Engine overspeed or other engine underspeed in AB212 or UH1N

[chiidzzz]

Hello,
Anyone got ideas how to differentiate engine overspeed or engine underspeed in non electronic controlled engines like AB212 or UH1N?
According to manual:
ENGINE OVERSPEED/FUEL CONTROL/GOVERNOR FAILURE
INDICATIONS:
1. High ENG RPM (N2) and ROTOR RPM ( N R ), possibly with
RPM caution light.
2. Definite TORQUE split (proportional to power demand).
3. High GAS PROD RPM (N1), ITT, and TORQUE of affected
engine.
4. Return of ENG RPM (N2) and ROTOR RPM ( N R ) to governed
value (if power demand is very high).

But if it's the case of engine overspeed, wouldn't the other unaffected engine lower torque to keep output XMSN torque the same?
For example, if I'm flying at 80% XMSN torque, I would normally be using 40% from each engine.
But N.1 engine overspeed, and its torque becomes 60%, wouldn't the other unaffected engine (N.2) lower torque to 20% to keep output XMSN at 80%?
If yes, how can I tell if it is N.1 engine overspeed or N.2 engine underspeed?

[Ascend Charlie]

'Coz when you beep the "low" engine up to fix the Tq difference, the RRPM goes high and stays there. Had one like this in a BK117, it can be a bit confusing when you are in a low hover over inhospitable ground and the Torque Split alarm goes off.

[SLFMS]

NR-N2, if your NR is lower than normal then you have a low side and the affected engine is the one with the least torque. There may or may not be a N2 split depending on the power in use, the severity of the malfunction and the ability of the good engine to maintain NR or alternately droop.

If your NR is higher then you have a high side and the affected engine is the one with the high torque. The good engine N2 should be in the normal range.

It’s quite easy to spot once you know what your looking for.

[paco]

The NR needle tends towards the duff engine

[Fortyodd2]

Torque Meter will tell that you have a problem.
Triple Tacho will tell you what the problem is.

[havick]

Originally Posted by Fortyodd2

Torque Meter will tell that you have a problem.
Triple Tacho will tell you what the problem is.

^^^^This!

RRPM is the key.

[albatross]

High Rotor RPM, High power (possible n1 Topping) on one engine, torque split, Low power on the other engine ( possibly at idle) = High side gov failure on the engine producing high power.
Normal or Low Rotor RPM , High Power (possible N1 Topping), on one engine, torque split, Low power on the other engine ( possibly at or below idle); = Low Side Gov Failure on the engine producing low power.
1) Yes I know I should use the term the term “power section” but I dislike the term.
2) Don’t do anything silly with the Auto/Manual governor switches! There are a lamentable number of engines that have been damaged and transmissions overspead just during training. ( two bright sparks even managed to cook both engines during a test flight in a remarkable demonstration of “persistence in the face of reality”. Their report won “Fiction Book of the Year”. Upon wading through it you became unsure that they were even aboard the aircraft or even in the country at the time of the incident. )

[212man]

But N.1 engine overspeed, and its torque becomes 60%, wouldn't the other unaffected engine (N.2) lower torque to 20% to keep output XMSN at 80%?

All good advice above. Also note that a highside failure would never give 60% torque. In the failure case for N2 governing, the engine will probably go to the N1 topping value, and for N1 governing failure you may get maximum possible fuel flow which will take the engine to goodness knows where! When the latter occurs on ground it can spin the aircraft on deck. I had an N2 highside failure on ground and it was relatively benign - I immediately heard the Nr rising and closed both throttles to the IDLE stop. That type of failure will allow throttle response, whereas an N1 governor failure will require the throttles to be fully closed.

[SASless]

All excellent replies.

The Torque Meter is just a warning sign of an engine problem of some kind.

I always killed the Torquemeter when teaching Engine problems in twins....forcing the use of the other engine gauges.

Once you get into a steady cruise....noting what the engine N1/Ng indications are helps in diagnosing problems with the same power setting.

Also remember engine malfunctions do not always exhibit "by the book indications during failures". Gauges sometimes go wonky although the engine is doing its thing as required.

[megan]

'Coz when you beep the "low" engine up to fix the Tq difference, the RRPM goes high and stays there

AC, unfortunately the aircraft only has one beep switch. From 412 manual, 212 will be same in principle,

[RVDT]

And of course while you are establishing just what is going on and probably severely distracted as a high side failure will normally be rapid, appreciate the differences with the RPM warning system.

LOW RPM - light plus audio

HIGH RPM - light only - NO AUDIO

It can affect the correct response and subsequent outcome.

VH-HOQ

Neither pilot appeared to recognise that the rotor RPM warning light, with the absence of the rotor low audio signal, was suggestive of a high rotor RPM and not a low rotor RPM situation.

[megan]

That accident was precipitated by the co-pilot calling 'Rotor RPM, Rotor RPM', what is any pilot going to do upon hearing such a call, dump the collective as an automatic reaction. Had it been a single pilot in the cockpit I'd bet he would have handled it correctly.

[RVDT]

Originally Posted by megan

That accident was precipitated by the co-pilot calling 'Rotor RPM, Rotor RPM', what is any pilot going to do upon hearing such a call, dump the collective as an automatic reaction. Had it been a single pilot in the cockpit I'd bet he would have handled it correctly.

The report may contradict your assumptions. I am assuming you have actually read it of course.

No doubt - what the CP said was correct. There was an issue with the RRPM. The failing was that neither of them understood the significance of with or without AUDIO warning.

If you have a high side failure it will be rapid and as pointed out in your posted RFM possibly accompanied by a surge because of it. Understanding the system and what it is actually telling you while you are preoccupied is a bonus at any time.

[212man]

Originally Posted by megan

That accident was precipitated by the co-pilot calling 'Rotor RPM, Rotor RPM', what is any pilot going to do upon hearing such a call, dump the collective as an automatic reaction. Had it been a single pilot in the cockpit I'd bet he would have handled it correctly.

I don’t agree. You don’t need a warning audio to tell you which way the Nr is going! There is something called ambient noise, and it gives a pretty clear indication of what the rotor is doing.

[megan]

The report may contradict your assumptions. I am assuming you have actually read it of course.

I am intimately familiar with the report, read it a thousand times, I take note you revel in "After all, what’s more important than proving to someone on the internet that they’re wrongI", I assume in your arrogance you took note where the report said, bolding mine,

The three very experienced simulator instructors, who took part in the simulator trials of the governor high-side failure, stated that their past trainees, with few exceptions, had failed to cope with the Np high-side failure until the practice of identifying the emergency and controlling rotor RPM had become instinctive as a result of training in the CPT. The instructors emphasised that experienced single-engine pilots training to fly the Bell 214ST were very prone to lower the collective instinctively in the event of any perceived emergency. The instructors were adamant that even most highly experienced twin-engine helicopter pilots often react like the captain of VH-HOQ until they have practised the Np overspeed failure drill in the CPT.

It was the opinion of the experts viewing the simulation that the actions of the captain of VHHOQ were instinctively those of a twin- engine helicopter pilot who had not had the benefit of previous simulator training to cope with an Np overspeed emergency at what was considered to be a most critical stage of flight.

Calling "rotor RPM" only accentuated the predilection for an untrained individual to drop the collective.

There is something called ambient noise, and it gives a pretty clear indication of what the rotor is doing

Except that hearing is the first faculty you lose in a stressful situation, had an engine failure at the exact same point in a rig take off as these guys, it was not not until we had leveled and beginning the climb that the other chap asked "do want me to cancel the tone", up to that point I wasn't aware it was on, nor the engine out light was on, nor did I hear him put out a mayday during the dive for the water. At the time of his question I was trying to regain rotor RPM from where it had dropped, 94%, and didn't know at that stage if a ditching was going to be the outcome. Bells and whistles only go so far. Ace co-pilot, Alex Crawford, thanks Mate.

[chiidzzz]

Thank you all for your responses, they really made a difference.

[SASless]

I suppose if one gets right down to brass tacks....it is how one. has been taught in the past that sets you up for success or failure.

Helicopter Pilots live and die by Nr.....too much Nr is usually an inconvenience with a rare occasion that it might be serious.....too little Nr can almost certainly lead to dire consequences especially in a single engine machine....not so much on a Twin.

The crucial teaching point is checking the Nr BEFORE moving the Collective Lever.

You move the Lever then check Nr and what you see is not going to be indicative of the problem you are experiencing necessarily.

Said PM could. have used a more descriptive announcement such as identifying whether the Nr was high or low.....and the PF would have had a clue as to what he should be seeing on the Rotor Tach before. he moved the Collective.

There is more to converting to a Twin Engine Helicopter than meets the eye....and add in a Second Pilot to the Mix and you have additional issues to work around.

The final observation I would make is not all malfunctions appear in the Check List or always have the exact symptoms discussed in training.

That is why I taught the importance of thinking first.....and acting second....to the point with some of the Dropped Shoulder Crowd I insisted they punch the Clock before doing anything at all.

It does not achieve any progress on resolving a problem but it darn tooting affords those who want to leap into action and do something.....as punching the clock does absolutely no harm.....but moving the wrong lever or throwing the wrong switch can surely ruin your day.

[212man]

That is why I taught the importance of thinking first.

I think you would have some empathy with my highside failure on the ground. Picking up senior client managers from a remote camp, as I watched the pax walk to the aircraft I heard the Nr rising. I immediately closed the throttles to idle and looked inside, to find the Nr decaying and both engines at idle. Knowing how the AFCU worked, I surmised that I’d had an N2 governor failure, but didn’t know which engine, and it wasn’t necessary to shut the engines down as per the checklist. To troubleshoot, I slowly increased the number one throttle and as the Nr reached 100% it stabilised and opening the throttle further had no effect. I then closed the throttle and repeated with number two, but the Nr did not stabilise at 100% and wanted to carry on increasing. After shutting down I phoned base to tell them we had an N2 governor failure on number two engine. A while later an engineer flew out with the required spares and it was quickly repaired, and we flew home. Soon after landing I was called into the Base Manager’s office and reprimanded for not following the emergency checklist - I.e. immediately closing both throttles to shut off. Hey ho…..

[SASless]

Seems to me you did just fine....blessed that. you were sat on the ground when it happened and all.

Your immediate action accomplished the. needed action.

Checklists cannot cover ever single malfunction or situation.

I suggest you did think....very quickly.

Had that fast reaction not cured the problem...what would have been the next action you would have taken?

[212man]

Originally Posted by SASless

Seems to me you did just fine....blessed that. you were sat on the ground when it happened and all.

Your immediate action accomplished the. needed action.

Checklists cannot cover ever single malfunction or situation.

I suggest you did think....very quickly.

Had that fast reaction not cured the problem...what would have been the next action you would have taken?

Thanks - just thought you would find the management response amusing/familiar.

Next action was IDLE stops open and throttles closed fully.