Rockwell Collins HGS-3500 brings small HUD to smaller airplanes

 - May 24, 2011, 9:15 AM

For more than five years, Rockwell Collins engineers have been working on a tough challenge: how to make a compact head-up display (HUD) system, one that could fit into much smaller aircraft than the big jets that currently carry HUDs. Now, thanks to ever-improving technology, Rockwell Collins looks to be first out of the gate with the new HGS-3500 head-up guidance system, a self-contained single-LRU HUD that does away with the bulky external projector.

The HGS-3500 head-up guidance system is targeting light to midsize business aircraft, from single-engine turboprops to midsize jets, and is designed to fit cockpits equipped with Rockwell Collins Pro Line Fusion avionics. At roughly one-fifth the installed cost of a typical long-range jet’s HUD, the HGS-3500 promises to bring the safety benefits of HUD technology into many more cockpits. No announcements have been made about which aircraft will be first to feature the HGS-3500, but, predictably enough, Rockwell Collins is in discussions with aircraft manufacturers, according to Adam Evanschwartz, principal marketing manager at Rockwell Collins.

Big-jet Functions in a Small Package

The breakthrough made by Rockwell Collins engineers was to fit the HGS-3500 into one 12-pound unit that mounts on the windshield sill beam in front of the pilot. Larger, heavier Rockwell Collins HGS units have a projector mounted behind the pilot, shining the image onto a combiner screen in the pilot’s line of vision.

What made the HGS-3500 possible is substrate-guided optics. LED backlighting in the pilot display unit’s internal active-matrix LCD feeds the image into the top of the HUD glass. The HUD glass contains a diffraction grating framework (an “optical waveguide”) that helps spread the light as it is “poured” into the glass so it fills the entire image space. The image on the HGS-3500, as on any other HUD, is focused on infinity so the pilot doesn’t have to adjust focus between the outside view and HUD symbology.

According to Rockwell Collins HGS director of marketing John Wilson, an LCD using ordinary fluorescent lighting would not be able to deliver enough light into the glass. “Without LEDs,” he said, “we would still be scratching our heads on how to pump enough light through.” Enough light for the HGS-3500 means luminance of more than 2,500 footlamberts. A typical 6000-series HGS delivers about 4,000 footlamberts, but images on both systems appear about the same to the viewer. As LED technology improves, Wilson expects the HGS-3500 to be able to deliver even greater luminance.

While the HGS-3500 offers a slightly smaller field of view, lower luminance and lower resolution compared with larger Rockwell Collins HGS, the result for the pilot is functionally the same, Evanschwartz explained. All the symbols on the HGS-3500 will look the same in terms of size, resolution and placement as they do on larger HGS. The field of view is also plenty wide enough so flight-path symbology remains viewable during approaches with a crosswind.

Like larger HGS, the -3500 meets head-injury criteria standards that protect pilots in case of an accident. When not in use, the glass part of the HGS-3500 is stowable, folding up and out of the pilot’s forward view. Controls are available to adjust the video image and symbology.

The HGS-3500 will display the Fusion’s synthetic vision system (SVS) view as well as infrared enhanced vision (EVS). A yoke switch will allow pilots to select between the normal, SVS and (if an infrared sensor is installed) EVS views. The reason that Rockwell Collins will offer the HGS-3500 only for Fusion-equipped cockpits is that the Fusion system is doing all the processing needed to drive the images delivered to the HUD. Making Fusion work with other avionics systems is possible but would require substantial additional engineering, Wilson said. “This is the quickest way to get to market, by tightly integrating with Fusion,” he explained.

One of the key benefits of HUD is that it enables pilots to keep looking outside during an instrument approach. According to Wilson, a NASA study on head transition during approach found that on a three-degree glideslope flown at 124 knots, the average time a pilot took to transition from head-down to looking outside was 3.5 seconds, and during this time the aircraft descended another 40 feet.

A 2009 Flight Safety Foundation study showed that HGS technology could have helped prevent 38 percent of accidents that occurred over a 12-year period. “The study also came to the conclusion that a staggering 69 percent of landing and takeoff accidents and 57 percent of loss-of-control accidents could have been avoided if the pilot had access to the information available on a HGS,” according to Rockwell Collins.

“We’re trying to get into a market that doesn’t have a HUD,” Wilson explained. “There is just such huge opportunity for a new wave of operators to enjoy the benefits of HUD.”

Rockwell Collins plans to fly the HGS-3500 on its Challenger 601 next year, with the goal of certifying the new HGS in 2014 or 2015. The company hopes to gain FAA approval for lower approach minimums using synthetic vision on the HGS.