Ask any aviation person you know – we always hate to see items in the news like last week’s British Airways flight 2276 where the engine caught fire in Las Vegas.  It’s probably fair to say that our entire industry is appreciative that this engine failure played out on the ground where people could react quickly, so that everyone could get out safely.

From the flight crew to ATC to the fire crews, this was an example of well-trained professionals managing a crisis. The worst we’ve heard reported were some minor abrasions related to evacuating the aircraft – the silver lining in all of this. Well-deserved kudos to all.

As my colleagues and I were watching the news unfold, some of the pictures that emerged are truly incredible, and it occurred to us that many non-aviation folks were likely curious as to how something like this could happen.

Just by looking at that fire and from the preliminary reports of engine parts being found on the runway, it’s easy to think that there was a huge explosion on the aircraft. And speaking of the aircraft – have you seen the damage? Yikes! 

What do we know so far?

As the jet engine’s internal parts sped up when the place was attempting to take off, something caused them to break apart and pierce the side of the engine wall – and, in turn, these parts punctured a fuel line or possibly the fuel tank (neither is confirmed yet) which caused a fire.

When you look at the picture to the right (where the wing connects to the body of the aircraft), you can see that fire did not actually burn through the fuselage. Instead, it burned through what are often referred to as “wing-to-body” fairings. These are essentially composite shapes that are screwed on to make a smooth aerodynamic surface at the point where the wing mounts to the side of the aircraft.  (It certainly was scary for the folks on the aircraft, nonetheless!)

But what about the engine – what caused the failure?

We’ll leave the official reporting to the NTSB, of course, but thought it might be useful to discuss a bit of what’s happened in the past to cause events like this. It certainly seems like a compressor stall or something similar to maintenance folks like us.

So what’s a compressor stall?

If you’re an airplane geek like us (or you just like training videos), you can watch a video to explain it, but essentially the “Intro to Compressor Stalls” version goes like this:

Normally air enters the engine through the front and exits out the back. As it flows toward the back of the engine, you can see in the picture below how the opening gets narrower.  That narrowing causes the pressure of the air to increase as it squeezes, or compresses, through that reduced opening. 

That’s an important thing to note, because once you have just one single item move out of place in this area of the engine (aptly called the compressor section), all that air pressure building up in the engine has to go somewhere else… and it does so pretty quick!

Typically you’ll see that the pressure will build up and momentarily reverse the direction of the air flow, forcing a mini-fireball out the front of the engine… a high-pressure burp of sorts. Along with it comes a loud thump or a bang. This usually just causes damage to the blades that spin in the engine and a resulting engine shutdown, but nothing further.

So why was this different?

Aircraft engines are designed to “contain” engine parts within the engine in the case of a failure – meaning that when you disassemble it later, all the broken bits will be right there. In the case of flight 2276, enough pressure built up to cause something to break through the side of the engine casing. When parts manage to leave the engine, it’s called an “uncontained” failure.

We suspect that the NTSB will find that one of the engine blades (a rotating part) or one of the guide vanes (helps increase the pressure of the air) is what failed in this case. And, unfortunately, the timing and the location of the uncontained failure appears to have been just right to rupture the fuel system and cause the fire as well.

The industry works hard to achieve the overall reliability and safety record that we have today. If you research the statistics, engine failures are rare – and when they do happen, uncontained failures like this one are even more unlikely.

As we wait for the final NTSB ruling for this incident, hopefully this explanation helps shed some light on how situations like this can happen.