Automatic dependent surveillance (ADS) technology is not limited to fixed-wing aircraft. A modified version of ADS has been operating successfully on helicopters in the Norwegian sector of the North Sea since the late 1990s.

In April 1999 it became mandatory for all helicopters operating in this sector to be equipped with modified-automatic dependent surveillance (M-ADS) satellite communication avionics and fly in designated lanes.

The programme was introduced in an effort to improve helicopter safety. Helicopters transport about 1 million passengers in the Norwegian sector of the North Sea, to and from oil installations, but before the introduction of M-ADS around 50% of the flight time was outside radar coverage. As a result, helicopter pilots were required to make voice position reports every 15min when outside radar coverage and operate in a racetrack-type pattern to maintain separation between inbound and outbound traffic.

M-ADS involves the automatic transmission of ADS messages, including helicopter position, ground speed and direction information, to the shore via Inmarsat satellite, allowing air traffic controllers to monitor a flight down to sea level and initiate search operations if the satellite signal disappears.

The programme was the initiative of the Norwegian civil aviation authority and the oil companies, which had long been concerned about the safety of offshore helicopter operations.

The CAA conducted the first trial of ADS on a helicopter in 1992, in conjunction with operator Helikopter Service, Norwegian Telecom, Arinc and Sita. The trial involved the installation of Rockwell Collins avionics and a Ball Airlink antenna on a SikorskyS-61N helicopter operating from Bergen to the oil fields of Statfjord, Gullfaks and Veslefrikk. During the trial 3,000 automatic position reports were transmitted via satellite to the air traffic control centre in Stavanger. Although the trial was successful, the avionics were found to be too cumbersome for helicopters and required modification.

Norwegian defence and aerospace company Kongsberg Aerospace was appointed prime contractor for the programme with responsibility for modifying the equipment to meet the needs of helicopter operations. Size and weight of avionics, antenna installation and effects of rotor blades were all major considerations. Kongsberg concluded that the satcom transceiver needed to be installed in the tail boom and the ADS unit in the electronic bay, with vibration protection for the equipment. Racal Avionics (now Thales) won the contract to supply avionics, comprising a combined satellite data unit, radio frequency unit and a high power amplifier, with Kongsberg developing the ADS unit.

The equipment was tested in two helicopters in 1996 in a programme funded by the CAA, Helikopter Service, Kongsberg and seven oil companies. The project led to implementation in 1999.

Source: Flight International