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Agusta AW139

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Agusta AW139

Old 18th Apr 2018, 20:27
  #1841 (permalink)  
 
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Not so Crab. The TQ Lim functions during OEI training by design. Part of the 'realism' involves drooping the Nr hence the Tq Lim function. The TQ LIM button will allow the limitation of TWIN ENGINE TQ thus (in the eyes of some) protecting the transmission when doing 'tricky' stuff - like MAUW take-offs or heavy load lifts.Personally, I think that to be a misguided philosophy but some companies have it as an SOP.

G
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Old 18th Apr 2018, 21:56
  #1842 (permalink)  
 
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Geoffers - I assume the OEI backs off the Nf of the 'failed' engine just enough that the Nr can be drooped with the 'good' engine for realistic profiles for Cat A.

At some point that drooping Nr would meet the backed off Nf and the 'failed' engine would start to pick up the drive as well.

Is it likely then, with a big pull (cocked up profile) the TQ LIM is there so that the combined Tq of both engines ('good' one very high and 'failed' one increasing) can't exceed 228% and the fact that AEO operation with TQ LIM on just happens to limit at 114% matched because 228% is the TOTAL Tq that the gearbox needs protection from?
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Old 19th Apr 2018, 04:48
  #1843 (permalink)  
 
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No, it doesn't work like that. Operating the OEI Training switch will select the engine you want to keep 'alive'. In fact neither engine spools back, instead the PFD will show that the selected engine is working normally whilst the other indicates zero TQ. Meanwhile, the MFD will show the pilot what is really happening. Both engines are working normally but have an artificial TQ limit of 70% each. Thus a total of 140% TQ is available for the 'fly-away' - this is 20% below the normally available 160% in a real OEI situation. This is why it is critical for the IP to check that the mass of his aircraft is in line with the appropriate training section of Supplement in the RFM. One that didn't do that made a horrid mess of the exercise because he was apparently, allegedly, about 900 kg overweight.

Of course, there are protection systems that take the OEI training switch out of the circuit when needed, so, if the TQ LIM switch is deselected (it is required to allow access to the OEI Training System), or if an engine fails, if either EMS is moved or the NR droops below 87% then the normal performance level is returned - INSTANTLY. That is important to note for the resumption of the normal configuration will result in such a rush of power that an overswing of T5 may occur. It has in the past which is why some companies now limit OEI training to the sim.

Incidentally, the OEI Training Switch is a three position, spring loaded switch. It will remain in the central (OFF) position until No1 or No2 engine is selected. If the TQ LIM switch has been selected and both EMS are in the 'FLIGHT' position then the OEI switch will be retained in the selected position by a magnetic clutch. It is the circuit holding the switch in the ON position that is controlled by the various safety circuits. If one of these operates the mag clutch is released and the OEI switch is then de-selected and it returns to the central (OFF) position.

G

Last edited by Geoffersincornwall; 19th Apr 2018 at 05:48. Reason: additional info
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Old 19th Apr 2018, 06:22
  #1844 (permalink)  
 
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Ah, OK, understood just going through groundschool now so full of questions
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Old 19th Apr 2018, 14:32
  #1845 (permalink)  
 
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Hi Geoff, although I agree with you on your thoughts about the use of the Tq limiter for normal ops, I do think there is a place for it.
I was doing night rig training once where the candidate was too fast and too high on final and in spite of my constant guidance to control that, botched the approach so bad that I called for an overshoot. He grabbed such a mitful of collective that before I could react we had a momentary over torque. Luckily it was within limits so not a costly one. We were relatively light on fuel with just the 2 of us on board so there was no need for all that power to be available. I'm of the opinion that this might be a good use of the Tq limiter.
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Old 19th Apr 2018, 15:37
  #1846 (permalink)  
 
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He grabbed such a mitful of collective that before I could react we had a momentary over torque.
Im interested here Outwest what was the experience of your candidate? was he behind the machine from the outset?

Did he pull 121% ?.....

Why did you let it develop to the point?
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Old 19th Apr 2018, 18:05
  #1847 (permalink)  
 
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Originally Posted by belly tank View Post
Im interested here Outwest what was the experience of your candidate? was he behind the machine from the outset?

Did he pull 121% ?.....

Why did you let it develop to the point?
He was a very experienced pilot, although not offshore.

Yes, actually if memory serves it was 125% but only for a sec before I could get the collective down.

Yeah...hindsight is 20/20. The approach and subsequent go around did not put the a/c in danger, the problem was the mishandling of the power for the go around. I take responsibility for not anticipating this action by this pilot.
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Old 21st Apr 2018, 18:43
  #1848 (permalink)  
 
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Outwest, having had a similar experience recently you have my full sympathy. However I disagree with your arguments for routine selection of the torque limiter for AEO operations. Let’s call it a divergence of priorities.

Anyone remember the massive overtorque incident in Nigeria some years ago (not in a 139)? Day visual approach to a rig, lost all visual references in heavy rain, disorientation and pulled IIRC 159% of allowable torque before recovery. If their available torque had been electronically limited to 114% they would have stalled the rotor and everyone would have died. As SASless puts it: “Ass, tin, ticket”. Having the torque limiter selected removes the crew’s option to use the tin to save the asses.

Ironically my operation’s SOP is to have the torque limiter selected throughout the flight; the argument that the belief that an epidemic of overtorques would ensue if we stopped doing so shows a worrying lack of confidence in our training program, has had very little effect. Plus, as Geoff points out, selecting the torque limiter basically “arms” the OEI TNG switch (in a situation where you really don’t want an inadvertent simulated OEI event).
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Old 21st Apr 2018, 19:21
  #1849 (permalink)  
 
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Well Buitenzorg,
I fly a helicopter from a different manufacture, so I don´t know, what Agusta programmed into their helicopter, but I think/hope, they have general a same approach to safety.
On our helicopter there is a safeguard in the trainingsoftware:
If, during OEI training mode operation, the RPM decreases down to 91% NR, or to 12% below nominal NR, the training mode is automatically deactivated. The rotorspeed is increased to its nominal (reference) value in a controlled manner while the torque of the engines is limited to an acceptable level (approximately 2x 95%), in order to avoid excessive torque and rotorspeed overshoots.
So in case the shit hits the fan you get the chance to use the tin to save your ass ;-)
Unfortunatly you can actually proceed an overtorque recording with the training switch active - cause TQ values permitted vary with speed...
If you pull the permitted OEI 30 sec TQ above Vy+10 for more than 12 seconds, you have to report to the boss ;-)
(By passing Vy you should already have reduced to 2 min TQ - but with a fast accelerating helicopter and in the heat of the training........)
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Old 21st Apr 2018, 19:37
  #1850 (permalink)  
 
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FB, below are the automatic deactivation criteria for the 139. So, not too different. Other than the PFD indications, assuming one doesn't trip one of these wickets, the only other indication one gets when using the training mode is, upon selection, a transient deceleration of the selected "bad" engine down to about 25% and a selected transient acceleration of the other engine up to about 110% before each settle down (in actuality) to about 70% while the PFD indications continue to simulate the malfunction.

I always found it to be pretty tame in use, but we also limited our usage to pretty tightly defined criteria as per our OMs. Like many things, regulating the usage tends to keep people out of trouble.

Note
The OEI TNG will be automatically disactivated for one of
the following conditions:
- either engine set to MANUAL MODE
- either engine ENG MODE switch not in FLT
position
- NR droop below 87%
- either engine flame out
- either engine detected fault on EEC
- TORQUE LIMiter disactivated.
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Old 21st Apr 2018, 21:27
  #1851 (permalink)  
 
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Originally Posted by Buitenzorg View Post
Outwest, having had a similar experience recently you have my full sympathy. However I disagree with your arguments for routine selection of the torque limiter for AEO operations. Let’s call it a divergence of priorities.

Anyone remember the massive overtorque incident in Nigeria some years ago (not in a 139)? Day visual approach to a rig, lost all visual references in heavy rain, disorientation and pulled IIRC 159% of allowable torque before recovery. If their available torque had been electronically limited to 114% they would have stalled the rotor and everyone would have died. As SASless puts it: “Ass, tin, ticket”. Having the torque limiter selected removes the crew’s option to use the tin to save the asses.

Ironically my operation’s SOP is to have the torque limiter selected throughout the flight; the argument that the belief that an epidemic of overtorques would ensue if we stopped doing so shows a worrying lack of confidence in our training program, has had very little effect. Plus, as Geoff points out, selecting the torque limiter basically “arms” the OEI TNG switch (in a situation where you really don’t want an inadvertent simulated OEI event).
You may have misunderstood my intent or I was not clear enough. I definitely don't agree with the use of the Tq limiter for day to day operations. I was suggesting it's use ONLY while doing this sort of training where the a/c is light and there is a risk of an overtorque if things go pear shaped.
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Old 22nd Apr 2018, 02:31
  #1852 (permalink)  
 
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Outwest,

Understood. Cheers.


Flying Bull,

I think you misunderstood me. I wasn’t talking about training, I was talking about routine revenue flying (carrying passengers etc. up to max gross weight) and taking a training system (the torque limiter) which was designed to be used only during OEI training at limited weights, and using it for something very different: the prevention of an overtorque due to slight mishandling at high gross weight; and the potential unintended consequences of doing so.
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Old 22nd Apr 2018, 09:26
  #1853 (permalink)  
 
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It pretty much comes down to the old dilemma - if the RFM says you can then it's fine but, if it doesn't say you can't, then can you or can't you?
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Old 22nd Apr 2018, 13:58
  #1854 (permalink)  
 
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Its interesting to compare the "old" philosophy. In the A109 power, the limiter is always operating, UNLESS you press the "limit override" button, which is diametrically opposite to what you have on a A139.
I was working with a Mexican customer over the last few days, who operates in an environment with a pressure altitude of 8-12,000', at temperatures of approx ISA +20.
Performance is absolutely critical, because an engine out in these conditions is a massively different kettle of fish to the relatively benign environment we have in Europe for example. This company has changed their SOP to require pilots always to fly with the limit override active, having identified several accidents in the past 18 months which have had running out of power as a contributory or primary factor.
We practised in the FFS with and without the limit override, and of course you may completely trash the engines by using every drop of power you can get, but its is surprising what situations you can fly away from, which you couldn't in the "normal" condition.
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Old 9th May 2018, 04:46
  #1855 (permalink)  
 
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Geoff - I have just been taught that in OEI TRG mode, the 'other' engine (ie not the one you select to 'keep') backs off to 92% Nf - are they wrong about that?
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Old 9th May 2018, 07:14
  #1856 (permalink)  
 
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They both back off to simulate the power available from one engine.
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Old 9th May 2018, 08:29
  #1857 (permalink)  
 
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You get an initial "backing off", which gives you a realistic feel and sound of engine failure. Then, the torques are subsequently quickly matched between the 2 engines, capped at 70% ( demand above which you start to get Nr droop). This is clearly displayed on the MFD. The PFD "lies" to you, showing one engine at zero PI, and the other going up to 140%, which helps understanding during training.
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Old 9th May 2018, 10:37
  #1858 (permalink)  
 
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So in that initial backing off does the Nf of the ‘bad’ engine drop and then recover? I can’t see how the engine ‘failure’ can be made realistic otherwise
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Old 10th May 2018, 08:48
  #1859 (permalink)  
 
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For engines pre SB41020:

When one engine is selected to "OEI TNG" the selected engine will operate at lower limits (MCP) and govern the power turbine / main rotor speed. The opposite engine will govern at a reduced speed of 92% N2. This will be what your instructor was referring to. Perhaps they don't have updated training material?

For post SB41020 software:

Both engines produce up to half of the OEI power (140% Q).

The OEI Training mode logic uses twin engine power to simulate an initial single engine transient to “maximum torque” and rotor droop. Then both engines are used but they are limited to a maximum total PI of 140%.

In order to simulate the transient following an engine failure the engine selected to OEI TNG will accelerate to a maximum of 110% to then reduce to approximately 70%, to while the inoperative engine will decelerate to a minimum of approximately 25% TQ then accelerate to around 70% TQ.

Hope that helps.
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Old 10th May 2018, 18:35
  #1860 (permalink)  
 
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Axioma - Thank you - that explains it perfectly and shows where the confusion has come from - was that SB part of the phase 7 upgrade?
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