West Atlantic ATP at Guernsey on Jan 26th 2016, control problems, crew perceived autopilot did not disconnect

Last Update: September 8, 2016 / 18:16:32 GMT/Zulu time

Bookmark this article

Photo of West Atlantic G-BUUR, BRITISH AEROSPACE ATP — West Atlantic G-BUUR, BRITISH AEROSPACE ATP (Photo credit: Aero Icarus / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jan 26, 2016

Classification
Report

Airline
West Atlantic

Flight number
QY-2889

Departure
Jersey, United Kingdom

Destination
Guernsey, United Kingdom

Aircraft Registration
G-BUUR

Aircraft Type
BRITISH AEROSPACE ATP

ICAO Type Designator
ATP

A West Atlantic British Aerospace ATP on behalf of European Air Transport, registration G-BUUR performing flight QY-2889 from Jersey,CI to Guernsey,CI (UK) with 2 crew, was on an ILS approach to Guernsey's runway 27 in strong southerly winds with possibility of severe turbulence and windshear, the reported weather conditions were within within the operator's advisory limits. The first officer, who had completed the operator's ATP training course one month earlier for his first commercial aircraft, was pilot flying and keen to fly the aircraft in these conditions that he believed were similiar to weather conditions experienced during training. The first officer briefed the approach and the route of a go around, however, did not brief the actions each pilot was expected to do in case of a go around. The aircraft joined Localizer and glideslope, the aircraft maintained Vapp and the approach was considered stable. Upon reaching 200 feet AGL the first officer pressed the autopilot disengage button, however, did not hear the aural autopilot disengagement alert. Unaware of that action the commander (60, ATPL, 6,843 hours total, 1,512 on type) recommended to disengage the autopilot. The first officer pressed the AP disconnect button one more time, again without the aural disconnect alert. The commander announced decision altitude, the first officer acknowledged and pressed the AP disconnect button a third time again without hearing the autopilot disconnect alert. The first officer then made small control inputs and felt the controls were extremely stiff as if the autopilot counteracted. In his peripheral vision the captain spotted the first officer was "frantically pressing" the AP disconnect switch, the first officer advised "it won't disconnect", the captain pressed his AP disconnect switch again without aural alert, the captain tried to connect his autopilot 1 (which would have disconnected 2 engaged by the first officer) again without alert. Both crew became aware they were deviating above glide, the commander called to go around being unsure sufficient control authority would be available to continue landing in these wind conditions, the approach had to be considered unstable at this point, too. The first officer in response advanved the power levers and pressed the TOGA button, which again should have disconnected the autopilot, however, again without aural alert, the flight director bars should have moved, neither pilot observed the flight director bars moving. The TOGA button was pressed a second time but remained again without response, the first officer now applied force to pitch up, the controls felt stiff but the aircraft responded and pitched up, a large speed deceleration trend was noticed by both pilots. After the engines had spooled up, both pilots perceived a large pitch up tendency and the first officer applied an unusual amount of force to push the controls nose down. The captain also instinctively applied a large nose down force followed by a caution annunciation and the activation of the "STANDBY CONTROLS" light. The pitch controls now seemed lighter than normal and in about experiences on the flight simulators after the elevator control had split. The go-around now normalized, the aircraft climbed to 2000 feet and levelled off, the pilots realized the autopilot was disengaged and re-engaged the autopilot 2. The crew worked the checklist for split elevator controls, AP2 was disconnected with the associated aural alert occurring and reconnected, the crew decided to divert to Jersey due to the longer runway and maintenance base present. The commander assumed control of the aircraft for the diversion and landed the aircraft in Jersey without further incident.

The AAIB released their final report complaining about the fact, that neither crew, operator or maintenance had perceived the occurrence as a reportable serious incident, the black boxes therefore had not been secured and the cockpit voice recorder (30 mins duration) was overwritten. The AAIB concluded:

Extensive examination and functional testing of the aircraft systems and components identified no failures that were associated with the reported occurrence. The available data indicated the autopilot disengaged on command although the pilots believed otherwise. As the operator had not isolated the recorders following the incident, a cockpit voice recording of the event was not available. It was therefore not possible to ascertain if the autopilot disengagement alert sounded at the moment the FDR recorded autopilot disengagement during the approach.

During the resultant go-around, the co-pilot recalled having to overcome a strong pitch-up force after power was set, which he then struggled to overcome. The data indicated the aircraft was trimmed nose-up after power was set, so this may have been the cause of the pitch-up force and the co-pilot’s opposition to this force may have led to the elevator control split. It is also possible the pilots briefly made opposing inputs on the control column and this caused the elevator split and activation of the SCS.

However, it was not possible to exclude the possibility that there was an intermittent fault within the autopilot system that then caused the system to oppose the co-pilot’s inputs and lead to the control split. The recorded data shows two brief recordings of autopilot engagement during the event which the investigation could not explain.

Once the elevators had split the pilots completed the go-around but deviated from SOPs while struggling with a stressful and disorientating situation. They re-engaged the autopilot without discussing any potential threats from this action and they did not use CRM principles designed to help deal with problem solving and decision making. The operator has since reviewed and updated its training of crews as a result of the findings from this incident.

The AAIB reported that according to the flight data recorder the autopilot had disengaged as the aircraft descended through 200 feet AGL precisely at the time when the first officer pressed the AP disconnect button for the first time. However, due to the lack of CVR recordings it could not be established, whether the associated autopilot disengagement sound occurred or not, neither pilot recalled hearing the sound however.

The AAIB reported that both pilots did not check the autopilot announciators, this check was not part of the procedure.

The AAIB analysed that the weather conditions at Guernsey were challenging requiring a high cognitive workload, in particular for a newly trained pilot. The AAIB wrote: "However, the reported wind was within the applicable limits, the co-pilot was confident of his own ability and had coped well with similar conditions during training."

The AAIB analysed:

In view of the conditions and his own experience level, the co-pilot decided to disengage the autopilot approaching decision altitude. He could see the runway when he pressed the disengagement switch, so was likely to be using both external and internal cues during the latter part of the approach. The flight data shows airspeed changes and power adjustments being made just above decision altitude. It is likely the speed changed due to the windy conditions and the co-pilot responded by making power changes. This suggests his workload was high when he pressed the switch to disengage the autopilot.

His primary indication of autopilot disengagement would be an audible alert, but he did not hear this and so believed the autopilot was still engaged. It is possible the alert did sound but was not registered by either crew member because of the high workload. Neither pilot looked to the PFD for confirmation of autopilot status. The operator, in its OM and during training, does not prescribe referring to the PFD to verify the autopilot has disengaged. The co-pilot pressed the disengage switch again, before trying to move the controls and felt resistance, as if the autopilot was still engaged.

The flight data indicates the autopilot disengaged at 220 ft aal, at about the point at which the co-pilot reports first pressing the autopilot disengagement switch. With the autopilot disengaged the co-pilot should not have experienced unusual resistance when he tried to move the control column. It cannot be entirely excluded that there was some intermittent fault within the autopilot system that resulted in the pilot experiencing resistance to his inputs, but subsequent tests have not revealed any defect with the system or with the flight controls.

The AAIB analysed that a large nose up pitch trim had been applied and wrote: "The nose-up pitch trim input would have increased control column loading so, when the co-pilot pushed forwards on the right column, he may have had to exert more than 100 lb force, causing the detent mechanism to operate and the elevators to split. It is also possible the pilots applied opposing forces to their control columns for a short time and this caused the columns to separate and the elevators to split. This does not conform to the pilots’ recollections but they were experiencing a high workload and a potentially disorientating situation."

The AAIB continued analysis:

Another possibility that may have led to the elevator split mechanism initiating would be if the co-pilot was having to oppose an input from some part of the autopilot system. The flight data does record brief, unexplained, engagement and disengagement of each autopilot channel in turn during the climb. However, subsequent examination of the aircraft has not revealed any technical defects that would have caused the autopilot to oppose the crew’s inputs.

Approximately 40 seconds after levelling at 2,000 ft amsl, AP2 was re-engaged, without any discussion of the potential complications this might cause. There was no acknowledgement that it must have disengaged during the go-around or that it might not disengage again. After a further 25 seconds the last stage of flaps were retracted.

The AAIB analysed: "The go-around was successful but did not follow standard practice. The likely reason for this was the distracting effect of the control problems encountered but the lack of a detailed go-around brief may have contributed to the actions taken."