If communication with the flight crew is unsuccessful, what action can the cabin crew take after a set time?

When communication with the flight crew is unsuccessful for an extended period, cabin crew members are trained to push on the flight deck door. This action is taken after assessing the situation and determining that there may be a need to check on the well-being of the flight crew. By pushing on the door, cabin crew members can alert the flight crew of their presence and the urgency of the situation, which may lead to further instruction or gaining access if necessary.

This protocol is critical for ensuring the safety of everyone on board, as the flight deck is a secure area where the pilots operate the aircraft. In emergencies, swift actions by trained cabin crew can help mitigate risks and maintain communication with the flight crew.

The other options are not considered appropriate responses in this scenario. Unlocking the emergency exit is not suitable because it could compromise the safety of passengers and crew. Contacting ground control may not be viable without proper communication lines established with the flight deck. Signaling for help from passengers does not address the immediate concern of checking on the flight crew's condition or ensuring control of the aircraft. Thus, pushing on the flight deck door is the most appropriate and effective action in this context.