Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Dassault Model Mystere- Falcon 900 and Falcon 900EX series airplanes. This proposal would require replacement of the protective screens of the underfloor structure boxes at frame 25. This action is necessary to prevent water from collecting and freezing in the structure boxes at frame 25, which could result in jamming of the flight controls and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition.