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Multi engine helicopters - Governor failure procedure

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Multi engine helicopters - Governor failure procedure

Old 2nd Jun 2021, 02:11
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Multi engine helicopters - Governor failure procedure

Hi team,

On the hunt for some resources on procedures for governor/ECU failures in multi engine helicopters. Does anyone have anything available online they can recommend?

Also open to any useful tips of the trade that you might have. Understand some things are airframe specific, more looking for generalisations for light twins.

Cheers!

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Old 2nd Jun 2021, 07:21
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Two simple general techniques beneath to kick off, for aircraft with manual backup in the event of a single governor/FCU failure. To my mind, the appropriate choice depends on what previous experience you have, how clear the cockpit indications are to easily differentiate between #1 and #2 engines, and whether the RFM specifies any differential TQ limits.

Note - before attempting either, make small collective inputs to ensure you have correctly identified which engine responds in TQ to collective inputs (automatically governed), and which does not (fixed/un-governed/manual).

1) Use manual control on the un-goverened engine to “match TQs” throughout (assuming TQ limited). This minimises the TQ differential between engines and if managed well reduces the likelihood of the automatically governed engine from approaching it’s upper or lower limits. However, the downsides are regular throttle inputs are required which can reduce capacity to fly a decent approach, which in turn may lead to larger collective/throttle inputs being required, exacerbating the problem. Also with both engine indications constantly moving there is the potential for inputs in response to the incorrect engine if the cockpit indications are not entirely clear which engine is in manual - these can be very confusing and rapidly lead to engines approaching limits.

2) set a nominal power on the manual engine appropriate to the phase of flight (low power for descent, mid power for cruise, higher power for climb), and allow the automatic engine to vary within it’s allowable limits for small fluctuations. Before lowering the collective to descend always roll off throttle a little, and never let the automatic engine reach <10% TQ, if it reaches 0% and you continue to lower the lever it cannot reduce TQ any less, and the reduction in drag from pitch reduction will lead to an engine/Nr over speed (or perhaps activation of the over speed protection circuit if fitted).

To a great degree the manner in which the approach is flown is more important to the outcome than excellent throttle control. My advice is fly a slightly shallow and slow approach. One really common error is over concentrating on the throttle control and being fast or steep at the end of the approach. Either case leads to larger than normal collective inputs which in turn requires corresponding throttle inputs. If you fly a slow and slightly shallow, constant angle approach, and get on the low speed side of the ‘power required for level flight’ curve early (generally <40-50kts by approximately 300ft) then throughout the remainder of the approach you progressively lose translational lift, meaning incremental small increases in collective and throttle until close to hover power is achieved which makes life very easy. Personally I try to keep the manual engine TQ just beneath that of the automatic engine when approaching the hover but that’s just preference for uniformity in indications. The single most common way to make life hard is to end up fast, with a flare at the bottom (large lowering of the collective), followed immediately by a rapid loss of translational lift leading to a large raising of the collective - avoid doing this...
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Old 2nd Jun 2021, 07:48
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My advice is:

1. read the procedure for this malfunction in the RFM, and
2. do what it says.

Then you can't go wrong. Problems arise when pilots think they know better and do something else.

With redundant digital engine controls in modern helicopters being so reliable, the chances of this malfunction happening are virtually zero. Whether you have a digital engine control or hydro-mechanical, the initial action is always the same. Keep flying. Collective follows the NR. If the NR is going high/low, follow it with collective. There is no real urgency to deal with this malfunction if the NR is maintained within limits.
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Old 2nd Jun 2021, 11:20
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Originally Posted by gulliBell View Post
My advice is:

1. read the procedure for this malfunction in the RFM, and
2. do what it says.

Then you can't go wrong. Problems arise when pilots think they know better and do something else.
I think that’s a given, for anyone with any airmanship. The problem I think Jelico is alluding to is that usually the RFM doesn’t give you any advice on technique for manual flight other than to ‘remain within limits’. You can make it hard for yourself, or easy for yourself depending how you are taught, and what techniques you use to remain within limits. I surmise Jelico refers to light twins which don’t have dual redundant fadec control: AS355, A109, EC135, MD902. Not many in that category do except the very latest variants, and the RFMs don’t give you any advice on technique. It is for instructors to teach the best practices, and to ensure the RFM procedures are handled. Jelico my advice, ask questions, take what you will from it, but above all else, fly with good instructors who can tell you how best to achieve the intent of the RFM.
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Old 2nd Jun 2021, 13:00
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Most RFM's are edited by Lawyers whose job is to protect the builder of the Aircraft thus they limit the RFM to that required to deal with the immediate failure.

The Airmanship part should come from the Training Department of the Operator and by means of hands on experience.

The danger of SOP's is they oft times try a one size fits all approach to things and begin to create "Cook Book" styles of flying.

Most good Cooks pull from many recipes to find the one that works for them.

We shall see that demonstrated here as folks post their ideas....most all of which work....but differ slightly.

An example....in general I agree with Aucky....but differ to the extent I leave the Torque Meter and Collective following Nr till after I do my initial assessment which is simple.....is the Nr higher or lower than previously set by the Pilot.

If the Nr is lower...sssuming the clollective has not been moved following the failure....then the low side engine is the. problem.....and if the Nr is higher....then it is the high side engine that is the problem.

Next step is to control Nr if it is outside normal limits.

Then I go to the N1/Ng to determine if the suspect engine is within normal governing range or at or below Flight Idle range.....that determines if it is a governor problem or a engine failure.

Other indications like exhaust gas temp, oil pressure, oil temp, are secondary indications.

Torque needles alone tell you squat....as they will always be one high and one low but don't tell you the actual cause....but they will tell you which engine is responding to Collective Movement....which I use as a confirming method rather than an initial method.

I always felt that if you had time. enough to get scared....you had no reason to be scared....and thus no need to get in a hurry.

The fright of my life due to an engine problem was in an empty Chinook...low on fuel...in cool air....with one engine running away high that would not respond to normal methods....and due to the high Rotor RPM (like way high....blade slinging kind of high)....and the Thrust Lever (Collective) tucked right up under my arm. to try to control the Rotor RPM....and thus adding the good engine power to the combination....it was hard to determine what was going on as BOTH Torque needles were almost matched. It took looking at. the N1 gauges and seeing one engine way beyond Topping Limits and the other within normal governing limits that allowed us to identify the failed engine and be able to shut off the fuel to it....and regain control of the aircraft.

We whizzed through a cloud layer like a Rocket headed to the Moon with the rate of climb that produced.

Once we were flying on the one engine...we made a normal recovery to the airfield and taxied to parking.....my evening case of beer tasted good that night.
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Old 2nd Jun 2021, 14:05
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Yes very fair point SASless. I was looking at it from a stuck/fixed governor perspective where the first thing you will see is a TQ mismatch caused by lever inputs, as opposed to run away up/down leading to an Nr change without collective input highlighting there is no one size fits all approach, but your Nr first (and comparison against high/low engine) does make absolute sense.

To diagnose any situation accurately requires a comprehensive understanding of the potential variables which is why I support Jelico’s curiosity, particularly as he has identified he is looking for ‘generalisations’. Whilst we can’t give a ‘this is what you do’, I think it is useful to hypothesise on some basic considerations which may make the RFM instructions easier to adhere to, and form part of the discussion with the instructor who is teaching you the type specific considerations.
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Old 2nd Jun 2021, 14:34
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Enough detail here to steer you in the right direction....



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Old 2nd Jun 2021, 14:57
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Originally Posted by Aucky View Post
..I was looking at it from a stuck/fixed governor perspective where the first thing you will see is a TQ mismatch caused by lever inputs...
With a digital engine control, such as in the S76C++, the first thing you will see is the blue DECU capsule light come on. This will remove power to the stepper motor in the fuel control unit resulting in a fixed fuel flow for that engine irrespective of collective position. Changing the collective position will now cause a torque mismatch. Although there could be a malfunction causing the stepper motor to go full open and things can then get exciting quickly, particularly if the collective position had a low power demand when the malfunction occurred.

If we had a very competent pilot in the simulator and he wanted a challenge to fill in some idle time, double DECU failure did the trick, one just after the other. i.e. both engines in manual fuel control. That malfunction would never happen for real, but it is covered in the RFM. It's a good challenge for the pilot to find a way to land without over spinning something.
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Old 2nd Jun 2021, 15:13
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the Thrust Lever (Collective) tucked right up under my arm. to try to control the Rotor RPM....and thus adding the good engine power to the combination.
How does that work then?

In addition to the above replies, remember to not lower the collective in a rush with relief once on the ground, or it tends to negate all the work you just did! I have seen an FDM trace of a flight with a stuck governor, where they spent over 2 min on the ground at 106% Nr after landing, and needed an engine change......

I had an incident, that SAS will sympathise with, where I was sitting on the ground in a B212 waiting for some client managers to board from their houses, in an estate about 25 min from our main base, when I had a runaway up. I closed both throttles immediately and was about to open the Idle Stop to close them completely (per ECL), when I realised that the engines had responded and were now at IDLE Ng - thereby telling me it was an Nf governor failure and not Ng. To assist with trouble shooting for the engineers, I slowly opened each throttle in turn to what should be the governed Nf/Nr range, to see which behaved itself and , sure enough, one throttle maintained 100% Nf/Nr when it continued to be opened, and the other just kept taking the Nf/Nr with it. So I shutdown and called base to say "Number 2 Nf governor failure" and in due course the engineer flew in and replaced it and we flew home. Cue bollocking for not following the ECL to the letter.......(i.e not opening the IDLE stop and shutting down during the run up!)
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Old 2nd Jun 2021, 15:17
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If you got a wild engine, as soon as you've found out which one it is and you're capable of single engine flight, idle it, don't touch it again and find a nice runway to run onto. All the pissing around in the SIM that I've struggled with over the years to try and deal with the situation is more pain than it's worth. Fly the damn thing to somewhere safe and land. 100 miles out at sea yeah I know.
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Old 2nd Jun 2021, 19:42
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212Man.....contradictions abound in that far off Centre of Excellenc don't they.

I had a Generator Light on an engine....and per the ECL...I was to turn that Generator Off and then shutdown the engine....which I did per the Checklist despite my gut feeling that there was no reason under the Sun for doing that.

Somehow...some Sky God in the lofty realms of the main Centre of Excellence had ordained that be the procedure due to some bad Generator Bearings somewhere in the World.

I got challenged by a lesser Sky God for following the ECL

So....I would suggest we broke even between us.

Do you recall the Pilot that had a high side governor failure at a hover at the Warri IA who set the aircraft down all the while with the throttle full on....and the rotor blades making a really unhealthy din and finally got around to rolling the throttles off.....then who rolled the throttles back on and repeated that bit of wonderful airmanship?






Aucky....your point about the stuck governor is absolutely correct....moving the Collective (or in the Chinook the "Thrust Lever") instantly identifies the bad engine.

You noted I use that same collective movement to confirm my analysis after going through my routine.

I have seen lots of flights cut short in the Sim after the wrong engine was shutdown or the wrong fuel valves moved....or fuel pumps shut off while at an altitude too high to do without them.

That is why I advocate not doing anything beyond what is absolutely required to regain control of the Nr..

Helicopter Pilots live or die because of Nr.
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Old 2nd Jun 2021, 20:05
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I used to teach my students to say “Engine malfunction” rather than “Engine failure”, to prevent adrenaline taking over before correct diagnosis of the problem.

As per SASless wrote, Immediate Actions should be:
1) Check and note the Nr...high or low? Correct as required with collective.
2) Raise and lower the lever .... which engine/s respond correctly.
3) Only then think about moving ECLs!

In the simulator (Puma) I once gave a student what was only going to be a spurious engine fire warning light whilst downwind in the circuit. All he had to do was confirm no signs of fire and continue to land. He overreacted by dumping the collective well below what was needed for single engined flight. He then looked at the Ng’s. Because he had dumped the collective and flared, both engines were backing right off, as advertised.

He then declared a double engine failure, shut down both engines and crashed!

Another, more senior student consistently misdiagnosed engine malfunctions. Quite worrying because he was a fairly experienced pilot, about to start a third tour and was refreshing on type. That was one occasion where the “record and playback” facility proved very useful....without it he would not have been convinced.
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Old 2nd Jun 2021, 20:09
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From old 212 daze:
High RPM High power on one engine = HIGH SIDE GOVERNOR FAILURE.
High Rotor RPM , High power on one engine, very low or even idle power on the other = High Side Gov failure on the high power engine. High power engine may not respond to throttle movement even if reduced to idle and you will have either shut down the high power engine or select manual governor as per the RFM ECL. NB. Do not select manual gov except when the throttle is on the idle stop.
In both cases Rotor RPM control is the first priority.


Low RPM low power on one engine = LOW SIDE GOVERNOR FAILURE.
Low Rotor RPM with high power demand on one engine and low power on the other = Low side governor failure on the low power engine. Reduce throttle to idle and select manual governor on the low power engine as per RFM ECL. NB. Do not select manual gov except when the throttle is on the idle stop..
In both cases Rotor RPM control is the first priority.
Once on the ground DO NOT lower the collective immediately as you may massively overspeed the rotor system. Best to set idle N1 on the failed engine or even shut it down before lowering the collective. Proceed slowly and think about what you are doing.
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Old 3rd Jun 2021, 01:02
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Things don't always occur by the book.

S-76A - during flight the engines started waving hands over a large range, as one went up the other went down and immediately reverse, Nr rock solid. Determined which engine was the rouge and pulled throttle out of governing range, all settled down and returned home for maintenance. Later in the day scheduled for same aircraft, after 40 minutes of flight one engine dropped to zero TQ, reduced collective to contain the good one and was in the process of reaching up to pull the throttle when with the snap of the fingers the engine went from zero TQ to max and attendant overspeed of Nr. As the hand was about three inches from the throttle when this occurred the pull collective to contain was out the window and completed the throttle pull. Snapped governor drive shaft, maintenance had done an hour flight in the aircraft and being unable to fault put it back on line after the initial problem.
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Old 3rd Jun 2021, 01:37
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Originally Posted by megan View Post
Things don't always occur by the book..
That's right. And not all malfunctions are covered in the RFM. In the C++ for engine oscillation malfunctions there is very scant information, pilot initiative is relied on to deal with it. Which is unfortunate in a "culturally aware" context because, unless it's written in the book some pilots have absolutely no idea what to do. Not doing anything and landing with oscillating engines will result in interesting outcomes.
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Old 3rd Jun 2021, 02:06
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...unless it's written in the book some pilots have absolutely no idea what to do.

Are you suggesting there are "Cook Book" Pilots out there somewhere?
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Old 3rd Jun 2021, 06:35
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Snapped governor drive shaft, maintenance had done an hour flight in the aircraft and being unable to fault put it back on line after the initial problem.
Ah, the old 'System tested, no fault found' attitude beloved of many maintainers.............
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Old 3rd Jun 2021, 09:52
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Originally Posted by SASless View Post
Are you suggesting there are "Cook Book" Pilots out there somewhere?
Regrettably there are a few pilots out there who can't even find the correct malfunction in the book (those mostly being where English is not their first language). Which can be less desirable launching into the wrong checklist than doing nothing at all. Getting on the right checklist can be an accomplishment. And if the malfunction isn't in the checklist, they will keep looking for it in the checklist until they eventually arrive at the scene of the accident. Particularly that engine oscillations malfunction because the book only gives basic guidance and you need to cook up a sensible plan to deal with it. Without having a good systems knowledge and a cook book to rely on the cooked up recipe can get mysterious.
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Old 3rd Jun 2021, 11:48
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We once had a semi-retired Hangar Queen transferred to our unit after it had been cannibalized for spare parts until our supply system caught up with demand.

Our mechanics (Engineers to the not. knowing) put her together again and off we went to do air tests....job done and she was put to work with the other Fifteen assigned aircraft.

Each time she went out....if she went Northwest towards the Cambodian Border and Indian Country....one of the engines would fix at a low power setting and nothing would cure the problem....go anywhere else and she worked fine. (I am not making this up.)

Everything she was returned for maintenance action....with air tests....no fault found was the result.

This went on for a month....and sure as houses...if she went Northwest...back she came.....with different crews each time (we thought it might be a crew issue.....).

One day...one of the mechanics being a brighter spark than most but who was guilty of the greatest Sin in the. military....being an independent thinker...upon reflection and much study of the Maintenance manual started chasing wires...wire bundles...and connectors for the various engine control systems.

One the "good engine" side...he found a pin pushed back on a connector on the a system that had to do with both engines....not just each engine....and just like that....the old girl was able to go to t he Northwest again.

Only the Gremlins know why it was only flying to the Northwest that had to do with the problem....them being the sneaky rascals they are.

They were undone by a Technician that knew what he was doing and would not give up until he found the fault.
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Old 3rd Jun 2021, 14:40
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Ah, the old 'System tested, no fault found' attitude beloved of many maintainers.........
crab, I must confess I wouldn't necessarily point the finger at the maintainers, we lived professionally beneath a mushroom, no intercourse was permitted with entities outside of our own few acres of dirt. When the 76's were purchased the C & T was sent to the US for endorsement and he was to come back to endorse we lower ranks, he suggested to the company that he stop over for a day or two at one of his transit points to chat with an established 76 operation, he was told that under no circumstance was he to make contact with said organisation. We saw it as the aviation advisor protecting his little patch/empire, nor did anyone, other than the advisor, ever attended international forums, just not done old boy. Engineers were under the same restraints, once they were licensed that was the end of any education, most were actually unlicensed, budget you know, you have to pay extra for licensed, the licensed signed off on the work done by the unlicensed. The biggest fracas I ever saw was a pilot came back with an aircraft that failed the trend by a monumental margin, engineers decided a ground run was in order and during the check the engine self destructed big time. I wonder if the trend was trying to say something?
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