When should you not press INTPH on the interphone system?

The interphone system on an aircraft is designed to facilitate communication among different crew members, including the flight attendants and the cockpit crew. In emergency situations, it is crucial to ensure that communications are clear and unobstructed so that all crew members can respond quickly and effectively to the emergency at hand.

Pressing INTPH should be avoided during an emergency call because this function may not prioritize or alert all necessary crew members in the same way as direct emergency communication protocols. Instead, crew members should use established emergency communication methods to ensure that their messages are transmitted without delay or interference, allowing for quick decision-making and action.

In non-emergency scenarios like calling flight attendants, talking to passengers, or using the cabin intercom, the INTPH function serves a useful purpose and can help facilitate those conversations efficiently. Hence, understanding the importance of prioritizing emergency communication is key in this context.