The FAA, following a review of icing accidents and incidents, issued a proposed rulemaking that would require Part 121 scheduled carriers to retrofit existing fleets with ice-detection equipment, or to make changes to the airplane flight manual (AFM) that ensure that ice protection systems activate at the proper time.

The rule proposes that ice detection equipment already installed on aircraft be capable of alerting crews as to when to activate the system. For aircraft without ice protection equipment, pilots would be required to active the system either at the first sign of icing at cruise altitude, or during cruise and descent based on requirements listed in the AFM.

The proposal addresses NTSB recommendations regarding airframe icing that was issued as a result of a Feb. 16, 2005, Citation 560 accident at Pueblo, Colo. In this mishap, the aircraft was operating in icing conditions and the crew failed to activate the airframe ice protection system during the approach as had been required by the AFM.

The FAA considered but did not include Parts 91 and 135 operators in the proposed rule for several reasons: One, because they are subject to previous airworthiness directives that call for activation of de-icing boots at the first sign of ice accretion. Another reason cited in the proposed rule is that aircraft operated under Parts 91 and 135 are smaller scale than those operated under Part 121, and therefore allow easier monitoring of ice buildup.

Operators would have 24-months' compliance time from the effective date of the final rule. The FAA assumes the proposal will become final in December 2010. Estimated implementation cost to operators $5.5 million, and the estimated benefits of averting one accident and four fatalities are about $17.3 million, according to the FAA.