Which of the following is a characteristic of a plug-type door used in aircraft?

• A. It swings outward
• B. It is designed to be opened inwards
• C. It has a locking mechanism that engages when the cabin is pressurized
• D. It is primarily used for cargo access

Answer: (C)

A plug-type door is specifically engineered to utilize the principles of cabin pressure to enhance safety and security during flight. When the aircraft is pressurized, the door's design allows it to be pushed tightly against its frame, making it virtually impossible to open from the outside. This characteristic is particularly important in emergencies and helps ensure that the door remains sealed under pressure, thereby maintaining the integrity of the cabin.

The mechanism that engages when the cabin is pressurized allows for proper operation whether the aircraft is on the ground or in the air. This means that when a plane is at cruising altitude, the pressure differential actually assists in keeping the door securely closed rather than allowing it to be opened. This feature ensures the safety of passengers and crew during flight.

In contrast, the other options do not accurately describe the plug-type door's functionality. While doors in aviation can be designed to swing inward or outward, the specific function and security of the plug-type door rely on its pressure-based locking mechanism rather than its swing direction or its use for cargo access.