Abstract:Aimed at the brake system in the military aircrafts made in China, the failure rate of bias brake is very high, which were caused by the contamination of the hydraulic oil. The nozzle flapper servo valve is the core accessory of the brake system, which operating principle is present briefly. The construction features and steady state characteristic of its first valve were analyzed in depth, and the main failure modes of the nozzle flapper servo valve caused by the contaminated hydraulic oil were stated in emphasis. Basing on this, the beneficial conclusions and the specific countermeasures which improve the reliability of brake system in the aircrafts are educed.