Replacing Allanshill Radome Summer 2018

Over the summer NATS completed a major civil engineering project to replace the radome at Allanshill radar station.

What is a radar station?

A critical part of national infrastructure, radar stations are used to locate and safely guide the 2.6 million aircraft that fly through controlled UK airspace every year.

In air traffic control, it is standard international practice to monitor airspace using two radar systems – primary and secondary. The use of radar assists controllers in their main task of ensuring safe separation between aircraft. There are radar sites at many airports around the country and at other strategic sites such as Allanshill. These ensure that the controllers who work at the various units around the UK receive the best possible picture and information from the radar network.

A map of our radar stations in the UK

These systems transmit pulses of radio frequency (RF) energy in the direction the rotating antenna is facing. If an object is on the path of the pulses, a proportion of energy is reflected back. The aircraft’s position is then derived by combining the time for the RF energy to hit the aircraft and bounce back, along with the angle the antenna was facing at the time of transmission. Equipment on board the aircraft will reply with encoded information such as the aircraft’s identity, height and the pilot’s intention to aid the controller’s awareness.

Many of the stations are in the country's most remote and inaccessible locations, making the radome (the golf ball-like structure) hugely important because it protects and conceals the radar antenna.

The existing radome at Allanshill was installed in 1993 and had begun showing severe signs of weathering.

In 2014, a radome of similar age in Lowther Hill, Scotland, was destroyed in high winds, causing damage to the radar and surrounding land. The project to replace the Allanshill Radome mitigated the risk of something similar happening there too.

The north of Scotland (Aberdeenshire to be precise) coastal location of Allanshill is notoriously windy, and an activity such as removing and replacing a radome can only be undertaken in the calmest of conditions.

This meant that the project had to be planned to complete during the summer months, a time when the weather should be at its best, but also when air traffic is at its highest - so minimal down-time was essential.

Allanshill sees a lot of extreme weather

Allanshill's purpose is to monitor the progress of mostly civilian airways traffic. It also provides a deconfliction service with the military air traffic in the area.

To reduce the outage time, the new radome was partially assembled at ground level before the radar was turned off.

This allowed access to the old radome for careful dismantling and removal around the surveillance antennas, and for the new Allanshill radome to be assembled and lifted into place.

The new radome was gently lowered over the antenna which remained in place throughout. This intricate process of lifting and lowering the radomes into position can only be done at wind speeds of less than 5mph so the warm summer weather helped ensure the lift was successful first time!

The old radome being lifted off
The old radome being lowered to the ground
The new radome being lifted on to it's base via crane

Allanshill radar was returned into operational service right on schedule on 4 September and is already demonstrating increased surveillance performance.

Noel McKinney, NATS' Head of Technical Services in Facilities Management, said:

I would like to thank everyone involved in this project. The timings were incredibly tight but the team really pulled together to ensure the whole schedule didn’t miss a beat, delivering a job to be proud of.

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