Twin Otter (N153QS) ditches into Pacific Ocean
The factory manual has a supplement that approves 40% overweight and the aircraft is more than capable of flying at this weight, especially with the -34 engine variants in the -400 model.
I recently (within the last month) turned back from 4 hours out of Hawaii in a Twotter with a failed oil seal on one engine, necessitating a shut down two hours out. At about 3000lbs still over MTOW and unable to maintain height, we started a drift down while pumping ferry fuel to fill the main tanks and then overboard to reduce weight. We levelled off at around A070, however if the ferry pumps were inoperative, I would have been opening the rear door (starboard - hinged on the forward edge) and either disconnecting hoses from the pumps and hanging them out the door to gravity bleed or cutting one or more tanks open.
I recently (within the last month) turned back from 4 hours out of Hawaii in a Twotter with a failed oil seal on one engine, necessitating a shut down two hours out. At about 3000lbs still over MTOW and unable to maintain height, we started a drift down while pumping ferry fuel to fill the main tanks and then overboard to reduce weight. We levelled off at around A070, however if the ferry pumps were inoperative, I would have been opening the rear door (starboard - hinged on the forward edge) and either disconnecting hoses from the pumps and hanging them out the door to gravity bleed or cutting one or more tanks open.
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RIP, what an awful situation to be in.
With fixed undercarriage, rather than floats, is it possible to ditch without the 'plane violently flipping nose down as soon as the main wheels touch the water?
With fixed undercarriage, rather than floats, is it possible to ditch without the 'plane violently flipping nose down as soon as the main wheels touch the water?
The factory manual has a supplement that approves 40% overweight and the aircraft is more than capable of flying at this weight, especially with the -34 engine variants in the -400 model.
I recently (within the last month) turned back from 4 hours out of Hawaii in a Twotter with a failed oil seal on one engine, necessitating a shut down two hours out. At about 3000lbs still over MTOW and unable to maintain height, we started a drift down while pumping ferry fuel to fill the main tanks and then overboard to reduce weight. We levelled off at around A070, however if the ferry pumps were inoperative, I would have been opening the rear door (starboard - hinged on the forward edge) and either disconnecting hoses from the pumps and hanging them out the door to gravity bleed or cutting one or more tanks open.
I recently (within the last month) turned back from 4 hours out of Hawaii in a Twotter with a failed oil seal on one engine, necessitating a shut down two hours out. At about 3000lbs still over MTOW and unable to maintain height, we started a drift down while pumping ferry fuel to fill the main tanks and then overboard to reduce weight. We levelled off at around A070, however if the ferry pumps were inoperative, I would have been opening the rear door (starboard - hinged on the forward edge) and either disconnecting hoses from the pumps and hanging them out the door to gravity bleed or cutting one or more tanks open.
A close friend of mine who remained in the business (long after I saw the light) had to shut down one engine on a F 27 ferry. When it became obvious that they couldn’t make it, they depressurised and he opened both rear doors. He took to the aluminium ferry tanks with the crash axe. The owner got his aeroplane back.
My mate’s next project was to design a dump system for the F27.
But this one doesn’t appear to be an engine problem - at least not while they still had some fuel available - rather a problem of ferry fuel not transferring. I imagine they initially concentrated on troubleshooting. It would be hard to deliberately dump fuel from one source when you are seriously short of the stuff elsewhere.
While surplus weight wouldn’t have been helpful in the ditching, dumping was unlikely to have got them to an airfield. A bit closer perhaps. If the sea is rough in deep water it’s often worse in shallow water, so the outcome could well have been the same, regardless of weight.
Or maybe they did dump? We don’t know. Does that model Twotter have a CVR?
Armchair speculation turned off now.
Last edited by Mach E Avelli; 24th May 2023 at 11:13.
In practice, so much depends on sea state. Beam on, a two metre wave can roll a ten metre boat doing six knots and designed to take stresses imposed by the sea. Head on it can sometimes break stuff on deck. I’ve seen strong stainless steel rails bent and a heavy canvas dodger completely demolished simply by a boat being knocked down at 8 knots. So, we can only speculate about what happens when a flimsy aluminium box or tube gets smacked by a wave at 60 knots.
Two metre waves are not considered all that rough. A fixed main gear could pitch an aircraft down right into the face of that two metre wave. Waves don’t always come at a constant angle, could be opposing swell or at 90 degrees to it etc. If the general sea state is two metres, it is likely that occasionally waves will reach three metres. So, while the advice about ditching parallel, on the back face blah blah is useful to know, it’s not always achievable. At speed, a wave could smash the windscreen, dump a couple of tonnes of water into the cockpit, knock out the crew. And so on…
Last edited by Mach E Avelli; 24th May 2023 at 12:19.
In similar circumstances I would do the same.
A close friend of mine who remained in the business (long after I saw the light) had to shut down one engine on a F 27 ferry. When it became obvious that they couldn’t make it, they depressurised and he opened both rear doors. He took to the aluminium ferry tanks with the crash axe. The owner got his aeroplane back.
My mate’s next project was to design a dump system for the F27.
But this one doesn’t appear to be an engine problem - at least not while they still had some fuel available - rather a problem of ferry fuel not transferring. I imagine they initially concentrated on troubleshooting. It would be hard to deliberately dump fuel from one source when you are seriously short of the stuff elsewhere.
While surplus weight wouldn’t have been helpful in the ditching, dumping was unlikely to have got them to an airfield. A bit closer perhaps. If the sea is rough in deep water it’s often worse in shallow water, so the outcome could well have been the same, regardless of weight.
Or maybe they did dump? We don’t know. Does that model Twotter have a CVR?
Armchair speculation turned off now.
A close friend of mine who remained in the business (long after I saw the light) had to shut down one engine on a F 27 ferry. When it became obvious that they couldn’t make it, they depressurised and he opened both rear doors. He took to the aluminium ferry tanks with the crash axe. The owner got his aeroplane back.
My mate’s next project was to design a dump system for the F27.
But this one doesn’t appear to be an engine problem - at least not while they still had some fuel available - rather a problem of ferry fuel not transferring. I imagine they initially concentrated on troubleshooting. It would be hard to deliberately dump fuel from one source when you are seriously short of the stuff elsewhere.
While surplus weight wouldn’t have been helpful in the ditching, dumping was unlikely to have got them to an airfield. A bit closer perhaps. If the sea is rough in deep water it’s often worse in shallow water, so the outcome could well have been the same, regardless of weight.
Or maybe they did dump? We don’t know. Does that model Twotter have a CVR?
Armchair speculation turned off now.
No CVR on DHC-6.
Thanks Capt for sharing your experiences.
Although not mentioned, the very first adsb report on the way back is showing altitude of ~16000ft with about 1.5hr gap, then slow but constant descent on the way back.
Could they be affected by hypoxia?
Although not mentioned, the very first adsb report on the way back is showing altitude of ~16000ft with about 1.5hr gap, then slow but constant descent on the way back.
Could they be affected by hypoxia?
Yes indeed, hypoxia is a possibility and could explain why they were late in realising their predicament. Without a CVR, any investigation will have to rely mostly on ATC tapes and tracking to get an idea of what they were doing
It is quite normal to transfer the ferry fuel into the main tanks in order to get increased range.
But if the transfer pump system is not working as required it all turns very bad.
For any ferry tank system it needs to be double checked on the ground before the ferry departure date and again in the air before reaching the PNR.
This prang sounds like that but we will await the finding of the NTSB/FAA in xxx months time.
At least the aircraft wreck is to be recovered.
R
But if the transfer pump system is not working as required it all turns very bad.
For any ferry tank system it needs to be double checked on the ground before the ferry departure date and again in the air before reaching the PNR.
This prang sounds like that but we will await the finding of the NTSB/FAA in xxx months time.
At least the aircraft wreck is to be recovered.
R
If I was screwed for fuel in a Twin Otter, I would shut an engine down at altitude to conserve fuel. Never done it, however I have considered it on one occasion when things got a little tight due to unexpected circumstances in PNG.
I would assume that the pilots were on supplemental oxygen above 14,000 ft, if not at least one pilot.
The Twin Otter has collector tanks that must have fuel in them at all times to prevent fuel starvation. The normal system is dependent on flapper valves and motive venturi valves to provide a positive fuel pressure to the tank boost pumps, which supports the engine driven pumps, hence the reason why the boost pumps are turned on for take-off and landing.
Last edited by Duck Pilot; 25th May 2023 at 22:04.
The Twin Otter has collector tanks that must have fuel in them at all times to prevent fuel starvation. The normal system is dependent on flapper valves and motive ventures to provide a positive fuel pressure to the tank boost pumps, which supports the engine driven pumps, hence the reason why the boost pumps are turned on for take-off and landing.
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Is loading an aircraft to the maximum 140% of mtow a normal ferry practice ?
Surely they don't need additional 1000gals of ferry fuel on top of existing 374gals in the main tanks for ~13hrs flight.
Surely they don't need additional 1000gals of ferry fuel on top of existing 374gals in the main tanks for ~13hrs flight.
Over 2200nm from California to Hawaii. Longest overwater leg without anywhere that doesn’t have somewhere to divert to. 358 USG useable gets you around mid 700nm. I’ll load two 400 USG and a 160 USG turtle-pac for this leg. At 40% over MTOW the Twotter is about the only GA level aircraft that is “factory certified” to carry this amount. 15 hours on the wing. Two pilots dead. Welcome to the world of ferrying…
That's certainly not the case on twin turbofan powered aircraft.
It worked for me once on a Metro ferry (adverse winds) and on another occasion with a F27when painted into a bit of a corner in Yemen (promised fuel not available at Hodeida). Depends much on weight.
It's not just twins - there have been cases of 747s that lost an engine shortly after takeoff that had to divert when they had insufficient fuel to reach their original destination.
Every ETOPS twin in the world burns more fuel with an engine out - the windmill drag is larger than any efficiency gain on the 'good' engine (and due to the shape of the TSFC 'bucket', it's highly unlikely that a turbofan run at or close to Max Con will have a better TSFC than at a normal cruise power setting). That's why they need to carry extra fuel reserves on ETOPS sectors.
It's not just twins - there have been cases of 747s that lost an engine shortly after takeoff that had to divert when they had insufficient fuel to reach their original destination.
It's not just twins - there have been cases of 747s that lost an engine shortly after takeoff that had to divert when they had insufficient fuel to reach their original destination.
I get it that today's monster twins with wing mounted engines would have a huge drag penalty with one windmilling, but what about rear fuselage mounted narrowbodies and bizjets? Having flown a couple of these, asymmetric forces don't seem high and not much rudder trim is needed.
I also get it that a B747 (and most other quads, probably) would be range-challenged if one were to quit soon after takeoff at max weight, but at mid weight in the cruise?
You did initially suggest extending range by shutting one down wouldn't work for turbofan twins. Now amended to "every ETOPS twin". Not picking, because I don't know the answer; genuine question here.
I've donated all my manuals to a museum, so can't look up the numbers, hence asking, not pontificating (if I had the numbers I would be the first to pontificate...).
Last edited by Mach E Avelli; 26th May 2023 at 06:24. Reason: asking the experts
Ideally the disabled engine is not windmilling - that presents a huge amount of drag compared with a feathered prop. I expect some additional drag from the deflected rudder to compensate for the asymmetric thrust.
It's too bad that parachutes and suitable raft weren't on the equipment list. Picking an open spot in the ocean should be easy enough and it's better to not be involved in the violence of the sudden stop of a small plane in the ocean.
It's too bad that parachutes and suitable raft weren't on the equipment list. Picking an open spot in the ocean should be easy enough and it's better to not be involved in the violence of the sudden stop of a small plane in the ocean.
If we want to take this “should have had X on board” to the ultimate conclusion, ferries would be banned totally. FERRYING IS DANGEROUS. IT IS NOT A GOOD WAY TO BUILD HOURS. It involves flying modified aircraft at way over normal weights for extended periods with few options in an emergency. It is risky. Don’t like the margins, stick with the airlines. Risk is minimised by proper engineering and planning, but it will always be there in this job.
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