A British Airways Boeing 777 suffered a catastrophic engine failure on takeoff from Las Vegas last week, with fire and debris shooting into the wing and fuselage.

It was the closest of close calls: The airplane, only seconds from lifting off the runway, was loaded with more than 20,000 gallons of fuel for an 11-hour flight to Gatwick, England. Had the gas tanks ignited there would have been a fire—greatly lessening the chance of escape for the passengers and crew.

The Daily Beast has learned that a version of the General Electric engine that failed was the subject of a safety warning from the Federal Aviation Administration four years ago.

A flaw had been discovered in the manufacture of the engine, the GE90-85B, that, the FAA warned, could lead to the disintegration of the engine’s turbine and the explosion of high-velocity debris that would endanger an airplane—exactly what happened in the dramatic emergency on the runway at Las Vegas, where a trail of engine debris has been discovered by investigators.

At the time both Boeing and General Electric objected to the FAA describing this as an “unsafe condition” and pushed back to get the term removed from the final ruling, arguing that the flaw could not lead to a catastrophic failure that would endanger the rest of the airplane.

The FAA disagreed and retained that definition in its final ruling, issued in July 2011. The ruling, known as an Airworthiness Directive, requires airlines to inspect the engines at specified intervals of 48,000 hours of operation or 6,000 flights. As long as these mandatory inspections were carried out, the FAA said, the risk of catastrophic failure would be eliminated.

A British Airways spokesperson told The Daily Beast: “British Airways complies with all Airworthiness Directives. We will not be commenting any further while the NTSB investigation is active.”

Soon after investigators from the National Transportation Safety Board recovered engine parts from the Las Vegas runway they identified them as coming from the same part of the engine, the high-pressure compressor spool, that was the focus of the FAA Airworthiness Directive.

What had happened, the NTSB investigators said, was precisely what the FAA had warned would happen: “uncontained engine failure and damage to the airplane.” Jet engines are installed inside a pod, or nacelle, that is designed to contain potentially damaging debris in the event of a failure.

General Electric did not respond to questions from The Daily Beast specifically about the Airworthiness Directive. They later put out a statement saying that the GE90-85B engines have two different versions of the compressor spool. The engine that failed on the British Airways 777, they stated, was an earlier version with a different configuration that did not include the weld joint that was the subject of the FAA warning.

If this is so, it does nothing to lessen the seriousness of the event: it means that investigators will be looking for the cause of a failure in the same critical part of the engine that has not shown up before.

The British Airways pilots acted with great skill, aborting the takeoff and braking so severely that some of the landing gear tires burst. At takeoff roll the engines are called upon for full power, a time of maximum mechanical stress. The high-pressure compressor is the most stressed part and, if it fails, can send high-velocity shrapnel into vulnerable parts of the airplane. The flaw identified by the FAA involves a welded joint in the compressor.

Photographs of the British Airways 777 show that the protective casing on the right side of the left engine was ripped into shreds by shrapnel, some of which ended up on the runway while other parts tore away at the inner wing and fuselage causing severe damage.

At the request of The Daily Beast, an expert on the Boeing 777 (who for professional reasons has to remain anonymous), looked at the photographs and said that normally the debris from an engine failure is contained in a way that avoids hitting critical components like the fuel tanks and fuel lines. The main fuel tanks in the wing of the 777, he pointed out, are purposely positioned where they are assumed to be outside the field of projected debris from an engine failure.

“In this case,” he said, “the damage appears to be so severe that it could very well have involved the burning of fuel, or oil, until the fuel flow was cut off.”

Video of the accident shows dark smoke and a burst of flame coming from the engine. Prompt action by airport firefighters suppressed the flames before they could reach the fully laden fuel tanks in the wings, which could have caused the total destruction of the airplane within minutes.

I asked NTSB spokesman Eric Weiss if their investigation was taking account of the Airworthiness Directive. “The investigation will be comprehensive,” he replied.

A Boeing spokesman said that they could not comment on the FAA Directive. “Boeing is providing technical assistance to the NTSB,” he added.

On Tuesday, the FAA responded to an earlier detailed request for comments from The Daily Beast. They confirmed that the engine involved in the Las Vegas emergency was an earlier version that was not subject to the 2011 AD. Consequently, it is clear that a flaw was introduced into a later version of the GE90-85B and that it was this flaw, the appearance of cracks in a weld joint, that caused the FAA to issue the warning and mandate inspections of the engine to prevent failure.

The FAA also confirmed that the AD remains in force for all the engines with that weld joint.

The statement by General Electric said “the AD was essentially a modification to the operating manual.”

This is seriously misleading. An airworthiness directive is exactly what it says it is – a directive concerned with the airworthiness of the engine and airplane. By law, ADs are posted in the Federal Register; they are an essential part of the regulatory framework that is intended to insure airline safety. If regulators say that a piece of equipment is unsafe, it’s unsafe.

A failure of this seriousness is highly unusual. Jet engines have become phenomenally reliable. This reliability is crucially important in the case of the 777 because it is the largest jet with only two engines. It is designed to be safely flyable after the loss of power from one engine, even to fly for up to five hours on that one engine.

However, had the British Airways flight already taken off, the uncontained failure would have made it highly unlikely that it would have survived for more than minutes.

Editor's Note: This story has been updated in response to a statement from General Electric and the FAA.