Tracking helicopters outside radar coverage
Feature Articles, Nov  27  2009 (Digital Energy Journal)

- Oil and Gas UK has launched a system to automatically track the location of helicopters when they are outside radar coverage – collecting data from their transponders

UK oil and gas industry association Oil and gas UK, together with the UK’s National Air Traffic Services Ltd (NATS), have built a system to track helicopters going to offshore platforms by their transponder data, when they are outside normal radar coverage.

The helicopters need to be tracked by the control tower when they are outside radar coverage (blue area). Their transponder data is picked up by receivers on North

Sea offshore platforms (pink area is radio coverage

area). This data is then sent back to the control tower

by satellite or fibre optic cable

Radar can be used to track the helicopters up to around 100 miles off the Scottish coast, but most of the platforms offshore Aberdeen are around 200 miles away.

Until now, when the helicopters were outside radar coverage, they reported their positions to Aberdeen air traffic control verbally every 10 minutes or every 20 miles.

This means that if they have an accident just after providing a position report, the authorities won’t know about it until 10 minutes later, and the rescue operation needs to look through 20 miles of sea to find it.

It also means that the helicopter positions are being tracked manually (at Aberdeen, using a system of plastic strips on a board), rather than by computer.

But with the new system, authorities will be able to keep continuous track of the helicopters, with a number of position reports every minute. So if there is a problem and the helicopter stops transmitting, the authorities will have a much more precise idea about where it is – and they will also be able to give its more precise position to nearby helicopters which might be able to provide equipment.

At the same time, the very high frequency (VHF) voice communications networks for communications with helicopter pilots have also been upgraded, with 3 more VHF stations installed.

Concentration: staff at Aberdeen Air Traffic Control track the position

of helicopters going to and from offshore platforms

£5.3m was spent on the multilateration and improved VHF systems. There will also be ongoing cost to support the system and pay for satellite and fibre optic communications from the platform.

Following the helicopter tragedy in Aberdeen on April 1st 2009, a helicopter Accident Issues Task Group has been set up at Oil and Gas UK, chaired by Bob Keiller, CEO of

Production Services Network, an 8,500 employee company headquartered in Aberdeen. Mr Keiller is also co-chairman of Oil and Gas UK.

There are about 90 round trip helicopter flights from Aberdeen each weekday, and there can be 15 helicopters in the air at the same time.

Helicopters go out from Aberdeen airport to the offshore platfoms along fixed routes, with 3 degrees separation between them, (like motorways of the air). Each route is alternatively in bound and outbound – so for two helicopters to be travelling outbound, the closest they can be is 6 degrees apart.

Helicopters normally travel outbound at 3,000 feet (sometimes 1,000 feet) and inbound at 2,000 feet.

SUBHEAD

Multilateration

The system works by calculating the position of helicopters from the variation in time their transponder radio signal reaches at least three different receivers, a process called multilateration.

All helicopters carry transponders which broadcast their call sign and altitude continuously.

Transponder receivers have been installed 16 different offshore platforms, in four clusters of four.

You need 3 receivers to calculate the position of a helicopter - the fourth will provide redundancy.

The data is sent back from the offshore platforms using whatever communications options are available – fibre optic or satellite.

Each receiver has a GPS system, which can provide super-accurate time information. The time the transponder signal was received is sent back to shore together with the transponder information.

The project was in a trial phase during September 2009, to try to work out exactly what coverage is available.

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