Autofeather logic
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Join Date: Jul 2006
Location: Yugoslavia
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Autofeather logic
being away of my library I can not check it in my books or notes so I will ask the question here.
All turboprops that I either flew or read about had the same autofeather logic. More or less and regardless is it FADEC controled feature or old fashion one.
The part of logic that I am refering here to is that after first engine failed the working one recives the signal to increase power and to inhibit autofeather.
My question is why is the autofeather feature inhibited on remaining engine.
Posibility for windmilling restart or somethin else?
Have a safe sky!
All turboprops that I either flew or read about had the same autofeather logic. More or less and regardless is it FADEC controled feature or old fashion one.
The part of logic that I am refering here to is that after first engine failed the working one recives the signal to increase power and to inhibit autofeather.
My question is why is the autofeather feature inhibited on remaining engine.
Posibility for windmilling restart or somethin else?
Have a safe sky!
Join Date: Oct 2006
Location: Ankh Morpork, DW
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Autofeather is active on takeoff and approach in the planes I've flown. If you have a dual engine failure in either scenario, you're going down if one or both engines are feathered. My guess only one A/F at a time to prevent spurious dual A/F.
It's really there to protect for a V1 cut and if you lose both engines at V1, you're not getting off the ground unless you go off a cliff.
It's really there to protect for a V1 cut and if you lose both engines at V1, you're not getting off the ground unless you go off a cliff.
In certification-land some assumptions have to be made or we could never fly. Multiple failures are considered where possible, and many systems are designed accordingly. But twins are assumed to always have one engine operative. Not to say both engines can't fail, as we saw with the A 320 that had to ditch after a multiple bird-strike and the ATR 42 that ran out of fuel and also ditched.
Regulations require continued flight performance to be guaranteed if one engine fails at V1 or anytime thereafter during flight, right through to the landing. Autofeather may be required to reduce drag quickly to meet the engine-out climb performance during takeoff or go-around. A delay while pilots manually feathered a windmilling propeller could prove critical. Ergo, the other engine must be protected from anything spurious (like a surge or false signal) that will shut it down at a critical time. Hence autofeather systems lock the 'good' engine out following auto-feather of the bad' engine. Some systems are active at all times, others only switched on for takeoff and switched off when at a safe height where it is considered that pilots would have time to deal with any associated problem.
Regardless of the type of autofeather system, if the pilot had a valid reason to feather the other engine (for example after running out of fuel and needing to glide) it can be done manually.
Regulations require continued flight performance to be guaranteed if one engine fails at V1 or anytime thereafter during flight, right through to the landing. Autofeather may be required to reduce drag quickly to meet the engine-out climb performance during takeoff or go-around. A delay while pilots manually feathered a windmilling propeller could prove critical. Ergo, the other engine must be protected from anything spurious (like a surge or false signal) that will shut it down at a critical time. Hence autofeather systems lock the 'good' engine out following auto-feather of the bad' engine. Some systems are active at all times, others only switched on for takeoff and switched off when at a safe height where it is considered that pilots would have time to deal with any associated problem.
Regardless of the type of autofeather system, if the pilot had a valid reason to feather the other engine (for example after running out of fuel and needing to glide) it can be done manually.
While the Darts I flew had the second engine lockout, they did not increase the thrust of the remaining engine automatically. As I recall, that was the only time the flight crew could set the fuel trim above 80% but it was done manually.
Last edited by MarkerInbound; 14th Jul 2010 at 23:20.
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The CASA 235 has the lockout feature so that the second engine cannot be mistakenly feathered. It also has an APR (automatic power reserve) that boosts the power on the remaining engine 30 ft lbs above MTOP. The autofeather is armed before takeoff but switched off slightly after. For some reason, it is not to be activated on approach although the 300 series allows this.
Of course in the sim all of these functions malfunction at V1!!
Of course in the sim all of these functions malfunction at V1!!
