A Ryanair jet suffered "significant damage' while parked at a Portuguese airport but it wasn't detected until the crew experienced control problems during a later flight.
Formal investigation of the 2011 “serious incident” at Faro Airport was delegated by the Portuguese authorities to the Irish Air Accident Investigation Unit (AAIU).
In it’s final report published today the AAIU outlined that in the early hours of October 24th, Faro airport was hit by the rare meteorological phenomenon known as a microburst associated with a supercell.
Wind speeds of up to 84.9 knots (157km/h) were recorded at the airport where the Ryanair Boeing 737-800 had been parked overnight on the ramp.
During the incident, the jet jumped its chocks and its nose moved approximately 5 metres to the left. The jet sustained significant damage to its rudder system caused by the wind gusts.
Several other Ryanair aircraft also jumped their chocks during the storm but no damage was reported.
The damage to the Ryanair aircraft was not visible from the ground and was not detected during the subsequent ramp and pre-flight checks.
The Captain told the investigation that he was aware of the overnight storm and that during his pre-departure walk-around he was “extra vigilant for damage.”
The Technical Log was found not to contain any specific reference to the overnight winds or to the fact that the aircraft had jumped its chocks and moved.
There was also no requirement in the Aircraft Maintenance Manual (AMM) to check the flight control systems of an aircraft after such severe weather.
Later however, shortly after the aircraft had departed on its first scheduled flight of the day, the flight crew encountered “significant control difficulties”. There were 145 passengers and a crew of six on the Beauvais (France)-bound flight.
The Captain told investigators that the initial take-off roll was normal. As the aircraft rotated, he observed that “we were drifting slightly right of the centreline. At the same time we had almost full left aileron deflection. The FO mentioned that the aircraft didn’t feel right.”
On the Cockpit Voice Recorder (CVR) the First Officer was heard saying: “Something’s seriously wrong with this” and “Look at that, look at it rolling.”
Despited thinking at first they had suffered an engine failure, the crew dealt with the control issues and returned to airport where they landed safely approximately 28 minutes after take-off.
As part of the investigation, the National Transportation Safety Board (NTSB) was requested to perform a metallurgical examination of the damaged Power Control Unit (PCU) tailstock attach hardware.
These items were crated and shipped to Washington DC where four support bracket attachment bolts were found to have been sheared. Several other brackets exhibited deformation, fractures and overload shear.
The investigation determined that the probable cause of the incident was “undetected structural damage caused to the rudder system by violent wind gusts associated with a microburst, while the aircraft was parked.”
One of the contributory factors cited by the report was “the absence of a requirement in the Aircraft Maintenance Manual (AMM) to comprehensively check the flight control systems of an aircraft which has been subjected to an extreme meteorological event.”
The AAIU has issued a single safety recommendation to the Federal Aviation Administration (FAA). The investigation also determined that "given the situation in which they found themselves once the aircraft became airborne, the issues were operationally well handled by the flight crew."