airspeed discrepancy

14th Flight Safety Conference

15-18 October 2007

Airspeed Discrepancy

Presented by

Hélène RebelHead of A330/A340 Operational StandardsFlight Operations Support

15-18 October 2007 14th Flight Safety Conference © A

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Foreword

• 2002: Just after takeoff on an A340-300, the following sequence of events occurred:

VFE OVERSPEED warning during climb associated with buffet, but with the Captain and First Officer airspeed indications below VFE.

VMO OVERSPEED warning with the Captain and First Officer airspeed indications below VMO.

ALTN LAW

ADR1 + ADR2 FAULT

• Erroneous speed led to unlimited rudder deflection

• Uneventful landing – Fin and rudder changed after the flight


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Foreword

• 2006: During descent on an A310, the following sequence of events occurred:

Sudden speed decrease associated with thrust increase and pitch attitude decrease.

VMO OVERSPEED warning with the Captain airspeed indication below VMO, but with the First Officer airspeed indication above VMO.

Significant nose down rate of descent, up to – 12 000 ft/min and speed increase up to 131 knots above VMO.

Speed indication eventually back to normal on Captain’s side - Uneventful landing


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Unreliable Speed

• Difficult to:Rapidly identify the situationFly the aircraft

• Generally however, not a permanent situation:It is transient, orIt can be stopped via use of an appropriate drill

Foreword

Good knowledge of the symptoms is important for: Early detection, Taking appropriate decision


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Contents

• Early detection: Symptoms and Cues

• Taking appropriate decision: Recommendations

• BackUp Speed Scale

• Increase Flight Crew Awareness


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• Detecting an Unreliable Airspeed presents some traps:

All indications may be consistent but equally unreliable,

Indications may differ => potential difficulties to determine the correct value.

• Important contributors to a timely detection:Instrument scanning,Flight crew awareness of typical characteristics of

speed / pitch / thrust

Early detection: Symptoms and Cues


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Speedrelatedcues

Autothrust orAutopilotrelatedcues


• No single set of cues can be defined, but the following observations are an obvious attention getter:

Altituderelatedcues

Warning /Systemrelatedcues


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Speed indication– Increasing with large nose-up pitch attitude,

– Decreasing with large nose-down pitch attitude.

Speed related cues


Unusual “CAPT - F/O” or “IAS - target speed” differences

Unusual speed / aerodynamic noise relationship

Abnormal large speed fluctuations

CAPT F/O


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Abnormal A/THR or AP/FD behavior, when in SPD mode.


Autothrust / Autopilot related cues

Altitude related cues

Inconsistency between radio altitude and pressure altitude

Constant indicated altitude while in climb or descent

Positive or negative V/S while in level flight


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Simultaneous activation of overspeed warning and stall warning / stick shaker.


Warning / System related cues

Unexpected stall warning (and stick shaker activation on A300/A310)

Unexpected and undue overspeed warning or ADR DISAGREE caution (Fly-by-wire aircraft)

Unexpected IAS DISCREPANCY caution (optional)

Unexpected system behavior:FLAP RELIEF message on the ECAM (A330/A340)Automatic flap retractionSlat Speed Lock FunctionNon-extension of the L/G via normal control


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Contents






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Recommendations

• The Unreliable Speed procedure concept includes:

Cues for recognition of the Unreliable Airspeed condition (expanded information in FCOM procedure),

Memory items (pitch/thrust data) for short term flight path control,

QRH action steps and fine pitch/thrust data tables for long term flight path control, down to landing.


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Recommendations

When an unreliable speed situation is suspected/detected:SAFE CONDUCT OF THE FLIGHT NOT AFFECTED

Crosscheck of Captain PFD, First Officer PFD and Standby

speed/altitude indicator


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Recommendations

When an unreliable speed situation is suspected/detected:

SAFE CONDUCT OF THE FLIGHT

AFFECTED

Memory Items


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Recommendations

General procedure philosophy

Memory Items

Stabilization and troubleshooting

Faulty ADR(s) identified

Faulty ADR(s)…… OFF

Flight Continuation, Diversion or Immediate turn back

Faulty ADR(s) not identified or

All ADRs unreliable

2 ADRs…… OFF(only for fly-by-wire)

Pitch/Thrust Tables


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Contents






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Backup Speed Scale

• When the crew select all ADRs OFF:The Backup Speed Scale replaces

the PFD speed scale on both PFDs.

GPS Altitude replaces the Altitude Scale on both PFDs.

• Enables flying at a safe speed:Above stall speed,Below maximum structural speeds.

• Allows to reach a safe speed, by adjusting thrust and pitch.

What is the Backup Speed Scale?


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Backup Speed Scale

• The BackUp Speed Scale (BUSS) will be offered:As an option on A320 and A330/A340 aircraft familiesAs a basic item on A380 aircraft

• It will be activated following ECAM procedure or paper procedure, when ADR 1+2+3 are selected OFF

• The new idea: If the crew detects an Unreliable Speed situation

Use of the BUSS instead of Thrust/Pitch tables

When the Backup Speed Scale can be used?


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Backup Speed Scale

General philosophy

Memory Items

Troubleshooting

Faulty ADR(s) identified

Faulty ADR(s) not identified or

All ADRs unreliable

ADR 1+2+3…… OFF

Flight Continuation, Diversion or Immediate turn back

Faulty ADR(s)…… OFF

““FLY THE GREEN”FLY THE GREEN”


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Contents






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Increase Flight Crew Awareness

• To help the airline in training, Airbus

Has provided several presentations during:

– Operational Liaison Meetings

– Performance and Operations conferences

Develops training aids:

– Specific Briefing Guide in the DVD 1 (FFS 7)

– PDP (Procedure Data Package) presentation on MFTD

– Flight Crew Training Manual ref. 03-34

– New tool: E-briefing available on Airbus World

Communicates:– During previous Flight Safety conferences– Via Safety First magazine


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Increase Flight Crew Awareness

The aim of these presentations/tools is to enhance the pilots’ awareness and provides some cues/information:

To ensure correct application of the procedure by

– Ensuring proper understanding the procedure structure

– Avoiding any mistake when isolating the faulty ADR

– Describing the flying technique

To facilitate the detection of the anomaly


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Contents





• Conclusion


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• Rapid detection of Unreliable Speed is essential

Conclusion

• Thanks to the procedure proposed by Airbus, Unreliable Speed could be a temporary situation:

It is important to apply the QRH procedure, in order to identify the faulty ADR,

Normal flight is recovered, once the faulty ADR(s) switched off.

• In the meantime, fly pitch/thrust memory items when needed.


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Conclusion

Be aware of the symptoms

Consider what could be wrong

Apply the procedure

To improve situation awareness and procedure understanding

TRAINING IS A KEY ELEMENT TRAINING IS A KEY ELEMENT


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