Ask Captain Lim

Dear Captain Lim,

Can you tell me your thoughts on whether wind affects an airliner in-flight? I was told once that wind direction and speed have no effect on an airplane in-flight except in relation to ground speed and ground track. This information was given to me before we really knew what wind sheer was all about. I also did a Google search and can still find this information today.

If this is really true all the time, then how do we explain the crash of Delta Airlines L-1011 on 2 Aug 1985 as it approached DFW for landing? It apparently flew right through the wind sheer that was encountered during a thunderstorm.

The wind surely did have an effect on this plane as it pushed it right into the ground. Is my thinking on target?

Yours,

TM

Hi TM,

It is indeed true that wind direction and speed have no effect on an airplane in flight except in relation to the ground speed and track.

This statement is correct only when the plane is in the cruising stage and not in the approaching to landing phase. When a plane is about to land, a strong crosswind may blow the plane off the intended center line of the runway. A strong tail wind would cause the landing speed to be excessive. This would cause the plane to run out of the runway! Similarly, fluctuating winds such as those found in the microburst-induced wind shear would cause control and speed problems to a landing aircraft.

This was what happened on August 2, 1985 when a Delta Airlines L-1011 TriStar crashed while on an approach to land at the Dallas-Fort Worth International Airport, killing 8 of the 11 crew members and 128 of the 152 passengers on board.

During the approach to land at 800 feet above ground level, the landing speeds fluctuated wildly due to the wind shear. It jumped from the optimum of 149 knots to 173, then 133 and finally to 119 knots very rapidly.

In trying to avoid a stall, the captain pushed the nose down causing the plane to impact the ground and bounce back into the air. It came down again on top of a vehicle, killing its occupant. The aircraft then skidded onto the airfield, collided with two 4-million US gallon water tanks at a speed of 220 knots and exploded into flames.

Yes, wind shear did have a great impact on the cause of the Delta Airlines TriStar crash.