire A/C:
With slats extended:
THRUST......................................................MCT
PITCH ATTITUDE...................................12.5
In clean configuration:
THRUST LEVER..............................CLB
PITCH ATTITUDE below FL 100...................10
PITCH ATTITUDE above FL 100.................5
aircraft climbs with the initial pitch and thrust (simpler than
A300/A310 to have common values for A320, A330 and A340).
Procedureto ensure safe flight before referring to QRH
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Procedure to continue the flight When the aircraft flight path has been
stabilized the crew should refer to the
unreliable speed indication procedure or , in
cruise, thrust setting for turbulence speed.
This permits to refine the initial pitch and thrustsettings
and prepare for the next phase of flight.
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Procedure to continue the flight Takeoff:
Pitch and thrust are provided for level flight at F and
S speeds for configuration change from Conf2 to 1
and from Conf1 to Clean.
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Procedure to continue the flight Climb , cruise and descent:
Pitch and thrust are provided for turbulence speeds
(speeds vary according to the FL)
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Procedure to continue the flight Cruise:
A detailed thrust table for the cruise is available inQRH 5.01 SEVERE TURBULENCE
Note that the crew may also use this table in case of
ADR disagreement to determine which ADR (s) is
wrong
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Procedure to continue the flight Approach:
decelerate from the descent speed to green dot speed:
increase pitch and thrust according to the table ( level flight
at green dot)
Green
Dot
Descentspeed
Clean conf
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Procedure to continue the flight Approach (contd):
Configuration changes are done in level flight
Green Dot S speed Vls conf2
+10
Vls conf 3
+10
5.5 7.5 7 6
Conf 1 Conf 2 Conf 3 (Conf full )Clean
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Procedure to continue the flight Approach (contd):
Deceleration to the speed for the next configuration
change is done in level flight by:
reducing the thrust towards idle, and
increasing the pitch to maintain the level flight
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Procedure to continue the flight Approach (contd):
how to decelerate to the speed for the next conf change ?
Actual
conf
Next
conf
Reduce towards idle
thrust
Adjust pitch to maintain
the level flight
When the pitch reaches
the pitch required to fly
the speed to select nextconf, adjust the N1 to fly
that speed
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Procedure to continue the flight Approach (contd):
Conf 1 Conf 2
Clean
5
59 %
Reducethrust,adjust pitchfor level off
When pitchreaches 7.5set 60% N1
pitch N1
7.5
60%
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Procedure to continue the flightFinal approach:
- Reach FAF in Conf FULL and Gear down
- At FAF, set the appropriate pitch and N1 to descend at -3
gradient at Vls + 10 kt.
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Conclusions A new procedure concept with memory items is
proposed based on extensive simulator testing
The FCOM has been revised to provide
expanded awareness information and guidance
material
The new procedure is incorporated in the QRH
for quick access.
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