As part of the testing of a new aircraft, the manufacturer must demonstrate that all passengers can be evacuated in a short amount of time when an emergency arises - within 90 seconds to be precise. If it doesn't comply, the aviation authorities won't approve its safety certification.

The 90-second rule is a mandatory safety standard set by aviation authorities (like the FAA and EASA) requiring that all commercial aircraft must be capable of a full evacuation in 90 seconds or less. During certification testing, the manufacturer must demonstrate that every passenger and crew member can exit the plane using only half of the available emergency exits in dark conditions. This specific timeframe is based on the "flashover" point—the moment during a post-crash fire when the cabin temperature becomes unsurvivable and fire consumes the interior. This rule dictates the design of emergency slides, the width of aisles, and the placement of emergency lighting. It is a critical benchmark that ensures aircraft are structurally and operationally equipped to handle the most time-sensitive life-saving scenarios on the ground.