A Chicago-bound Air India Boeing 777-300ER returned to Delhi three hours after take off following a technical snag early on Monday. According to sources a defect in the aircraft transponder, a device which helps air traffic controllers in identification of an aircraft, forced the Air India commander to return to Delhi at around 5 a.m. No emergency was declared and all passengers were deplaned safely on arrival.

Apart from technical reasons the flight to Chicago was delayed as an alternate set of pilots and cabin crew was not immediately available to operate the plane. Pilots and cabin crew are governed by flight duty rules which stipulates number of hours which can be flown by them in a duty period. The plane's return to Delhi led to the airline managers seeking an alternate crew who are on stand by to operate the flight but since adequate number were not available the flight was delayed.

An Air India spokesperson did not respond to a SMS seeking comments.

In January an Air India Boeing 787 on a London-Delhi flight had to return to London after a problem in its transponder. "Transponder issues are plaguing both Boeing 777 and Boeing 787,'' an Air India official remarked.