Weakest Corner

In 1929, a 22-year-old RAF officer named Frank Whittle walked into Britain's Air Ministry with an idea that sounded a little ridiculous.

Airplanes had always relied on propellers. Engines turned the propellers, the propellers pulled the airplane through the air, and that was more or less how powered flight worked. Whittle thought there might be another way.

Instead of using an engine to turn a propeller, he imagined compressing air, mixing it with fuel, igniting it and blasting the hot gases out the back of the airplane. The reaction would push the airplane forward.

A jet engine.

The Air Ministry wasn't impressed.

Whittle's proposal was reviewed and dismissed as not promising enough to pursue. Fortunately, one of his friends convinced him to patent the idea anyway, which he did in 1930. For the next several years, Whittle continued working on the concept largely outside the government's enthusiasm, eventually helping form a small company called Power Jets.

On April 12, 1937, Whittle finally tested his first working gas-turbine engine.

Four years later, an airplane powered by one of his engines flew.

The idea that had been brushed aside was about to change aviation forever.

World War II accelerated everything. Jet engines went from strange experiments to military technology, and by the end of the war it was obvious that propeller-driven airplanes were eventually going to have a problem.

Jets could fly faster. They could fly higher. And unlike a propeller, which becomes increasingly inefficient as its tips approach the speed of sound, the basic jet engine had enormous room for improvement.

When the war ended, Britain saw an opportunity.

The Americans had emerged from the war with an enormous aviation industry. Douglas and Boeing were building increasingly capable passenger airplanes, but they were still powered by piston engines and propellers.

Britain had something else.

It had jet technology.

And Geoffrey de Havilland intended to use it.

De Havilland was already one of the most famous names in British aviation. During the war, his company had built the Mosquito, an extraordinarily fast and versatile aircraft made largely from wood. Now his company began working on something far more ambitious.

A passenger jet.

The first prototype of the de Havilland Comet flew in July 1949. Even sitting on the ground, it looked different from the airliners around it. Instead of four giant propellers hanging from the wings, its four jet engines were tucked neatly into the wing roots. The fuselage was smooth and clean. The passenger cabin was pressurized so the airplane could cruise high above much of the weather.

It looked like the future because it was.

On May 2, 1952, British Overseas Airways Corporation put the Comet into scheduled passenger service.

There was nothing else like it.

The Comet could cruise at roughly 450 miles per hour, around 50% faster than comparable piston-powered airliners. A trip from London to Tokyo that had taken more than 86 hours on BOAC's older Argonaut aircraft could be scheduled in around 36 hours aboard a Comet. In its first year of service, Comets carried more than 30,000 passengers.

For Britain, this was more than a new airplane.

It was proof that the country was still capable of leading the world technologically.

American manufacturers were years behind.

Passengers loved it. Airlines wanted it. BOAC suddenly had the most advanced passenger fleet in the world.

Then, on January 10, 1954, BOAC Flight 781 left Rome for London.

There were 35 people aboard.

The airplane climbed normally over the Mediterranean and continued north toward England. There was no obvious emergency and no long sequence of mechanical problems.

Then the airplane simply came apart.

Wreckage fell into the sea near the island of Elba.

All 35 people aboard were killed.

Nobody really knew why.

BOAC grounded the Comet fleet while investigators looked for answers. Engineers inspected the airplanes and made modifications. Possible causes included engine problems, control failures and other mechanical issues, but nothing provided a completely satisfying explanation.

Eventually, officials decided the airplanes could return to service.

On March 23, they did.

Sixteen days later, another Comet disappeared.

On April 8, another aircraft left Rome on its way toward Johannesburg. Once again, the airplane broke apart over the Mediterranean. All 21 people aboard were killed.

The Comet's certificate of airworthiness was withdrawn the next day.

Britain now had a very uncomfortable problem.

It had created the most advanced passenger airplane in the world, and nobody knew why it was falling out of the sky.

The investigation that followed became nearly as remarkable as the airplane itself.

The Royal Navy began recovering pieces of Flight 781 from the bottom of the Mediterranean. Eventually investigators recovered roughly 70% of the airplane and painstakingly reconstructed the wreckage.

At the Royal Aircraft Establishment in Farnborough, engineers decided to conduct an experiment that had never been attempted on this scale.

They took another Comet, registration G-ALYU, and put most of the fuselage inside a gigantic water tank.

The wings stuck through sealed openings in the sides.

Instead of repeatedly flying the airplane up to altitude and back down again, investigators used water pressure to simulate what happened to the cabin during flight. Hydraulic equipment simulated the loads on the wings.

A three-hour flight could effectively be recreated in about ten minutes.

Then they did it again.

And again.

And again.

Thousands of simulated flights.

Eventually the fuselage failed.

Investigators finally had their answer.

The problem wasn't the jet engines.

It wasn't the wings.

It wasn't that jet-powered passenger travel had been a bad idea.

The problem was pressure.

Every time the Comet climbed to cruising altitude, the cabin had to remain comfortable for the people inside. The air outside became thinner as the airplane climbed, while the pressure inside the cabin remained much higher.

That difference pushed outward on the airplane's skin.

Then the airplane descended, the pressure difference disappeared, and the fuselage relaxed.

Expand.

Contract.

Expand.

Contract.

The stresses on any individual flight weren't enough to tear the airplane apart.

But metal can fail differently when the same load is applied thousands of times. Tiny cracks can form and slowly grow through a process known as fatigue.

Investigators discovered that the Comet's fuselage was developing those cracks around openings in the pressure cabin. In the test aircraft, the eventual failure began at a rivet hole near an escape hatch. Reconstruction of the crashed aircraft confirmed that fatigue cracking in the pressure cabin had caused the catastrophe.

One part of the story became particularly famous.

The Comet had relatively square windows.

A rounded opening distributes stress fairly smoothly around its edge. But corners concentrate stress. Add repeated pressurization, manufacturing details and thousands of cycles, and those little areas could become places where cracks began.

It's slightly too simple to say that the Comets crashed solely because they had square windows. The actual engineering failure involved the larger design and construction of the pressurized fuselage, and investigators found critical cracking around more than just passenger windows.

But the windows became the perfect symbol of what went wrong.

Britain had invented a new kind of airplane.

It flew higher than almost anything passengers had experienced before. It was faster, quieter and more comfortable. Its engines represented one of the greatest technological breakthroughs of the 20th century.

And one of the things that brought it down was a corner.

There is something about that story that I think applies surprisingly well to financial planning.

Most financial disasters don't happen because every part of a plan was terrible.

Usually, most of it was perfectly reasonable.

Someone has a good income, saves consistently, invests for decades and builds a substantial portfolio. They may have a sophisticated retirement plan, tax strategy and estate plan.

Then there is one weak corner.

Maybe half of the portfolio is tied up in one company because the stock has always performed well.

Maybe the retirement plan works beautifully as long as spending stays exactly where the software assumes it will.

Maybe an estate plan was created fifteen years ago and nobody ever updated the beneficiaries.

Maybe there is plenty of money but very little liquidity.

Maybe one spouse understands every account, password, insurance policy and investment while the other understands almost none of it.

None of those things necessarily looks catastrophic by itself.

Neither did the corner of a window.

The real lesson of the Comet isn't that sophisticated plans are bad. The jet engine was sophisticated, and it changed the world. The basic idea behind the Comet was so good that almost every major passenger airplane flying today follows the same basic concept.

The problem was that as the airplane became more advanced, the stresses placed on the rest of the system changed too.

The engineers solved the obvious problems. They figured out how to build jet engines,