The reason why he took off initially is likely due to the ground effect. It's basically an…

The reason why he took off initially is likely due to the ground effect. It's basically an phenomena where the airplane creates a high pressure cushion between the ground and wings, giving it initial (fake) lift. However, when the aircraft leaves the close proximity of the ground, this lift disappears completely. Considering the airplane did not fly very high to begin with, may suggest this phenomina was partially to blame (considering the flaps where up, they did not manage to create enough lift to sustain the flight). Several cargo aircraft have already been lost due to overloading, yet they managed to take off initially because of this lift effect.

(Note: There are a seperate class of vehicles using this effect called GEV's (Ground effect vehicles). Look it up it's actually really cool.)