One of his achievements was rescuing the reputation of NATS when the delivery of a £337m air traffic control system for the New En Route Centre at Swanwick in Hampshire, was repeatedly delayed.
To cope with the delays, Agnew managed the enhancement of obsolete IBM-based systems, running in an operating environment called Jovial, at the London Air Traffic Control Centre (LATCC) at West Drayton near Heathrow.
In the original NATS business case for the new Swanwick centre it was said that the London Centre was not capable of managing the skies over England and Wales beyond 1996. The aim was for a purpose-built centre at Swanwick, with new air traffic control systems, to take over from LATCC in 1996.
But the systems, built by IBM, Loral and Lockheed Martin, were not ready by 1996 and were repeatedly delayed during the 1990s. So Agnew presided over a major expansion of the London systems, which are still operating today, in parallel with the Swanwick site, which eventually went into live operation in January this year.
Although the London systems had long ceased to be supported by IBM because the hardware and software was so old, Agnew succeeded by early 1999 in making them year 2000 compliant. He told newspapers in January 1999: "It won't just be safe to fly on 31 December 1999, it will be business as usual."
In May 1998 Computer Weekly magazine described Agnew as an "exemplary communicator," although he was working in an organisation that was depicted in an independent audit report in 1999 as not welcoming openness.
An assistant at his office in London said that Agnew has left NATS but will not working as a consultant until July. A spokesman for NATS said Agnew has "left on voluntary terms" following a restructure of the organisation after the events of 11 September. His replacement is Dr Rob Witty who will take a different job title, that of chief technology and programmes officer. Agnew is said to be seeking "new challenges".