NEW DELHI: A rat on board Air India ’s Delhi-San Francisco flight delayed it by over nine hours on Sunday.The Boeing 777 was taxiing at IGI airport to operate one of the world’s longest nonstop flights when the rodent was spotted. As per safety protocol, it had to be brought back to the terminal and fumigated. Then with a new crew, the almost-full flight ( AI 173 ) finally took off around noon on Sunday instead of the schedule time of 2.30am.Air India’s new chairman Rajiv Bansal has taken a serious view of this delay. He has sought a detailed report on how the rat managed to get on the aircraft and how this could be prevented in future.The B-777 was almost full with 172 economy and 34 business class passengers.Just when the plane was taxiing, the rat was spotted. By the time fumigation was being done, the maximum flying time for the crew — four sets of pilots are needed for this ultra-long haul flight — or flight duty and time limitations (FDTL) kicked in. The airline had to, at the last minute, look for a replacement crew,” said a source.So while fumigation of the aircraft, to ensure that the rodent is eliminated, was over in six hours, it took time to find two commanders and two copilots for this flight. The combined impact was that the plane took off with a delay of nine hours. Passengers were unhappy at the long delay.An aircraft needs to be fumigated after a rodent is sighted to ensure it is eliminated and does not pose a threat to safety by cutting electric wires and sending the systems haywire. “Rats on board an aircraft can lead to a catastrophe if they start chewing up electric wires of a plane. If that happens, pilots will have no control on any system on board leading to a disaster,” a senior commander said.What usually leads to such a situation is that passengers inadvertently drop a lot of food on the cabin floor, which keeps rats busy. The most common way for rats to get on board an aircraft is through catering vans. “This is a universal phenomenon. Rats follow the large storage cases in which food trays are kept. The catering vans are like a home for them as food keeps getting dropped. Rats get on the high lifts that take those storage cases to aircraft and then remain there. This happens across the world,” said an official.AI flies on the Delhi-San Francisco route over the Pacific, making it the longest flight in terms of distance flown nonstop by a commercial aircraft. The 15,300-km journey covered in 16 to 17 hours needs two sets of crew, with one commander and copilot operating first half of the flight and the other two, the second half. “Taking off with the same crew originally rostered for AI 173 was not possible as their maximum flying duty time would have got over.AI had to look for more pilots and this took additional time,” said a source.