Air India has apologised and offered a travel voucher of USD 350 each to the passengers of the San Francisco flight that took off from the national capital after a delay of more than 30 hours.

There were 199 passengers in the flight, according to a source.

After a delay of over 30 hours, the flight took off from the national capital at 2155 hours on Friday and landed at San Francisco at 1245 hours (IST) on Saturday. The flight duration was around 16 hours.

"Please allow me to sincerely apologise, on behalf of Air India, for the extended delay in bringing you to San Francisco, which was caused by several technical delays and other operational constraints," Air India Executive Vice President and Chief Operating Officer Klaus Goersch said in a letter to the flight's passengers.

As a gesture of apology, Air India has offered a "travel voucher worth USD 350" for future travel with the airline, the letter dated May 31 said.

The passengers will also have the option to credit the amount instead of using it for travel.

"We are very sorry for this lapse in our service and the inconvenience caused to you," Goersch said in the letter.

The Delhi-San Francisco flight that was originally scheduled to take off at around 1530 hours on Thursday faced an inordinate delay due to various factors, including technical glitch, non-functional air-conditioning system and payload issues.

On Friday, aviation regulator DGCA issued a show cause notice to Air India for some flight delays and failure to take due care of the passengers.

In the show cause notice, the watchdog mentioned the inordinate delay of two international flights -- AI 183 from Delhi to San Francisco on May 30 and AI 179 from Mumbai to San Francisco on May 24.

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