cabin

The cabin is the enclosed section of an aircraft fuselage where passengers sit during flight. It is a pressure vessel maintained at a controlled altitude equivalent, typically 6,000 to 8,000 feet, even when the aircraft flies at 35,000 feet or higher. The cabin walls, floor, and ceiling are structural elements that must withstand cyclic pressurization and depressurization with each flight, a process that creates fatigue stress over the aircraft's service life.

Modern commercial aircraft cabins are divided into sections by class of service: first class, business class, economy. The cabin also includes the galley, lavatory modules, and crew rest areas on larger aircraft. Each class section has different seating density, pitch (the distance from one seat back to the next), and amenities. A Boeing 777, for example, might have a first class cabin of 8 rows, business class of 40 rows, and economy of 70 rows, depending on the airline's configuration.

Maintenance and structural concerns

The cabin experiences repetitive stress from pressurization cycles. A transoceanic flight with many pressure cycles can accumulate several hundred equivalent cycles in a single day. Maintenance inspectors look for cracks radiating from rivet holes, corrosion in aluminum skin behind interior panels, and delamination of composite panels. Pressurized cabins are fitted with pressure relief valves and outflow valves that regulate internal pressure; failure of these systems forces the aircraft to descend to unpressurized altitude.

Interior cabin components, including overhead bins, seats, and monuments (galleys and lavatories), are removable and are regularly inspected or replaced. The cabin floor is designed to distribute loads from seated passengers and service carts across the underlying fuselage structure. Between the cabin interior trim and the structural fuselage skin lies insulation and wiring; maintenance access to this space requires removal of panels and furnishings, making interior cabin work labor intensive.

Cabin pressurization is maintained by engine bleed air or, on newer aircraft with electric compressors, by dedicated pneumatic systems. Loss of cabin pressure triggers automatic descent procedures and deployment of oxygen masks. The cabin altitude limit is determined by aircraft certification; most commercial transport aircraft are certified to maintain cabin pressure equivalent to 8,000 feet even in the event of a single failure in the pressurization system.