Loud bang on Aer Lingus flight - what was it?

Elessar

Recently I took an Aer Lingus flight from Dublin to Berlin. On the takeoff run, just as the aircraft rotated there was a loud bang from the right engine and I saw a bright orange flash out the rear of the engine. Not 10 seconds later there was a distinct and strong smell of burning coming through the cabin, like burnt rubber or soot. Obviously I started to become a little alarmed but no-one else seemed bothered. I think the pilots noticed something, as the landing gear remained down for a couple of minutes after takeoff and were only retracted one we levelled off on the SID.

My initial thoughts were that a tyre had burst on rotation. But after a 5 minutes or so the smell dissipated and the rest of the flight was uneventful. We landed safely and nobody seemed in the slightest concerned. As we disembarked I looked back and all 4 tyres of the main landing gear were fine.

I guess I should have asked but it was loud and I was at the window seat and didn't want to make a fuss (the cabin crew probably would have looked at me as if I had 10 heads). Despite flying many years and being familiar with many of the systems and how safe flying is, part of me was wondering if this would be my last couple of hours on earth

Just wondering if anyone would know what could have happened?

Miaireland

Bird strike although that probably would not explain the flash.

Irish Steve

There's no reports of an incident on a flight recently, and if it had been anything dangerous, you can be sure that the crew would have returned to Dublin for checks. The description you've given sounds like an engine surge, which could have been caused by a bird going through the engine, but I would have expected that to have been responded to by the flight crew, if the bang was that significant, you may be sure that one of the crew would have been aware of it.

The fact that the flight continued to Berlin would suggest that there were no abnormal indications on the flight deck instruments to cause concern, so it would have been hard to justify coming back in the absence of any warnings or indications of a problem.

Elessar

Irish Steve wrote: »

There's no reports of an incident on a flight recently, and if it had been anything dangerous, you can be sure that the crew would have returned to Dublin for checks. The description you've given sounds like an engine surge, which could have been caused by a bird going through the engine, but I would have expected that to have been responded to by the flight crew, if the bang was that significant, you may be sure that one of the crew would have been aware of it.

The fact that the flight continued to Berlin would suggest that there were no abnormal indications on the flight deck instruments to cause concern, so it would have been hard to justify coming back in the absence of any warnings or indications of a problem.

I looked up a few videos of engine surges and you're spot on - that is exactly what happened. Interesting to know! I would have thought any kind of bird strike would cause catastrophic engine damage? Regardless from what I'm reading it can be caused by some things a lot more harmless:

Just like a wing, an individual blade, or a small component of one, can experience an airfoil "stall", where the air flow over the blade separates into a cell of "stuck", highly turbulent air behind the blade, and the air flows around the cell instead of smoothly around the blade.

When a flow separation occurs, the airfoil's ability to push the air in proper direction at the right flow rate—and thereby contribute to the compression of air behind the fan assembly—is inhibited.

Since these blades are rotating, the blade quickly moves away from the packet of stagnant air. Of course the stalled air packet has some momentum from the intake air, and it will experience a drift along with the rotating blade, but it is not moving with the average flow of the air through the engine anymore.

Thus the next blade spinning round tends to encounter the stalled air packet. If the stalled air cell is not particularly large, it may be absorbed by the air flow at this stage and dissipated. Alternatively, it might be large enough to stall the subsequent blade as well. At this point, it is called a "rotational stall".

If the stall continues to propagate, the ability of the fan stage to deliver air to the subsequent compression stage is impeded, and it will lead to an abrupt drop in pressure inside the combustion chamber. This causes a reduction in available oxygen for combustion. The engine's performance, measured by the thrust delivered, is strongly impaired, and there is likely to be a lot of unburnt fuel remaining after the oxygen in the compressor is exhausted. That unburnt fuel may ignite in a bright exterior flame as it escapes out the back of the combustion chamber and mixes with the oxygen-rich bypass flow, or in the case of a jet engine, after it exits the engine altogether.

The drop in back pressure in the compressor will, under normal conditions, enable the compressor fan blades to begin operating as proper air foils again.