Pyrotechnics in Manila

[christep]

Apologies again for an SLF intrusion, but I was on CX918 in Manila last night when we got a pyrotechnic display as the engines spooled up for takeoff, followed by a quick stop (albeit only from about 10 knots), a return to the gate and hoards of techie types quickly decreeing an engine change.

Could someone give me a slightly more technical explanation of what happened beyond "Engine Anomaly Indication" (the captain's rather dry description of the problem) and "BA-BANG" with accompanying flashes, which is what we saw down the back?

Thanks in advance.

[Flap 5]

Engine stall. Basically the fuel/air mixture going in to the engine is wrong and you get flames shooting out. Looks spectacular and can damage the engine so needs looking at.

[FlexibleResponse]

It's just a minor problem that pilots get paid to take care of and engineers get paid to fix.

[christep]

Thanks - I wasn't trying to suggest that it was a drama of any sort. But it did sound and (being dark) look spectacular. Must have been a pain for the crew who weren't planning to spend the night in Manila. I'm not sure that they all managed to squeeze on the later flight.

[FlexibleResponse]

Christep,

Both of us have been around a long time.

For all the bravado that you might see displayed at downtown bars or at parties, I am the first to admit we may appear to be a little different from the average Joe. But, I can guarantee you that we are a dedicated bunch and work very hard at what we do.

We are glad that you continue to choose to fly with us and in return, we will turn ourselves inside out, undergo medicals, training, testing many times per year, endure the most incompetent rostering, family disruptions, dysfunctional arrogant bully-boy colonial management in our dedication to keeping you alive.

[christep]

Indeed. But if I had my time over I'd rather, at the age of 44, be a Cathay captain than what I am currently doing. Unfortunately some of us realise too late in life...

[Basil]

Simple explanation here (http://www.b737.org.uk/enginemalfunctions.htm)

In a turbine engine, compression is accomplished aerodynamically as the air passes through the stages of the compressor, rather than by confinement, as is the case in a piston engine. The air flowing over the compressor airfoils can stall just as the air over the wing of an airplane can. When this airfoil stall occurs, the passage of air through the compressor becomes unstable and the compressor can no longer compress the incoming air. The high-pressure air behind the stall further back in the engine escapes forward through the compressor and out the inlet.

This escape is sudden, rapid and often quite audible as a loud bang similar to an explosion. Engine surge can be accompanied by visible flames forward out the inlet and rearward out the tailpipe. Instruments may show high EGT and EPR or rotor speed changes, but, in many stalls, the event is over so quickly that the instruments do not have time to respond.

Once the air from within the engine escapes, the reason (reasons) for the instability may self-correct and the compression process may re-establish itself. A single surge and recovery will occur quite rapidly, usually within fractions of a second. Depending on the reason for the cause of the compressor instability, an engine might experience:

1) A single self-recovering surge

2) Multiple surges prior to self-recovery

3) Multiple surges requiring pilot action in order to recover

4) A non-recoverable surge.


or a bit more complicated here. (http://www.math.ucsb.edu/~birnir/research/outline.html)

[N1 Vibes]

FlexibleResponse,

your statement in response #3 is correct. The engineers are now fixing what the pilot broke. :}

Brgd's

N1 Vibes