Answer
With Compressor A out of service and the ETO investigating, the Chief Engineer must manage the immediate risk to propulsion availability:
Line Up Standby Unit: Ensure Main Air Compressor 'B' is immediately lined up, switched to manual/auto mode, and verified running to maintain the main air receiver pressures between 25 and 30 bar.
Conserve Control & Start Air:
Isolate any non-essential auxiliary air lines on deck or in the workshop to avoid waste.
Inform the Bridge/Pilot of the temporary restriction. Minimize unnecessary engine starts/stops during maneuvering if possible, optimizing the starts per sequence.
Emergency Back-up: Ensure the Emergency Air Compressor is lined up and tested, ready to charge the designated emergency air bottle if a total loss of power (blackout) occurs concurrently.