DAVID LEARMOUNT / LONDON & ANDREW DOYLE / SINGAPORE
Radar returns strengthen icing theory, but conditions delay flight recorder recovery
The theory that icing may have been a factor in the loss of control of a TransAsia Airlines ATR 72-200 freighter has been strengthened by data from ground-based weather radar returns. The aircraft crashed into the sea off Taiwan's west coast on 21 December (Flight International, 31 December-6 January).
Signals from the flight data recorder have been picked up by the Taiwanese navy, but it cannot be recovered from 60m (196ft) of water until the weather improves.
The aircraft took off from Taipei Airport at 01.05 on 21 December bound for Macao. Taiwan Aviation Safety Council managing director Kay Yong says weather radar returns show the aircraft entered light rain and cloud as it climbed through 14,100ft towards its intended cruising level at 18,000ft, but that the cloud thinned at the higher level where the ambient temperature was –9°C (16°F) and there was light turbulence. Yong has mentioned icing as a possibility, but insists it cannot be deduced from information known so far. Cargo shift or uneven loading, for example, have caused freighter loss-of-control accidents in the UK and USA in recent years.
The crew called for descent to 16,000ft and were given clearance almost immediately, and acknowledged it. That was the last call received from the crew. Within seconds of initiating descent, the aircraft appears to have gone out of control into a dive. There were two points in the descent at which the crew appeared to have recovered control before losing it again. Then the aircraft disappeared from radar.
After a 1994 American Eagle ATR 72 accident in Indiana in icing conditions beyond the aircraft's design limits, the US Federal Aviation Administration ordered the type's wing leading edge de-icing boots be enlarged. The TransAsia aircraft was modified, says Yong.
Source: Flight International
