Investigation
The Portuguese Aviation Accidents Prevention and Investigation Department (GPIAA) investigated the incident along with Canadian and French authorities.
The investigation revealed that the cause of the incident was a fuel leak in the number two engine, caused by an incorrect part installed in the hydraulics system by Air Transat maintenance staff. Air Transat maintenance staff had replaced the engine as part of routine maintenance, using a spare engine, lent by Rolls-Royce, from an older model. This engine did not include a hydraulic pump. Despite the lead mechanic's concerns, Air Transat ordered the use of a part from a similar engine, an adaptation that did not maintain adequate clearance between the hydraulic lines and the fuel line. This lack of clearance — on the order of millimeters from the intended part — allowed vibration in the hydraulic lines to degrade the fuel line and cause the leak. Air Transat accepted responsibility for the incident and was fined CAD 250,000 by the Canadian government, which as of 2009 is still the largest fine in Canadian history.
Although pilot error was listed as one of the lead causes for the incident, it was the skill of the pilots, and of the military Air Traffic Controller in service at the time, 1st Sgt. José Ramos, that allowed the flight to land without fuel, causing only minor injuries to the passengers and minor damage to the airplane, which is still in service. The pilots returned to a heroes' welcome from the Quebecois press.
The incident also led to the French Directorate General for Civil Aviation (DGAC) and Federal Aviation Administration (FAA) issuing an Airworthiness Directive, forcing all operators of Airbus model A318-100, A319-100, A320-200, A321-100, A321-200, and A320-111 aeroplanes to change the flight manual, stressing that crews should check that any fuel imbalance is not caused by a fuel leak before opening the cross-feed valve. The French Airworthiness Directive (AD) required all airlines operating these Airbus models to make revisions to the Flight Manual before any further flights were allowed. The FAA gave a 15-day grace period before enforcing the AD. Airbus also modified its computer systems; the on-board computer now checks all fuel levels against the flight plan. It now gives a clear warning if more fuel is being lost than the engines can consume. Rolls-Royce also issued a bulletin advising of the incompatibility of the affected engine parts.
Read more about this topic: Air Transat Flight 236