Originally Posted by
A Squared
Chris, the BMEP gauges are simply torquemeters. For whatever reason Pratt&Whitney decided to lable them as psi of Brake Mean Effective Pressure, an abstract theoretical quantity representing the average pressure in the cylinders during the power stroke. Ultimately I guess it doesn’t matter whether ithe units are psi bmep or inch-pounds, you learn the numbers and apply them in operation. Thats why i said earlier that it would be interesting to know what the bmep gauge for the left engine showed, bmep is the best indication of how much power is being developed, whether it was producing more thrust or more drag
Yes, as you say, the precise meaning of the numbers on a torquemeter are of little significance, provided the crew can confirm that they are within the normal range for the phase of flight.
I imagine the auto-feathering system would look at BMEP and throttle angle? On take-off, with the throttle at or somewhere near the gate, a critical loss of BMEP would presumably activate auto-feathering. But we know the captain commented that the auto-feathering light was not working [report, 1.1.12]. I'm unable to identify the light he was referring to on the photo posted by
megan, but would there not be a separate one for each engine? Maybe the auto-feathering system was inoperative, at least on the No.1 (L/H) engine.