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Through The Looking Glass

Marketing for the Boeing 787 has focused heavily on its oversized windows, which replace the mechanical blinds found on other commercial aircraft with an electrochromic dimming function.

Glass that darkens at the touch of a button may lend a futuristic feel to the cabin, but the most advanced windows technology is typically found in the cockpit.

Unlike the acrylic passenger windows on modern aircraft, pilots’ windshields are still made from glass, albeit chemically-tempered glass produced to unique specifications.

At three plies thick, glass windshields are designed to protect against bird strikes; de-ice from minus 50 degrees; resist fogging and provide exceptional optical qualities.

Bonded between the plies of certain windshields is a conductive plasma coating only a few nanometers thick, which can generate heat for de-icing and de-fogging.

Together, the three plies are around 2cm thick, though only the inner two layers of glass are structural elements; the outer layer acts as a barrier and aircraft can be flown even if it suffers damage, although pilots are understandably loth to do so.

“Even if [the outer layer] fails it’s totally safe for the pressure from bird strikes and so on, but pilots are scared and they don’t know which ply cracked, so most of the time they abort the mission,” explains Sylvain Mourlhon, sales director, aerospace, for Saint-Gobain Sully.

Like many other component manufacturers, aircraft transparency suppliers rely on the aftermarket for the bulk of their profits.

It is perhaps surprising, then, that their products are largely designed to be maintenance-free, beyond the odd polishing. However, foreign object damage from events such as bird strikes and hail means that an aircraft will typically go through three to four windshields in its lifetime.

Since windshields cannot be repaired on airframe, this provides a lucrative opportunity for their manufacturers to sell spares and conduct repairs, which usually involve delaminating and rebonding the glass plies.

To find out more about the aircraft windows business pick up the next issue of Inside MRO.

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