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View Full Version : What causes this large GE90 VIB difference?


iewadc
23rd Mar 2017, 23:49
Please find attachment.

Jet II
24th Mar 2017, 01:12
Its not actually that large - perfectly within limits (max 4 units). As to what causes the difference, well it could be anything from engines of a different age to dirty blades.

wiggy
24th Mar 2017, 09:10
What Jet II said, that magnitude of difference is not that unusual.

OTOH a lot of the numbers on the screenshot are remarkably well "matched" for a pair of engines on the wing. (especially EGT, N2 and Fuel flow).

sleeve of wizard
24th Mar 2017, 10:49
Jet II, there are no limits on vibration, there is no amber or red line.
Yes the auto popup of the secondary engine instruments will occur at 4.0units.

Boeing does not publish AVM procedures on EICAS equipped airplanes unless the engine manufacturers provide "hard" AVM limits. Boeing recommends that the AVM system be used for long term engine condition trend monitoring. This can be accomplished by the flight crew recording the AVM values in the airplane log book during stabilised cruiser by automatic recording as appropriate.

In line with the above, flight crews in the absence of published AVM procedures, not to shutdown engine/s based solely on high AVM indications. However, high AVM indications combined with other abnormal engine indications, extreme vibrations, severe damage, and/or engine limit exceedances should be addressed in accordance with the appropriate non-normal checklist.

TURIN
24th Mar 2017, 11:23
It is indeed a robust bit of kit.

In December 2003, a second development engine completed 3,000-cycle ETOPS ground demonstration and three 330-minute diversions at GE's test facility in Peebles, Ohio. During the ETOPS ground demonstration, the development engine was the first GE90-115B engine to operate at more than two times the production vibration limits in both the high-pressure and low-pressure systems at multiple thrust levels. This engine is currently undergoing a complete teardown and piece-part inspection to identify leading indicators of durability issues.

From GE90-115B Completes 11,000 Cycles of its Unprecedented Maturation Program | GE Aviation (http://www.geaviation.com/press-release/ge90-engine-family/ge90-115b-completes-11000-cycles-its-unprecedented-maturation)

However, high N2 vibration (above 4.0 units) has been the cause of VBV actuator fuel line failures including one in flight fire and shutdown.

Page 27 of this report is worth looking at.

http://dgca.nic.in/accident/reports/A6-EBO.pdf

skkm
24th Mar 2017, 13:18
That looks pretty normal to me... not unusual to see vibration indications similar to that in the photo.

wiggy
24th Mar 2017, 17:51
Given general opinion I wonder what provoked the original question?

tdracer
24th Mar 2017, 22:13
Am I the only one hoping the OP isn't a 777 pilot?

galaxy flyer
25th Mar 2017, 01:51
tdracer,

Unfortunately, he probably is.

At one time in the past, pilots were expected to actually, you know, know the mechanicals in their airplanes. No more, part of the dumbing down process.

Jet II
25th Mar 2017, 02:00
Jet II, there are no limits on vibration, there is no amber or red line.



I was talking about the limits for releasing the aircraft from Maintenance after completing the appropriate FIM task. ;)

wiggy
25th Mar 2017, 12:28
I suspect some of theses queries are from flight simmers et.al. ( I have suspicions about the EGTs and other parameters being so well matched in the OP, but maybe the OP got lucky).

Failing that some companies are producing ops manuals that are not fit for purpose..( see threads on the likes of LNAV/VNAV, etc ..but if that is the case the worrying thing is we are sharing airspace with these companies aircraft and crew......

Amadis of Gaul
27th Mar 2017, 20:39
Am I the only one hoping the OP isn't a 777 pilot?

That ship has sailed, tdracer. Long ago.

Offchocks
27th Mar 2017, 20:53
If you look at his profile, it gives you a good idea of why he is asking these questions.

wiggy
28th Mar 2017, 11:39
I see what you mean - in which case if the OP had explained their background it might have reduced some of the more critical replies the OP got, and perhaps improved the answers because they could have been given in the context a PPL would understand.. ..

I'm not sure if the OP has gone off radar as the result of some posts but we still don't know where he/she got the snapshot from...... and in any case at least a hint of a thank you might nice....

JammedStab
28th Mar 2017, 11:50
Now that you guys have hopefully finished with the condescending remarks, perhaps we could continue the conversation. Some replies did give a good reminding information about vibration and I now have an incident report that I plan to read. Thanks to those posters.

I expect that tdracer has some more good information that he could post on the subject which is what normally happens. Obviously, making useless comments on a thread by people who don't know what they are talking about is frustrating(as we frequently) but a technical question that is obvously showing that the person is a neophyte can lead to some interesting info, if we don't intimidate them off the board.

No Fly Zone
28th Mar 2017, 19:34
For the most part, a Non-Event, unless the differences are very great. To next stop or - we hope, a Mx base, you'll get there, even if one or both have to be tuned back a bit. Once at your Mx base, RAISE HELL, even of one or both engines need a change. Personally, I would not fly it again, without a dual engine change, but we all have slightly different standards. If you do not like it - history or current performance, so not fly it.
That's a truly great airplane and engine combo, but the secondary market may not be paying the attention that they should. Suggesting nothing, the crews on these antiques DO need to be alert for all indicators. Mx at some carriers is sub-standard yet still 'legal,' and seats 0A and 0B ought to know their immediate potential for problems. It the start and run up is a four-minute procedure, give it six. You know the drill and you do want to get home that night or the next.

JammedStab
28th Mar 2017, 19:58
For the most part, a Non-Event, unless the differences are very great. To next stop or - we hope, a Mx base, you'll get there, even if one or both have to be tuned back a bit. Once at your Mx base, RAISE HELL, even of one or both engines need a change. Personally, I would not fly it again, without a dual engine change, but we all have slightly different standards.

OK...this might be an example of not knowing what you are talking about. A dual engine change....please.

ACMS
29th Mar 2017, 07:19
"One or both have to be tuned down a bit" :D

Oh brother........:mad:

D-OCHO
29th Mar 2017, 08:58
I am happy when I see VIB numbers like those.
Above 2 I start to advise maintenance. Not because it is at limit but because of the CC advising me of the irritating resonance in the aircraft.
(Captain B737NG, 11K+ hrs.)

STBYRUD
29th Mar 2017, 09:02
The only time I've complained to maintenance about engine vibration in the 777 was when my personal vibration detectors in fingers and butt detected an exceedance - the whole plane vibrated at 10-20 Hz around 80-85 N1, really uncomfortable on a long sector. Never saw anything higher than 1.8 units vibration indicated that time.

Jet II
29th Mar 2017, 14:56
For the most part, a Non-Event, unless the differences are very great. To next stop or - we hope, a Mx base, you'll get there, even if one or both have to be tuned back a bit. Once at your Mx base, RAISE HELL, even of one or both engines need a change. Personally, I would not fly it again, without a dual engine change, but we all have slightly different standards.

No we dont - there is only one standard and that is the one that Mr Boeing puts in the book. This aircraft is totally within limits and I doubt that you would find a maintenance department in the world prepared to change both engines (or even just one) for this - quite why you would want to replace the right engine anyway escapes me. :ooh: