Status:	Definitief
Datum:	06 MRT 2005
Tijd:	03:15
Type:	Airbus A310-308ET
Luchtvaartmaatschappij:	Air Transat
Registratie:	C-GPAT
Constructienummer:	597
Bouwjaar:	1991-09-24 (13 years 6 months)
Aantal vlieguren:	49224
Aantal vluchten:	13444
Motoren:	2 General Electric CF6-80C2A8
Bemanning:	slachtoffers: 0 / inzittenden: 9
Passagiers:	slachtoffers: 0 / inzittenden: 262
Totaal:	slachtoffers: 0 / inzittenden: 271
Schade:	Groot
Gevolgen:	Repaired
Plaats:	nabij Varadero (Cuba)
Fase:	Kruisvlucht (ENR)
Soort vlucht:	Internationale lijnvlucht
Vliegveld van vertrek:	Varadero-Juan Gualberto Gomez Airport (VRA/MUVR), Cuba
Vliegveld van aankomst:	Quebec Airport, QC (YQB/CYQB), Canada
Vluchtnummer:	961

Beschrijving:
Air Transat flight 961 departed Varadero, Cuba at 02:48 in the early morning. The A310 climbed to its cruising altitude of 35000 feet.
At approximately 03:02 the flight crew heard a loud bang immediately followed by several seconds of vibration. Cabin crew members located in the back of the aircraft were thrown to the floor and unsecured galley carts moved freely. The aircraft started to Dutch roll, and the captain took control and disconnected the autopilot. The aircraft was difficult to control in the lateral axis. In an attempt to better manage the cockpit workload, the other autopilot system (No. 1) was engaged. As the Dutch roll movement started to intensify, autopilot No. 1 was disengaged and the aircraft was hand-flown.
During these actions, the aircraft climbed to about FL 359. The flight crew requested a descent and informed air traffic control that they had experienced an autopilot problem and had reverted to flying manually. While descending, the crew cycled through the electronic centralized aircraft monitor (ECAM) system pages in an attempt to diagnose the problem. Throughout the event, there was no ECAM message relating to the control problem that the aircraft had experienced, and there were no warning lights or cockpit indications of an aircraft malfunction. Even with limited clues as to the cause of the Dutch roll, the crew knew that descending to a lower altitude might lessen or stop the Dutch roll motion. Initial indications led to the possibility of the loss of both yaw dampers (YD) but both YD switches were engaged. Had a dual YD failure occurred, the flight warning computer would have triggered appropriate warnings and messages, and the autopilot would have disconnected.
The Dutch roll gradually decreased in the descent and ceased when the aircraft passed FL 280. The crew continued the descent to 10 000 feet above sea level in preparation for a landing in Fort Lauderdale. The captain returned control of the aircraft to the first officer and called the flight director to provide the standard briefing to the cabin crew for emergency or abnormal situations.
The crew contacted company dispatch to discuss the situation and elected to return to Varadero, where the company was better equipped to deal with the aircraft and the passengers. At 03:39, the flight was cleared to Varadero at FL190.
During the climb to FL190, the crew engaged autopilot No. 1 and disengaged it during the final portion of the visual approach to runway 06 at Varadero. During the landing flare, nose wheel steering was used for directional control on the runway. An uneventful landing was completed at 04:19.
The crew conducted a flight control check after landing and the ECAM indicated that everything was normal. The aircraft was taxied to the gate where the passengers were deplaned normally through the main door. After shutdown, a visual inspection revealed that the aircraft rudder had broken and most of it was missing.

FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS:
1. The aircraft took off from Varadero with a pre-existing disbond or an in-plane core fracture damage to the rudder, caused by either a discrete event, but not a blunt impact, or a weak bond at the z-section of the left side panel. This damage deteriorated in flight, ultimately resulting in the loss of the rudder.
2. The manufacturer's recommended inspection program for the aircraft was not adequate to detect all rudder defects; the damage may have been present for many flights before the occurrence flight.
3. This model of rudder does not include any design features in the sandwich panels to mechanically arrest the growth of disbond damage or in-plane core failure before the damaged area reaches critical size (such a feature was not specifically demanded for certification).

FINDINGS AS TO RISK:
1. A cockpit voice recorder with a 30-minute recording capacity was installed on the aircraft, and its length was insufficient to capture the rudder-loss event, resulting in critical information concerning the rudder failure not being available to investigators.
2. There was no published procedure for disabling the recorders once the aircraft was on the ground; valuable investigation information can be lost if the data are not preserved.
3. The sampling intervals for lateral and longitudinal acceleration captured by the digital flight data recorder were insufficient to record the highly dynamic conditions present at the time of the occurrence. This resulted in incomplete information being recorded.
4. The rudder position filtering and the necessity for additional analysis adversely affected the accuracy and effectiveness of the investigation efforts.
5. There are insufficient published procedures available to flight crew members to assist in recovering from a Dutch roll.
6. Declaring an emergency and clearly communicating the nature of the problem allows air traffic control to more easily coordinate between units and anticipate the needs of the crew in planning traffic management.
7. Procedures and practices that do not facilitate information sharing between crew members increase the likelihood that decisions will be based on incomplete or inaccurate information, potentially placing passengers and crew at risk.

Bronnen:
» TSB Investigation Update Number A05F0047