throttlecondom

i just want to clear up this whole confusion on rpm limitations. Coming out of our maintenance manual, ground idle is 94% to 102%. Because of the low pitch stop and fuel scheduling at flight idle, it is 92.5% to 100.5%. Normal rpm in flight will be 98% to 102%. Of course, the upper and lower rpm limitations allow for an rpm gauge to have 2% rpm error in either direction, which is strange considering an rpm gauge is legally bad with 1% error. As measured with an accurate tachometer, ground idle is 96.3%-99.1%. Flight idle is 94.4%-98.3%. Normally in flight, rpm will be 99.8%-100.2% under no throttle movement. If you know your rpm indicator is dead on, rpm should never drop below 94% at any time because that is when the acceleration bleed valve are scheduled to open.

As for the manifold pressure, between ground idle and takeoff, it is possible for bleed air pressure to change from 70psi to up to 110psi on ground runs with only a minor rpm increase. This is measured with all bleed air operated equipment turned off and one engine outputting air-- not exactly something you'd check in flight, but with jet engines, bleed air equals power and temperature.

With all 4 engines at flight idle, some engines pull more torque than others. The engines that pull less torque will tend to nts more often on decent. Because of the nature of the nts system, the props will increase blade angle, then decrease back to the low pitch stop again when the nts condition is gone. This can create an rpm and torque flux situation which probably won't make an engine go below 94%, but you'll wonder what's going on with it.

As for why your squadron rules differ from the -1 guidance, who knows. These planes have been around for a long time and it makes sense to change the way we do business based on experience. It would just be nice if whoever thought it up would change the manuals if it's that important. Otherwise it's just an opinion.

these acceleration bleed valves you speak of, how do they know when the engine is at 94%? Also how do they know when to open and close?

My interpretation is that the Gearbox oil pressure will not go outside the limitations for any reason as long as the engine is at operating temperature and at 100%. I don't care what the mean of the flux is, it should not drop below 150 at all. It does seem to be open to interpretation solely because the engine oil pressure flux is clearly allowed to be outside normal limitations.

I wouldn't fly on it, and I'm a maintainer. Besides, I'm kind of lazy. I'd rather fix the flux than change an engine;)

I wouldn't fly on anything you work on. Sounds like you have no idea what you are talking about and on top of that lazy mechanics are the reason why we can't get in the air to do our job.