Makila 2A1 Negative Torque Margin

[DTD585]

Subject engine Makila 2A1

Could someone tell me why a Makila 2A1 as fitted to an H225 would show a negative torque margin when the TOT margin looks good.

I have asked the technicians to explain this to me but all I get is shrugs!!!

The graph on their M'ARMS shows the TOT positive with a margin of 25 to 35 degrees C

The torque margin on the other hand shows values between +2 and -2 with no obvious trend but a wide scatter of points.

I know Airbus monitor these figures, but should I be worried??

This engine is installed as number one, number two has positive for both TQ and TOT..... why the difference.



Can anyone help

Cheers

DTD

[twisted wrench]

DTD585:
I am no expert on the 225 aircraft or the Makila engines, but we do have them operating where I work. Talking with the engineers who do work on them told me.


If a negative torque margin the aircraft would be grounded until rectified.
This is not normal. Same as if you had normal torque margin and negative T5 margin would not be acceptable either. Both should be positive figures.

One interesting issue we had recently with this problem of negative torque margin and positive T5 , and also was on the #1 engine, after numerous torque system checks, engine swapped. Airbus finally agreed the problem was more then likely in the main module.
Replaced the MGB and torque margins back to normal readings.

[DTD585]

Very Interesting ......... thank you!

[TipCap]

Ask Helicomparator. He would know. He is well up on 225's

[HeliComparator]

Well I'm a bit out of touch now but I do know that each engine is tuned at manufacture, the nozzles (bits that direct the combustion gasses onto the turbine blades) are selected to give a compromise between torque and TOT margin. So you can have a good torque margin (gasses directed with little divergence) or a good TOT margins (gasses diverging more = cooler) but not both.

Historically with Makilas the TOT margin tended to get worse with age so they erred on the side of giving new engines a good TOT margin. But in fact the 2A1 seems to suffer more from worsening torque margins, so some time ago they altered the adjustment to favour torque margin. At least I think it was that way round!

Anyway if the torque margin is low as you describe I'd suspect the torque measuring system. Although it can be "calibrated" in the field in reality this seems fairly crude. It is certainly the case that you can move and engine from one aircraft to another and get a significantly different torque margins.

But an engine with negative torque margin is un-airworthy and should not be accepted by pilots or engineering. If it is on power by the hour it's easy, replace the engine.

However you mention that the torque margin has scatter with an average around zero, this is probably OK as the EPC can be subject to inaccuracies caused by heavy rain, high humidity or slight intake icing. One side tends to have slightly worse figures than the other due to installation issues (down/side wash from the rotor system) but I can't remember which side is worse (think it's LH side).

So I wouldn't worry about it too much if the average is zero. Make sure the engine wash procedure is done correctly with de-ionised water and that the pipes up to the spray rings aren't blocked.

Don't forget it's only an issue if you suffer an engine failure on the "better" engine at a critical stage of flight and as we know, that only ever happens in the simulator! By which I mean that if you ever have an accident, it won't be due to a torque margin of -1%.

Editing to say that air leaks from the bleed valve / heater takeoff area are a common cause of low torque margin but looking at the history of the EPCs usually shows a step change when the leak first occurred.

If the history shows that the engine has never been much good, and it's just dropped a % or so, I wouldn't worry. Worry about step changes.

I've done a lot of acceptance flights from the factory and some of the brand new aircraft had a torque margin of less than 1% but we had to accept them since it just has to be non-negative.

[Dragoon52]

Thank you for the information. Respect.

[DOUBLE BOGEY]

DTD585 - try running the EPC with the aircraft flying at AEO MCP. Stabilise for 3 mins before running the test at least 3k p.a. May get a more "optimised" result.

DB

[DTD585]

To everyone who has taken time to contribute.

Certainly food for thought and it seems as if the techs are more interested after your comments, so again thank you!

If there is a resolution, I will post!!

[drakkar]

There is an other possibility to perform an EPC when the reading seems to be not accurate. FLM authorises to perform it engine by engine in training mode. The training OEI Hi is equivalent to the real AEO take off power, it will not damage the engines if you respect the limitation. Stabilisation 3 minutes, EPC 50 seconds, computation 20 seconds. Total time below 5 minutes.
Cheers

[Cougarnaut]

Have a look at T.I.P.I for IN 2244-I-71 POWER PLANT - Engine Power Check (EPC) (torque and temperature margins) from 2010.

[HeliComparator]

There is an other possibility to perform an EPC when the reading seems to be not accurate. FLM authorises to perform it engine by engine in training mode. The training OEI Hi is equivalent to the real AEO take off power, it will not damage the engines if you respect the limitation. Stabilisation 3 minutes, EPC 50 seconds, computation 20 seconds. Total time below 5 minutes.
Cheers

This is called a reference check. In the old days (pre 2A1) it used to give better results than the AEO check. However this was simply because of the way the graphs were drawn up. The AEO graphs were of course trying to extrapolate what was happening at cruise power, to what might happen when the engine was flat out at OEI power.

However with the 2A1 the graphs are better or even slightly the other way so it is rare to get better results by doing a reference check, although I'll agree it is the more accurate way of doing it. That said, the way the engines are tuned now for greater Tq margin and less TOT margin it is really easy to exceed the 5 minute (AEO takeoff rating) TOT limit. You need to "pre-heat" the engine at highish power before going right up to training OEI Hi since for some reason, the TOT tends to reduce a bit over a minute or so at training OEI HI rating. If you go straight to it there is a fair chance of an AEO TOT exceedance and the limit is not clearly marked on the gauge in training OEI mode.

[DTD585]

It seems as if the leasing auditor picked this up as contrary to the lease agreement the other week.