Originally Posted by C J Driver
...Most PT6 aircraft I am familiar with (I should say that list does not include the Twotter) have a start limitation, such as three start sequences per hour, or something similar.
The Twin Otter does have a limitation similar to what you describe, but this would not be a factor because the starter cooling limitation only applies to ground operations. Once the aircraft takes flight, all the timers get reset, so to speak, because the limitation only exists because the generator is very tightly cowled and it is very slow to cool down on the ground at zero airspeed.
Once the aircraft takes flight, the generator is more than sufficiently cooled by ram air. Thus, even if the crew were making five minute sectors with ten minute turnarounds, they would not be restricted by the generator cooling limitation.
The limitation for Twin Otter starter use is:
25 seconds on, one minute off;
25 seconds on, one minute off;
25 seconds on, 30 minutes off.
but, as mentioned earlier, as soon as you take flight, everything gets reset to zero again.