Mumbai/Kolkata, June 18 -- Troubles continued at Air India, which is facing the biggest crisis since Tata group bought the airline three and a half years back, with its flights to London and Paris on Tuesday being cancelled for varied reasons and a glitch forcing fliers on San Francisco-Mumbai flight to deplane during a stopover. While Air India cancelled the Delhi-Paris flight after some problems were detected during pre-flight checks, its Ahmedabad-London one was cancelled due to unavailability of aircraft, the airline said. Separately, Air India terminated its San Francisco-Mumbai flight at its scheduled stopover at Kolkata early on Tuesday morning after one of its engines developed a technical snag. In a statement, Air India said flight AI143 from Delhi to Paris has been cancelled after "mandatory pre-flight checks identified an issue which is being presently addressed".It did not detail the issue that came to light during pre-flight checks. "However, in view of the flight coming under the restrictions on night operations at Paris Charles de Gaulle (CDG) airport, the said flight has been cancelled," Air India said. The airline, which on Monday resumed flights from Ahmedabad to London Gatwick with a new code AI159 instead of AI171 of the flight that crashed on June 12, had to cancel the flight on Tuesday due to unavailability of aircraft. It denied claims that a technical snag led to the cancellation and maintained that it has made alternative arrangements for the affected passengers to their destination and offered full refunds on cancellations or complimentary rescheduling if opted by them....