Air India B773 near Delhi on Mar 10th 2014, transponder failure

An Air India Boeing 777-300, registration VT-ALS performing flight AI-127 from Delhi (India) to Chicago O'Hare,IL (USA) with 313 passengers and 16 crew, was climbing out of Delhi when the crew stopped the climb at FL280 reporting a problem with the transponders. The aircraft descended to FL150, entered a hold to dump fuel and landed safely back in Delhi about 140 minutes after departure.

A replacement Boeing 777-300 registration VT-ALT reached Chicago with a delay of 15.5 hours.