What is the PSI of bleed air start?

• A. 60 psig
• B. 20 psig
• C. 30 psig
• D. 45 psig

Answer: (D)

Bleed air start uses a controlled supply of high-pressure air to drive the pneumatic starter and spin the engine until ignition. The air must be high enough to overcome starter inertia and the gear load, but within the system’s design limits. A nominal bleed-air start pressure of about 45 psi provides the right balance: it delivers enough flow and energy to accelerate the starter to the speed needed for light-off without overloading or damaging components. Pressures around 20–30 psi are typically too low to reliably start the engine, while notably higher pressures (like 60 psi) can exceed the starter’s rating and risk damage. So, 45 psi is the standard, appropriate bleed-air start pressure for reliable starts in these systems.