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Monday, January 3, 2011

Airbus Issues Pitot Tube Warning

Airbus warns about a potential malfunction of speed sensors on aircraft like the Air France A330 that crashed into the Atlantic last year, killing all 228 people aboard.

Airbus sent the warning regarding Pitot tubes to the 100 operators of its A330 and A340-200 and A340-300 jetliners..

Airbus said in some cases two Pitot tubes can give matching, incorrect speed data, which could lead pilots to re-engage autopilot prematurely. The warning advises pilots not to re-engage automatic pilot following questionable readings from airspeed indicators until they have double-checked the readings.

Pitot Tubes are suspected of a role in the June 1, 2009, Rio-to-Paris crash that came during a strong thunderstorm over the Atlantic. Automatic messages sent by the plane's computers just before it crashed show it was receiving false air speed readings from its Pitot tubes.

The Air France crash probe is still centering around possible icing of the jetliners pitot tubes. Telemetry received from the airplane gave inconsistent airspeed readings just before contact with the aircraft was lost. Investigators have insisted that a series of failures, and not the Pitot tubes alone, likely caused the crash.

The telex from Airbus cautions flight crews to check airspeed indications before engaging the autopilot.

The complete text of the telex reads:

FROM : AIRBUS CUSTOMER SERVICES TOULOUSE

TO : ALL A330/A340 CFM GE PW RR OPERATORS

FLIGHT OPERATIONS TELEX - FLIGHT OPERATIONS TELEX

OUR REF: 999.0112/10 dated 20 December 2010

Subject: ATA 22 and 34 - Loss of AP and A/THR associated with alternate law reversion

CLASSIFICATION: AIRWORTHINESS

Notice: This FOT provides information about a significant operational issue that is related to airworthiness or safety. It is each Operator�s responsibility to distribute this FOT or to distribute the information contained in this FOT, to all of their applicable flight crews without delay. Failure to apply this FOT may have a significant impact on safe aircraft operations. This FOT and the OEB advance copies will be available in pdf format in AirbusWorld within two days.

1. PURPOSE

The purpose of this FOT is to recommend the flight crew to check airspeed indications before engaging the autopilot, when in alternate law.

2. EXPLANATION

When there are significant differences between all airspeed sources, the flight controls revert to alternate law, the autopilot (AP) and the autothrust (A/THR) automatically disconnect, and the Flight Directors (FD) bars are automatically removed. It has been identified that, after such an event, if two airspeed sources become similar while still erroneous, the flight guidance computers:

  • Display FD bars again.

  • Enable autopilot and autothrust re-engagement.

However, in some cases, the autopilot orders may be inappropriate, such as possible abrupt pitch command. Therefore, the flight crew must apply the following procedure.

3. OPERATIONAL RECOMMENDATIONS

When autopilot and autothrust are automatically disconnected and flight controls have reverted to alternate law:

  • Do not engage the AP and the A/THR, even if FD bars have reappeared

  • Do not follow the FD orders

  • ALL SPEED INDICATIONS......................................X-CHECK

If unreliable speed indication is suspected:

UNRELIABLE SPEED INDIC/ADR CHECK PROC...........APPLY

If at least two ADRs provide reliable speed indication for at least 30 seconds, and the aircraft is stabilized on the intended path:

AP/FD and A/THR ......................................As required.

4. CORRECTIVE ACTION

This procedure will be cancelled by the next FCPC standards that will be available before end 2011. This modification will inhibit autopilot engagement in the above described situation.

5. FOLLOW-UP

For A330 aircraft, these operational recommendations will be issued by beginning of January 2011 in red OEB 82/1 and its associated OEB PROC 82/1 in the QRH. For A340-200/-300 aircraft, these operational recommendations will be issued beginning of January 2011 in red OEB 95/1 and its associated OEB PROC 95/1 in the QRH.

No specific follow-up to this FOT is planned.

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