The Directorate General of Civil Aviation is probing how repeated distress calls were made from a private Airbus 319 owned by India's wealthiest man, Mukesh Ambani , when it was not even air-borne. On Monday night at 8.32 pm, Mumbai Air Traffic Control's main tower received a Mayday alert. Even before the ATC officials could understand what was happening, they received another Mayday call six minutes later at 8.38 pm. Mayday is the code used internationally to signal distress or life-threatening situation. The first call to the Surface Movement Control of the ATC reported that the engine was on fire and that the aircraft was in rapid descent.

The plane, the pilot said, was on a Delhi-Lahore-Muscat route. By the time the ATC identified the aircraft by its unique registration number as belonging to Mukesh Ambani, came the second distress call which repeated that the engine was on fire and the Airbus was ditching into the sea. "We contacted the air traffic controls of Delhi and Muscat if they reported an emergency. We also checked with planes flying in that zone if they could see any aircraft with its engine on fire," said a senior ATC official.

When Delhi and Muscat both reported that all operations were normal, and the other planes reported no unusual sighting, the ATC shifted its attention trying to locate the radio frequency of the Airbus from where the distress signals were coming. To their surprise they found the source of the call pointing towards not somewhere up in the sky but the southwest of the airport where the hangars for private jets are.

"We sent a team to verify the aircraft parked there," said the official. The team found the Airbus — the same aircraft that had been gifted by Mukesh Ambani to his wife Nita for her 44th birthday in 2007 — in the hangar but there was no one inside the aircraft. The ATC team after confirming the plane to be the source of the distress calls reported the incident to the Directorate General of Civil Aviation which started its investigation on Tuesday.

According to ATC officials, pilots and maintenance crew routinely check emergency radio systems but "they always notify us in advance so that there is no panic or confusion but that was not done in this case." The entire operation took two hours before calm was restored. "Initial investigations show the pilot was probably checking whether the emergency systems and the radio were functioning. But he forgot to inform the ATC that he was conducting these tests," said a senior DGCA official, close to the investigation. The maintenance of the Ambani Airbus jet is done by Jet Airways with the help of in-house Reliance engineers.

A Jet Airways source corroborated that the pilot was testing the emergency radio systems when the incident occurred, while the aircraft was on ground. Reliance spokesman Tushar Pania also confirmed that the emergency systems were being tested. He, however, said that all the relevant authorities were informed. "It was a regular mock drill to test the emergency systems and the ATC and the DGCA were informed," he said.

THE AIRCRAFT

The Rs 242-crore aircraft was gifted by Mukesh Ambani to his wife Nita in 2007. It is one of the biggest private jets in the country, the other one is owned by beleaguered UB chief Vijay Mallya. The jet is custom-fitted with an office and a cabin with game consoles, music systems, satellite television and wireless communication. It also has a master bedroom, a bathroom with a range of showers and a bar with mood lighting.

EMERGENCY FREQUENCY 121.5 MHZ

The aircraft emergency frequency (also known as guard) is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress. The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD) or VHF Guard. Although the Ambani aircraft used 121.9, the ATC can assign any frequency as emergency or distress.