After the start of the first engine, both pack valves remain closed unless ______ has elapsed before beginning the start of the second engine.

After the start of the first engine, both pack valves remain closed unless ______ has elapsed before beginning the start of the second engine.

• A. 30 seconds
• B. 60 seconds
• C. 90 seconds
• D. 120 seconds

Answer: (B)

After the first engine lights off, the environmental control system keeps the packs isolated to prevent their bleed air draw from interfering with the start sequence. A fixed delay is built in so the first engine’s bleed air and pneumatic system can stabilize before the second engine is started. Sixty seconds is the chosen interval to ensure the start remains clean and stable and that there’s adequate bleed air/pressure available for the second start and for cabin conditioning. If the second engine is started sooner, the packs may still be stabilizing and could cause pressure or flow fluctuations; waiting longer than sixty seconds doesn’t add safety or performance and just delays the start.

After the first engine lights off, the environmental control system keeps the packs isolated to prevent their bleed air draw from interfering with the start sequence. A fixed delay is built in so the first engine’s bleed air and pneumatic system can stabilize before the second engine is started. Sixty seconds is the chosen interval to ensure the start remains clean and stable and that there’s adequate bleed air/pressure available for the second start and for cabin conditioning. If the second engine is started sooner, the packs may still be stabilizing and could cause pressure or flow fluctuations; waiting longer than sixty seconds doesn’t add safety or performance and just delays the start.