NEW DELHI, July 14 (Reuters) - A preliminary investigation into the crash of an Air India passenger jet last month that killed 260 people raises additional questions about the incident and the investigation is far from over, Air India's CEO said in a memo on Monday.

The CEO of Air India sought to draw a line under rife speculation around the cause of last month's air disaster in Ahmedebad, saying the preliminary investigation had ruled out a mechanical cause for the crash.