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Air Crash Investigation: Twin Otter DHC-6 300 Flap Actuator

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Air Crash Investigation: Twin Otter DHC-6 300 Flap Actuator

Old 17th Jul 2013, 21:03
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Air Crash Investigation: Twin Otter DHC-6 300 Flap Actuator

Hi there,

I work for the television show "Air Crash Investigation" that airs on National Geographic channels around the world. We're working on an episode about the 2007 Twin Otter Air Moorea accident, which was investigated by the BEA.

Can someone help me with a flap actuator question? If you look at the BEA report on page 27, you'll find a small underwater shot of the flap actuator, which they found in the "flaps retracted position". We need our Art Department to build this flap actuator, so that we can demonstrate on television how it was found in the flaps retracted position versus the flaps takeoff position. I'm having a difficult time visualizing it. Could someone possibly explain this to me - ideally with some photos?

Thank you in advance.
Sonya Buyting
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Air Crash Investigation / Mayday
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Old 18th Jul 2013, 01:27
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Can't seem to access the report. As a former Twin Otter pilot, I can tell you that I always visually checked the flaps(of course you only can see one side from a particular pilot seat) prior to departure. Not an SOP thing, just something I always did as an airmanship thing. You are not going far in a DHC-6 with the flaps up on takeoff....or so I was told.

Perhaps, your company should purchase a maintenance manual. I'm sure it is not too expensive and if you want credibility, it should be an accurate depiction based on more than info from a pilot forum.

Last edited by JammedStab; 18th Jul 2013 at 01:28.
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Old 18th Jul 2013, 01:57
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O.K., I downloaded the report but only looked at it briefly. I think a Pilots operation book would be satisfactory. The Flap Selector Handle is in the upper left of the picture and very difficult to see. The flap actuator which actually would move the flaps is probably hidden in the upper fuselage somewhere.

The pilots view of this center portion of the overhead panel would be different than the picture. If the picture was rotated 45 clockwise, it would be more accurate.

Try this link:
cockpit photo twin otter - Google Search

and

Cockpit Overhead Panel - 8Q-TMQ | Flickr - Photo Sharing!

Note the small square thing at the aft end of the handle. That thing has to be pushed(normally your thumb is used) to unlock the handle in order to move the handle for a new selection.

Last edited by JammedStab; 18th Jul 2013 at 02:00.
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Old 21st Jul 2013, 21:07
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Hi JammedStab,

The part we're trying to figure out is actually the flap actuator, which is the second image on page 29. It's the part attached to the elevator in the back that lifts it up or retracts it, etc. The image of the actuator underwater doesn't really show it in its entirety. The investigators found the actuator in the flaps retracted position, so somehow I have to figure out how that part would look - on its own - in the retracted position and the takeoff position.

Thanks for any help you might be able to provide!
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Old 21st Jul 2013, 21:17
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Hi there,

I'm actually looking for a visual of the actuator that controls the actual flaps on the wings - not how it's set in the cockpit. If you look at the second image on page 29 of the final report, it says this is the flap actuator that was found in the retracted position. Unfortunately, I don't know what this flap actuator would look like on its own or how to tell if it's in the retracted position versus the takeoff position.

I'd appreciate any help you might be able to provide on this.

Last edited by Jetdriver; 21st Jul 2013 at 21:32.
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Old 22nd Jul 2013, 13:37
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Check your email - Flap description section of -300 training manual sent.

I have higher resolution copies if you need them.

Also these guys will have the info and might have photos as well.

Viking Air

Last edited by Jetdriver; 22nd Jul 2013 at 14:22.
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Old 23rd Jul 2013, 17:15
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The flap actuator is located inside the upper mid-fuselage (approx stn. 250.0 inside fuselage, between wings). The best way to confirm flap position on the Twin Otter, post-crash, is to measure the flap operation jack extension. Flap 0 would equate to an actuator having .45 inch extension, measured from the jack body to the lug attach hole. Also, in some cases where this method is not possible, if the wing is displaced aft post-crash, the wing flaps will leave an indentation on the side fuselage, you can use that witness mark to determine flap position, but the actuator is best. Cheers
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Old 24th Jul 2013, 11:34
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The flap actuator itself is the hydraulic cylinder in the upper part of the picture. When it is actuated by hydraulic pressure, a rod extends out of the actuator, moving the bellcrank mechanism.

Find a hydraulic repair shop or tractor/backhoe shop and have them show you an actuator.
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Old 24th Jul 2013, 18:28
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Thank you, all of you!

You guys rock. Much appreciated.
Cheers!
Sonya
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