Easyjet A320 near Brest on Jul 27th 2016, jammed trimmable horizontal stabilizer

Last Update: April 13, 2017 / 16:23:26 GMT/Zulu time

Bookmark this article
Incident Facts

Date of incident
Jul 27, 2016

Classification
Incident

Airline
Easyjet

Flight number
U2-5462

Aircraft Registration
G-EZWX

Aircraft Type
Airbus A320

ICAO Type Designator
A320

An Easyjet Airbus A320-200, registration G-EZWX performing flight U2-5462 from Heraklion (Greece) to London Gatwick,EN (UK) with 177 passengers and 6 crew, was enroute at FL340 about reaching the top of descent into Gatwick, in contact with Brest Air Traffic Control (France), when the crew received indication the Trimmable Horizontal Stabilizer (THS) was jammed. The crew advised air traffic control and continued to London Gatwick for a safe landing on runway 26L about 30 minutes later.

The French BEA reported the investigation into the serious incident has been delegated to the AAIB of the United Kingdom.

The aircraft remained on the ground for 29 hours before resuming service.

On Apr 13th 2017 the AAIB released their bulletin reporting that the aicraft was enroute at FL340 when a pitch oscillation occurred followed by the autopilot disconnecting and a master caution associated with an ECAM message "STAB JAM". The first officer took manual control of the aircraft while the captain carried out the ECAM actions. Following the ECAM actions requiring to move the stabilizer manually until the elevator was in a neutral position the captain moved the stabilizer trim wheel a little, the first officer stated however the aircraft was in trim, hence no further movement of the stabilizer trim wheel was done. As result of the fault the control law degradated to "Alternate Law", which reduced levels of protection and lost the use of the autopilot. The crew descended the aircraft below RVSM airspace and continued to destination. As designed the control law changed to "Direct Law" upon gear down selection, the crew continued for a safe landing.

The AAIB reported that according to the flight data recorder a handover between ELAC1 and ELAC2 (ELevator Aileron Computer) happened in rapid succession at the time of the pitch oscillation, the stabilizer position changed to 0.6 degrees more nose down compared to the setting prior to the upset and the elevator position changed to 2 degrees nose up. The stabilizer moved again 70 seconds after the upset, probably as result of the manual trim, but not sufficient to return the elevator to 0 degrees. The fact, that the stabilizer did move however suggests, that the stabilizer was not physically jammed.

The Trimmable Horizontal Stabilizer Actuator (THSA) was sent to the manufacturer for further analysis. The AAIB wrote: "They discovered that the mini reduction gear assembly was not driving the COM transducer, so the COM transducer could not sense the commanded stabiliser position. About 2 ml of water was found inside the mini reduction gear liner/cavity, which was an unusual finding. The output shaft of the mini reduction gear was found to be jammed and disassembly of the unit revealed damage to the gears. The COM transducer was opened which also revealed the unexpected presence of water. Corrosion was also found within the transducer housing. The seals and sealant used to seal the component were in satisfactory condition. However, a leak check of the seal was not conducted before the transducer was opened as the manufacturer was not expecting water to be present. According to the manufacturer this was the first instance of water ingression into this component."

The AAIB analysed:

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 THSA.

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.
Incident Facts

Date of incident
Jul 27, 2016

Classification
Incident

Airline
Easyjet

Flight number
U2-5462

Aircraft Registration
G-EZWX

Aircraft Type
Airbus A320

ICAO Type Designator
A320

This article is published under license from Avherald.com. © of text by Avherald.com.
Article source

You can read 2 more free articles without a subscription.

Subscribe now and continue reading without any limits!

Are you a subscriber? Login
Subscribe

Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.

Free newsletter

Want to know more and stay ahead? Get our free weekly newsletter and join 5462 existing subscribers.

By subscribing, you accept our terms and conditions and confirm that you've read our privacy policy.

Send tip

Support AeroInside by sending a small tip amount.

Related articles

Newest articles

Subscribe today

Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.

Pick your plan and subscribe

Partner

Blockaviation logo

A new way to document and demonstrate airworthiness compliance and aircraft value. Find out more.

Virtual Speech logo

ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.

Get updates

Never miss an article from AeroInside. Subscribe to our free weekly newsletter and join 5462 existing subscribers.

By subscribing, you accept our terms and conditions and that you've read our privacy policy.

AeroInside Blog
Popular aircraft
Airbus A320
Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American Airlines
United
Delta
Air Canada
Lufthansa
British Airways