Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Learjet Model 23, 24, 25, 28, 29, 31, 55, and 60 series airplanes. This proposal would require a one-time detailed visual inspection of the electrical wire leads of the horizontal stabilizer anti-ice system to verify that the numbers on the wire leads correctly correspond to the numbers on the connected airframe wiring; installation of a wire ID strap on the left- and right-hand sides of each terminal block; and installation of a warning placard. This proposal is prompted by a report of severe flight control buffeting of a Learjet Model 55 series airplane due to a malfunction of the horizontal stabilizer anti-ice system. The actions specified by the proposed AD are intended to prevent undetected accretion of ice on the leading edge of the horizontal stabilizer, which could result in the loss of pitch control and consequent reduced controllability of the airplane.