TAKEOFF ABORT = NL (Lp COMPRESSOR FLUCTUATION)
Thread Starter
Join Date: Jul 2012
Location: Tarmac
Age: 39
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
TAKEOFF ABORT = NL (Lp COMPRESSOR FLUCTUATION)
Is it justified to abort the takeoff if Lp compressor stage reading drops down to 50% and less, then fluctuates at that value. All other parameters remaining quite normal. Aircraft at low speed-below 60 Kts.
Will appreciate if you can cite technical data to support it and any incident that was caused by Such.
Will appreciate if you can cite technical data to support it and any incident that was caused by Such.
Thread Starter
Join Date: Jul 2012
Location: Tarmac
Age: 39
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
Turboprop with Pratt and Whitney turboshaft engine, centrifugal compressors and the shafts for all three Nh, NL and Np are concentric but not linked to one another. Weather = warm about 33C at 500ft pressure altitude.
Join Date: May 2014
Location: In thin air
Posts: 186
Likes: 0
Received 0 Likes
on
0 Posts
It sounds like a problem with the low pressure compressor rpm indication. On a turbo-propeller engine you probably use torque to verify engine power. Below 60 knots I think it would be prudent to abort to have the problem investigated. Without rpm indication you cannot check that it stays within limits.
An actual drop in Nl will result in a reduction of air mass flow. This must lead to a torque loss and most likely will not leave Nh and ITT unaffected either. What else is this but engine damage as defined by the OM-B and QRH (associated indications)? Reasons may vary, be it a dying bearing, rubbing blade tips or whatever. It is most certainly a perfectly good reason for a takeoff abort.
If all the other values apart from Nl are still indicating normal, chances are that the engine is still working perfectly, but Nl indication is failing. However: during the takeoff run, will You have the time to analyze this fully so as to be satisfied that it is indeed an indication problem and nothing else, making continuing the best course of action, or will You prefer not to take an engine with a possible and not fully analyzed problem airborne?
I dare say that I would tend to abort the takeoff in such a situation and have maintenance look at the engine and indication.
If all the other values apart from Nl are still indicating normal, chances are that the engine is still working perfectly, but Nl indication is failing. However: during the takeoff run, will You have the time to analyze this fully so as to be satisfied that it is indeed an indication problem and nothing else, making continuing the best course of action, or will You prefer not to take an engine with a possible and not fully analyzed problem airborne?
I dare say that I would tend to abort the takeoff in such a situation and have maintenance look at the engine and indication.
Join Date: Nov 2010
Location: CE
Posts: 86
Likes: 0
Received 0 Likes
on
0 Posts
I concur with gysbreght, it's more likely to be (but not guaranteed) an instro fault, especially if all other engine parameters are reading ok and there's no obvious loss of power.
Re. the question "is it justified to abort the take off?". If the fluctuations occur prior to V1 then erring on the side of caution is usually considered the safest option so why take any chances?
Re. the question "is it justified to abort the take off?". If the fluctuations occur prior to V1 then erring on the side of caution is usually considered the safest option so why take any chances?
Thread Starter
Join Date: Jul 2012
Location: Tarmac
Age: 39
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
I have the same in mind gentlemen but, need input from experienced guys for arguments.
Can u cite any example for such an incident. Any reference will be appreciated.
Can u cite any example for such an incident. Any reference will be appreciated.
Did You check Your documentation already? What does the OM-B and QRH have to say about "Severe engine damage before V1" and how to spot it? Here, one is pointed towards "abnormal indications" among others - an unusually low Nl reading would doubtlessly fit this description.
Consider also that a takeoff abort due to such a malfunction will usually not be investigated into by the authorities and no report will be issued, so it is nearly impossible to serve You with hard facts here. Maybe You will find one or another incident at Aviation Safety.net, although what You find there might not be related to Your type.
Consider also that a takeoff abort due to such a malfunction will usually not be investigated into by the authorities and no report will be issued, so it is nearly impossible to serve You with hard facts here. Maybe You will find one or another incident at Aviation Safety.net, although what You find there might not be related to Your type.
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
To add: Do you bother with a take-off emergency briefing in your outfit? If so, what does it contain?
One assumes there has been a 'disagreement' between you and a Captain over such an incident. Remember the Captain always has the final decision on go or stop.
You can always ask your management for a decision.
One assumes there has been a 'disagreement' between you and a Captain over such an incident. Remember the Captain always has the final decision on go or stop.
You can always ask your management for a decision.
Thread Starter
Join Date: Jul 2012
Location: Tarmac
Age: 39
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
Dear all, thanks alot for your interest and help. I can't refer to the exact incident here, as it is being investigated and the engineering team geniuses are opposing the decision to abort.
I know my books well and I know Crm and have no problem understanding the chain of command. Besides consider it as a combined crew decision.
The checklist for abnormal parameters applies to
flight phase and doesn't refer to NL (low pressure compressure) issues.
I know my books well and I know Crm and have no problem understanding the chain of command. Besides consider it as a combined crew decision.
The checklist for abnormal parameters applies to
flight phase and doesn't refer to NL (low pressure compressure) issues.
I REALLY SHOULDN'T BE HERE
In my previous outfit we would need two abnormal indications or a power assymetry on a PW150 to abort. On that engine though there is no torque meter, the torque figure is mathematically derived from the propellor rpm and the Np rpm. Having said that with an occurrence 80kts I would have definitely been on my way back to the ramp.
1jp,
that argument is valid as soon as there is a documented MEL release for the aircraft and engine in question on the books. Failing that, the takeoff run is not the time to examine any failure or even consider their releaseability under MEL.
Was the safety of the flight impaired by aborting at the 60kts You mentioned? Certainly not. Had it been impaired by continuing? I dare not say with the information at hand. So I say: If the Commander erred here (and I doubt he did; many here including myself would have acted the same), he did so on the side of safety and deserves no blame.
that argument is valid as soon as there is a documented MEL release for the aircraft and engine in question on the books. Failing that, the takeoff run is not the time to examine any failure or even consider their releaseability under MEL.
Was the safety of the flight impaired by aborting at the 60kts You mentioned? Certainly not. Had it been impaired by continuing? I dare not say with the information at hand. So I say: If the Commander erred here (and I doubt he did; many here including myself would have acted the same), he did so on the side of safety and deserves no blame.
Join Date: May 2000
Location: Seattle
Posts: 3,196
Likes: 0
Received 0 Likes
on
0 Posts
There is NO error on the part of the Captain. ALL abort decisions in the low-speed regime are HIS ALONE! If he is biased to the conservative side, so be it.
The "engineering team geniuses" are free to second-guess all they want IN PRIVATE, but they are NOT free to call the Captain's judgement into question on a matter over which he has SOLE DISCRETION! They are also free to defer the errant gauge (if that's what it was) and send the crew and customers off in the same airplane after all the paperwork is done.
Of course, if the OP would tells us under which rules he operates, it would be MUCH easier to cite the specific regulations...
The "engineering team geniuses" are free to second-guess all they want IN PRIVATE, but they are NOT free to call the Captain's judgement into question on a matter over which he has SOLE DISCRETION! They are also free to defer the errant gauge (if that's what it was) and send the crew and customers off in the same airplane after all the paperwork is done.
Of course, if the OP would tells us under which rules he operates, it would be MUCH easier to cite the specific regulations...
Thread Starter
Join Date: Jul 2012
Location: Tarmac
Age: 39
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
I second your thoughts gentlemen, CAA has based it's rules over JAA. Do you think that an LP compressor shaft shear can also produce same or similar readings. I thought so.
A shear, as in a shaft break?
This may or may not briefly show such an indication depending on the location of the break, but You would have noticed this pretty soon even without indication. If the turbine had been no longer connected to the compressor and therefore ran without load, things would have gotten interesting rather quickly.
This may or may not briefly show such an indication depending on the location of the break, but You would have noticed this pretty soon even without indication. If the turbine had been no longer connected to the compressor and therefore ran without load, things would have gotten interesting rather quickly.
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes
on
0 Posts
Hi 1jz,
No.
If all other parameters are normal, then it must be an indication fault.
At high speed (above 100kts) we never rejected take off for a single parameter - we had to have at least two indications (e.g. a swing + a gauge indication).
At low speed (below 100 kts) we could consider stopping for anything.
What is your low speed limit during take off?
Lp compressor stage reading drops down to 50% and less, then fluctuates at that value. All other parameters remaining quite normal.
Do you think that an LP compressor shaft shear can also produce same or similar readings
If all other parameters are normal, then it must be an indication fault.
At high speed (above 100kts) we never rejected take off for a single parameter - we had to have at least two indications (e.g. a swing + a gauge indication).
At low speed (below 100 kts) we could consider stopping for anything.
What is your low speed limit during take off?
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
This is an almost impossible question to answer given the info you have provided. For example, as GR has asked "What is your low speed limit during take off? ".
I read in to it that you would choose/chose to abort and the Captain did not agree.
Intruder expresses clearly the fact that no matter how many million "engineering team geniuses" are debating, they have no say over the Captain's decision.
Personally, if this was a 'known recurring problem' with this aircraft and the symptoms EXACTLY matched 'the known':-
1) It should have been fixed/MEL'd
2) I would possibly be prepared to continue the take-off provided I had the necessary background information and written support.
3) If the 'company' come down on the 'go' side, they should have the balls to put out a flight crew instruction to that effect - and I very much doubt doubt that would happen. In the meantime, stick with written SOPs regarding aborts.
I read in to it that you would choose/chose to abort and the Captain did not agree.
Intruder expresses clearly the fact that no matter how many million "engineering team geniuses" are debating, they have no say over the Captain's decision.
Personally, if this was a 'known recurring problem' with this aircraft and the symptoms EXACTLY matched 'the known':-
1) It should have been fixed/MEL'd
2) I would possibly be prepared to continue the take-off provided I had the necessary background information and written support.
3) If the 'company' come down on the 'go' side, they should have the balls to put out a flight crew instruction to that effect - and I very much doubt doubt that would happen. In the meantime, stick with written SOPs regarding aborts.