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Flightwatch
2nd Sep 2005, 20:57
As alluded to in the thread on Freight Dogs, CV have had a spate of engine failures with the above engine during the last couple of months. The problem has been identified as a deformation of the casing causing a reduction in the surge/stall margins due to a distortion of the airflow through the HP compressor. The EEC autorecovers the EGT before crew action but of course the limits are exceeded and the engine has to be pulled.

Apparently RR do not know the reason for this situation which only happens in some engines (rumoured to be high time) and not others but it is causing a lot of angst in CV with schedules being disrupted and very unfavourable comparisons v. the GE engines in the fleet. A mod is in hand but will take a long time to incorporate throughout the fleet.

My question is, is there anybody in BA/CX/QF who can state whether these companies are suffering the same problems? Is it only apparent in the H-T or does it happen to the G/H also?

There is some speculation the the relatively high cycles in CV at high weights together with the high utilisation of a/c (15+ hours/day) may play a part. If it is apparent in other companies are there any new crew procedures being promulgated to alleviate this?

The problem is compounded by all the RR approved overhaul facilities being maxed out and the reputed overhaul time for an engine has increased from 120 to 180 days.

Anyone with any info?

Flightwatch

gas path
3rd Sep 2005, 11:39
We operate a mixed fleet of non Trent and Trent cored engines and haven't suffered ......yet! Although the engines have been derated to 'G' power on the 744, the 767 still operates at the 'H' rating.
The engines were derated to extend the life somewhat and most of the engines pulled have been for time-ex. One recent example though suffered a TOD surge but although the exceedance was within inspection limits the engine was pulled for LPT1 blade platform damage.
The engine has in the past suffered from compresor Metco lining loss, is this what you are refering too?
Look on the brightside though it only takes a couple of hours of change a Roller.........if you have a (complete!!!!) spare.:ok:

Flightwatch
3rd Sep 2005, 15:21
I don't believe it is lining loss, not being an engineer but a mere driver I don't know the exact details but it has been described to us as I stated. I appreciate the possibility of a fast change but unfortunately there doesn't seem to be an engine complete or otherwise on the face of the planet. We got one "loaner", I believe from RR but it was far from complete and had to have all the ancilleries strapped on in the field on change. Also it is a non Trent core and it constantly runs 30C hotter than the rest with a potential over temp over 24C MSL. Possibly G rating is the answer but unfortunately we have some destinations that wont handle it either because of high altitude ot short runway at our normal operating weights.

I well remember in BA when the "good" engines were transferred to the 767 and the ones with low margins were hung on an inboard position on the 744!

Thanks for the info.

Flightwatch

Torquelink
8th Sep 2005, 09:56
Not a techie, so not really qualified to comment on serviceability issues. However at SA average on-wing time for non-Trent core engines was 13 - 14k hours but, since being re-cored, they are getting 21k - 25K plus improved sfcs. Although SA have hour: cycle ratio of 8.25 which helps, JHB ops won't allow de-rated take-offs. I'd be interested to know how these on-wing times compare to typical PW and GE equivalents?

gas path
8th Sep 2005, 23:51
flightwatch
Doing a bit of digging around, the problem lies in the HPC 'birdmouth' locating points on the casing in some engines they can wear and drop slightly this can cause wear on the blades and as a result the airflow and subsequently the compressor stall margin is compromised.
I believe RR can monitor for this in the trend monitoring thats downloaded during flight.
Our engines are around the 30k mark for both the non Trent and the Trent cored engines.

PCav8or
9th Sep 2005, 01:42
This QF report might shed some light

http://www.atsb.gov.au/aviation/tech-rep/200205895/200205895.pdf#search='RB211%20surge%20stall'

N1 Vibes
16th Sep 2005, 14:22
Flightwatch

Apparently RR do not know the reason for this situation

RR are fully aware of the main driver for this situation, that is birdmouth wear and are working towards a solution. But, yes it's not a 5 minute fix.

is there anybody in BA/CX/QF who can state whether these companies are suffering the same problems? Is it only apparent in the H-T or does it happen to the G/H also?

Yes other operators are experiencing this, speak to your local smooth talking bar steward RR rep. CX did, and were told everyhting was pretty much fine with other operators.

There is some speculation the the relatively high cycles in CV at high weights together with the high utilisation of a/c (15+ hours/day) may play a part. If it is apparent in other companies are there any new crew procedures being promulgated to alleviate this?

Yes related to cycles, again RR aware that engines over 2,000 cycles are coming into the band of birdmouth wear. No, it is not related to crew operations as far as RR are aware, or so they say.

Deterioration of the -T is not uniform from engine to engine. CX has seen engines surge at a shade under 2,000cyc and others that can achieve 4,200 cyc before scheduled removal with not one surge.

Also it is a non Trent core and it constantly runs 30C hotter than the rest with a potential over temp over 24C MSL

Adding the Trent core to the knackered old 524H gave it an instant EGT margin boost of about 35 degC. RR haven't upgraded any of their tired 524's to the -T as far as we know.

gas path

I believe RR can monitor for this in the trend monitoring thats downloaded during flight.

Sadly RR cannot detect this deterioration underneath the normal ECM trends as it is too gradual. But, you are right about the deterioration mode.

Although, I'm sure you remember the good old 535C 'spike-check'. They have got something similar developed to light up the night sky on the 524-T.