Gulfstream has become the first airframe company to commit to certifying an infrared enhanced vision system, or EVS. Next month the firm will begin flight testing an IR sensor developed by Kollsman for use with the Honeywell/GEC-Marconi HUD 2020 head-up display. Federal Aviation Administration approval is expected in June, and the EVS is being offered as an option on the Gulfstream IV-SP and V.

In an EVS, a thermal image is displayed on the HUD combiner, allowing the pilot to see runway lights at a safe distance despite fog, rain or smoke, and continue an approach that would otherwise have to be aborted. Currently, in the U.S., there are only 50 runway ends where it is possible to land with a runway visual range of 700 feet, and then only if the aircraft is equipped with Category III landing systems and the crew is trained to use them. With EVS, says Kollsman, a Category I aircraft and crew can use more than 700 approaches under such conditions.

EVS procedures are designed so that the system is not critical to safety. As in the case of a normal Category I approach, the pilot must be able to see the lights and other features at a 200-foot decision height-with EVS, however, the pilot will see these at a distance well above the unaided visual range. If the pilot loses sight of the lights between the decision height and the end of the runway, a missed approach is executed.

EVS has been highly controversial since the early 1990s. Northwest Airlines and Sextant launched a program to fit EVS to older Category I aircraft, but encountered problems and dropped the project. One major avionics company concluded that IR sensors could not penetrate weather to any useful extent, as has a leading HUD supplier.

A key difference in the Kollsman system, however, is that the IR camera itself is specifically designed for EVS applications, including a lens and image processor which are optimized for detecting runway cues at normal approach distances. The camera is designed to be installed inside the radome, behind the radar. A prototype has been flying since 1997 on a Cessna 402 operated by the Maryland Advanced Development Laboratory. MADL and its director of plans and analysis, Glenn Connor, have been tireless advocates for EVS since the 1980s.

EVS should provide other safety benefits. At night, both air traffic and aircraft and vehicles on the ground stand out much more clearly, avoiding ground collisions and runway incursion incidents.

Almost half of the customers for the Gulfstream V want EVS, according to Kollsman. American Airlines has ordered EVS-capable HUDs for its 737-800 fleet, and is considering a move to the new technology.

By Bill Sweetman