A version of this story appeared first on Forbes.com
A troubling string of incidents involving aircraft window failures has caught public attention over the past few weeks, including one where the cockpit windshield of a Sichuan Airlines A319 blew out at 30,000 feet, and the tragic death of a passenger on a Southwest 737 when an engine failed, ejecting metal shrapnel that shattered her window, causing her to be sucked partway out of the plane. It’s raised questions for many over the safety of aircraft windows. Here’s what you should know about the rules, standards and methods of design, and testing and manufacturing of these critical aircraft structures.
Effectively, airplanes are not so different from submarines. Both involve structures that have to withstand a stark difference in pressure and temperature outside and in. In both cases, the outside environment is not hospitable to life. A tiny flaw or weak point can quickly spread and lead to tragedy.
Airplanes face other challenges. They operate at very high speeds in an environment where other flying objects—birds or debris—may pose a threat.
All of these risks are considered in the rules and standards governing the manufacture of aircraft structural parts and components.
The guidelines on various accepted methods of composition and stress testing of aircraft windows can be found in the FAA’s AC (Advisory Circular) 25.775-1. For anyone who, like this writer, really likes to deep dive into things like chemical treatments, material loads and other stress tests, this document is good reading material.
In summary, the AC makes clear that aircraft windows undergo the same degree of stringent testing as aircraft fuselages or engines. They are all built to be tough.
One of the world’s oldest manufacturers of aerospace transparencies (windows) is PPG, headquartered in Pittsburgh. It was founded as a specialist glass, paints, coatings and materials manufacturer in 1883, and their first aircraft windows were installed in 1926 on the Ford Trimotor. They have placed high-performance panes on planes ranging from commercial aircraft to fighter jets and business jets and specialize in flight deck windshields.
PPG labs developed an Opticor Advanced Transparency Material with advanced impact and crack propagation resistance properties, which can be used in the manufacturing of both windshields and passenger windows.
Brent Wright, PPG global business director for aerospace transparencies explains, “On the cockpit there are two primary purposes for the windshields. Number one, protect the crew from the outside harsh environment and number two allow the crew to see outside and in doing so. Getting to that, to protect the crew from the outside environment, the windshield has to be designed to be structurally capable and safe.”