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Twin Otter crash

Old 31st May 2023, 15:24
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Originally Posted by BFSGrad
That would mean an aircraft would cross the threshold at 1.3Vso, bleed off 30% of the airspeed in the flare, and touch down at Vso with the wing at the critical angle of attack?

I donít think that is a typical airplane landing technique.
For big commercial stuff, not advisable, though for small C172 alike, in principle yes (for the PPL, there is a zero -assumed malfunctioning- flaps training item to fly the C172 at a very shallow angle, without flare, against the deck, with suitable power). I'd say, a dead-stick twin otter should be treated like a (dead-stick) C172 (no power to support shallow-angle approaches. Feel free to correct me.
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Old 31st May 2023, 17:26
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I'd say, a dead-stick twin otter should be treated like a (dead-stick) C172 (no power to support shallow-angle approaches. Feel free to correct me.
Yes, I'd like to correct you, there are a number of assumption errors with respect to the differences between how a wheelplane Twin Otter, and a wheelplane 172 fly, particularly in respect of flaps and power/propeller pitch. With some Twin Otter type training, these differences will become apparent, and result in change in your perspective on this type of flying.

One very common feature of both the Twin Otter and 172 will be that if you don't flare it, you're likely to bounce it off the nosewheel, and expensive damage will result.
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Old 31st May 2023, 17:32
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Originally Posted by WideScreen
For big commercial stuff, not advisable, though for small C172 alike, in principle yes (for the PPL, there is a zero -assumed malfunctioning- flaps training item to fly the C172 at a very shallow angle, without flare, against the deck, with suitable power). I'd say, a dead-stick twin otter should be treated like a (dead-stick) C172 (no power to support shallow-angle approaches. Feel free to correct me.
That's the way I've been approaching the water entry.
It makes a lot of sense to ship the floats over in the belly of a big rig.
Less drag, and safer ditch if needed...

I think your summary makes sense, keep the nose up as long as possible, hoping when it hit, submergence is in the "shallow angle enough such that it pops back up, instead of pitching the whole business over" domain.

Also, hoping for a tail low aspect, so when the gear enters fully, the Nose coming down will plop, rather than sink and trip the a/c over its nose....(then again, if sufficiently entry vertical, the floats are sturdy enough to absorb alot of energy. Keeping them on for the journey for that reason however, implies alot of defeatism at the outset)

something like that?

Last edited by Concours77; 31st May 2023 at 17:42.
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Old 31st May 2023, 17:54
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The Viking/deHavilland Flight Manual for the Twin Otter describes the recommended ditching procedure for the wheelplane in section 3.9.7.
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Old 31st May 2023, 17:59
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Nosegear first

Originally Posted by Pilot DAR
Yes, I'd like to correct you, there are a number of assumption errors with respect to the differences between how a wheelplane Twin Otter, and a wheelplane 172 fly, particularly in respect of flaps and power/propeller pitch. With some Twin Otter type training, these differences will become apparent, and result in change in your perspective on this type of flying.

One very common feature of both the Twin Otter and 172 will be that if you don't flare it, you're likely to bounce it off the nosewheel, and expensive damage will result.
Done that, though in a 182. It didn't land first by much, but enough to cost me $483.00 when that was real money...
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Old 31st May 2023, 18:21
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In a Twin Otter, it's called "Station 60 damage". Sadly common, and easy to do if careless in the flare. Always expensive, and usually done far from home....
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Old 31st May 2023, 19:28
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Originally Posted by Pilot DAR
Yes, I'd like to correct you, there are a number of assumption errors with respect to the differences between how a wheelplane Twin Otter, and a wheelplane 172 fly, particularly in respect of flaps and power/propeller pitch. With some Twin Otter type training, these differences will become apparent, and result in change in your perspective on this type of flying.
Please elaborate.

Originally Posted by Pilot DAR
One very common feature of both the Twin Otter and 172 will be that if you don't flare it, you're likely to bounce it off the nosewheel, and expensive damage will result.
Yes, unless your approach angle is flat, IE, the no-flaps with power, fly the C172 against the deck situation.
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Old 31st May 2023, 19:47
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Originally Posted by Concours77
That's the way I've been approaching the water entry.
It makes a lot of sense to ship the floats over in the belly of a big rig.
Less drag, and safer ditch if needed...

I think your summary makes sense, keep the nose up as long as possible, hoping when it hit, submergence is in the "shallow angle enough such that it pops back up, instead of pitching the whole business over" domain.

Also, hoping for a tail low aspect, so when the gear enters fully, the Nose coming down will plop, rather than sink and trip the a/c over its nose....(then again, if sufficiently entry vertical, the floats are sturdy enough to absorb alot of energy. Keeping them on for the journey for that reason however, implies alot of defeatism at the outset)

something like that?
Yep, something like that, a vertical splash, with minimal horizontal speed, though this twin otter is reported to be without floats, only regular wheel stuff.

With sufficient vertical speed, the time it takes for the gears to get submerged is less. Once the airplane's belly is on the water, there is a big floating surface at the front, that will take care that the flip-over tilt point will be much further forward, and as such, the energy/impulse required to flip the airplane (IE rotate over its nose) is much higher. As well, the time for the airplane to start the rotation before something else hits the water is much shorter. Add to that, the nose will dig in significantly more shallowly, which will also make the flip-over more difficult.

Still nasty to stop in such a way, though.
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Old 31st May 2023, 19:50
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LeoLake

Originally Posted by Pilot DAR
In a Twin Otter, it's called "Station 60 damage". Sadly common, and easy to do if careless in the flare. Always expensive, and usually done far from home....
Knew what I'd done when the shimmy started... there goes the schedule... I just kept taxiing to maintenance past the tie down. Leo tried to make me feel better about it..."It's not uncommon..."

How Long? "Maybe a week?" There went two Revenue trips to the Bay...

A week later he called, "She's ready..." I walked in to the office past the coat rack, and the Naval flight jacket. "Good news, bad news, Batman. Good news first Leo. "The parts cost $8.50...."
I brightened up. "And labor is $474.50...."

Kidding aside, I am hoping to learn more soon. I believe our two friends would want there to be no mysteries.
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Old 31st May 2023, 19:51
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Originally Posted by Pilot DAR
In a Twin Otter, it's called "Station 60 damage". Sadly common, and easy to do if careless in the flare. Always expensive, and usually done far from home....
When ditching, the airplane would not be my worry. My worries would be how to survive the ditch (initially and later on), and I'd like to use every part of the airplane as a crumble zone ......
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Old 31st May 2023, 19:54
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Originally Posted by Pilot DAR
The Viking/deHavilland Flight Manual for the Twin Otter describes the recommended ditching procedure for the wheelplane in section 3.9.7.
What does it say?
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Old 31st May 2023, 20:57
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Going out with a parachute, personal flotation vest, an emergency locator beacon, and a life raft still seems the best approach and should be included for long over-ocean ferry flights. Nothing good comes from riding it into the waves. I'd rather not be anywhere near a crumple zone if the way to avoid it was to open the door and leave.
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Old 31st May 2023, 23:45
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S

Originally Posted by MechEngr
Going out with a parachute, personal flotation vest, an emergency locator beacon, and a life raft still seems the best approach and should be included for long over-ocean ferry flights. Nothing good comes from riding it into the waves. I'd rather not be anywhere near a crumple zone if the way to avoid it was to open the door and leave.
Sold... Knowing the C130 had your location to within ten feet, and Black Hawk enroute, the chute would be attractive...hoping I don't have to step over a ferry tank...
Spent hundreds of hours fishing the Pacific... once in awhile I would imagine a forced landing.

The ocean moves in mysterious waves....

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Old 1st Jun 2023, 09:28
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Originally Posted by netstruggler
Where does the '..about six hours airborne' figure come from?
This seems to be to most common (and verifiable via ADS-B) reported departure and ditching times. Five hours, fifty-four minutes.

Aviation-Safety.net
The aircraft had departed Santa Rosa-Sonoma County Airport, California (STS) at 15:21 UTC (08:21 local time) on a flight to Honolulu International Airport, Hawaii (HNL).
ADS-B data suggests that the aircraft at some point turned back, heading for HAF, until it crashed at 14:15 local time.
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Old 1st Jun 2023, 12:01
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Yes, unless your approach angle is flat, IE, the no-flaps with power, fly the C172 against the deck situation.
Still... comparing the landing of a 172 and Twin Otter is not a good comparison. The affect of the use of flaps between the two types is very different, and specifically trained during Twin Otter type training.

But neither type suggests an "against the deck..." type landing for the wheelplane. In all cases, the airplane should be flared to a landing. The Twin Otter ditching procedure specifies the use of full flaps, land as normal, and not to stall the plane.

The use of full flaps in a Twin Otter results in very different handling than a full flap 172. Depending upon how either type is wrongly flown to a runway landing, contact of the nosewheel before the mains is possible, and really bad!

As I have said, type specific operation is appropriate, and we should credit the crew with doing their best to fly the airplane using prescribed techniques for the type. Second guessing how they ditched the plane while comparing what they had to do with flying a 172 is not really relevant, nor useful.
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Old 1st Jun 2023, 16:15
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Almost regardless of type, it would be very, very difficult not to Stall, trying to avoid the water til the last second.... Hopefully just as the tailcone kisses the surface, the wing pays off, the a/c flops horizontally onto the sea. And we're grabbing for survival gear, beacon first....

Without power, I don't think that happens. AOA isn't going to be nose high long enough to bleed off speed. Just trying to flare may immediately cause Stall. The airplane has two thirds of the planned fuel load still aboard, and how close is that to normal gross?

Thirty eight miles short, who wouldn't try to extend the flight path to land. My old house is next to that runway, on the Mavericks side... sad, just prayerful sad...rip

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Old 1st Jun 2023, 22:34
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One thing not mentioned so far is the direction of ditching. Over the years there has been quite a bit of debate, especially about ditching smaller aircraft. One side had it that in any noticeable sea state one should ditch along the direction of the waves (swell) to avoid catching a wave top and going nose down into the next one. Certainly when I owned a seaplane in the early 2000s we were concerned that you could hit a wave top, get thrown back into the air at less than flying speed and stall into the sea nose first. Some thought that a smooth entry along a wave top might be better though I don't think the debate was ever settled.
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Old 2nd Jun 2023, 01:54
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one should ditch along the direction of the waves (swell)
Waves and swells are not always the same, there can be waves on swells, which are moving a different direction.

For the Lake LA-4 flight manual:

"Swells: (avoid if possible) Movement: Always parallel, never perpendicular - regardless of wind. "

So, never land/ditch across swells, always along them. If only waves, land/ditch into the wind (which is probably into the waves also).

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Old 2nd Jun 2023, 02:48
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Originally Posted by Pilot DAR
Waves and swells are not always the same, there can be waves on swells, which are moving a different direction.

For the Lake LA-4 flight manual:

"Swells: (avoid if possible) Movement: Always parallel, never perpendicular - regardless of wind. "

So, never land/ditch across swells, always along them. If only waves, land/ditch into the wind (which is probably into the waves also).
There is no "along them". Unless you can predict their velocity, and movement relative to the flight path. They are similar to the deck of the carrier, except not only do they move up and down, they travel sideways....so I'm told....

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Old 2nd Jun 2023, 03:30
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There is no "along them". Unless you can predict their velocity, and movement relative to the flight path
I have been able to predict the "along" of small swells sufficiently to land along the crest for practice, such that the landing was safe. Though that was only a foot or so swell, not the seemingly ten foot swells I have seen in the Pacific off Point Loma! It requires some judgement as to the small acute angle to be flown relative to the swell crest so the plane follows the crest as it moves. Those were short wavelength boat swells rather that longer wavelength open ocean swells I have seen, and fear! If I had to ditch in the open ocean, I sure would be trying to work out that acute angle to the swell crest, as slamming into the water (face of a swell at a near right angle) in an airplane is a much harder stop than it would seem! I have spent a lot of time looking down at ocean from the cockpit of a single, thinking how I would ditch it. In my flying boat, in mild conditions in the nearby lake, I can practice.
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