French investigators have concluded that icing on the wings of an Air France Regional Fokker 100 contributed to a fatal departure accident at Pau nearly two years ago.
Although the jet rotated quickly, after the co-pilot warned of birds during the take-off roll, the Bureau d'Enquetes et d'Analyses (BEA) states that ice contamination led to the jet's subsequent aerodynamic behaviour.
As it lifted off for Paris the aircraft oscillated violently, rolling 35° left, then 67° right, and 59° left again. It reached a height of 107ft before descending and touching down to the right of runway 13 at 160kt, just 14s after becoming airborne.
The Fokker travelled hundreds of metres along the ground - crossing a road, where it hit a truck and killed the driver - before coming to rest. There were no fatalities among the jet's 54 passengers and crew.
© Bureau d'Enquetes et d'Analyses
Meteorological conditions at Pau, where the humidity was high and the air temperature was 0°C, presented a risk of ice contamination. In the hour prior to the Fokker's departure four aircraft - an Airbus A320, A319, Embraer ERJ-135 and a Casa CN-235 military transport - all took off, but only the A320 requested de-icing.
The Fokker crew similarly did not ask for the jet to be de-iced. In its final report into the 25 January 2007 accident, the BEA points out that, without the aid of a stepladder or similar means, the crew could not detect whether there was ice on the wings during pre-flight checks.
During the take-off roll, the sudden sighting of birds prompted a reflex decision by the pilot to apply a higher-than-normal rotation rate of 6.1° per second.
No birds struck the airframe or engines. But the BEA says that the rapid rotation partly contributed to the loss of control during take-off.
It cites previous icing accidents Fokker jets, including a take-off crash involving a Palair Macedonian Fokker 100 at Skopje in March 1993. The inquiry into that accident recommended de-icing the type in freezing conditions, regardless of observations from pre-flight checks.
BEA says the Pau inquiry discovered "insufficient awareness" among the French aerospace community regarding icing and its effects on aircraft performance. "Risks associated with this phenomenon, particularly when the weather is not exceptional, are not well-known," states the BEA.
Investigators have put forward seven recommendations, five of which focus on implementing better training and procedures for dealing with on-ground icing.