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Miss Creant
20th Mar 2009, 09:28
Does anyone have any idea about the nature of the failure spread (percentages) on these engines.

Are they mostly immediate failures as per the sim (e.g. instantaneous rundown /fire / catostropic failures etc).

OR

Are there more of the subtle failures (e.g. gradually reducing oil pressure/slow oil temperature increase/slow build up of vibration etc).

The reason I ask is that I have never had a sim where the failure has been anything other than a V1 cut.

Also our SOPs discourage monitioring of slow trends by having the engine instruments displayed (again assuming that the only failure will be an instantaneous one).

I seem to remember a Tristar report where the engineers had changed all the O rings (incorrectly) during maintenance and there was a gradual loss of oil over a long period of time.

On the 737 NG this would not "pop up" until the oil pressure decreased to 13 PSI (amber band)....similarly with oil temp and vibration indicators (4.0).

Surely there are sufficient instances of gradual failure to justify training of this in the sim and continuous display of engine instruments.

parabellum
20th Mar 2009, 11:10
It is normal under most regulating authorities to require a pilot under check to demonstrate their ability to deal with a V1 cut. Subtle failures can be dealt with during training SIM details.

Tee Emm
20th Mar 2009, 11:12
My guess is the instantaneous failure during take off and initial climb (flame-out, engine separation, severe damage) is by far the more critical in terms of handling - particularly with severity of yaw and probability of overcontrolling (spoiler activation). If you can cope with these type of engine problems satisfactorily, then "slow" engine failures would be a non-event. For example a flame-out of one engine just as take off N1 has been attained usually around 25 knots), requires fast reaction by the PF and by the captain if the PF was the first officer.

Be careful if the instructor fails an N1 gauge during the take off run near V1. I have observed a crew member calling "engine failure - STOP" when the N1 gauge was failed and the captain aborting the take off...because he reacted on the call without confirming first that an engine had actually failed or not.

Meikleour
20th Mar 2009, 12:28
The larger CFM56 on the A340 is known to suffer from HP turbine bearing failures at around the 20,000hrs point. In the case I experienced, this resulted in massive surging from the engine, power loss and an EGT in excess of 1200C. Plenty of clues there then!

lomapaseo
20th Mar 2009, 14:25
I can't imagine why a concern about a slow engine failure.

If the pilot flys the airplane by SOP then a gage (bell horn, color change, etc.) warning on the engine is sufficient.

The problems that have occurred in flight is where a slow thrust loss goes unnoticed until it eventually results in an aircraft upset because the pilot was not monitoring the more critical flight instruments.

Could be I don't understand the question (spoken words are so much better :)

Rainboe
20th Mar 2009, 20:33
The pop-ups are well designed and thought out. It is the same on the 747-400. In over 20 years of operation on a fleet of 57, nobody ever questioned this philosophy. You do get good warning of pending failure. The Cfm56 is an outstandingly reliable engine anyway. Giving you all those extra instruments to monitor will detract your attention from the important ones.

TheCosmicFrog
20th Mar 2009, 21:09
The CFM-56 can fail?

Miss Creant
20th Mar 2009, 21:49
The CFM56 is clearly outstandingly reliable but does anyone have facts about instantaneous vs gradual failures.

Lompo -You ask why the concern about gradual failures ... an example would be crossing the Atlantic in a 737 - 900 with a slow oil leak. We are taking delivery of some NGs over the next few months (and there is than one 737 ETOPs operator routinely flying across the pond).

You will not get a pop up until two thirds of your oil pressure is lost. This is not "good warning of pending failure" and could make the difference between a two engined precautionary landing at KEF and a much more unpleasant in flight shut down / single engine approach into Kangerlussuak.

It is not as if half a dozen extra instruments give us a massive increase in workload crossing an ocean. the information is there any sensible argument for not using it?

V1 cut is clearly highest risk/consequence failure point and rightly tested. Be nice to do something different once in a while is all I was saying on this.

Rainboe
20th Mar 2009, 22:56
All it takes is pressing one button to get your pop-ups up! Include it in your waypoint change checks if you like, and half way along. You will still get plenty of warning, or if it is a rapid loss of oil, it won't make much difference anyway. I've been flying these instruments for 10 years and never had a problem with it. In a way, it's better than having the instruments there displaying all the time. At least your attention is drawn to a fault.

Capt Chambo
21st Mar 2009, 00:34
Starting from the premise that the CFM56 series engines are very very good all I can really add is that I agree with Rainboe, rely on the "pop-up" function that will get your attention!

Historically the earlier versions as fitted to the classic 737's were prone to flame outs in heavy rain, now fixed by a re-designed spinner boss and higher flight idle N1s with start switches/engine anti-ice ON. Fan blade failures on the early -C1 variants, fixed by a redesigned blade. Failure or seizure of the No.3 bearing, fixed on the engines on the -NG series. This was usually an instantaneous failure but according to a friend who had it happen to him, not nearly as dramatic as practised in the sim. If the engine chip detectors, and subsequent oil analysis, are done correctly the imminent bearing failure should be detected and the engine is changed before it happens. I have heard of the oil pressure dropping below limits in the descent at flight idle, the engine was shut down IIRC. I have had a problem with one engine "hunting" (ie not as dramatic as surging) I can't remember whether the problem was with the electronics (FMC, A/T computer, or PMC (it was a -300)), or whether the problem was more mechanical, ie fuel pump or fuel monitoring.

The variants as fitted to the -NGs have built on the quality of the earlier models. I have read a document by GE or SNECMA about engine failures when the airframe has been struck by lightning in the vicinity of the engines. The only case I know of was when an -NG was struck by lightning on about an 8nm final (so c2400' AAT). The engine failed and the crew carried out a OEI operative landing. Subsequent interrogation of the FDR and other "black boxes" showed the engine to have stalled, which was common to the other cases reported by GE/SNECMA, and was presumed to be caused by a disrupted airflow into the engine!
Not really in the same vein, and I presume that you are in the "desert" so probably not relevant to you, but my company has introduced a new procedure when taking off with the Engine Anti-Icing ON. Basically we do a standing T/O, setting 70% N1, confirming the engines are stable, before hitting TOGA. This is because we have had a number of instances of the MC> AMBER COWL AI OFF lights, and subsequent RTOs. The problem is apparently caused by either a faulty batch of valves and/or contamination in the system caused by operations into "dirty" strips. NB this procedure is not to be confused with the periodic 70% N1 ice shedding procedure!

Apologies for the thread drift but hope there is something useful for you in there! :)

alosaurus
22nd Mar 2009, 15:55
Although the CFM 56 is one of the most reliable engines around the point you raise is a fair one. I personally always fly around with this screen displayed. It just improves my situational awareness in the larger sense of the word...and as you say there is no real reason not to.If something big breaks the displays will rapidly start changing colour etc...so it is not like you are going to miss it if just because it doesn't "pop up".

The engine itself has an an historical in flight shutdown (IFSD) rate of 0.001 / 1,000 flying hours. If you were to fly 30,000 hours in your flying career then you have a 6% chance of an IFSD.

Can't give a split of instataneous vs gradual run downs but a lot of IFSDs are due to loss of oil. Loss of oil will result in a catastrophic failure of your engine and the only place where oil temp / pressure / quantity is displayed is on this screen.

A quick internet search brings up the V HTJX incident where for one hour a significant change in vibration on one engine was not spotted by the crew before it ultimately failed.

lomapaseo
22nd Mar 2009, 17:07
Loss of oil will result in a catastrophic failure of your engine and the only place where oil temp / pressure / quantity is displayed is on this screen.


Not true unless you are using a very subjective definition for catastrophic.

Loss of oil alone will result in low oil pressure, high oil temperature and gradual wear of the bearings over a single flight. As the hours progress high vibration will be rfelt associated with the loss of centerline of the rotors. This often leads to engine stall symptoms due to blade tip and seal wear.

It's pretty easy to see this coming in a timely fashion and to idle the engine or shut it down as circumstances permit.

The data fields confirm the above (see FAA CAAM report) and the most serious events were associated over multiple flights where continued events of loss of oil leaking internally caused an internal engine fire.

There is no need to beome paranoid about things that are already covered in your SOPs

alosaurus
23rd Mar 2009, 10:31
Lomapaseo - I would be interested in seeing the FAA report you mention please provide a link.
You should check out http://www.faa.gov/aircraft/air_cert/design_approvals/engine_prop/media/CAAM2_Report.pdf

This is the FAA's "second technical report on propulsion systems and APU related safety hazards - 2005".

Regarding loss of oil pressure not being potentially catastrophic -

(1) - In the section "Multiple engine power loss - non fuel - high bypass engines" it quotes three major incidents.
i) Four engine oil loss due to maintenance failure to reinstall O rings.
ii) Dual engine oil pressure loss due to boroscope crank pad cover left off
iii)Low oil pressure on both engines (completely out of oil).

In all these cases oil was being progessively lost whilst taxying out and during the climb. This problem could have been picked up before take off, during initial climb well before it became life threatening.

(2) - On page 41 a mention of "under cowl fires occur from flammable fluid leakage onto hot surfaces in the nacelle"

Whilst most of the reports 1,876 "oil and hydraulic fluid leaks - Turbofan engines" were not as serious as this many of them did result in In Flight Shut Downs,(from loss of engine oil). Many of these incidents would have resulted in significant damage to a multi million dollar engine had the pilots waited until the severe symptoms you describe had presented themselves.

With regard to monitioring secondary engine instruments being "paranoid" look up the dictionary definition....I think you'll find that a tad OTT. I prefer to call it airmanship.

It costs the Boeing a fortune to put every instrument, lever switch etc into our cockpit. They have been put there for a reason...for pilots to use.

TyroPicard
23rd Mar 2009, 12:00
Also our SOPs discourage monitioring of slow trends by having the engine instruments displayed

Airbus SOP's encourage the monitoring of all systems at regular intervals in the cruise, precisely in order to spot slow trends - I bet your airline does too. Every 30 minutes recommended - most pilots seem to do it more often. Pop-ups are great for a quicker parameter change, and give you time to analyse the system and think about a course of action before ECAM gives a warning.

It's not just about engines, what about Hyd Qty, IDG oil temp etc. The Cruise page has engine oil quantity and vibration on it - but also the very important Cabin Altitude, so best to leave that displayed when not checking a system.

Miss Creant
23rd Mar 2009, 12:31
Tyro - Good to hear that Airbus SOPs don't wait for the aircraft to tell you something is broken. Our company trainers give you a sideways glance if you even bring this info up (apart from during pre flight checks/engine start)!

Unlike ECAM Boeings secondary systems indicators (oil, Hyd, Vib etc) don't give a pop up for rate of change only when the system reaches a trigger level (normally the caution range)!!!

I personaly scan before entering the runway...at the 40 % N1 stable check and frequently during the climb (less so during cruise / descent).