Autofeather vs NTS

[avbug]

With autofeather armed, the T-56 would NTS on an idle high angle descent; getting the lights on the drops wasn't uncommon. Not all T56 installations used both, I believe. I'd dig out my manuals if they weren't stuck in storage. (Thinking early series C-130, here).

Autofeather shouldn't take over for NTS during normal operations, as the prop isn't going to feather.

 

[Donsa320]

With autofeather armed, the T-56 would NTS on an idle high angle descent; getting the lights on the drops wasn't uncommon. Not all T56 installations used both, I believe. I'd dig out my manuals if they weren't stuck in storage. (Thinking early series C-130, here).

Autofeather shouldn't take over for NTS during normal operations, as the prop isn't going to feather.

Yep, the autofeather would not actuate even if armed in a descent because the throttles would be at or near flight idle. The throttles have to be up quite high to arm the autofeather.

The Allison 501D engines and Aeroproducts 606A propeller were my meat on the Allison Convair 340/440 (580) <grin>

 

[transpac]

The C-130s I flew didn't have autofeather. (C-130B &E)

 

[pilotyip]

Avbug and Donsa, I left that part out. The power lever had to be at around 66% coordinator to arm auto feather. So at Flt Idle you could NTS. Also taking off with birds in the area, you were not suppose to use auto feather, because a bird might cause a momentary power drop and activate auto feather on an engine that would normally stay on line. AAL lost one at rotate in BOS back in 1960 due to this problem. #4 auto feather and shut down, #3 NTSed, VMC air 2 eng 138KTs, rotate 115 Kts, equal upside down airplane.

 

[avbug]

This comes back to the differences between autofeather and NTS, again. Autofeather is generally an customer (airframe manufacturer) supplied function, like prop sync, while NTS is an engine function. The autofeather system is the airplane letting the engine know what it wants, whereas the NTS is the engine letting the airplane know what it's doing, and when the engine doesn't like what the airframe has told it to do...doing what it thinks is necessary to fix it.

 

[GravityHater]

OK, read and tried to digest all that, thanks.

Next a question about operating an twin turboprop with AF in the event of an engine failure. Completely hypothetical.

Would you expect most flight manuals to say when one quits, do NOT pull a power lever to idle (ie the dying engine) as this will inactivate the AF system?

 

[pilotyip]

When it autofeathers, you don'ta toucha nothin. Unless of course it is on fire then follow fire procedures

 

[Donsa320]

OK, read and tried to digest all that, thanks.

Next a question about operating an twin turboprop with AF in the event of an engine failure. Completely hypothetical.

Would you expect most flight manuals to say when one quits, do NOT pull a power lever to idle (ie the dying engine) as this will inactivate the AF system?

I can only speak for the Allison engine installation and there, once the feather button has been sucked in by the autofeather system, it would make no difference what you did. The fuel has already been shut off and the feather solenoid actuated and electric pump is already running. In my experience, turbine engines usually don't gradually die. They either run or they don't. The exception could be bird ingestion, hence the need to turn off autofeather if you see birds about to collide on take off. My failures were instantaneous. Only had one on take-off at about 90 knots. I heard the bang, perceived the left prop feathering as the nosewheels started to howl and I stopped. Enroute with the autofeather not armed of course, bang and the safety coupling let go so that the prop and engine were no longer connected. The NTS never had a chance to operate and prop sync never even was broken. Manually feathered it and landed.

 

[avbug]

As others said, with autofeather, your first indication of a problem is quite possibly that the propeller has already feathered. Your function at that point is securing items after you address flying the airplane.

The failure I experienced late this summer was a case of the engine continuing to run, but the prop feathering, without an autofeather system available. All my oil ported overboard with a turbine bearing seal failure, and the prop moved toward feather (kept turning, however), while I had engine response. I could push the power up, see the EGT climb, but had no thrust through the prop as I'd lost propeller control. I didn't have much time to evaluate it, but in the back of my mind I was thinking about a possible shaft failure. The propeller didn't fully feather, the engine didn't quit turning, and while I had appropriate power response through the power lever, I had no torque. In that case, the trained response for that engine installation was to keep pushing up the power lever, as the lever controls both the fuel controller and the propeller; it offered the best chance for minimal prop drag in the event the propeller didn't automatically feather. Lots of conflicting signals and no altitude to sort it out. Temps went through the roof, but the engine was already toast, and my only concern was making my forced landing site.

With autofeather, once the system has done it's job, you follow up with the appropriate pilot actions per normal. However, in order for it to work, the power levers must be far enough advanced to activate the microswitches that arm the system.