Downwind turn to boot !!!!!
If a young pilot, I wonder if his GPS had groundspeed prominently displayed?
Not much is said about ground obstructions, but this is a fine example that I believe had a big impact on the final results.
A heavy plane like a loaded Beaver does not accelerate quickly, it has about 15% less horsepower to weight ratio than a 2000 pound 150 cub. When taking off this beaver had a quartering headwind and turned to give himself a slight downwind...
While low and on the water the winds were obstructed by buildings at TS international and even more from hangars surrounding the lake. Those obstructions block the airflow low, but also push the airflow up- at some point in a climb there will be a windshear where the plane enters the higher velocity undisturbed air above the obstructions. If you are low and slow, facing downwind a all, that shear can be almighty scary; like climbing above the trees and finding a slight tailwind as you try to out climb the trees at the end.
Amongst the other things going on, it appears the climb stopped just above the buildings where that slight wind shear would be.
I don't get a good enough quality of video to see control surfaces, but the plane got slow, which is not a good look for a loaded beaver.
MTV: flap selector should be set to 'down' unless raising flaps, Correct? That is one of the teachings of all the old timers I flew with. But agree that pilots need to think ahead when flying these beasts. The good thing is that unless the windscreen is full of ground, it is close to flap speed, so as soon as you roll into a turn and give a touch of pressure your speed is low enough to start pumping flaps, but you better be pumping quick because that 110 MPH stall is coming.