A 26 March icing-related in-flight upset involving a Comair Embraer Brasilia was so severe that the US National Transportation Safety Board (NTSB) is holding a full investigation, even though the aircraft landed safely. At one point the aircraft carried out a complete 360° roll, according to the flight data recorder (FDR).

The twin-turboprop commuter, with 25 passengers and two pilots onboard, was cruising at 17,000ft (5,180m) with autopilot engaged when the crew saw ice building up on the windscreen and airframe at an unusually fast rate. Anti-icing systems were selected to the highest settings, but the aircraft's indicated airspeed (IAS) dropped from 200kt (370km/h) to 140kt despite crew action to increase power and begin a descent. When the aircraft had auto-trimmed to the highest acceptable pitch angle, the autopilot disconnected, and the Brasilia rolled "about 90° left", then wings levelled. Further roll oscillations 110° left and 120° right followed, then a complete 360° left roll. Maximum nose-down pitch was 60°, IAS reached 240kt, and vertical acceleration during the recovery, at about 10,000ft, peaked at 3.6g.

The pilots reported to the NTSB that, during the descent, the electronic attitude display indicator intermittently "provided no useful information". The Board says it is checking the electronic flight instrument system and the FDR to determine whether the latter recorded the aircraft attitude extremes correctly.

The aircraft, on a scheduled flight from Nassau, Bahamas, to Orlando, Florida, diverted to West Palm Beach and landed.

Source: Flight International