Airbus A306 at Toulouse on Sep 13th 2011, uncommanded fall back of autothrust on takeoff

Last Update: July 23, 2013 / 14:56:38 GMT/Zulu time

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Incident Facts

Date of incident
Sep 13, 2011

Classification
Report

Aircraft Registration
F-GSTA

Aircraft Type
Airbus A300

ICAO Type Designator
A306

An Airbus Industries Airbus A300-600 Proto Super Transporteur, registration F-GSTA performing a freight flight from Toulouse (France) to Chester,EN (UK) with 3 crew, initiated takeoff from Toulouse's runway 14R in VMC, when the first officer called during initial acceleration "FMA indications verified", the flight engineer confirmed the thrust levers had reached TOGA position. The captain continued takeoff, rotated and after the aircraft settled in the initial climb commanded the gear up. At that point the commander noticed that the autothrust announciator no longer showed the expected "SRS" (Speed Reference System) mode but "THR L" (thrust lock). The flight director showed a pitch down command. The commander moved the thrust lever which resolved the thrust lock to manual thrust mode, a subsequent re-engagement of autothrust resulted in SPD mode rather than SRS mode, the first officer prevented the thrust levers from retarding, then disengaged autothrust and autopilot. The climb was manually continued to 3500 feet, then the automation was re-engaged and the flight continued to destination without further incident and landed safely in Chester.

The French BEA released their final report in French concluding the probable causes of the incident were:

Lack of detection by the crew while monitoring announciators, that TAKE OFF mode had not engaged during takeoff roll.

The failure of not engaging in TAKE OFF mode probably was due to erratic wiring.

The BEA analysed that based on flight data recordings the crew were never shown the requested/required autopilot and autothrust modes, during the takeoff run they were shown: "THR L", "V/S" and "HDG". On the next flight, without occurrence, the announciators showed: "THR", "SRS" and "HDG SEL", the second next flight showed "THR", "SRS" and "RWY". Hence the takeoff mode was never active for the incident flight, and the engines never reached commanded takeoff thrust.

This FDR recordings were in disagreement with recollection by the crew, the captain specifically stated to have seen "THR" and "SRS" at the beginning of the takeoff run, the first officer could not recall particular modes.

The BEA reported that the Thrust Control Computer, the Thrust Levers and associated switches were examined with no faults found, the occurrence could not be reproduced. However, another crew had reported a similiar occurrence on the very same aircraft on May 11th 2011. An examination following that occurrence also did not reveal any fault.

Due to the wiring the only explanation of the failure to engage TAKEOFF mode despite TOGA being commanded is a faulty wiring between the thrust levers and buttons and the thrust control computer.

Another case by another operator was identified to have been caused by a temporary disturbance of the localizer signal during the takeoff run.

There were no specific procedures established for a case where TAKEOFF mode would disengage/fall back during the takeoff run after the initial verification call. The correct response would be to either reject takeoff upon discretion of the commander if below 100 knots or engage GO AROUND mode, which would, if the aircraft is still on the ground, effectively engage TAKE OFF mode again or if airborne engage the GO-AROUND mode.
Incident Facts

Date of incident
Sep 13, 2011

Classification
Report

Aircraft Registration
F-GSTA

Aircraft Type
Airbus A300

ICAO Type Designator
A306

This article is published under license from Avherald.com. © of text by Avherald.com.
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