Saab 340 operators ordered to modify stall warning

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Safety regulators have ordered modification of Saab 340 stall-warning systems after a number of incidents in which the system failed to alert the crew of possible stall situation.

The European Aviation Safety Agency said "a few natural stall events" without prior warning had been experienced on the type, specifically while operating in icing conditions.

It has issued an airworthiness directive covering almost the entire Saab 340A and 340B fleets, instructing operators to upgrade the stall-warning systems.

EASA said the modification follows the development of "improved logic" for the aircraft's stall-warning computer.

The new system includes stall-warning curves "optimised for operation in icing conditions", it added, activated during selection of engine anti-ice.

While the stall warning activated on the Sol Lineas Aereas 340 which crashed during a domestic service to Comodoro Rivadavia in May, the fatal accident illustrated the risks of ice build-up on the type.

Investigators found that the crew had observed the accumulation of ice as the aircraft climbed, and had chosen to descend in conditions which made the icing worse.

Australian investigators sought an improvement in stall warning logic on the type back in 1999, after finding that the crew of a Kendell Airlines 340 received "very little warning" of an impending stall in icing seven months earlier.

Saab manufactured almost 460 turboprops in the 340 series. The modifications must be carried out within two years.