3 loud bangs from landing a/c

[mrdavidcyprus]

Around 1500L on Wed 25th July.
Landing excels aircraft inbound PFO Cyprus, made 3 loud bangs all one after another.
No smoke, no visible effect on flight.
Possible a/c went tech for a good few hours and or replacement a/c flown in? This could be complete rubbish however.
Any idea what these loud bangs could have been, it sounded like it would a car engine back firing or excess fuel being burnt off, just on a much louder scale.

also no birds seen entering or coming out the back of the engine.

Thank you

[Ranger 1]

It is possible that perhaps Birdscaring cartridges may have been fired, nearby in close succession, this has been reported in the past as possible bangs from aircraft to us. :confused:

[mrdavidcyprus]

could be, but didn't sound like that, the a.c on app was still a fair distance from the airfield, it was too loud to be bird scaring on the airfield.

Do a/c engines back fire?

[unablereqnavperf]

Sounds like a compressor surge could be many reasons for this!

[Georgeablelovehowindia]

On all the jet airliners I've flown, you had to be in idle reverse as the speed decreased to around 60 knots, except in an emergency such as a rejected takeoff. If you retain reverse thrust above idle to a slow speed, the engines are liable to re-ingest the hot air, leading to surging, loud banging, and possibly brief bursts of flame.

It isn't catastrophic, but clearly doesn't do the engines any good. :bored:

[BOAC]

GLHI - as mentioned elsewhere, the 737 requirement is that you are out of operating reverse (that is up to max) by 60 kts and then at reverse idle by normal taxy speed. Surges are unlikely if you operate the 737 in that way. There is no requirement to be at idle reverse at 60kts.

Mr David - you have not told us where you were when you heard these 'bangs' - were you on board? Could they have been the undercarriage locking down perhaps?

[mrdavidcyprus]

Thanks for above replies, BOAC I was on the beach at the time, I work in OPS in the UK and can rule out any noises such as you mentioned, wheels locking, flaps deploying, bird scaring etc.

Was deff something I have never heard before.

[Rainboe]

Sounds like an engine surging. 3 regular 'cannon shots'. Notoriously non directional sound, but very strong. It's not much more than a loud 'cough' and usually self recovers quite happily. It's caused by an excessive pressure mismatch through the engine.

The VC10 Conway engines used to surge merrily at altitude given the slightest excuse. I was once occupying the Engineers seat whilst he saw to his 'ablutions'. We were given a climb, and I opened up the throttles what I thought was 'gently'. The engines gave 2 loud bangs, followed about 3 seconds later by a lanky Scottish Flight Engineer bursting onto the flight deck with his trousers around his knees swearing at me what I know not- I don't speak Celtic, but I think I've heard it at Rangers/Celtic football matches. It was also guaranteed to shatter knicker elastic of the cabin crew working in the rear galley right next to the engine- apparently it was a sound beyond human comprehension. But quite harmless.

I was also walking across a car park at one of the Heathrow hotels under 28R lift off end when a Pan Am 747 surged just after lift off right next to me. I can confirm the destructive effect on underwear elastic. I'll swear the whole aeroplane shuddered and shook, but neither I nor the people within were probably actually too observant at that particular moment.

I was also in a 707 cabin in South America right next to the engine when the aircraft landed and lost all hydraulics. The only way to come to a complete halt and stay there was by keeping the engine in reverse. It surged continually until somebody came out with chocks, and in the evening twilight, it was spectacular. Big sparks flying 20 feet, explosions every few seconds, incredible racket, smoke. It was the most fascnating thing I have seen in aviation, tremendously entertaining.

I would assume the XLs were 757s. The 737 engines are quite boringly stable. the RB211s of 757s can have their moments.

[NudgingSteel]

Rainboe,

"spectacular...sparks...smoke...fascinating...entertaining..." all from a seat INSIDE the aircraft while this was going on?

Sir, you have a larger pair than I do....I'd have been sobbing like a child;)

[Rainboe]

There wasn't much choice! Reverse right down to a halt, then we started rolling, and on came high reverse again, with continual spluttering. Eventually they kept us stationary with low reverse, but still regular surging. I was sat next to number 3 with a grandstand window view. One lost fear of surges (and one's hearing!). Having experienced many 747 surges as well, it appears jet engines like to react violently whenever I'm near- much as many members of pprune! Except for the 737 CFM56s- they are quite boring engines.

Maybe I shouldn't have said that.

[Kolibear]

I feel sorry for the poor bloke who had to put the chocks in place, it couldn't have been much fun having a jet engine havinf a hissy-fit a few feet from his ear'ole.