Expert knowledge would have been needed to disable the transponder on the missing Malaysia Airlines plane, according to the former head of aviation trade body IATA, who said a fight involving the pilot could have taken place in the cockpit. The mystery surrounding the disappearance of Malaysia Airlines flight MH370 deepened after officials said the last radio message from the plane came from the co-pilot who signed off with an informal message of, "all right, good night", adding to fears the plane could have been hijacked. A transponder that sends key information about the flight such as altitude and speed back to air traffic controllers was shut down on the plane without any explanation, creating one of the biggest headaches for authorities. (Read more: Malaysia police probe flight engineer on missing plane)

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But Giovanni Bisignani, the former director general and CEO of International Air Transport Association (IATA), the world airline trade body, told CNBC that technical knowledge would have been needed to disable the device. "It is not easy, it is not something that you click in the cockpit. You have to open a box with a special screw, go in, take cables out. It is not something that is very easy to identify. You have to be an expert," Bisignani told CNBC. Fight on board The Beijing-bound plane was carrying 239 passengers and vanished off the radars of the Malaysian authorities on March 8. Investigators believe the plane was diverted thousands of miles off course, but mystery still surrounds the plane's whereabouts and sequence of events. According to officials, the plane flew at an altitude of 45,000 feet, before descending to 23,000 feet in an erratic flight path. Bisignani said this could be down to a fight in the cockpit. (Read more: MH370 a 'complex' mystery: Air France lead investigator)

"After three minutes that this happened, the plane went up to 45,000 feet, a very risky altitude. What's the reason? A fight on board? Because an experienced pilot who wants to hijack the plane doesn't go at 45,000 feet. So that is something to consider, if it was a fight between the pilot and the co-pilot," he said. Bisignani also suggested a terrorist could have muscled their way in to the cockpit when one of the pilots opened the door. 'Difficult task' An extraordinary search operation is on-going with twenty-six countries collaborating to find the jetliner. It involves teams spanning a vast area from the shores of the Caspian Sea in the north to deep in the southern Indian Ocean. (Read more: Timeline of Flight MH370)

But Malaysian authorities have come under fire for their handling of the situation which has been unclear for many of the families waiting to hear the fate of their relatives. As time goes on, Bisignani said the task of finding the missing jet is only going to get harder. "The problem is that now it's a very difficult task because it has never happened that you have to search for a plan 8,000 kilometers north and 10,000 kilometers south. It is an enormous wide area. I think the international cooperation has been good but it's a really difficult time," he said.