What panel is responsible for selecting the APU as the bleed-air source?

The AIR COND/BLEED panel is responsible for selecting the Auxiliary Power Unit (APU) as the bleed-air source. This panel is integral to aircraft systems as it controls the distribution of bleed air for both environmental and pneumatic needs within the aircraft.

When the APU is engaged, it can provide necessary bleed air, particularly during ground operations or when the engines are not running. The functionality of this panel allows pilots and operators to optimize the use of bleed air, ensuring the environmental control system operates efficiently and reliably.

The APU CONTROL panel, while related to the operation of the APU itself, focuses on the start and operational parameters of the APU rather than the selection of bleed air sources. The FLIGHT CONTROLS panel pertains to the operation of the aircraft's flight control systems. The ENGINE panel deals with engine parameters and does not play a role in bleed air selection either.

Thus, the correct answer highlights the specific function of the AIR COND/BLEED panel in managing bleed air sources.