Twin Otter (N153QS) ditches into Pacific Ocean
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CG nightmare
I've flown several crossings from California to/from Hawaii.
The aircraft was loaded with fuel for a ferry flight. The ferry fuel system did not function as designed and could not deliver fuel to the aircraft. The pilots were limited to the fuel in the main tanks, which was the farthest forward fuel most likely.
As a result, as the aircraft exhausted the fuel in the main tanks and the CG moved aft. The aircraft must have been difficult to control (in pitch).
There are pictures of N153QS on floats and wheels. No reliable source has told us if the aircraft was on floats. I agree with those who guess the floats were taken off and shipped.
I ferried a light twin out of Oakland to Honolulu. I can't imagine someone installing a ferry fuel system and then loading up the aircraft with all that fuel before testing the ferry system. That would take a little extra time and money, but it is better than landing a VERY heavy plane loaded with fuel.
This story brings back lots of memories. I'm sure other pilots who have made that crossing have been thinking about this.
Edit: In my original post, I assumed the main fuel tanks on the Twin Otter were in the wings. They are, in fact, in the belly of the aircraft. I have never flown a Twin Otter.
The aircraft was loaded with fuel for a ferry flight. The ferry fuel system did not function as designed and could not deliver fuel to the aircraft. The pilots were limited to the fuel in the main tanks, which was the farthest forward fuel most likely.
As a result, as the aircraft exhausted the fuel in the main tanks and the CG moved aft. The aircraft must have been difficult to control (in pitch).
There are pictures of N153QS on floats and wheels. No reliable source has told us if the aircraft was on floats. I agree with those who guess the floats were taken off and shipped.
I ferried a light twin out of Oakland to Honolulu. I can't imagine someone installing a ferry fuel system and then loading up the aircraft with all that fuel before testing the ferry system. That would take a little extra time and money, but it is better than landing a VERY heavy plane loaded with fuel.
This story brings back lots of memories. I'm sure other pilots who have made that crossing have been thinking about this.
Edit: In my original post, I assumed the main fuel tanks on the Twin Otter were in the wings. They are, in fact, in the belly of the aircraft. I have never flown a Twin Otter.
Last edited by autorough23; 2nd Jun 2023 at 14:52.
I've flown several crossings from California to/from Hawaii.
The aircraft was loaded with fuel for a ferry flight. The fuel system did not function as designed and could not deliver fuel to the aircraft. The pilots were limited to the fuel in the main tanks, which was the farthest forward fuel most likely.
As a result, as the aircraft exhausted the fuel in the mains (wings) the CG moved aft. The aircraft must have been difficult to control (in pitch).
There are pictures of N153QS on floats and wheels. No reliable source has told us if the aircraft was on floats. I agree with those who guess the floats were taken off and shipped, but the aircraft floating inverted suggests the floats might have been on the plane.
IF the aircraft was on floats, AND they were successful in landing on the floats, the CG was so far aft that the aircraft would probably have sank tail first after landing.
I ferried a light twin out of Oakland to Honolulu. I can't imagine someone installing a ferry fuel system and then loading up the aircraft with all that fuel before testing the ferry system. That would take a little extra time and money, but it is better than landing a VERY heavy plane loaded with fuel.
This story brings back lots of memories. I'm sure other pilots who have made that crossing have been thinking about this.
The aircraft was loaded with fuel for a ferry flight. The fuel system did not function as designed and could not deliver fuel to the aircraft. The pilots were limited to the fuel in the main tanks, which was the farthest forward fuel most likely.
As a result, as the aircraft exhausted the fuel in the mains (wings) the CG moved aft. The aircraft must have been difficult to control (in pitch).
There are pictures of N153QS on floats and wheels. No reliable source has told us if the aircraft was on floats. I agree with those who guess the floats were taken off and shipped, but the aircraft floating inverted suggests the floats might have been on the plane.
IF the aircraft was on floats, AND they were successful in landing on the floats, the CG was so far aft that the aircraft would probably have sank tail first after landing.
I ferried a light twin out of Oakland to Honolulu. I can't imagine someone installing a ferry fuel system and then loading up the aircraft with all that fuel before testing the ferry system. That would take a little extra time and money, but it is better than landing a VERY heavy plane loaded with fuel.
This story brings back lots of memories. I'm sure other pilots who have made that crossing have been thinking about this.
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Jet A weighs 6.75 lbs/gallon, water weighs 8.34. So yes, once the full fuel bladders are under water they will float.
I think it is logical to assume they could not access the fuel in the bladders. I don't know if they were able to empty them, but I'm assuming they were not. I could be wrong.
I think the plane is floating upside down because the main fuel tanks are empty. As others have pointed out, I was wrong when I assumed there were fuel tanks in the wings. The main fuel tanks are in the belly, under the floor.
I think it is logical to assume they could not access the fuel in the bladders. I don't know if they were able to empty them, but I'm assuming they were not. I could be wrong.
I think the plane is floating upside down because the main fuel tanks are empty. As others have pointed out, I was wrong when I assumed there were fuel tanks in the wings. The main fuel tanks are in the belly, under the floor.
How do I know this for sure? Because I wrote the AFM and the supplements for the DHC-6 Series 300 and 400. FWIW, I also delivered that aircraft from the factory to the operator when it was new.
A CVR is standard equipment on Series 400 Twin Otters, every one that ever left the factory was equipped with both a CVR and a FDR.
The change in CG between full fuel (with or without wing tanks) and empty fuel is negligible and normally does not need to be considered as long as the fuel load was equal (front/rear) to begin with, and fuel is consumed equally from each tank.
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No, the supplement does not "approve" operations above the certified MTOW of 12,500 pounds. The supplement provides performance data for overweight operations, but it is always the responsibility (and legal obligation) of the operator to obtain written approval for any overweight operations from the appropriate regulatory authority (or authorities, if the flight is international) before conducting such a flight.
How do I know this for sure? Because I wrote the AFM and the supplements for the DHC-6 Series 300 and 400. FWIW, I also delivered that aircraft from the factory to the operator when it was new.
As noted above, there is no factory certification of any kind for overweight operations. The manufacturer provides performance information to enable planning for ferry flights. It is the responsibility of the operator to obtain regulatory approval for each and every overweight flight.
A CVR is standard equipment on Series 400 Twin Otters, every one that ever left the factory was equipped with both a CVR and a FDR.
The main fuel tanks of the Twin Otter are located in the fuselage, below the cabin floor. Optional wing tanks are located at the end of each wing.
The change in CG between full fuel (with or without wing tanks) and empty fuel is negligible and normally does not need to be considered as long as the fuel load was equal (front/rear) to begin with, and fuel is consumed equally from each tank.
How do I know this for sure? Because I wrote the AFM and the supplements for the DHC-6 Series 300 and 400. FWIW, I also delivered that aircraft from the factory to the operator when it was new.
As noted above, there is no factory certification of any kind for overweight operations. The manufacturer provides performance information to enable planning for ferry flights. It is the responsibility of the operator to obtain regulatory approval for each and every overweight flight.
A CVR is standard equipment on Series 400 Twin Otters, every one that ever left the factory was equipped with both a CVR and a FDR.
The main fuel tanks of the Twin Otter are located in the fuselage, below the cabin floor. Optional wing tanks are located at the end of each wing.
The change in CG between full fuel (with or without wing tanks) and empty fuel is negligible and normally does not need to be considered as long as the fuel load was equal (front/rear) to begin with, and fuel is consumed equally from each tank.
I appreciate your knowledge of the Twin Otter in this discussion.
In my comment, I was assuming the Twin Otter had ferry fuel bladders in order to have the fuel needed to cover the 2000+ nm flight to Honolulu. The fuel bladders were, presumably, on the floor of the aircraft, and probably extended to the rear of the cabin. If that is true, then as the fuel in the main tanks was consumed the CG would have moved aft.
As others have said, the flight to/from Hawaii from the west coast of the US is the longest over water distance without an alternate on the planet. I have made that crossing 3 times, the last one solo in a light twin.
Thanks for your comment.
Dhc-6-400 technical brochure states endurance 7hr 10min on main tanks.
N153QS was in the air for 5hr 33min, minus ~15mins when they radioed no fuel.
Would 5hr endurance be normal for 140% mtow, or could missing 2hrs be the fuel leak, or aux pump pumping fuel in reverse out of mains ?
N153QS was in the air for 5hr 33min, minus ~15mins when they radioed no fuel.
Would 5hr endurance be normal for 140% mtow, or could missing 2hrs be the fuel leak, or aux pump pumping fuel in reverse out of mains ?
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Dhc-6-400 technical brochure states endurance 7hr 10min on main tanks.
N153QS was in the air for 5hr 33min, minus ~15mins when they radioed no fuel.
Would 5hr endurance be normal for 140% mtow, or could missing 2hrs be the fuel leak, or aux pump pumping fuel in reverse out of mains ?
N153QS was in the air for 5hr 33min, minus ~15mins when they radioed no fuel.
Would 5hr endurance be normal for 140% mtow, or could missing 2hrs be the fuel leak, or aux pump pumping fuel in reverse out of mains ?
Assuming an empty weight of 7700 lbs, with that amount of fuel on board the aircraft would weigh 15,300 lbs or 122% MTOW before pilots and other equipment, less the seats which (I hope) were removed and shipped.
I don't find anything that says the maximum range time aloft is 7 hours 10 min. I see max range of 763 miles. Assuming a speed of 160 kts, that leads to 4.77 hrs aloft. 45 minute reserve, gets you to 5.52 hours.
5 hrs 33 min seems pretty close to those numbers.
I have no experience with this aircraft.
With 4000hr in Twin Otters ill say this (yes its a long tine going nowhere)
Standard Fuel capacity is a little over 2400lb, PT-6's (-27/-34) plan on 600lb/hr all day every day doing utility work low level
at regular MTOW 12,500lb and an high (dont laugh) cruise FL100+ you can get fuel flows down to the 520lb/hr mark.
With a ferry permit the highest weight i've seen was 17500lb, it used a lot of runway and a lot higher than usual take off speed. If you lost one on departure then close the other throttle and land ...... wherever that is. Our ferry kit in the day was a wood base with the cut out for a bunch of 44 gal drums connected by 2 inch hose that fed a manifold into the two under floor tanks.
Any ferry was preceded by a flight test to ensure the ferry set up would work and there were no blockages. Usually we would climb on the mains for 90 min after departure then open the feed on the ferry tanks and see if the fuel gauges increased, if not we'd turn back.
My opinion in this case is for whatever reason the ferry set up would not feed the main tanks, The crew exhausted there mains and were screwed after that.
Standard Fuel capacity is a little over 2400lb, PT-6's (-27/-34) plan on 600lb/hr all day every day doing utility work low level
at regular MTOW 12,500lb and an high (dont laugh) cruise FL100+ you can get fuel flows down to the 520lb/hr mark.
With a ferry permit the highest weight i've seen was 17500lb, it used a lot of runway and a lot higher than usual take off speed. If you lost one on departure then close the other throttle and land ...... wherever that is. Our ferry kit in the day was a wood base with the cut out for a bunch of 44 gal drums connected by 2 inch hose that fed a manifold into the two under floor tanks.
Any ferry was preceded by a flight test to ensure the ferry set up would work and there were no blockages. Usually we would climb on the mains for 90 min after departure then open the feed on the ferry tanks and see if the fuel gauges increased, if not we'd turn back.
My opinion in this case is for whatever reason the ferry set up would not feed the main tanks, The crew exhausted there mains and were screwed after that.
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With 4000hr in Twin Otters ill say this (yes its a long tine going nowhere)
Standard Fuel capacity is a little over 2400lb, PT-6's (-27/-34) plan on 600lb/hr all day every day doing utility work low level
at regular MTOW 12,500lb and an high (dont laugh) cruise FL100+ you can get fuel flows down to the 520lb/hr mark.
With a ferry permit the highest weight i've seen was 17500lb, it used a lot of runway and a lot higher than usual take off speed. If you lost one on departure then close the other throttle and land ...... wherever that is. Our ferry kit in the day was a wood base with the cut out for a bunch of 44 gal drums connected by 2 inch hose that fed a manifold into the two under floor tanks.
Any ferry was preceded by a flight test to ensure the ferry set up would work and there were no blockages. Usually we would climb on the mains for 90 min after departure then open the feed on the ferry tanks and see if the fuel gauges increased, if not we'd turn back.
My opinion in this case is for whatever reason the ferry set up would not feed the main tanks, The crew exhausted there mains and were screwed after that.
Standard Fuel capacity is a little over 2400lb, PT-6's (-27/-34) plan on 600lb/hr all day every day doing utility work low level
at regular MTOW 12,500lb and an high (dont laugh) cruise FL100+ you can get fuel flows down to the 520lb/hr mark.
With a ferry permit the highest weight i've seen was 17500lb, it used a lot of runway and a lot higher than usual take off speed. If you lost one on departure then close the other throttle and land ...... wherever that is. Our ferry kit in the day was a wood base with the cut out for a bunch of 44 gal drums connected by 2 inch hose that fed a manifold into the two under floor tanks.
Any ferry was preceded by a flight test to ensure the ferry set up would work and there were no blockages. Usually we would climb on the mains for 90 min after departure then open the feed on the ferry tanks and see if the fuel gauges increased, if not we'd turn back.
My opinion in this case is for whatever reason the ferry set up would not feed the main tanks, The crew exhausted there mains and were screwed after that.
I'm struggling with what the pilots went through when they knew they could not feed from the ferry system. They went too far into their ferry flight before they discovered they were not feeding from the ferry fuel system. Based on the math in my last post, it seems pretty clear they flew the mains dry. Not being able to get out of the aircraft after ditching is puzzling, but perhaps there was not much attention paid to securing the fuel bladders. If that was the case, then when they ditched the bladders may have come forward and trapped them or rendered them unconscious.
It is all very sad.
I'm not familiar with that figure, and it doesn't sound sensible to me.
The main fuel tanks on the Twin Otter hold approximately 2,400 pounds of fuel. Fuel burn in normal cruise is about 540 to 560 PPH (series 300 or Series 400, no difference). That gives you a 4 hour aircraft with 45 minutes (VFR) reserves left at the end of the 4 hours. Expressed another way, it's a 600 NM aircraft (750 NM with wing tanks).
It might be possible to keep the aircraft in the air for 7 hours 10 minutes when operating at a power setting that gives maximum endurance (maximum time aloft), but I can't think of any reason why an operator would do that other than perhaps a military operator using the aircraft for surveillance of a stationary object.
The main fuel tanks on the Twin Otter hold approximately 2,400 pounds of fuel. Fuel burn in normal cruise is about 540 to 560 PPH (series 300 or Series 400, no difference). That gives you a 4 hour aircraft with 45 minutes (VFR) reserves left at the end of the 4 hours. Expressed another way, it's a 600 NM aircraft (750 NM with wing tanks).
It might be possible to keep the aircraft in the air for 7 hours 10 minutes when operating at a power setting that gives maximum endurance (maximum time aloft), but I can't think of any reason why an operator would do that other than perhaps a military operator using the aircraft for surveillance of a stationary object.
I've done dozens of intercontinental ferry flights with the factory ferry fuel system installed. The most prudent way to manage fuel is to replenish the main tanks - by gravity feed - from the ferry system before reaching any PNR along the route.
Other ferry fuel systems, different from the factory system, have been used by operators and ferry service providers. These Rube Goldberg setups use bladders and an electric pump to transfer fuel, rather than the stainless steel drums and gravity flow that the factory system uses. I have never seen an accident report that cited "failure of gravity" as an accident cause.
https://www.vikingair.com/twin-otter...al-description
Maximum endurance paragraph
Maximum endurance paragraph
If a ferry is 'only' 40% over certified MTOW, it is unlikely that pilots would use max endurance power. Time to climb and best cruise altitude would be compromised. They require extra power until they burn fuel down to normal weights. Thereafter, power selected would typically be best RANGE (not endurance).
Ditto with brochure airspeeds - overweight ferries never achieve these (at least not until down to normal weight).
Last edited by Mach E Avelli; 3rd Jun 2023 at 10:48.
A CVR is standard equipment on Series 400 Twin Otters, every one that ever left the factory was equipped with both a CVR and a FDR.
CAN BE FITTED I believe is the exact wording used in the -400 AFM for both devices.
As noted above, there is no factory certification of any kind for overweight operations.
(BTW, Something in inverted commas/quote marks, such as "Factory Certified" normally can be taken to be a generalisation.)
https://media.giphy.com/media/qs6ev2pm8g9dS/giphy.gif
My comment was more directed at the fact the Twin Otter is one of the few types IME that actually published a ferry system in the AFM (B-N Islander is another). And (as you wrote it) the DHC-6-400 does mention this in Section 7 Systems in the AFM as well as further information in a supplement.
