Investigators probe restricted pitch control incident that left two crew members injured

Pilots of BAe 146s have been alerted to an icing condition that may have caused an in-flight incident in which two crew were seriously injured, according to the UK Air Accident Investigation Branch (AAIB). An AAIB special bulletin says that its inquiry is continuing, but confirms the aircraft's pitch controls were temporarily restricted, possibly by icing.

The Flybe BAe 146-200 (G-JEAX) was flying from Birmingham to Belfast City Airport, UK, on 12 December 2002 with 36 passengers and five crew. Having engaged the autopilot at 3,000ft (915m) in the climb, the crew noticed slight pitch oscillations during the ascent to flight level 240 (24,000ft), where the captain levelled the aircraft manually and re-engaged the autopilot.

Oscillations began again and the aircraft began to diverge from its flight level. When the captain tripped out the autopilot he felt "a strong pitch-up tendency", so counteracted with force and nose-down pitch trim. The aircraft suddenly pitched down, and as the nose passed through the straight and level attitude, the captain applied pitch-up force and called for the co-pilot's help. "They both pulled back with considerable force. The control column suddenly moved aft, the aircraft pitched up and the flightcrew noticed a violent shudder through the whole airframe that lasted for two or three seconds", says the report. After this, control column forces returned to normal and the crew levelled the aircraft at FL240.

The flight data recorder had registered vertical acceleration forces ranging from 0.4g to 3g, and two cabin crew were badly injured. The pilots declared an emergency and landed safely on runway 04 at Belfast City Airport.

The aircraft was on the last leg of a four-sector shuttle between the two cities, and had been de-iced after overnighting at Belfast. The crew did not de-ice at Birmingham for the final leg because, although during the 55min turnaround "a mixture of rain, sleet and snow" fell, it was not settling on the airframe.

During the pre-take-off full and free control movement check, the crew held the control column fully back for 25s to allow excess water to drain from the elevator. After take-off they activated the aircraft's anti-icing systems. Cloudbase was at 1,000ft, and the UK low level area forecast warned of severe icing in freezing rain and moderate icing in cloud. The aircraft had emerged from the cloud tops at 18,000ft.

The AAIB is looking at possibilities of "natural icing", of frozen moisture in the elevator servo tab rod-end bearings, or the effects of accumulated de-icing fluid residues.

Source: Flight International