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.

An official report on the world’s deadliest aviation accident in a decade, seen by CNN, has answered one key question – but raised others.

All mandatory maintenance tasks, including the pilots clearing the pre-flight breath analyser, had been completed, preliminary report identified no “mechanical or maintenance issues with the aircraft or engines,