Editing Decca Navigator System (section)

=== Dectra ===
In the early 1960s the [[Radio Technical Commission for Aeronautics]] (RTCA), as part of a wider [[ICAO]] effort, began the process of introducing a standard long-range radio navigation system for aviation use. Decca proposed a system that could offer both high accuracy at short ranges and transatlantic navigation with less accuracy, using a single receiver. The system was known as '''Dectra''', short for "Decca Track".{{sfn|Blanchard|1991|p=304}}

Unlike the Delrac system, Dectra was essentially the normal Decca Navigator system with the modification of several existing transmitter sites.{{sfn|Blanchard|1991|p=304}} These were located at the East Newfoundland and Scottish chains, which were equipped with larger antennas and high-power transmitters, broadcasting 20 times as much energy as normal chain stations. Given that the length of the chain baselines did not change, and were relatively short, at long distance the signal offered almost no accuracy. Instead, Dectra operated as a track system; aircraft would navigate by keeping themselves within the signal defined by a particular Decca lane.{{sfn|Blanchard|1991|p=305}}

The main advantage of Dectra compared to other systems being proposed for the RTCA solution was that it could be used for both medium-range navigation over land, as well as long-range navigation over the Atlantic. In comparison, the [[VOR/DME]] system that ultimately won the competition offered navigation over perhaps a 200-mile radius, and could not offer a solution to the long-distance problem.{{sfn|Blanchard|1991|p=305}} Additionally, as the Decca system provided an X and Y location, as opposed to the [[Rho Theta Navigation|angle-and-range]] VOR/DME, Decca proposed offering it with their Decca Flight Log moving map display to further improve ease of navigation. In spite of these advantages, the RTCA ultimately chose VOR/DME for two primary reasons; VOR offered coverage over about the same range as Decca, about 200&nbsp;miles, but did so with a single transmitter instead of Decca's four, and Decca's frequencies proved susceptible to interference from static due to lightning, while VOR's higher frequencies were not quite as sensitive.{{sfn|Blanchard|1991|p=303}}

Decca continued to propose that Dectra be used for the long-range role. In 1967 they installed another transmitter in Iceland to provide ranging along the Scotland-Newfoundland track, with a second proposed to be installed on the [[Azores]]. They also installed Dectra receivers with Omnitrac computers and a lightweight version of the Flight Log on a number of commercial airliners, notably a [[BOAC]] [[Vickers VC10]]. The Omnitrac could take inputs from Decca (and Dectra), Loran-C, VOR/DME, an air data computer and doppler radars and combine them all to produce a latitude/longitude output along with bearing, distance-to-go, bearing and an autopilot coupling.<ref>"Dectra in Iceland", Decca Navigator News, October 1967</ref> Their efforts to standardize this were eventually abandoned as [[inertial navigation system]]s began to be installed for these needs.{{sfn|Blanchard|1991|p=305}}