The aircraft was returning to Bankstown at the completion of a cargo charter flight. Takeoff from runway 35 proceeded normally until the aircraft reached a height of about 90 feet when severe wind shear was encountered, resulting in a high rate of sink. The pilot was unable to prevent the aircraft from settling back onto the runway with the landing gear retracted. The prevailing conditions were conducive to the formation of mechanical turbulence in the lee of nearby mountains. At the time of the accident it was reported there were large fluctuations in the wind velocity at Wollongong aerodrome.