Abstract : This work presents a preliminary evaluation of the use of the CompCert formally specified and verified optimizing compiler for the development of level A critical flight control software. First, the motivation for choosing CompCert is presented, as well as the requirements and constraints for safety-critical avionics software. The main point is to allow optimized code generation by relying on the formal proof of correctness instead of the current un-optimized generation required to produce assembly code structurally similar to the algorithmic language (and even the initial models) source code. The evaluation of its performance (measured using WCET) is presented and the results are compared to those obtained with the currently used compiler. Finally, the paper discusses verification and certification issues that are raised when one seeks to use CompCert for the development of such critical software.