TNMOC reveals iconic air traffic control technology

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Tango November Mike Oscar Charlie – they’ve got Pushing Tin working again, but it was Ben and Peter actually

The technology that for decades kept airspace over Southern England safe can now be seen in action in public for the first time ever at The National Museum of Computing at Bletchley Park.

For 25 years the British-designed IRIS investigative radar recording system operated behind closed doors at West Drayton handling millions of aircraft movements without a single incident ever being attributed to an Air Traffic Control failing. With the transfer of Air Traffic Control to Swanwick, the last of the PDP11-based radar stations were decommissioned early in 2008. Two were transferred to The National Museum of Computing where expert volunteers have brought them back to life after many months of diligent reconstruction.

The two large radar displays, affectionately known as the Big Green-Eyed Monster because of their size and remarkable retro appearance, can be viewed for the first time by the public replaying historical recordings of flights in and out of London's Heathrow Airport

“We first saw the IRIS working at West Drayton in 2001 and we immediately knew that we wanted the decommissioned technology as a working exhibit in the museum,” said Kevin Murrell a Director and Trustee of TNMOC. “IRIS finally came out of service in early 2008 and it’s been a major task to rebuild it, but volunteers Ben Trethowan and Peter Vaughan have succeeded in sparking it into life. The final trick was to replace some wiring that had become faulty.

“The reconstruction feat is truly outstanding because these are highly complex systems that were originally put together by experts trained in the intricacies of the technology. TNMOC volunteers Ben Trethowan and Peter Vaughan not only got the DEC PDP11 machines back up-and-running but they also managed the even more difficult task of getting all the radar signal processing and application software working again. And they did this one-off job as dedicated amateur enthusiasts in their spare time!

“The result is a marvellously visual display that complements our existing live Air Traffic Control monitoring system.”

The NATS exhibit is an excellent example of what TNMOC does best: providing a platform for working examples of the best of British technology – in this case 1980s Plessey software that has stood the test of time. Only now is that technology being superseded because of the recent massive increases in computer processing power and the relocation of NATS to Swanwick.

These last two consoles were kept for auditing purposes and used to replay incidents. NATS were very supportive of the Museum’s plans and were careful to keep spares and documents. They allowed Ben Trethowan of TNMOC to watch the dismantling of the machines and, when they were moved to TNMOC at Bletchley Park, Ben and colleague Peter Vaughan expertly reconstructed and restored the system to working order.

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