Design, Safety, and Maintainability Aspects for Hydrazine Use in Emergency Secondary Power Systems

The current trend toward turbofan engines with high compression ratios is taking its toll in a reduced engine windmill start envelope. Engines now require in-flight starter assist and emergency electrical and hydraulic power for flight controls. When considering schemes that provide these capabilities it is important to consider that an emergency power system which drives engine accessories may be unsuitable, since it must provide hydraulic control and electrical power with an inoperable engine.

System evaluation will be briefly considered since the approach selected is dependent upon the aircraft mission. A rationale for the selection of hydrazine as a primary system, or in conjunction with other systems, has been developed. This paper will address the influence of safety and maintainability considerations upon hydrazine systems design. Concerns in these areas have limited the widespread use of hydrazine in aircraft secondary power systems. To dispel these concerns, extensive experience accumulated to date with hydrazine are examined and applied to operational considerations to provide increased confidence required in considering hydrazine as a viable candidate energy source for aircraft secondary power systems.