Originally Posted by
GS Pilot
"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.
Being of Irish ancestry I had to figure out something less confusing than my first twin-engine type - the 212.
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.