There is at least one other victim of Malaysian Airlines Flight 370 besides the 239 people who are presumed dead: the airplane itself. The disappearance of the flight and the lack of information about it is a terrible tragedy for the families of those lost, but for as long as it remains a mystery, it will also cast a shadow over an airplane with an exemplary record for safety: the Boeing 777.

Right from its conception in 1990, the 777 became in Boeing’s eyes more than just a new airplane. It became the vehicle for a game-changing cause—for a concept that would upset a long-settled orthodoxy about the safety margins for long-haul flights over the ocean.

Boeing would use the 777 to drive a long campaign to change the minds of regulators—and to undermine the plans of its main competitor, Airbus.

Driving the campaign was a simple equation: What was the most economical way to fly between 300 and 400 passengers over long transoceanic routes?

The answer was clear but controversial. It had to be a big wide-body airplane with only two engines, The Big Twin. For the airlines seeing the same equation, it was a mouth-watering dream of an as yet unattainable return on the heavy capital costs of buying new airplanes.

And it was controversial because nobody had ever built an airliner this large with only two engines. From the beginning of the jet age the safety regulators remained adamant: If you flew long distances over water where for much of the flight the airplane would be hours from the nearest airport you needed three or four engines in case one failed.

This view was crystalized in 1980 when the then-head of the Federal Aviation Administration, Lynn Helms, told Boeing: “It’ll be a cold day in hell before I let twins fly long-haul over-water routes.”

However, in the decade that followed, a smaller Boeing twin, the 767, had proven so reliable flying over water that the FAA began to relax the regime and allow twins to fly routes where they could be as much as 180 minutes from the nearest airfield. And it was toward the end of that decade that the form of what would become the 777 took shape—what Boeing touted would be the first 21st century airliner.

As I discovered at the time, there were people at Boeing who had yet to be persuaded that a jet as large as the 777 could be safe over oceans with only two engines. The four-engined 747 had already shown that it could lose two engines out over an ocean and still make it back to land, and this level of “redundancy” was hard-wired into the generation of men who created the 747 in the 1960s.

The designers at Airbus felt the same way. As Boeing drew up plans for the 777, they were building a competitor, the A340, with four engines, also aimed at the very long transoceanic routes. Nobody doubted that the Big Twin was more efficient. For the same number of passengers it used significantly less fuel. But Airbus and Boeing were soon conducting very public disagreements about the safety issue.

Boeing knew that the Big Twin would need to be the most dependable airplane they—or anyone else—had ever built if it was to meet their goal. And that dependability rested as much on the engines as on the airplane. Its engines would need to be a step change in both the power they delivered and in their reliability.

So the 777 was not just big itself but its engines were very, very big—giant turbofans. All three major engine makers, Pratt & Whitney, General Electric, and Rolls Royce, developed engines for the 777. All were betting that airlines would love the airplane and they could not afford to be left out of such a promising new market.

By early 1995, Boeing had put the 777 through many demanding test flights and they were about to start delivering it to airlines. Everything they had learned about making airplanes safer was absorbed into its development, including the use of new alloys that were much more resistant to corrosion and metal fatigue and a cabin that was more robust to make crash impact more survivable for passengers.

But the purpose of flight testing is to push a new airplane to the limits to see if anything breaks, particularly when as, in this case, many innovations were involved, including Boeing’s first use of “fly-by-wire” controls, in which digital commands are sent to the control surfaces instead of the old mechanical system. The 777 tests proved the value of this advance in making such a large jet smoother to handle. When trouble came, however, it came suddenly, unpredictably, and in the form of a very basic mechanism.

On February 2, 1995, a media junket was under way at Boeing Field, Seattle, to celebrate the delivery of the first 777 ordered by British Airways. But before this 777 appeared, another came in, descending rapidly for an emergency landing. It was the second 777 to be built and still deep into the flight test program. Watched by the media assembled for the British Airways event, it was greeted by fire trucks and ambulances.

The test plane had been flying north of Seattle at 43,000 feet—the upper limit of its flight envelope—when it suffered a rapid decompression. The pilot had to make an extremely fast dive to get down to 10,000 feet, where the pressure of air in the cabin begins to become equalized with the pressure outside.

Deprived of oxygen by the decompression, the flight test crew had to grab for oxygen masks. Four were not able to do so in time and were rushed to hospital for hyperbaric chamber treatment—as are divers who suffer the “bends” for decompression sickness.

Had the pilot not responded as quickly as he did, the results could have been a lot worse; as it was it then transpired that another 777 on a test flight had suffered a similar failure the day before and made an emergency landing in Hawaii.

The cause of both failures was traced to air conditioning packs in the belly of the 777. Hot compressed air “bled” from the engines goes through these packs to cool it before it flows on into the cabin. A relatively simple valve in the packs, supposed to stop leaks, had broken open and released pressurized air from the cabin into the outer atmosphere in an explosive surge.

The flawed valve was rapidly replaced by a more robust system. But the episode raised eyebrows among Boeing engineers because it was what is called a “single point” failure—there was no backup system to cover for the failed valve. (Since the fix, there have been no recurrences of this failure.)

And so Boeing pressed on toward the ultimate target: prove that the 777 could safely fly long distances over deep oceans (as far as 9,000 miles), taking it further from land than any previous airplane had been allowed to go.

The courses flown on the long haul routes were not the most direct, A to B. They were plotted to keep within the restrictions demanded by the FAA, meaning that as far as possible they tracked over or stayed close to the continental coastlines. Boeing wanted fewer cranked course alterations and more straight lines.

As the 777 built up a record of reliability, Boeing pressed the FAA for incremental increases in the time allowed needed to reach the nearest airfield.

And the FAA yielded.

The upper limit went first from 120 minutes, then to 180, then 207 and, most recently, to 300 minutes—that’s over five hours for the airplane to get to an appropriate runway in an in-flight emergency.

In 2012 Airbus was forced to throw in the towel: they stopped production of the A340. It was no longer competitive. (Their Big Twin, however, the A330, with a narrower cabin than the 777, has done extremely well.)

Airlines loved not only the safety record of the 777 but its overall dependability, its ideal combination of capacity and range and, at a time of soaring fuel costs, the efficiency of its engines.

One way of measuring the durability of an airplane is to check how many of those built are still flying. I ran this check and the result is astonishing. Of 1,181 777s so far delivered to airlines over 18 years, only 11 are no longer flying. Some of those were in storage and three are classed as “written off”—involved in accidents. One was a non-fatal heavy landing by a British Airways 777, one the Asiana 777 that crashed last year at San Francisco with three deaths—and Malaysia Flight MH370.

That after such a long and impressive record the 777 should now be at the center of the most mysterious disaster in modern aviation is deeply perplexing. This is what makes it absolutely essential that, no matter how long it takes, the reasons that made this airplane disappear have to be found. (Ironically, whatever catastrophe did overtake Flight MH370 the 777 was still able to make a long flight over water until its fuel was exhausted.)

And an important distinction has to be made in any speculation that the cause will turn out to be technical. That does not necessarily indicate a flaw in the airplane itself—just that a thoroughly dependable machine was compromised by some event that nobody could have foreseen. Or, perhaps, one that could have been foreseen only with 20/20 hindsight.