Summary
We propose to adopt a new airworthiness directive (AD) for all The Boeing Company Model MD-90-30 airplanes. This proposed AD was prompted by reports of stick shaker activation at airspeeds that were above the stall protection system's stick shaker schedule. This proposed AD would require installing angle-of-attack (AOA) sensor external case heaters and AOA sensors, changing wires, and doing a functional test and applicable corrective actions. We are proposing this AD to correct water intrusion and subsequent ice formation between the AOA sensor vane and face plate, which could cause the vane to become immobilized. If the vane becomes immobilized, the stall protection system could become unreliable or non-functional, which could result in loss of control of the airplane.