Ice or frost on the wing

 - March 26, 2008, 10:52 AM

A preliminary report issued by the UK Air Accidents Investigation Board on the January 4 crash of Challenger 604 N90AG at Birmingham, England, raises a suspicion that frost or ice on the wing may have been a factor. The aircraft, operated by Epps Aviation of Atlanta on behalf of agricultural machinery manufacturer Agco, had arrived the previous evening at 8:39 p.m. after a nonstop flight from West Palm Beach, Fla. The temperature at the time was 30 deg F with the dewpoint just one degree lower, and overnight it dropped to 16 deg F with variable cloud cover.

Mid-morning the next day each pilot carried out an independent walkround. Following this, the aircraft was fueled to full tanks. After the passengers arrived, a start clearance was given at 11:56 a.m. and taxi clearance followed at 12:01 p.m.
Other aircraft that had been parked overnight at the airport required de-icing for moderate or severe ice and frost contamination, and those crews reported they saw frost or ice on the wings of N90AG. However, the Challenger crew did not request de-icing by the handling agent.

At the time of departure the wind was almost straight down 8,400-ft Runway 15 at six knots, and N90AG was cleared for line-up about a minute after a BAE 146 had landed and several minutes after the last departure.

The Challenger captain, with some 10,000 hr TT and about 500 in type, was in the right seat, with the pilot flying in the left.

It appears from the FDR that the wing and cowl anti-ice systems were not selected on before takeoff. The takeoff run appeared normal until liftoff, when the aircraft started to roll to the left, with a left bank angle of 50 deg two seconds after becoming airborne. Full right aileron and rudder were applied within one second and were held until the end of the recording.

About 4,600 ft from the start of the runway, the left winglet made contact with the ground. As the aircraft continued to bank to about 80 deg, ground contact became more positive and the left wing started to buckle. About 400 ft after ground contact the fuel in the left tank ignited, and at the same time the fuselage hit the ground heavily in the area above the cockpit. Soon after this the horizontal stabilizer hit the ground and the tail section separated.

The remainder of the aircraft slid another 1,000 ft before coming to rest with the forward fuselage upright. The airport fire service, on the scene in less than one minute, quickly extinguished the fire in the forward fuselage but all five people aboard died. Both cockpit voice and flight data recorders were recovered from the wreckage and were fully serviceable.

The Birmingham Airport was closed for two days to allow recovery of the wreckage, which is now at the AAIB’s Farnborough facility for further investigation.