What constitutes the signal from ground staff to open doors?

• A. Knocking on the aircraft door
• B. Thumbs up signal through the viewing window
• C. Knocking on the aircraft door; then "thumbs up"
• D. Verbal clearance through interphone

Answer: (C)

The signal to open doors is a clear two-step visual cue that combines attention and clearance. Ground staff first knock on the aircraft door to grab the crew’s attention, then, after the crew acknowledges, show a thumbs-up through the viewing window to indicate it’s safe to open. This sequence ensures everyone knows someone is ready at the door and that it’s permitted to proceed, minimizing the risk of an accidental or premature door opening.

Knocking alone can alert but doesn’t confirm safety. A thumbs-up alone might be misinterpreted without first getting the crew’s attention. Verbal clearance through interphone relies on radio contact and isn’t the visible signal the crew uses at the door; it can be obscured by noise or misheard. The combined knock followed by a thumbs-up provides a consistent, unambiguous signal that the door may be opened.