Description

On 6 March 2005, an Airbus A310-300 being operated by Canadian airline Air Transat on a passenger charter flight from Varadero Cuba to Quebec City was in the cruise in daylight Visual Meteorological Conditions (VMC) at FL350 seventeen minutes after departure and overhead the Florida Keys when the flight crew heard a loud bang and felt some vibration. The aircraft entered a Dutch roll [1] which was eventually controlled in manual flight after a height excursion. During descent for a possible en route diversion, the intensity of the Dutch Roll lessened and then stopped and the crew decided to return to Varadero. It was found during landing there that rudder control inputs were not effective and after taxi in and shutdown at the designated parking position, it was discovered that the aircraft rudder was missing. One of the cabin crew sustained a minor back injury during the event but no others from the 271 occupants were injured.

The fin and rudder remains as seen after arrival back at Varadero; are shown in the photograph below taken from the official report.

Investigation

An Investigation was carried out by the Canadian Transportation Safety Board. It was established that after the onset of the Dutch Roll and the disconnection of the autopilot by the crew, the aircraft had gained nearly 1000 feet of altitude before recovery to FL350 was achieved. In the subsequent descent below FL350, the Dutch roll intensity lessened and then stopped passing FL280. No emergency was declared and when the aircraft was abeam Miami, the crew decided to return to Varadero. During the landing flare, the rudder control inputs were not effective in correcting for a slight crab. When it was seen that the rudder was missing, small pieces of it were visible still attached to the vertical stabiliser.

Subsequent analysis found that the rudder loss during flight had been progressive, and that by the time the aircraft landed, most of the rudder had separated from the aircraft with the missing pieces having fallen into the ocean. None were recovered.

It was noted that the problem the crew had faced was “flight control difficulties of unknown origin” for which there was no established procedure. It was accepted that “the ambiguous nature of the symptoms made it difficult for the crew to assess the situation and to form a clear diagnosis of what had caused the control problems that they had experienced” since “only when rudder inputs were made in the final stages of approach and landing did it become apparent that rudder response was abnormal”.

In respect of the decision to return to Varadero at low level rather than divert to either Miami or Fort Lauderdale, the Investigation determined that the aircraft had not been in danger of losing the vertical tail plane during the flight, either through loss of static strength or loss of stiffness.

In respect of the decision of the flight crew not to declare an emergency, the Investigation noted that “In this occurrence, by the time the crew was in a position to communicate to ATC, they had full control of the aircraft and did not feel it necessary to declare an emergency.”

The Investigation also noted that the flight crew had not sought, nor had the cabin crew volunteered, information on the experience in the cabin at the onset of the event and that, as a result, useful information had not been available to the flight crew, specifically in respect of the magnitude of the forces incurred in the aft galley and the subsequent adverse effects or a description of the noise (volume and type of sound) heard by the cabin crew. It was found that all members of the cabin crew had assumed that their experience was representative of the experience throughout the cabin and that the Captain had assumed that if potentially valuable information existed within the cabin, the cabin crew would provide it without being asked.

It was concluded that the most likely rudder failure scenario was that:

“Some time before the occurrence flight, a disbond or in-plane core fracture occurred. The cause of this initial damage may have been a discrete event or a weak bond at the z-section. An indication of weak bonding was found at the z-section along the interior lower front of the left side panel. This damage then grew, possibly due to reduced pressure cycling loads associated with normal flight, without detection until it reached a critical size.

During the occurrence flight, having reached the critical size, the damage rapidly propagated, resulting in a loud and sudden explosion of the skin. This separation could have damaged the opposite side panel and created a large sideways force on the empennage. The resulting sudden reduction in torsional stiffness led to the onset of rudder flutter. About one second later, there was a large aft and downward force associated with failure of the upper hinge points, as the rudder separated. The rudder-separation event lasted about seven seconds, after which only 16 per cent of rudder effectiveness remained. During the remainder of the flight, more rudder pieces separated, and the aircraft landed with no aerodynamically effective rudder remaining.”

The Investigation findings in respect of Causes and Contributing Factors were as follows:

• 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.
• 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.
• 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).

The Investigation findings as to risk included the following:

• The sampling intervals for lateral and longitudinal acceleration captured by the DFDR fitted to the aircraft were insufficient to record the highly dynamic conditions present at the time of the occurrence. This resulted in incomplete information being recorded.
• There are insufficient published procedures available to flight crew members to assist in recovering from a Dutch roll.
• 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.
• 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.

Two Safety Recommendations were issued during the investigation and reproduced in the Final Report:

1. That the (Canadian) Department of Transport, in coordination with other involved regulatory authorities and industry, urgently develop and implement an inspection program that will allow early and consistent detection of damage to the rudder assembly of aircraft equipped with part number A55471500 series rudders. (A06-05)
2. That the European Aviation Safety Agency, in coordination with other involved regulatory authorities and industry, urgently develop and implement an inspection program that will allow early and consistent detection of damage to the rudder assembly of aircraft equipped with part number A55471500 series rudders. (A06-06)

The TSB also issued a number of “Safety Advisories” to Transport Canada in respect of matters arising from the Investigation and noted Safety Actions taken by both Airbus and Air Transat.

The Final Report of the Investigation was authorised for release on 21 June 2007 and may be seen in full at SKYbrary bookshelf: TSB Canada Aviation Investigation Report A05F0047

Notes of the SKYbrary editor

1. ^ Dutch roll - (aerospace engineering) - A motion of an airplane which consists of simultaneous oscillations of the bank (or roll) angle, the slideslip angle, and the heading angle, and which, when poorly damped, is annoying to passengers and pilots.

Further Reading

• Ageing Aircraft - Structural Failure
• Damage Tolerance
• Loss of Control
• Recovery from Unusual Aircraft Attitudes