Development of a hub-and-spoke network increases the importance of keeping an airline's home runways open. Rather than wait for the US Federal Aviation Administration to upgrade the landing aids at airports, airlines in the USA in the early 90’s began to look at what could be done to their aircraft to enable them to land in low visibility.
In the early 90’s the US Federal Aviation Administration (FAA) began a flight test programme of a synthetic vision system (SVS) to gather data for that certification. The SVS was a joint programme with the US Defence Department to develop technology enabling low visibility landings on what they called "cooperative" and "non-co-operative" runways. A Gulfstream II testbed was equipped with a HUD and both IR and MMW, to balance the advantages and disadvantages of the two sensors. The pilot was able to switch between the two sensors initially, but there were plans to blend the images later.
The most promising solution appeared to be a system to enhance the pilot's ability to see the runway in fog. An enhanced vision system (EVS) comprises a head-up display (HUD) onto which is projected an image of the runway from an infra-red (IR) sensor or millimetre-wave (MMW) radar. The enhanced image allows the pilot to recognise the runway from a greater distance and to continue the approach, rather than divert.
In a cockpit of a transport aircraft there are two general areas in which a projection unit can be installed: the glareshield or the overhead area. The overhead area is generally preferred (the C-17 was a notable exception) but installation is bounded by the structure and pilot’s head clearance. In general, the space available reduces sharply going outboard and increases going inboard. Overhead switch panels and eyebrow windows often reduce the space available. Installation of a HUD in the cockpit overhead area was generally preferred. Overhead Projection Units were developed by the Company and in 1992 a HUD was test flown at the Maryland Advanced Development Laboratory on their Gulfstream II testbed aircraft under the "Synthetic Vision Experimental Program".A separate Electronics Unit was located in the avionics bay. Kodak supplied the mid-wave IR and Honeywell and Lear two different MMW radars.
