Virgin Australia Regional F100 near Argyle on Mar 7th 2014, flight control problems

Last Update: August 7, 2014 / 13:51:55 GMT/Zulu time

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Incident Facts

Date of incident
Mar 7, 2014

Classification
Incident

Airline
Virgin Australia Regional

Flight number
DJ-9203

Departure
Perth, Australia

Destination
Argyle, Australia

Aircraft Registration
VH-FZO

Aircraft Type
Fokker 100

ICAO Type Designator
F100

A Virgin Australia Regional Airlines Fokker 100, registration VH-FZO performing flight DJ-9203 from Perth,WA to Argyle,WA (Australia), was enroute at FL350 about 130nm northeast of Perth when the aircraft, on autopilot, uncommandedly descended to FL346. The crew disconnected the #1 autopilot and continued the flight. Later, while on approach to Argyle, the crew found the thrust levers were stiff, the pilot monitoring took control of the thrust levers. The crew continued for a safe landing, the #2 thrust lever however remained stuck after landing.

Australia's ATSB have opened an investigation into the occurrence.

On Aug 7th 2014 the ATSB released their final report commending the crew for their performance in following safety message:

This incident provides an excellent example of how an experienced flight crew faced with a novel and unanticipated threat, were able to modify their roles and work together to safely complete the flight. Once on the ground, the crew reverted to their normal duties to ensure all operations and checks were completed normally until the aircraft engines were shut down.

The ATSB reported the crew consisted of a captain under supervision in the left hand seat assuming the role of pilot flying and a training captain, pilot in command, assuming the role of pilot monitoring.

About 130 minutes into the flight the pilot monitoring observed that the aircraft made an uncommanded pitch down and began a descent while the displays at the primary flight display remained normal as if the flight director was commanding the pitch down and the autopilot followed. The autothrust reduced thrust levers towards idle. The pilot flying changed the autopilot modes in order to permit manual control of the vertical profile, the aircraft however continued the descent and the rate of descent reached 1700 fpm. After the aircraft had descended about 300 feet the pilot flying disengaged autopilot 1 and engaged autopilot 2, then returned to assigned altitude. The crew notified ATC about the altitude deviation reporting a system malfunction.

About one hour later the aircraft was on approach to Argyle established on final approach descending through 1000 feet AGL about 3nm before touch down, when the pilot flying noticed the thrust levers were stuck, he assumed alpha floor had activated, pushed both autothrust disconnect buttons and pushed the thrust levers forward to disengage the thrust lock, the levers however continued to be stuck. The pilot monitoring attempted to move the thrust levers but was unable to move them. The announciators on the PFD confirmed autothrust had disconnected and thrust was in manual control.

The speed trend indicator moved below the target speed, the pilot monitoring advised he'd take control of the thrust levers and the pilot flying should continue to fly the approach. Applying force with both hands onto the thrust levers the pilot monitoring managed to jerk the levers forward permitting both engines to deliver about one quarter of maximum thrust available. This setting was appropriate for the current phase of flight without losing speed, the aircraft settled at target speed + 15 knots. The training captain instructed the captain to get the aircraft back onto normal approach profile, the pilot flying extended full flaps.

Just prior to touch down the pilot monitoring extended the speed brakes and applied sufficient force onto the thrust levers to move them to idle at 10 feet AGL. The aircraft touched down smoothly, the pilot monitoring selected reverse thrust. Then both pilots returned to their assigned roles as pilot flying and pilot monitoring to complete taxi to the apron and aircraft shut down.

The ATSB reported that the altitude deviation enroute was caused by an elevator that had become stuck for about 20 seconds.

After the aircraft had been powered down engineers found the right hand thrust lever had become stuck and suspected the #2 autothrottle servo had not disengaged. The servo was replaced which rectified the fault. No fault was found with autopilot #1 although initially suspected to have caused the altitude deviation.

As a safety action the operator reduced the servo replacement schedule from 9600 to 8000 cycles.

The ATSB reported Fokker took following safety action: "Fokker released Service Bulletin 70/100, to upgrade to a new servomotor and servomount for the elevator position, to solve the pitch oscillations. The associated Service Experience Digest stated that the most probable cause of a temporary stuck elevator servo (elevator ‘stiction’) was ice accretion on the elevator servo-mount capstan or elevator servo-drive cables when the aircraft was flown into a humid environment such as cloud. A lubrication task was advised to prevent ‘stiction’."