US-registered Saab 340 turboprops may be required to install a new stall warning computer to remain airworthy, the Federal Aviation Administration (FAA) says in a forthcoming notice.
Both Saab 340As and 340B models have reported incidents where stall events during icing conditions were not preceded by a stall warning, the FAA says.
"This condition, if not corrected, could result in loss of control of the aeroplane," the agency adds.
The FAA will issue a notice of proposed rulemaking on 27 June in the Federal Register to initiate a process that could lead to an airworthiness directive.
The directive would order airlines to install a modified stall warning system with improved logic that has been developed to solve the problem, the FAA says. The cost to modify all 162 Saab 340s operating under US registry would amount to $6.42 million, or about $39,600 per aircraft, the FAA says.
The cost assumes a labour rate of $85 per work-hour and no charge for the improved computer, as the equipment is available under warranty, the FAA says.
The notice invites Saab 340 operators and other stakeholders to comment on the proposed directive. Responses must be submitted to the Department of Transportation within 45 days of the notice's publication in the Federal Register.