When will the crew be alerted concerning cabin masks?

The crew will be alerted concerning cabin masks primarily when the pilot in the right seat pulls the oxygen handle, which releases the cabin masks. This action is a direct and immediate trigger for the deployment of oxygen masks and alerts the crew that supplemental oxygen is necessary for safety due to potential issues such as cabin depressurization.

Understanding this mechanism is crucial because it reinforces the immediate response required by the crew in the event of an emergency where oxygen is needed. The action of pulling the oxygen handle is specifically designed to initiate the use of oxygen systems, ensuring that crew members are prepared to administer supplemental oxygen to themselves and passengers without delay.

Other provided scenarios, such as exceeding a certain cabin altitude, emergency landings, or drops in air pressure, while relevant in broader safety contexts, do not specifically trigger the alerting mechanism as the action of pulling the oxygen handle does. Thus, option A accurately reflects the primary action leading to crew awareness regarding cabin masks.