In the NTSB report LAX81FA044 premature lift-off is blamed for the crash. What is pre-mature lift-off?

Answer 1

An airplane will lift off, to an altitude aproximately half it's wingspan in what's called the ground effect. Essentially, the ground effect is a the air underneath the airplane's wing being compressed by the angle of attack and downwash off the top side of the wing, which results in increased air pressure under the wing.

Remember that the airplane flys by accelerating the air over the top of the wing, (Bernouli's Principle,) which reduces the air pressure above the wing and causes higher air pressure beneath it to push it into the air.

Aside from some duncery that I've occasionally seen, a jet aircraft has to be moving through the air at V1, which varies from aircraft to aircraft, and is the speed that the airplane can satisfactorily climb out of the ground effect and continue climbing.

An attempt to continue climbing out of the ground effect without cleaning up the airframe, (flaps and gear up,) can have one of two results, depending on how dumb the pilot is, (and belive me, I've met some total spanners with ATP's;) the aircraft's airspeed will either slow or the wings will stall as the air over the upper surface of the wings is disrupted by the angle of attack

Neither of which is something you wish to have happen in this particular event, should you experience it and have a desire to survive such a cock up.

If you have to clear objects of greater elevation than half your wingspan and the airspeed gets lower, you're going to start descending and will need sufficient runway to settle the aircraft onto and rethink you're loading or flight plan. You don't usually have that in airliners with a lower landing speed than most single engine airplanes consider Vne, (never exceed.)

Runways are typically laid to point the aircraft into the locally prevailing winds for take off and landing, but there's almost aways a crosswind coefficent, which means that one wing will stall before the other does as you yank the nose higher to climb with insufficient speed. This results in the downwind wing stalling before the upwind wing does, and a wing hitting the ground, which also promises numerous fatalties and a mushroom cloud in the vicinity of an airport if not actually on it.

Airplanes that lack sufficient airspeed to climb out of the ground effect at the point of lift off are probably best measured with ballistacs rather than flight parameters.

Answer 2

An aircraft wing and fuselage are engineered with a very specific shape which produce lift under certain circumstances. The primary requirement for lift is sufficient airflow around the wings to cause low pressure above the wing and high pressure below.
(Bernoulli's Law - P + 1/2pV2 = constant) Until an aircraft reaches the minimum velocity for this lift to sufficiently counteract the effects of the aircraft's weight and drag, it will not fly. Now - an aircraft will rotate and lift into the air below this speed, but once out of ground effect, the lift will not be sufficient to support the aircraft. This speed is a dynamic number and a lot of variables go into it - such as aircraft weight, outside air temperature, density altitude ET.

Before every take off three speeds are calculated. These velocities are labeled V1 (decision speed - having to do with runway remaining to effectively stop the aircraft with braking while it is still on the ground) VR (rotation speed - essentially the point that you pull back on the stick and the aircraft can take flight - the speed we are talking about here) and V2 (single engine climb out speed - because pilots always preplan for the worst case scenerio)

What the report is saying is that rotation/take off was attempted prior to reaching the correct VR speed. The speed may have been miscalculated.

Answer 3

Premature lift off is simply trying to make the plane fly before sufficient airspeed is attained to sustain flight.

Answer 4

I would assume the aircraft did not have enough speed to take off in a safe manner considering conditions.

Answer 5

I haven't read the report, but sounds like he rotated prior to reaching V1.