Originally Posted by
Bosi72
DHC-6-400 technical brochure states endurance 7hr 10min on main tanks.
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.