This paper was presented at a meeting of the RIN History of Air Navigation Group held at Shoreham Airport on 20 September 1995. In the paper, Group Captain Johnston tells the story of the distinguished and extraordinary career of his father, Squadron Leader E. L. Johnston. Bound up with this is the brief and glorious, but ultimately tragic, story of the operation and navigation of British airships.

This year marks the twentieth anniversary of the introduction of Concorde into commercial airline service. The first commercial flights were on 21 January 1976 – British Airways from Heathrow to Bahrain and Air France from Paris to Rio via Dakar. Later in that year commercial flights to Washington/Dulles began on 24 May. Services to New York were delayed until 22 November 1977. The first flight of Concorde was some seven years earlier. The prototype took off out of Toulouse on 2 March 1969 and this was followed by 002 from Filton to Fairford on 9 April. At the time it was anticipated that this was the beginning of an era when supersonic flight would be the normal way to travel long distances. Now, in 1996, Concorde is still the world's only supersonic commercial passenger airliner in airline service. This is an extraordinary achievement. The Boeing SST proved to be too ambitious and the programme was halted in 1971 after the United States Government withdrew support, while the Russian TU 144 was beset with problems. One TU 144 crashed at the Paris Air Show in 1973. The aircraft entered internal airline service in December 1975, flying supersonically between Moscow and Alma-Ata, capital of Kazakhstan, carrying mail and freight, but it did not have the range to operate viable intercontinental passenger serives. Certainly by 1985, if not many years before, the TU 144 was out of service.

Whilst unmanned aircraft (UMA) can be said to encompass missiles, targets for weapon training, preprogrammed reconnaissance drones and civilian systems such as radio-controlled models used to carry cameras, for the purpose of this paper we will restrict ourselves to aircraft which are capable of sustaining autonomous flight and accepting navigation commands whilst airborne. The terms applied to unmanned aircraft are variously UMA, remotely piloted vehicle (RPV), Drone and Unmanned Aerial Vehicle (UAV).

The transmissions from GPS and GLONASS navigation satellites include information about the state of those transmissions as perceived by the control centre. In the case of GPS, for example, this information is contained in the data stream in Subframe 1 Word 3. However, with some of the failure conditions that can arise there is a delay of the order of half an hour before this message is altered to signal that a failure exists. A situation can therefore arise when the satellite signals that all is well, whereas in fact it is not. The very high levels of integrity which civil aviation require before satellite navigation can be used with confidence therefore means that the warning messages from the satellite must be augmented by some other form of monitoring. Two alternatives exist: (1) to have a monitor at some fixed and surveyed ground location which broadcasts a warning to the navigating aircraft when there is a malfunction (ground monitoring), or (2) to arrange for the navigating receiver to perform its own internal monitoring, known as receiver autonomous integrity monitoring (RAIM). Each alternative is beneficial in its own way.