Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-400 series airplanes. This proposal would require an inspection to detect miswiring of diodes in the heating system of the pitot static probes, and corrective action, if necessary. This action is necessary to prevent reduced power to the heating system of the pitot static probes, leading to ice accumulation on the pitot static probes, which could result in erroneous airspeed or altitude indications to the flight crew, and consequent reduced operational safety in all phases of flight. This action is intended to address the identified unsafe condition.