AS355 F2 Engine Power Problems

[amzhkm147]

Hai, I'm new here and seeking advice on as355 f2.

We are operating in Malaysia where the temperature here is constantly 29-30 Degree Celcius. Below is the reading when we do single-engine power checks on the ground. My No.2 engine T4 is limiting the TQ for the a/c

No.1 Engine
NG = 101
TQ = 90
T4 = 770

No.2 Engine
NG = 99
TQ = 83
T4 = 810

Our No.2 engine is not generating enough TQ.

The thing that we already do on the aircraft.
1) Calibration check on all NG, TQ, and T4 Gauge
2) Compressor replacement on No.2 engine
3) Turbine replacement on No.2 engine
4) Bleed valve replacement on No.2 engine
5) PTG replacement on No.2 Engine
6) FCU replacement on No.2 Engine
7) Engine fuel pump replacement on No.2 Engine
8) All Air pipelines have been replaced on No.2 Engine
9) Re-rig the NG adjustment for both Engine
edit
10) Fuel Nozzle Replacement for No.2 Engine
Yet the problem is still there after I replace all the above-mentioned.

Reading on both engines at natural trim and power lever is at flight (fully forward position)

No.1 Engine
NG = 83
TQ = 29
T4 = 575

No.2 Engine
NG = 83
TQ = 29
T4 = 640

as you can see there is a 65 Degree Celsius difference on the T4.

but when we start to pull the collective, the No.1 engine will accelerate faster compare to the No.2 engine and will lead on TQ at around 40%, by now my pilot will trim the No.2 Engine up in order to match TQ for both engines hence T4 on No.2 engine will play around the yellow arc area.

Been contacting Airbus about this problem but none of the instructions given by them has helped to lower down the No.2 engine T4.

As I mentioned above I'm seeking guidance on where can I tackle the problem. Some did mention is the "Combiner Gearbox" Problem. but I need advice.

Calling pilot that has flown AS355F2, did you use to fly with the TQ split? Thank you.

[Kulwin Park]

What figure is your NR set at whilst operating?

Did you replace the fuel spray nozzle?

What are your fuel pressures, oil temps & oil pressures? Are they different to indicate parameters of hot or colder operational differences?

[albatross]

That is a big temp difference.
I know you have calibrated the T4 gauge.
Was this done for both #1 and #2 engines?
If not try switching the T4 gauges side to side just to see what happens. I suggest doing this even if both are newly calibrated.
You also may have a Temp probe or harness problem..
Make sure both bleed valves are functioning properly. A ground run with the aircraft at a high gross weight will let you do this.
Do the engines pass a power check as per the chart?
Does the aircraft have the particle separators fitted? If so check that.
Long time since I flew one. Usually flew with torques matched.
(Funny story not on a 335…spent some time chasing a high T4 problem on one engine…turned out that the problem was not high T4 on that engine but a false low T4 indication on the other engine.)
Best of luck. Always liked flying in Malaysia. Very nice people.

[wrench1]

The thing that we already do on the aircraft.
1) Calibration check on all NG, TQ, and T4 Gauge
2) Compressor replacement on No.2 engine
3) Turbine replacement on No.2 engine
4) Bleed valve replacement on No.2 engine
5) PTG replacement on No.2 Engine
6) FCU replacement on No.2 Engine
7) Engine fuel pump replacement on No.2 Engine
8) All Air pipelines have been replaced on No.2 Engine
9) Re-rig the NG adjustment for both Engine

Yet the problem is still there after I replace all the above-mentioned.
Since you have basically replaced all the normal engine components that cause this type problem, you may want to check the #1 and #2 engine wire harness and airframe indicating system wire harnesses for proper specifications. As mentioned above your #1 engine could be indicating low. Regardless, I would be 100% positive you have no indicating problem on the #1 and #2 engine indicating systems before replacing anymore components.

Was the #2 "T4" harness replaced when you replaced the #2 power turbine?

[Hughes500]

compressor case halves all ok, ie no cracks bits of plastic missing ?

[RVDT]

One saving grace with a twin is that you swap items from side to side as a troubleshooting exercise that makes life pretty easy to see if the fault goes with the component.

A couple of things that you may have missed that you didn't list but no doubt have looked at -

Anti-ice valve good? From memory (which may have faded as it's ~30 years since I worked on one) they are spring loaded to one direction cant remember which. Cap both lines and do a ground power check.

Bleed air heater/demister leak - from memory the lines are alloy and water accumulates in the low point from compressor washing and the line rots from the inside out before the valve. It is not obvious as the line has a heat sleeve on it and you cant see the holes in it. 350 has the same problem. Fix is to run the heater regularly after each wash to vent the line and dry it. Again cap all the lines right at the engine and do a ground power check.

Your TQ split is a pain on the 355 and will depend on your governor condition. From memory again I think you can adjust the bias on the droop compensation.

If you are really in a bind swapping engines from side to side isn't that difficult.

Talking to Airbus on a model this old would be about as effective as asking your grandmother unless the tech rep is really old.

[albatross]

Good stuff there RVDT.
Should have thought about the anti-ice and the heater. Both probably haven’t been used much if at all.
You are right about Airbus support. Better to try the engine folks.

.

[amzhkm147]

My NR during Full power on the ground is 390

on flight is somewhere between 393-394

Fuel pressure, oil temps, and oil pressure are identical for both engine

[amzhkm147]

I've done T4 calibration for both #1 and #2 engines.

T4 gauge has been switched and we have cross-wired the wire harness to check whether we got different results yet still producing the same result.

The bleed valve is working fine. I try to swap the bleed valve from #1 to #2 engine. still, both engines got the same result as before

Engine #1 passes the chart and engine #2 is borderline pass the chart with 83% of TQ and during hot day #2 engine TQ will be somewhere at 81-82 %

No particle separator was fitted on the aircraft.

[amzhkm147]

Yup, we swap the wire harness from #1 to #2 power turbine

[amzhkm147]

We did check the compressor case halves before we do the replacement. all satisfactory

[Sir HC]

1. When did this problem start? After maintenance? Suddenly? Gradually?
2. Bleed air leak, cracked discharge tube, cracked combustion can? I'm no Twin Star mechanic, does #2 provide a customer bleed? If so, cap it for testing. As above, cap the anti-ice too. Biggest culprit of high

Ultimately, if it passes a power check, then you can keep running that engine but if you're exhausted all your other options, I'd hazard a guess that your turbine assembly is damaged.

Make sure you report back with your findings!

[Jelico]

Bleed air heater/demister leak - from memory the lines are alloy and water accumulates in the low point from compressor washing and the line rots from the inside out before the valve. It is not obvious as the line has a heat sleeve on it and you cant see the holes in it. 350 has the same problem. Fix is to run the heater regularly after each wash to vent the line and dry it. Again cap all the lines right at the engine and do a ground power check.



I have seen two situations with our twin squirrels here in NZ with similar symptoms. One was as above, we had a bleed leak caused exactly as described. The other was a crack in the hot section can... The cracked can was in an awkward place but identifiable during preflight. The bleed air was harder to find but fixed the issue straight away, From memory it was about a 40 degree split.

I have flown 5 different twin squirrels (F1 & F2 models) and yet to find one with two engines that match perfectly.

[haihio]

Is the pilot doing the engine anti-ice check and bleed air heating/demisting check and getting the rise in T4 when they are tested ?

[sycamore]

Only a suggestion ,from someone who is unfamiliar with the type..can you check each T4 probes for damage,bending ,calibration,correct installation,burning ,etc,or swap with spares(Correct type)...and the jet exhaust pipe for alignment...?...on both engines...?

[wrench1]

Engine #1 passes the chart and engine #2 is borderline pass the chart with 83% of TQ and during hot day #2 engine TQ will be somewhere at 81-82 %
Keep in mind some small twin engine aircraft have an inherent operating difference due to how the airstream/rotorwash crosses over the #1/#2 engine cowling intakes. Sometime it can be as high as 20 degrees TOT.

Given you have replaced so many engine components are you saying you still have the same instrument reading on the #2 engine?

Are you performing the ground power checks into the wind? Have you tried performing 3 separate power checks at different headings and compare them?

In line with what was mentioned above, have you blocked off the customer bleed air fitting at the engine scroll?

[RVDT]

Is the pilot doing the engine anti-ice check and bleed air heating/demisting check and getting the rise in T4 when they are tested ?

As haihio has stated - quickest way to see if you have a bleed problem - and no doubt you or pilot would have checked change in TOT from OFF/ON of each? If no change in TOT that would kind of indicate the issue?

Something I normally do on any ground run on any machine - cycles the systems that normally don't get used and in your case being in Malaysia neither probably do due to the climate, and it also dries out the plumbing.

The reverse applies in colder climates if you have AC - run it regularly otherwise the seals dry out and you lose the gas.

[Heli.doctor]

Hi there, a friend showed me your problems earlier today, hopefully you have fixed your issues already. If not have you checked the P2 system double check valve, located on the main gearbox decking? If this valve leaks it will leak air from the engine being tested in to the other engine and you will T4 limit! Also if the P2 system bleeds from the compressors are leaking at the banjo gaskets then this may also be a problem.

You can blank off the P2 system from the ports on the compressor and test the engines again to be sure, (you shouldn't fly the machine like this but instead load it with weight so you can pull power without getting airborne).

The acceleration differences are because the governors require setting up better, this is done on the beep motor cam or slot dependent on version. Again this is on the gearbox decking on the right hand side of the aircraft.

Let me know how you get on, good luck.

THOS IS ADVICE ONLY AND ALL MANUALS AND AIRWORTINESS REQUIREMENTS SHOULD BE TAKEN IN TO CONSIDERATION!!

[PEASACAKE]

I think you have a Tq indication problem, T4 and Ng are fine, Tq indication is low and requires calibration (30 minute job for 2 engines).

After 35 years working on the AS355 series myself, I have seen owners and engineers throw a lot of labour at the aircraft to get the engines balanced (as best as possible).

Always do your engine checks in flight iaw the flight manual, that is where you will be when you need full power on one engine if you have a problem.

1. Engine Tq calibration MUST be carried out and adjusted correctly (Intake airflow is different on each side in flight), if this is not done nothing will make sense. Remember we balance engines on Tq but adjust Ng.
2. Fly aircraft at 73% Tq and apply collective friction
3. Beep each engine in turn till you reach a TQ or T4 limitation, record figures
4. Adjust engine Ng on adjuster/ PTG arm angle / Beep trim actuator arm angle (on mgb decking) to ensure both engines are perfectly balanced

After this you will see if one engine is low power or not, I doubt it is, just needs a Tq calibration, ON BOTH ENGINES .

All pilots on this forum just love a well matched pair of engines on the AS355, not having to beep up or down every time he moves the collective makes flying so much nicer.

I have never failed to match engines on these aircraft unless their was a tired or faulty component