Twin Otter Crash May 20, 2023

[J31]

https://aviation-safety.net/database/re ... 20230520-0

A DHC-6 Twin Otter 400, N153QS, crashed into the Pacific Ocean about 54 km west of the Half Moon Bay Airport (HAF), California.
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.

[W5]

With pic.
https://www.avweb.com/aviation-news/twi ... ingID=1353

[FL030]

Are those Kenn Borek colors?

[porcsord]

No, not Borek.

It's a corporate Twin Otter that operates out of Fiji by Southern Cross.

[Meatservo]

Oh dear. Sounds like maybe an engine failure with ferry tanks nearly full, unable to maintain level flight due to weight. Hope they're OK.

[porcsord]

From a few reliable sources:

Aircraft was on the California- Hawaii leg of a ferry, the ferry system for whatever ever reason did not provide fuel, and they ran out of fuel pretty much exactly at the point you'd expect (time wise) from full belly and full tip tanks. Unfortunately the turn around happened after the PNR.

I can't imagine how terrible the last several hours of that flight were, and how the last you'd ever want is to have to ditch with 6k+ Lbs of unaccesible fuel in the bladder.

[digits_]

From a few reliable sources:

Aircraft was on the California- Hawaii leg of a ferry, the ferry system for whatever ever reason did not provide fuel, and they ran out of fuel pretty much exactly at the point you'd expect (time wise) from full belly and full tip tanks. Unfortunately the turn around happened after the PNR.

I can't imagine how terrible the last several hours of that flight were, and how the last you'd ever want is to have to ditch with 6k+ Lbs of unaccesible fuel in the bladder.

Do you know why they waited so long before attempting to use the ferry fuel?

[porcsord]

Unfortunately I don't have any more information.

[Capt. Underpants]

The standards for the design of ferry fuel systems aren't exactly robust and there's a reason why most could never be certified for passenger operations. It's also possible that the system started out working just fine and then failed later on well past the PNR, similar to the PC12 crew that ditched successfully northeast of Hawaii last year.

[pelmet]

One should get on the ferry tank fuel as soon as reasonably possible. I ferried a Trinidad across the Atlantic for the manufacturer and that is what I did.

As an example.....Use some from the mains(but not too much) to start, then transfer from the ferry tank to the mains to make sure it works and get towards full again, then stop transferring to prevent overflow and repeat. At minimum, do the first transfer fairly soon so that you don't discover a transfer problem without the ability to divert somewhere, such as where you departed.

Probably not a bad idea, even if one is not using a ferry tank but has aux tanks.

[cncpc]

I'm not sure how a turbine aircraft handles this, but I do know in every piston aircraft with aux tanks or ferry tanks that I ever flew, you had to make space in the main tank for the excess fuel returned to the main from the total amount delivered to the engine. In all cases, I think you flew an hour on mains, and could then initiate draw from auxes or a ferry system.

Not sure, but in my limited turbine operation (J32/32) I don't recall anything about whether or not the engine took all the fuel coming at it.

[CLguy]

They were about 2 hours off the coast when they tried to transfer. For whatever reason, it wouldn’t transfer so they turned back. Got within 35 miles off the coast and ended up ditching into the sea. Neither guy survived the ditching.

[cncpc]

One should get on the ferry tank fuel as soon as reasonably possible. I ferried a Trinidad across the Atlantic for the manufacturer and that is what I did.

As an example.....Use some from the mains(but not too much) to start, then transfer from the ferry tank to the mains to make sure it works and get towards full again, then stop transferring to prevent overflow and repeat. At minimum, do the first transfer fairly soon so that you don't discover a transfer problem without the ability to divert somewhere, such as where you departed.

Probably not a bad idea, even if one is not using a ferry tank but has aux tanks.

It's a good idea.

[goldeneagle]

The linked photos online show the aircraft on amphibs. Does anybody know if it was on the floats, or on wheels for the ferry flight ?

[TrilliumFlt]

In a former life I ferried many airplanes including Twin Otters. It has by far the simplest and as close to fool proof as possible. Its a gravity feed directly into the main fuel tanks and thereafter its the airframe system that feeds the engines.

[TailwheelPilot]

The linked photos online show the aircraft on amphibs. Does anybody know if it was on the floats, or on wheels for the ferry flight ?

http://www.twinotterarchive.com/DHC-6_8 ... 4092013_02 says in 2013 it did the Pacific crossing on wheels to Tahiti, French Polynesia then went on floats before continuing to Fiji, where it seems to have been based.

It was photographed in March 2022 on wheels in Tahiti and in August 2022 on wheels in Atlanta. Supposedly in the South Pacific until 2022...perhaps back to wheels for the flight back to the US in March 2022. Somewhere I saw it was busy in the Caribbean and Central America more recently, but I have not seen anything about it being on wheels or floats.

https://www.twinotterworldseries400.com/msn-869 (last photo is in Tahiti)
https://www.planespotters.net/photo/131 ... twin-otter (in Atlanta)

I saw an ADS-B Exchange screenshot in one news article showing 150-160 knots outbound and 130 return. From my limited exposure to Twin Otters that seems like it is on wheels, but I may be wrong.

[albertdesalvo]

People on other well known aviation forums have stated the floats were removed for this flight. Seems reasonable, but the posters have questionable credibility. Would be nice to hear from someone who really knows something.

Bad break for Viking.

[groncher]

The Twin Otters I am familiar with used two ferry tanks, and each one gravity fed into the mains, they were plumbed together, but one fed the front and one the aft. I think this is a pretty common system, but i have no knowledge of what this aircraft had.

You would burn a bit from the mains (an hour or so if i recall) and then open the taps. The mains qty indication would pretty much stay stable while the ferry tanks were gravity feeding. At some point the gravity feed would slow down and you would pressurize the ferry tanks with a bleed air source and this would help push the last of the fuel into the mains.

It was a pretty bullet proof system, with one exception. If you don't know what you are doing and you apply the bleed air to the tanks too soon or apply too much pressure, the fuel would vent out the wing vents. I would keep my eyes out the windows, and if anything started to vent would shut off the air supply.
I had a colleague on a ferry flight once who asked for ferry fuel and the AME in the back opened the taps and turned on the bleed air right away...both tanks vented overboard. Fortunately this happened before they were over water.

No idea what happened here but condolences to the families of those lost.

[groncher]

double post

[porcsord]

A few points.

Firstly, there is no way they were ferrying to Hawaii with amphib floats on. Even with the largest of furl bladders, it wouldn't have have the range.

As for ferry systems, there are a few different options. The original system is a series of 9 drums daisy chained together and piped to the front a rear main tanks. This system doesn't provide enough fuel for a Hawaii crossing.

There are rigid tanks, which function roughly the same way, except there are two of them. I'm not sure on the capacity as I've never used them.

Finally there are bladder systems. These are lighter, but every one I've seen requires fuel pumps which are run off ship power. They are independent of the boost pums. The system I used had 4 independent pumps and I want to say that 2 could keep up with fuel burn of the engines.

Then there is the power setting, for best range, it's quite throttled back, so I'm not surprised to see well under 150kts, even on wheels.

There's also one other catch, the -6 has performance charts for single engine best range (its further than with 2), HOWEVER at ferry weights, the airplane can't maintain altitude on one engine.