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High above Britain's railways, Network Rail's 'eye in the sky' helicopter helps protect and maintain its infrastructure. Ed Owen climbed aboard.

For two years now Network Rail has, in partnership with British Transport Police, flown daily missions across its eight UK regions in an attempt to better protect and maintain its infrastructure.

The track operator's Air Operations Unit comprises a twin-engined helicopter, call sign Osprey 6-3, which makes on average two flights a day. These are mainly to check track and overhead cables, but also to ensure the track is free from obstructions.

"There are eight regions. If you imagine Britain divided like a pie, with London at its centre, we spend 10 days in each region, checking the track and cables, but we could also be called away in an emergency," explains pilot Matt Leaver.

Helicopters are expensive to run, but the system is quicker and more cost-effective than track patrols, says Leaver. Using thermal imaging, overhead lines and track glow white-hot from the heat they emit. Areas that are too hot, for example faulty points, or too cold, for example where track heaters are not working, can be spotted easily.

For NCE's run, Osprey 6-3 takes the Thameside Route, following the line from Southend to Fenchurch Street, then over central London to Liverpool Street, following the Great Eastern Main Line to Shenfield via the Olympic park, and finally the Shenfield-Southend line.

The journey in to London is breathtaking but uneventful. A couple of track crews are checked: the high-resolution "spotter" camera can record number plates from white vans parked nearby the rail lines. The position of the crews and the number plates check-out – Balfour Beatty crews – and on we go.

Network Rail mobile operations manager Jason Floyd points out spots where defects in the overhead line had been seen with the thermal imaging camera earlier in the week. He says defects are easy to spot – the clean lines of the track or overhead wire suddenly break up.

On the return into London, something shows up brightly on the thermal imaging camera. On this setting it appears to be a blanket, covering the line – a possible obstruction and a serious concern. Hovering nearby, we cannot see anything with the standard camera. It is not a blanket, but something generating heat, showing-up white. Defective cables under the track, or something dumped on the line are obvious candidates.

A closer look with the spotter camera and a brown tinge can be seen around the track. Something has been dumped over a wall backing onto the line. It is still warm, picked-up by thermal imaging.

Floyd checks to ensure there are no obstructions and sends the GPS coordinates over to ground teams to investigate. The material seems to be sand or earth.

On the approach to Southend there is a second incident. An unidentified crew are at work. "In a worst-case scenario, they could be stealing the cabling," says Floyd. Thefts of Network Rail property – usually copper and other high-value metals – are a serious concern. Leaver says a professional high-point had been catching a team stealing cables near Southampton red-handed last year.

"We followed them back to their hideout. They had 10 strands of cable, each worth around £1,000," he says.

Back on patrol, Floyd is finally able to confirm the crew's identity, the spotter camera can even pick-out names on hard-hats, and move-on.

Osprey 6-3's repertoire is also extending to more specialised planning work, with an engineer in the back directing the flight.

Its first two years in flight have been so successful that the Air Operations Unit has been commissioned by Network Rail to run for at least another five years.

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