The US Air Force has demonstrated low-level night approaches using Rockwell Collins synthetic-vision displays on its Boeing C-135 Speckled Trout testbed. Collins says the tests were the first to use synthetic vision on a zero/zero approach to an assault landing. Actual landings were not conducted.
The synthetic-vision symbology, generated from an onboard terrain database, was presented on head-up and head-down displays (HUD and HDD). The tests were conducted in daylight, with cross-polarised glasses stopping the pilot from seeing outside the cockpit, and simulating night instrument flying conditions, according to Ray Liss, Collins business development manager, integrated applications.
Flight guidance was displayed as a "highway-in-the-sky" corridor made up of 90 x 90m (300 x 300ft) boxes 0.3nm (0.5km) apart along the flightpath. Terrain was represented by a wireframe grid on the HUD and a chequerboard on the HDD. US military Level 1 and 2 digital terrain elevation data generated the onboard database. There was also a digital moving-map display.
The flight tests at Edwards AFB, California, involved low-altitude, tactical-type missions, says Liss. All approaches were conducted to a 15m decision height. Blind landings were not performed because the differential GPS needed for precision approach guidance was inoperative. "But they could have flown [the synthetic-vision system] to the ground," he says.
The evaluation pilots had limited transport aircraft experience, says Liss. "They were tactical pilots, but they flew the box and stayed within the corridor in the sky with minimal problems." Collins says there are a "couple" of US military programmes eyeing synthetic vision technology in the near term.
Source: Flight International
