Summary
This document withdraws a notice of proposed rulemaking (NPRM) that would have applied to all LET, a.s. (LET) Model L-420 airplanes. The proposed AD would have required you to revise the Airplane Flight Manual (AFM) to include requirements for activation of the airframe pneumatic deicing boots. The proposed AD was the result of reports of in-flight incidents and an accident (on airplanes other than the referenced LET airplanes) that occurred in icing conditions where the airframe pneumatic deicing boots were not activated. LET only manufactured one Model L-420 airplane and LET controls that airplane. For an unsafe condition to exist, there must be a condition that could exist or develop on other airplanes of the same type design. Because there is only one affected airplane, an AD is not necessary and we are withdrawing the NPRM.