Autofeather System

[FGD135]

Sorry mate but you are wrong. Once the torque on the failing engine falls below 400 ft lbs the autofeather armed light on the operating engine will extinguish indicating that the operating side autofeather is disarmed.

Groggy, that is correct and is exactly what I said - though in different words.

To the question of engine damage in the event of inadvertent autofeather:

An inadvertent autofeather will have no effect on turbine temperature but may overtorque the engine.

At typical crusing altitudes the torque would get nowhere near the limit but the lower the altitude, the more likely the overtorque. At any altitude below about 5000' I would suggest it was an absolute certainty.

[Shadowfromthesky]

Thanks for all of your responces. Has really shed some light on my question! Got a much better understanding than just reading the POH.
Cheers.

Shadow.

[Grogmonster]

FGD135

My apologies. Overzealous as usual. Have great weekend.
Groggy

[sms777]

It is all good so far but.....is there anyone here with experience on B1900 regarding same settings and difference to B200 if any? I have spent some time on B1900 backseating and i could not tell otherwise.
Cheers for input

[Tango Bar]

On the -65 it's about the same- microswitch in the power quadrant set to approx 90% N1 position, opposite side disarmed below 400 torque, same-side autofeather solenoid energized below 200 torque.

I've been trying to puzzle out why the AF is turned "off" for cruise. The argument that the pilot has more time to consider courses of action, including relight, seems unconvincing; if you're going to check gages and take a bit to think things over, it'd be easier without a windmilling prop.

I suppose it reduces the chance of an inadvertent autofeather caused by a malfunction of one or more compnents in the AF system; during cruise, the 1900's engines are often above N1, so some combination of weird coincidences could cause an Np rollback without an associated failure of the gas generator, or maybe even an FTG problem could cause an Ng rollback, though I doubt that would go below 400 or 200 torque.

[kingRB]

I wasn't prepared for this level of thread resurrection

[pithblot]

My thought too - impressive thread resurrection TB.

FWIW, I had the same question when I was flying B200s - never got a convincing answer.

Some familiar names here, I’ve not heard for quite a while.

I hope your all doing ok in these strange days.

Cheers,

pithblot.

[blackburn]

Reference Leadsleds post number 4, for what it’s worth, the Bristol Freighter did not have an Auto Feather System. It had an Auto Pitch Coarsening System. This worked by a comparison between air flows utilising two pitot tubes on each wing, one mounted within the propeller arc to detect the propeller airflow and one mounted at the wingtip in the free airflow.

The operation required the Master Auto Coarsening switch to be on, the Throttle levers to be at the marked Take Off position and the Propeller RPM levers to be fully forward, Should an engine fail during take-off, then reduction in the airflow within the propeller arc will reduce to something akin to the free airstream flow and result in no pressure differential between the pitot at the wingtip and the pitot behind the propeller arc. This would cause the propeller blades to be driven towards the coarse pitch position. Manual feathering from that position would then be required. Without Auto Coarsening being serviceable the aircraft was limited to a take-off weight of 40,000lb.

[junior.VH-LFA]

The B350 operator I work for leave auto feather armed in all phases of flight; just for something different.

[Mach E Avelli]

On every type I have flown it does no harm to leave auto feather armed for the entire flight. Nothing will overheat or wear out. In fact the old RR Dart system had no pilot controlled arming switch.
If an engine fails at normal cruise power, because the throttle switch is not ‘made’ , it won’t auto feather(PT6 system, others vary).
PT6 system in cruise prop will windmill (unless gearbox or something nasty seizes).
The Pilot is then able to identify and manually feather, or simply advance the throttles and let the auto feather do its thing. Advancing both throttles ensures two things. 1. safe flight path. 2. the failed engine is not misidentified.
Switching automated systems off is generally not clever. Complicating checklists with unnecessary items is not clever either, but some operators insist on making work for the sake of it.
The old B200 cockpit is as ergonomically bad as they get, with switches easily confused until really familiar with the type and even then mistakes occur, particularly at night or under duress. A good reason to keep it simple.

[Dora-9]

...and speaking of the mighty (and noisy) RR Dart, I can confirm from personal experience that the auto-feather system will work in cruise.

[Propstop]

Where was the control lock positioned??

[Mach E Avelli]

Control lock? If you are thinking of the Dart/Dowty Rotol set up, most would attempt to go to ground fine pitch if you engaged the control lock in flight. Various safety stops would prevent it going all the way, but still not recommended to try it in flight.

[Dora-9]

most would attempt to go to ground fine pitch if you engaged the control lock in flight.

Not quite - the Ground Fine locks would be removed (those pretty amber lights would come on) but the props would constant speed where they were - until you slowed down anyway!

And if you did engage the gust lock in flight you'd have rather more pressing problems - ask ANSW.

[Mach E Avelli]

Dora is of course correct! In steady state cruise prop pitch barely moves. The fun begins when you add power, reduce speed or come back to flight idle.
Years ago while ferrying an old Vickers Viscount I got to test the auto feather system, and its ability to prevent remaining engines auto feathering following failure.
Long story which I have related here somewhere in the past.