During engine start, is it required for the pilot to select OFF with the AC packs and open the ISOL valve?

• A. True - pilot must
• B. False - proper operation will be automatically controlled by the ASCS computers
• C. False - the ISOL valve must be opened by maintenance
• D. False - the bleed air source can be selected manually

Answer: (D)

Bleed air source selection and isolation during engine start. You need a source of pneumatic air to start the engine, and this aircraft allows the crew to choose which bleed source powers that start. Because you can select the bleed air source manually, you are not required to set the AC packs to OFF and open the ISOL valve as part of the start procedure. The system can route the chosen bleed source (for example, engine bleed or APU bleed) to the start air without relying on a fixed automatic sequence. As always, follow the specific airplane’s start procedures, since exact valve states and automatic versus manual control can vary by type.