ASN Wikibase Occurrence # 194819
Last updated: 29 April 2017
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Narrative:EasyJet flight U25462 was in cruise at FL340 over northern France when it experienced an oscillation in pitch and in normal acceleration during which a fault was detected in the stabiliser system. The flight crew were alerted to the fault when the autopilot disengaged and the Master Caution annunciated with ECAM message stab jam. The co-pilot took control of the aircraft while the commander carried out the ECAM actions. The checklist required the flight crew to check that the manual trim was available and to move the stabiliser trim until the elevator was in the neutral position. The commander stated that they moved the stabiliser trim wheel a little but the co-pilot stated that he felt that the aircraft was largely in trim and so they decided not to move the stabiliser significantly after that.
Airbus A320-214 (WL)
|C/n / msn:|| 6192|
|Fatalities:||Fatalities: 0 / Occupants: 183|
|Airplane damage:|| None|
|Location:||over Compiègne -
|Phase:|| En route|
|Nature:||International Scheduled Passenger|
|Departure airport:||Heraklion Airport (HER/LGIR)|
|Destination airport:||London-Gatwick Airport (LGW/EGKK)|
|Investigating agency: ||Air Accidents Investigation Branch (AAIB) - United Kingdom |
As a result of the fault the control law degraded into ‘Alternate Law’, which provided reduced levels of protection and the use of the autopilot was lost. However, ‘load factor demand law’ was maintained as were load factor protection and low/high speed stability functions.
During the time when the flight crew were performing the checklist items, the aircraft started a gradual climb 100 feet from its assigned altitude; however, the flight crew were able to bring the aircraft back to the assigned altitude with minor control stick inputs. The flight crew descended below RVSM airspace and continued the flight to Gatwick with the autopilot disengaged. When the landing gear was lowered during the approach the control law changed to ‘Direct Law’, as designed, and an uneventful landing was carried out.
After arrival, maintenance actions were carried out and the trimmable horizontal stabiliser actuator (THSA) was removed for further examination to determine why the fault occurred.
According to the THSA manufacturer and the aircraft manufacturer the failure of the THSA was most probably due to water ingress into the THS COM transducer which then migrated into the mini reduction gear. The water in the mini reduction gear probably froze during flight and movement of the THSA caused torque on the gear to damage the mini reduction gear.
The stabiliser would have moved as commanded and been sensed by the MON transducer but there would have been no movement sensed by the COM transducer; this discrepancy was detected and the system logic then prevented any further electrical commands to the
Although the source of the water and how it entered the transducer could not be determined, the aircraft manufacturer stated that the worst case scenario from water in this component is the one experienced by G-EZWX. Due to the system monitoring no increased attitude deviations would be expected, and the aircraft would remain fully controllable in ‘Alternate Law’ with manual stabiliser trim remaining available.
||Updated [Time, Location, Country, Narrative, Photo, ]|