New Delhi, Dec. 23 -- An Air India Boeing 777 flying to Mumbai had to return to Delhi airport on Monday after one of its two engines developed a technical snag that required it to be shut down shortly after take-off, prompting the regulator to order a probe into the latest incident involving the airline and its subsidiaries. Pilots observed low oil pressure on the B777-300ER aircraft's right-hand engine during flaps retraction after take-off. The pressure shortly thereafter dropped to zero and the crew shut down the engine and turned back as per procedure, the Directorate General of Civil Aviation said. Officials said the flight took off around 6.10am and returned by around 6.55am. All passengers were safely disembarked and alternative trav...