Do Twin Otters Have Autofeather?

[xsbank]

Do they?

[ahramin]

Yes, they do.

[xsbank]

Thank you.

[MUSKEG]

Depends on if you're talking 100,200 or 300 series. 1/200 do not unless it's a mod.

[Rowdy]

Yep, and if it's U/S it changes a slew of things...

[seniorpumpkin]

I've flown one twin otter that had autofeather, I think I've flown nine that don't.

[PanEuropean]

Below is the autofeather system description from the most recent issue of the DHC-6 Series 300 AFM.

Michael

[algore]

One thing to note. If this is in relation to the Twin Otter accident reciently, I don't believe auto feather would have helped from what I understand. It appears the accident occured on a go around, after a landing attempt. I know nothing of the Twin Otter, but on the aircraft I fly, you cannot land with the auto feather on. It is only for a takeoff... In a go around, Autofeather is useless...

[pelmet]

The autofeather article talks about a mod giving a two second delay to allow for discing. Is this to help you briefly slow the aircraft down. What about directional control difficulties on the ground or in the air.

[Brantford Beech Boy]

...but on the aircraft I fly, you cannot land with the auto feather on. It is only for a takeoff... In a go around, Autofeather is useless...

I find this interesting...could you elaborate?

In my BE20 the autofx is armed for t/o and landing, but I appreciate there is more than one way to design a system...

BBB

[nightguy]

The otters auto feather system is just for T/O. STOL ops require it for the climb below VMC. The system has been changed over the years due to issues with it feathering both engines. The system in it's latest form works a lot like the BE20. That is to say when one side drops below a given value the other side is disarmed. As far as I know Viking has not changed anything on the 400. I will see what I can find regarding the old system and get back to you.

[algore]

...but on the aircraft I fly, you cannot land with the auto feather on. It is only for a takeoff... In a go around, Autofeather is useless...

I find this interesting...could you elaborate?

In my BE20 the autofx is armed for t/o and landing, but I appreciate there is more than one way to design a system...

BBB

As I said, I don't know the Otter's system at all, but on the Q400, the autofeather is only for takeoff. I can't remember the exact explanation, but I think it had something do with on landing, if the props dropped below a certain rpm before going into disc, the engines would feather on landing, or something like that. I just thought all planes were the same, although I see from an above response that some aircraft seem to have the system armed on landing as well. I asked this exact question in ground school because it seems like it would be a good thing to have it feather if a prop stops in the go around... It's actually quite a nuisance, since we have a very different drill should the engine fail in a go around, and is in my opinion the hardest drill in the q400. In every other engine fail scenario you wait until above 1000' to begin the engine shutdown drill, but since it won't feather in a go around, it means you have to shut down the engine immediately, during a very high workload period, and very close to the ground. Eventually I got the hang of it in the sim, but it’s a very tough drill.

[SAR_YQQ]

it means you have to shut down the engine immediately

Doesn't the Q400 have feathering buttons or some kind of prop lever that allows you to feather the prop very easily? Is it FADEC that makes the drill more complicated?

[PanEuropean]

The autofeather system on the Twin Otter is used for takeoff only.

The reason is extraordinarily simple: During the takeoff phase of flight, the aircraft has low kinetic energy and low potential energy. During the approach and landing phase of flight, the aircraft has significant reserves of both kinetic and potential energy.

In any case, due to the design of the autofeather system on the Twin Otter, it would never arm during an approach and landing. One of the conditions required for the DHC-6 autofeather system to arm is that both power levers have to be 'sufficiently far forward' that each engine is running at about 86 to 88% Ng. It is extremely unlikely that the power levers would be this far forward during any portion of the approach and landing phase of flight. Even if they were... the kinetic energy present at that power setting would be substantial, which brings us round to the paragraph above...

Michael

[Brantford Beech Boy]

Ok...again I was just curious....

Our Autofx requires 3 conditions be met in order for the system to function..unless required by thebelow conditions, it just remains ARMED....

a.the switch must be in the armed position and
b. both power levers must be at a forward position (roughly corresponding to apprx 90%) NG and
c. one of the torqumeters must register 400lbs of Tq or less.....

when all these conditions are met, the opposite (good?) engine will disarm it's autofeather cct.
when the failed engine's Tq falls below apprx 250 lbs of Tq, that propeller is then feathered....

so in the event of a go-around, the system is disarmed till the power levers are advanced to max power and when the engine fails, it meets the 3 requirements and Bob's you uncle..feather prop in the go-around....

Our Twin guys are told [SOP] to ARM the autofx system for the same basic reasons, to assist the pilots in timely feathering a dead prop in the go-around (the pwr levers are advanced beyond to the 86 to 88% Ng in the go-around).....it seems to work just fine in the sim?

but then again I haven't been current on the Twin in years...and Pan Euro probably knows way more than I do..

Cheers
BBB

[glorifiedtaxidriver]

On the airplane I fly it's active all the time. There's no turning it off. If the torque drops below a certain point with the throttle above a certain point, it automatically autofeathers. It also disables the other engine from autofeathering.

[KK7]

On the DHC-7, it is only available for use during take off.

We have a switch to select it on or off, and it is armed when all engines produce over 2150 ft-lbs of torque AND the #1 and #4 power levers are above 88% Ng. When armed, when an engine's power decreases below 2130 ft-lbs of torque, the ENGINE FAIL lights come on, and there is a 2 second delay before the oil pressure in the prop is dumped and the prop feathers, and the Auto Feather system disarms to prevent any further engines from auto feathering.

In the engine failure after rotate drill (and in our case V1 is always the same as Vr), if the autofeather system fails, we can bring the condition lever for the failed engine directly to fuel shut off very easily, which will likely feather the prop.

One problem with the system however, arises when securing an engine that has autofeathered if it is either the #1 or #4 engine that has failed. If the engine autofeathers we leave it as is until 400' AGL, but after cleaning up the first step in securing the engine involves bringing the affected engine's power lever to flight idle, which when done on #1 or #4 also disarms the autofeather system and the prop will come out of feather if there is still oil pressure (for example in a roll back to idle). The prop will be feathered again when the condition lever for that engine is brought back to fuel shut off. The problem is that this is not explained in the AFM so it sometimes come as a surprise to people.

[PanEuropean]

Our Autofx requires 3 conditions be met in order for the system to function..unless required by thebelow conditions, it just remains ARMED...

BBB:

I think you have accidentally and unintentionally confused the 'SEL' (selected) light with the 'ARM' light on the autofeather annunciator.

When the autofeather switch is selected to the on position, the SEL (for selected) light illuminates. The only criteria required to illuminate the SEL light is turning the system on with the switch. The SEL light will illuminate if the switch is moved to the on position, even if both engines are off and the aircraft is still in the hangar.

When the three criteria described in the excerpt from the AFM (a few posts above) have been met (switch selected on, torque on both engines above a specified threshold, power levers sufficiently far forward to ensure that both engines' Ng is greater than 86 to 88%), then the autofeather system arms, and this is annunciated by the ARM light illuminating. The SEL light remains illuminated, so, you then have both annunciator lights illuminated.

Note that the current version of the Series 300 AFM explicitly states that the autofeather system should not be turned on for the approach and landing phase of flight. There are solid technical (safety related) reasons for this. Other types of aircraft will have different procedures, and may either call for the autofeather system to be turned on for approach and landing, or on some aircraft even automatically turn the autofeather system on for approach and landing. But... not the Twin Otter.

Below is an image from the current issue (revision 53) of the Transport Canada approved Twin Otter AFM. It is pretty explicit.

Michael

[Brantford Beech Boy]

ahhh, yeah..that's what I meant..the SEL feature!
(although the conditions I listed are for my beloved BE20)

guess I'm more rusty on the -6 than I thought!

Cheers
BBB

[just curious]

it meets the 3 requirements and Bob's your uncle..feather prop in the go-around....

Actually, although Bob is not your uncle, let's face it, he could be your older brother. Oh, and his nephews don't use the autofeather on landing