[agurk]

The EPU on the F-16 is actually quite interesting itself and is a good fit for what is needed with 70s technology.

Redundant systems are normal on aircraft and the F-16 has a particular need for hydraulic and electrical power as its inherently unstable airframe needs various onboard systems to keep it stable and flyable.

If the main generator disconnects from the bus or the hydraulic pressure drops[0] the EPU will automatically operate to provide electrical and hydraulic power. It can run from engine bleed air, but if the (single) engine has failed then pressure will be provided from the hydrazine system.

It achieves this using a 70% solution of hydrazine in water as a monopropellant, which is decomposed over an iridium catalyst. The water helps keep it stable, and cools the catalyst when it boils, keeping it around 850C and the high pressure gasses are fed into the EPU.

This has the advantage of being light (25L of hydrazine and simple as only a single liquid), reliable and fast acting (~2s to max power).

[0] https://www.slideshare.net/matheusgaldino355/usaf-flight-man... (section 1-101)