Description

On 9 April 2008, an Eastern Airways BAe Jetstream 41 operating a passenger charter flight departed Aberdeen for Vagar, Faroe Islands in snow and freezing conditions, but had not been de-iced and anti-iced appropriately. After takeoff the flight proceeded uneventfully until the autopilot pitch trim warning illuminated during the climb in Instrument Meteorological Conditions (IMC). The crew concluded that the elevator had become jammed because of ice. A MAYDAY call was made to ATC, stating that the crew were having problems with the elevator controls and that they did not have full control of the aircraft in pitch. The crew then used changes in power and higher forces on the elevator controls to gain sufficient control to descend into warmer air, where the ice melted. The aircraft then completed a diversion to Wick without further problems.

The Investigation

The UK AAIB carried out a Field Investigation into the occurrence. It found that prior to flight departure, considerable quantities of wet snow had been swept from the aircraft by untrained personnel who anticipated that de/anti icing action would follow. In the event, the Aircraft Commander noted the delay implicit in this action and elected not to undertake it, noting that earlier heavy snowfall had given way to lighter sleet. The Investigation considered that it was highly likely that prior to take off, slush and/or ice had been present on the horizontal tail surfaces and that, as the aircraft entered colder air at altitude, this contamination caused the mechanical pitch control to become restricted.

It was noted that although there was an autopilot pitch trim warning checklist, the emergency and abnormal checklist did not include a relevant checklist for the circumstances in which the crew had found themselves. It was also noted that the advice in the Operations Manual stated that flap setting greater than 15 degrees should be avoided following an icing encounter. Given that the consequences of a tail plane stall could be catastrophic, it was considered that extension of flaps beyond 15 degrees should be prohibited in the case of ice-related elevator jams unless a safe landing was dependent upon the use of flap 25 (for example, because the landing distance is limiting).

The Investigation also considered the decision making and the fitness to fly of the aircraft commander. His decision-making was seen to have been critical in the sequence of events, particularly the decision not to have the aircraft de-iced and anti-iced prior to departure and also his assumption that the tailplane had been ‘mechanically de-iced’. It was concluded that the additional ‘full and free’ checks of the controls which had been carried out prior to departure indicated a concern about the state of the aircraft, as did the commander’s decision to hand-fly the initial part of the departure. Also, before the flight, the commander was noted to have discussed with the co pilot his (the commander’s) fitness and the poor quality of his pre-flight sleep and said he would monitor his performance as the duty went on. He knew there was no other captain at Aberdeen available and qualified to operate to Vagar so the flight would be cancelled, or significantly delayed, if he did not operate it. It is thus possible that the commander’s physical condition, coupled with a motivation to complete the flight, was a contributory factor in this incident.

The Report of the Investigation was published on 8 October 2009 and contained two Safety Recommendations:

1. It is recommended that BAE Systems review the emergency and abnormal checklist for the Jetstream 41 aircraft to ensure that it includes adequate instruction and advice for flight crews who encounter in-flight control problems associated with airframe ice.
2. It is recommended that BAE Systems review the advice contained in the emergency and abnormal checklist concerning flap extension following failure of the aircraft’s ice protection systems, or when ice is present on the airframe, to ensure that advice and instruction relating to flap extension is optimized for safety.

Related Articles

• Aircraft and In Flight Icing Risks
• Ice Formation on Aircraft
• Ice Contaminated Tailplane Stall
• Aircraft Ground De/Anti-Icing
• De/Anti-Icing Code

Further Reading

• The full Report (AAIB Bulletin: 10/2009, G-MAJV, EW/C2008/04/02)

AEA

• Recommendations for De-icing/Anti-icing Aeroplanes on the Ground, 30th Edition, July 2015
• Training Recommendations and Background Information for De-Icing /Anti-Icing of Aeroplane on the Ground, 12th Edition, August 2015

Note: Although the AEA ceased to exist in 2016, the most recent of their publications still contain some pertinent information. Readers are cautioned to validate the recommendations of these guidebook using more current information sources.