Why so few companies make aircraft windows

Cockpit windows, Vermont says, are “totally different”.

They are generally made of glass, which is chemically reinforced by adding potassium to it. This involves swapping smaller sodium ions for larger potassium ions, which helps to fill out the molecular structure of the glass, meaning that when it cools during production, it compresses into an extra strong, tight formation as it cools.

Some of the latest aircraft feature cockpit windows that are also curved, to make the plane more streamlined, which improves fuel efficiency. But curved cockpit windows are challenging to make – the slightest distortion or defect is clearly visible to the pilot.

Quality control checks are used to ensure no such impediments exist in the final product.

All aircraft windows must be resistant to impacts but cockpit windows, at the front of the plane, are especially vulnerable to bird strikes, says Vermont: “The issue is not the speed of the bird, the issue is the speed of the aircraft.”

Saint-Gobain uses numerical simulations and “physical tests representative of a sizeable bird impact” to test its windows against this threat.

“Typically, if you go through a hailstorm or if you hit a large enough bird, the external ply will crack,” says Vermont. “The cockpit window is designed for that.”

A London to Londonderry flight was recently affected by a cracked cockpit window. While a mid-air emergency was declared, the plane landed safely. “There can be [such] cases,” says Vermont, though he adds that Saint-Gobain’s windows have not been involved in any recently.

“You’re obviously dealing with a surface that is interfacing with two very different environments,” says Stengel. “That’s why these are more highly-engineered products.”