Saturday, 18 March 2017

Why Plane Windows Are Round, Not Square

plane window

It was January 10 in 1954, FLIGHT 781 left the tarmac at Rome’s Ciampino Airport to carry its 35 passengers and crew to London.

About 15 minutes into the flight, the de Havilland Comet jet disintegrated in the sky and crashed into the Mediterranean Sea, killing everyone on board.

Just two years earlier, the de Havilland Comet was the toast of skies when it became the world’s first scheduled commercial flight.

But that tragedy outside Rome and a second fatal crash just months later meant the Comet left a unique impact on the future of aviation — it’s the reason why you never see square windows on a plane.

Why the Comet was such a big deal

The de Havilland Comet became the world’s first commercial jetliner in 1952, and in terms of design, it was a total game-changer.

In the age of propellers, this British-made jet had four turbojet engines, as well as the bullet-shaped fuselage that planes still have today, a pressurised cabin, and wings that swept backwards.

It also had large, square windows — a desirable feature for the ever-expanding jet set.

As the first jet in history to make a scheduled commercial flight, the Comet made air travel possible for millions.

plane window

In its first year, it flew 30,000 passengers, including the Queen, to places like Tokyo, Singapore, Johannesburg, and Colombo.

However, the Comet’s most important contribution to aviation wasn’t measured by its successes but its most horrific failures, as The Telegraph revealed recently.

What went wrong?

Comet jets experienced a few fatal crashes in those early years, but its two crashes in 1954 were the ones that changed things forever.

The first was the ill-fated flight 781 from Rome that exploded 20 minutes after takeoff.

Investigators later found a confusing pattern of injuries among the recovered bodies, including fractured skulls and ruptured lungs.

Months later, 21 passengers were killed when South African Airways flight 201 from London to Johannesburg crashed in the Mediterranean sea, and recovered bodies showed similar head and lung injuries to those on flight 781.

Investigations into the crashes eventually found both were caused by in-flight metal fatigue failure, which led to explosive decompression and mid-air breakup.

So what’s the link to windows?

As The Telegraph explained, the square shape of the Comet’s windows played a big role in the metal fatigue that caused those crashes.

The sharp corners of the windows put the surrounding metal under extra stress in high altitudes — as much as two or three times more than other places on the plane.

plane window

The stress was concentrated in the four corners of every window, causing the metal fatigue.

Following the investigations, de Havilland made a number of changes to its aircraft design, including rounder windows.

The lack of sharp corners allowed the stress to flow more evenly around the edges of the window.

This article originally appeared on



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