View Full Version : Noise from jet engine - normal or not?
On our citation cj1+, the right engine made sort of a humming, low tone when we were on cruising altitude FL400. This tone was audible for 2-3 minutes and then disappeared. All engine displays were normal, no vibrations whatsoever. The tone would come on again now and then for 30 seconds to 1minute. The tone was not audible when we had to level-off on several occasions when descending. BTW, the tone was conspicous enough to make our passenger ask us if everything was alright with the right engine. Besides the obvious thing to do (call maintenance), I would appreciate any input.
Cheers
Cecco
lomapaseo
2nd Sep 2010, 13:58
Sources of very low tones are many. Keep in mind that there are two parts, the tone generator and the speaker. The tone generators for low tones could be engine associated pumps, gears, shafts etc. Unlikely internal gas path stuff.
The speaker is more likely to be the nacelle ,engine ducts. Very very unlikely to cause damage although upsetting to passengers.
There are some tones that could be of concern but always associated with major vibration signatures (things visibly shaking).
SNS3Guppy
2nd Sep 2010, 14:17
Tone generators on an engine? Say again? Speaker?
A low frequency hooting or rumbling is indicative of a low grade or incipient compressor stall, but could be a number of other things, too. Did you note any changes in engine parameters?
eckhard
2nd Sep 2010, 17:49
An interesting event happened to a friend of mine in a CJ1+ recently. He has kindly agreed to share his experience with other CJ pilots. This is his report:
I was doing a Jersey to Murcia flight. About half way through the two hours flight time, I became aware of an intermittent humming resonance. To start with I wasn’t sure if I was just imagining it, plus we had kids in the back with their I-pods on full blast ! There were no abnormal indications and I certainly couldn’t pin-point where it was coming from, even when I asked everyone to switch off their music.
A few minutes further along, the master caution light and left generator warning annunciator came on. I followed the emergency checklist. The generator re-set and the voltage was normal, so I switched the generator back on. I wasn’t thinking of diverting, just sorting out the problem once we were on the ground in Murcia. But the resonance didn’t go away and after about ten minutes the generator failed again. I don’t remember what the voltage showed on re-setting this time, but it wasn’t normal ( zero ? ) so the generator stayed off. The electrical load was nowhere near the limits so I didn’t switch anything off.
It must have been only minutes after this second failure that I knew that the resonance was getting worse. We were coming up to Valencia, not far from TOD, but common sense told me not to carry on but get the aircraft on the ground. I plumped for a diversion into Alicante for both good and bad reasons. Valencia would have meant a steep descent or simply an extended routeing to lose height ( FL370 ), whilst Alicante would give us a near normal descent profile, get everyone within a reasonable distance of their destination, and give me the best chance of getting home ! In fairness, it also wasn’t going to involve rushed re-planning for the diversion. As it happened, the noise all but disappeared with descent power.
In the end the aircraft was grounded in Alicante for about four or five days. Luckily the damage was limited to the generator bearings, so we were up and running after fitting a new generator and doing some ground runs.
Sounds like he handled it pretty well!
This may not have anything to do with your problem, but I thought you may find it interesting anyway.
Eck
Eckhard, this sounds just like my case, I called maintenance and they also said that it could be the generator. As opposed to your friend's incident, we could say for sure that the humming came from the right engine. Maintenance advised to switch the right generator off, if the sound comes on again, to see if the noise disappears or not (BTW, voltage was normal on both generators in flight).
Sounds like he handled it pretty well!
Yup, I would agree.
Many new(er) pilots are completely unawares of 'odd sounds or vibrations'.
They had better learn, otherwise... up the creek without a paddle is a distinct possibility.
He (personally), did well, IMO.