Telex Sent To A330/340 Operators Recommends Checking Airspeed Indications Before Engaging Autopilot

A telex message sent by Airbus to companies operating A330 and A340 aircraft seems to acknowledge a problem with the airspeed sensors on the aircraft.

The telex, which was sent to ANN by a reader and which is also published in the French newspaper Le Figaro, cautions flight crews to check airspeed indications before engaging the autopilot, when in alternate law.

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 stabilised 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.

FMI: www.airbus.com