Plug door

Alternatively, the door may have locking hinged panels at the top and bottom edges that can make it smaller than the opening, so it may be swung outward.

This did not prevent the door plug from detaching on Alaska Airlines Flight 1282 on January 5, 2024, which has been attributed to missing bolts in the upper guide fittings and the lower hinge assemblies.

An inward opening plug hatch design was used on the Block I Apollo Command Module, because the explosive-release hatch of Gus Grissom's Mercury capsule Liberty Bell 7 prematurely blew at the end of the flight, causing the capsule to sink in the Atlantic Ocean and nearly resulting in Grissom's drowning.

A cabin fire during a 1967 Apollo 1 ground test raised the pressure even higher (29 pounds per square inch (200 kPa)), and made the hatch impossible to remove for the crew to escape.

Because of this, NASA decided to change to a quick-release, outward opening hatch on the Command Module.

Deep-submergence vehicles such as the Alvin use a plug hatch which is sealed inward by the pressure of the ocean water.