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.

India's Directorate General of Civil Aviation (DGCA) issued the order Monday to investigate the locking feature on the fuel control switches of several Boeing models including 787s and 737s.

A preliminary assessment in last month’s disaster focusing on fuel being cut to both engines only deepened the mystery for people grieving loved ones.