Helicopter Guiding Principles.....To Live By!
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In the 212/412/214ST/61/76 - LOW/LOW, HIGH/HIGH
"Bad torque follows rotor"
A previous Chief Pilot (and excellent instructor) taught me this to help navigate the situation that Nick mentioned above; differentiating from a high-side vs a low-side gov/fuel issue in a twin, specifically a B212/412 with a dual torque gauge. During a failure, the torque needles will split, one increasing, the other decreasing...how do you know which is the affected system?
If Rotor is increasing and your TQ is split with Eng 1 TQ increasing then you have a high-side failure on Eng 1.
If Rotor is drooping, and Eng 2 TQ is decreasing, you have low-side (or failure) on Eng 2.
Bad torque follows rotor.
A previous Chief Pilot (and excellent instructor) taught me this to help navigate the situation that Nick mentioned above; differentiating from a high-side vs a low-side gov/fuel issue in a twin, specifically a B212/412 with a dual torque gauge. During a failure, the torque needles will split, one increasing, the other decreasing...how do you know which is the affected system?
If Rotor is increasing and your TQ is split with Eng 1 TQ increasing then you have a high-side failure on Eng 1.
If Rotor is drooping, and Eng 2 TQ is decreasing, you have low-side (or failure) on Eng 2.
Bad torque follows rotor.
The Bell manual described four scenarios - High side/High power, High side/low power, low side/high power, low side/low power all of which involved looking at Nr, Q (a pointer and 2 long needles with tiny numbers) and N1, if I remember correctly.
So I'm with Nick. In any engine malfunction look at the Nr FIRST. Secondly, look at the N1/Ng's.
Three needles on three guages - you require nothing else to correctly diagnose the situation.
If the Nr is low it is a low side failure. If you are low collective pitch it may only be a bit low (say 97%) but will be below normal (obviously, if you are high collective pitch Nr will be really low). Then look at the N1/Ng's, the engine with the low N1/Ng is the failed engine. Hence LOW Nr - LOW N1/Ng. Proceed accordingly depending on aircraft type.
If the Nr is high it is a high side failure. If you are high collective pitch it may only be a bit high (say 101/103%) but will be above normal (obviously, if you are low collective pitch Nr will be really high). Then look at the N1/Ng's, the engine with the high N1/Ng is the failed engine. Hence HIGH Nr - HIGH N1/Ng. Proceed accordingly depending on aircraft type.
I have taught this method in all the types listed above and it seems to work fairly well.
Last edited by oleary; 17th Jul 2017 at 06:21.
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Thread Starter
Mr. O,
I learned on the Chinook....one Torque Gauge with two needles, an Nr Gauge, and two N-1 gauges.
We looked at Nr first, followed by N-1's.....the Torque Split merely indicated a potential problem.
As in all helicopters....Nr is of immediate importance.
Is it higher, lower, or as set before the problem....?
Then check the N-1's.....within the Governing Range...or above or below?
That usually told the story for you.
Then perhaps you could decide if it was the AC or DC system that was acting up....as it was an AC system that normally controlled the Nr.....and a quick Circuit Breaker pull would disable that Engine's Governor System and you reverted to direct control of the engine by means of a Momentary switch that you would have to manually balance the faulty engine to the normal one still using the DC system.
Of course there was the possibility of a stuck actuator that showed up as Torque Splits upon moving of the Thrust Lever (For the unwashed heathens....Colllective Lever).
Key to all this discussion is all failures are not Text Book style failures.
GS Pilot and his Instructor Pal are right as well....in that the Good Engine will move according to Collective Movement....but that should be well down the line in the troubleshooting tree and be more a confirmation than a diagnosis method.
At least in my opinion.
Understanding what the "Governing Range" N-1/Ng for your aircraft is will aid in assessing both a high side failure....and particularly a Low side failure....which may determine if it is a Governor Failure or an Engine Failure of some sort that leaves the Engine running but below the Governing Range.
I learned on the Chinook....one Torque Gauge with two needles, an Nr Gauge, and two N-1 gauges.
We looked at Nr first, followed by N-1's.....the Torque Split merely indicated a potential problem.
As in all helicopters....Nr is of immediate importance.
Is it higher, lower, or as set before the problem....?
Then check the N-1's.....within the Governing Range...or above or below?
That usually told the story for you.
Then perhaps you could decide if it was the AC or DC system that was acting up....as it was an AC system that normally controlled the Nr.....and a quick Circuit Breaker pull would disable that Engine's Governor System and you reverted to direct control of the engine by means of a Momentary switch that you would have to manually balance the faulty engine to the normal one still using the DC system.
Of course there was the possibility of a stuck actuator that showed up as Torque Splits upon moving of the Thrust Lever (For the unwashed heathens....Colllective Lever).
Key to all this discussion is all failures are not Text Book style failures.
GS Pilot and his Instructor Pal are right as well....in that the Good Engine will move according to Collective Movement....but that should be well down the line in the troubleshooting tree and be more a confirmation than a diagnosis method.
At least in my opinion.
Understanding what the "Governing Range" N-1/Ng for your aircraft is will aid in assessing both a high side failure....and particularly a Low side failure....which may determine if it is a Governor Failure or an Engine Failure of some sort that leaves the Engine running but below the Governing Range.
Last edited by SASless; 17th Jul 2017 at 15:57.
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I've used a simple subset of 3 rules:
1) Nr - maintain. Because rotor rpm is your life. Sometimes this means lower collective, sometimes it means raise.
2) Hi/Hi bad - low/low bad. Distillation of Nick's description to decide whether the high or low engine is the bad one. You can always tell by Nr.
3) No fast hands in the cockpit. Regardless of rule 2, deliberate and consult with the other pilot before moving ANYTHING other than a primary flight control.
1) Nr - maintain. Because rotor rpm is your life. Sometimes this means lower collective, sometimes it means raise.
2) Hi/Hi bad - low/low bad. Distillation of Nick's description to decide whether the high or low engine is the bad one. You can always tell by Nr.
3) No fast hands in the cockpit. Regardless of rule 2, deliberate and consult with the other pilot before moving ANYTHING other than a primary flight control.
Just a technique I liked. I imagine a scenario in cruise where I detect abnormal high or low RPM. That's confirmed quickly with a glance at the rotor tach. Looking at Torque I will see split needles which very cleary (at least to my eyes) indicate which engine is high and which is low. Works for me. I hope I didn't imply that N1 info was somehow excluded during the evaluation. That would be silly.
Just a technique I liked. I imagine a scenario in cruise where I detect abnormal high or low RPM. That's confirmed quickly with a glance at the rotor tach. Looking at Torque I will see split needles which very cleary (at least to my eyes) indicate which engine is high and which is low. Works for me. I hope I didn't imply that N1 info was somehow excluded during the evaluation. That would be silly.
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Try whacking a throttle open (acceleration check on a PT6 or T58 for example) and see which moves first - N1/Ng, ITT/T5 or N2/Nf. On some engines N1/Ng and temp will move almost together, but on all engines Nf moves slowest.
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First rule of helicopters when something is wrong - do NOTHING unless the NR needs to be controlled.
Second rule - think about it
Third rule - always have an escape route.
Second rule - think about it
Third rule - always have an escape route.
Do we really mean N1? N2 governing is what our day to day existence is based on. N1 governing just ensures the engine keeps running after the start sequence is completed.
A torque split might be the first indication of a governor runup or rundown or engine failure but the Nf and Nr relationship will be the easiest (often bigger gauges) to assess, especially with a triple tacho (two Nfs and an Nr needle). Teaching for us has always been to use the triple tacho for diagnosis and reaction (if any required) and use PTIT/T4/T6 and N1/Ng as confirmation.
Thread Starter
With high Nr and one Nf/N2 high....what kind of failure(s) are the options?
If the N-1/Ng is within the governing range....or outside the governing range....how does that "confirm" what the Nf/N2 indications are?
Which gives you the better indication of the cause of the problem?
When we discuss general rules we have to remember there are differences between aircraft types and models of those types to take into consideration.
If the N-1/Ng is within the governing range....or outside the governing range....how does that "confirm" what the Nf/N2 indications are?
Which gives you the better indication of the cause of the problem?
When we discuss general rules we have to remember there are differences between aircraft types and models of those types to take into consideration.
When we discuss general rules we have to remember there are differences between aircraft types and models of those types to take into consideration.
None of the aircraft I have flown have a governed N1 range, the N1 spools up and down to keep the N2/NF in a governed range. The exception would be the Gazelle but since that is fixed spool, it doesn't count.
In your example, a high Nr with one Nf high would be a runaway up (highside gov failure I believe you chaps with the dodgy president call it). A high N1 and T4 on the same engine would confirm that that one is working really hard and the 'good' engine would have the Nf in the normal range but the N1/T4 back at something like flight idle.
Further confirmation could be made by making a small collective lever movement to note the response - if you lower the lever slightly (not into auto) and the Nr goes up further then you have identified the culprit.
