Aviation Disaster that Change the Way Aircraft Looked

Hello everybody,

Have you ever wondered why aircraft windows are circular and no other shape? Round windows were put in place of square windows due to the fatigue cracks that were present around square windows. Unfortunately, 3 air disasters, all de Havilland Comet aircraft, exploded mid-fight and the only reason was because it had square windows (FAA, 2020).

The square windows allowed the aircraft to endure more stress during pressurization due to the sharper edges. The illustration below shows that with square windows the expansion and contraction of the skin of the aircraft during pressurization produces targeted stress on the edges of square windows.

Due to the increased stress, the skin cracked and led to the disintegration of the aircraft in flight at high altitudes.

Following the incident, an Airworthiness Directive was issues, as well as, a new FAR stating the requirements for windows to withstand high pressurization differences in flight. According to the e-CFR title 14, part 25, chapter 25.775, all windows in pressurized aircraft must be able to withstand the probable pressurization differentiation (Aeronautics and Space, 2020). Furthermore, in chapters 25.365 abd 25.843, all windows must be tested for pressurization on the ground to ensure no stress fractures are found, and are able to withstand it (Aeronautics and Space, 2020).

This is now why round windows are used on all cabin windows today. It has moved the aviation industry forward and unfortunately we had to learn a valuable lesson in aircraft design. 

References

Aeronautics and Space, 14 C.F.R § 25 (July, 2020)

Federal Aviation Administration. (2020). De Havilland DH-106 Comet 1. Retrieved from https://lessonslearned.faa.gov/ll_main.cfm?TabID=1