The future of head-up display technology

 - September 26, 2006, 2:50 PM

Head-up displays (HUDs) provide pilots with an array of flight-related information, when and where they need it most. The thick piece of HUD combiner glass that folds down and locks into position in front of the pilot’s eyes puts a veritable visual feast of instantly recognizable symbology directly in the forward field of vision. On a nonprecision approach at night or in poor weather, this data is of huge value, particularly when viewed in the context of past aircraft accident investigations.

Early HUDs developed for civil aviation typically showed the same data that is available on a head-down primary flight display (PFD)– namely airspeed, altitude, localizer, glideslope and so on. Today’s HUDs offer a far broader menu of symbology, including a flight-path marker, path and airspeed trend vectors, angle-of-attack readout, runway depictions, landing-flare cues, runway-remaining information, tailstrike warning, unusual-attitude-recovery symbology, TCAS resolution advisories and other vital data. Add to this list the recent certification of HUD-based infrared enhanced-vision systems (EVS) and the ongoing research of database-derived synthetic-vision systems (SVS), and the potential value of HUDs as a tool for improved situational awareness is readily evident.

Talk to any pilot who uses a HUD regularly and you’re likely to hear nothing but praise for the technology. But besides anecdotal evidence about the usefulness of HUD, there is solid scientific data that points to the safety benefits of the technology. A detailed analysis by the Flight Safety Foundation determined that HUDs might have prevented or positively influenced 31 percent of 1,079 civil jet transport accidents that occurred during its study period between 1959 and 1989, before HUDs had entered aviation’s mainstream.

After completing its study, the foundation recommended that airlines and business-jet operators install HUDs that display angle-of-attack information and airspeed-trend data to help pilots monitor the airplane’s energy state and projected touchdown point during approach and landing, saying these were keys to improving safety during this critical phase of flight.

“The growing use of head-up displays is a positive trend for improving safety,” noted Stuart Matthews, Flight Safety Foundation president and CEO, in a recent status report on civil HUDs, adding that foundation studies “have pointed to HUDs as a potent and available tool for safety enhancement.”

Available, yes, but not quite commonplace in business aircraft cockpits in spite of the clear safety benefits of the technology. While a number of manufacturers have begun offering HUD as standard equipment in their top-of-the-line aircraft, such devices are still generally the exception in the vast majority of cockpits.

The high cost of HUD hardware (current systems sell for more than $500,000 apiece) has made the technology a tough sell for many operators, not to mention that the sheer size of the overhead projection equipment that constitutes a modern HUD system fits only in larger jets.

But all this could be about to change. The introduction of very light jets (VLJs) into aviation’s mainstream will no doubt create markets for a host of products and services to cater to the needs of the new breed of VLJ pilots and operators, and compact, low-cost HUD systems could be part of this trend.

Kollsman, a division of Elbit Systems in Israel (which manufactures the EVS for Gulfstreams), is targeting a slice of this potential market with a unique, bargain-priced head-up display and EVS that the company is promising will make even low-time pilots perform like seasoned pros.

A HUD for Everybody Else

Kollsman first started exploring ideas for commercial HUD systems several years ago, but it wasn’t until recently that senior executives gave the green light to the Micro-Vis HUD, a unique LCD-projection system developed with assistance from sister company El-Op Electro-Optics Industries, a manufacturer of military HUDs based in Israel. The product was unveiled at the NBAA Convention in November, and the formal development program kicks off this month.

Randy Moore, Kollsman executive vice president and general manager, explained that the Micro-Vis HUD avoids using a bulky and expensive overhead image projector by attaching the image source to the combiner glass instead of using an overhead image projector. The Kollsman design actually “injects” the HUD image between two pieces of combiner glass. The result is a complete package that Kollsman said will fit in even the most cramped cockpits, something sure to pique the curiosity of VLJ makers, especially considering that the target selling price of the system is around $50,000.

“We identified this technology as being something that might be essential to the very light jet market early on because of the increase in accuracy during approach and landing and the tendency for lower-hour pilots to be better performers with HUD technology,” Moore said. “The micro HUD technology was exactly what we felt was needed to make these aircraft safer and perhaps more insurable for single-pilot operations.”

The leading causes of air accidents and incidents haven’t changed much over the years. Topping the list continue to be controlled flight into terrain, runway incursions, and approaches and landings in low visibility. Incorporating a HUD can improve safety in each of these categories, which is precisely what led Kollsman to start an R&D program about three years ago to determine whether the technology the company had in mind could indeed be installed in midsize jets or smaller business aircraft.

Moore said Kollsman has held discussions with a number of would-be VLJ manufacturers and that the early reaction to the technology has been “overwhelmingly positive.” In fact, Moore said that Eclipse Aviation founder and CEO Vern Raburn, after seeing the Micro-Vis HUD sales presentation, described it as potentially “disruptive technology.” That’s high praise from a man whose Eclipse 500 VLJ is shaping up to be about the most disruptive technology the industry has seen since Bill Lear launched the original Learjet 23 in the early 1960s.

Moore said Kollsman anticipates that the Micro-Vis HUD will make its debut in a current-production business jet or turboprop, and that its introduction in a VLJ will likely come later. This is due primarily to the anticipated certification schedule of the VLJs, none of which are yet in production.

Still, like many of the nascent VLJs, Kollsman’s Micro-Vis concept is far from being in a production-ready state. Moore explained that at this early stage the HUD image itself looks good, but that the company is still refining the projection optics used to create the HUD symbology.

The trouble is that the physical joining together of the combiner creates “artifacts” that appear as vertical streaking on the glass. Moore said engineers at El-Op (where the combiner is produced) suspect the problem is related entirely to the process used to glue the two panes of combiner glass together, a technique that is being continuously refined to create as clean an image as possible.

Moore said he has flown with the Micro-Vis HUD in Kollsman’s Cessna 340 testbed and that despite the low-intensity artifacts on the glass, after a few minutes the pilot’s eyes naturally tend to focus on the HUD symbology and ignore the background join lines. FAA pilots have also seen the HUD in action, Moore said, and their reaction has been positive.

To get an idea of how the Micro-Vis HUD works, imagine stacking a number of prisms horizontally and shining a light through the center of them, Moore explained. This light, created by an LCD image source, fans out laterally and hits a mirror, which reflects the image straight down into the HUD combiner. This technique allowed Kollsman to eliminate the overhead projector traditional HUDs use, thereby reducing size and allowing the display to be mounted either overhead or on the glareshield.

Itzhak Hevlony, Kollsman vice president for commercial aviation systems, said the Micro-Vis HUD has a field of view of 32 by 24 degrees and weighs less than 10 pounds. Certification is scheduled for the middle of next year, after which Kollsman plans to turn its attention to certification of a companion EVS. Designed to provide improved situational awareness in night VFR, Kollsman’s GAViS enhanced-vision system is an uncooled infrared sensor that Hevlony said can be mounted in a fairing on the aircraft nose. Price for the EVS would also be around $50,000, Hevlony said.

This microbolometer-type camera differs from the EVS certified in the large Gulfstreams primarily in terms of light sensitivity and sensor cooling. Whereas the cryogenically cooled Gulfstream EVS is designed to serve as an “all-weather window,” the non-cooled GAViS is intended for VFR flight only. As a result, pilots flying with GAViS will not be eligible for the operational landing credits that have been extended to properly trained Gulfstream crews flying with EVS.

Kollsman has spent the last two months flying with the HUD in its Cessna 340 every chance it could in preparation for a sales demonstration tour that will continue for the next couple of months. The company is targeting both retrofit applications and new airplane programs, with in-service King Airs and Citations being of particular interest, Moore said.

LCD TechnologyTakes Center Stage

As Kollsman is demonstrating, new head-up display technologies based on LCD scanning techniques promise to clear the way for smaller, lighter and, many say, more reliable hardware that will be capable of providing brighter images and new HUD capabilities.

Makers are moving away from traditional cathode ray tube (CRT) projection techniques in favor of devices based on LCD technology, which will mean less wieldy projection equipment installed in the cockpit and a crisper HUD picture. In fact, it is unlikely that civil HUDs under development in the future will use CRT projectors as manufacturers turn to LCDs.

“LCD is really where HUD technology is going,” said Chad Cundiff, displays and crew interface portfolio director for Honeywell. “There are several different reasons for that, one being image quality and others being size and power consumption.”

Honeywell is developing an EVS-based HUD for FedEx based on LCD projection
technology. By moving away from traditional CRT-based HUDs, Honeywell is developing a system that should be much smaller and lighter than anything yet built for civil aviation, Cundiff said.

A key feature of this system is the integration of an EVS that uses infrared sensors to cut through darkness and weather. The Honeywell HUD will combine flight symbology with this EVS imagery and project it onto a display that will be fitted to all FedEx widebodies flying around the world.

“When you start putting EVS on a HUD you need a bright image source and good optics, and that was really the focus of our development for FedEx,” Cundiff said.

The first LCD HUD for business aviation will be the HGS-5860 head-up guidance system, under development by Rockwell Collins for the Dassault Falcon 7X. This HUD will provide a wider field of view and larger “eyebox” than past HUDs, allowing the pilot to view information conformal to the outside world in stronger crosswinds, and to more easily manage approach angle and energy on circling and other non-standard approaches, according to Collins. New sensor and database technologies, such as EVS and SVS, are planned for the system later on, through onboard software loading and development of an imaging sensor interface for the French business jet.

Rockwell Collins provides the CRT-based HUD systems in a variety of Falcons, as well as in the BBJ and Challengers. The 900EX and 2000EX with EASy avionics are undergoing EVS sensor testing using an infrared camera system developed by CMC Electronics. By replacing the vacuum-tube CRT and its power supply with an LCD design in the 7X, Rockwell Collins hopes to bring about significant increases in overall reliability, as well as sharper pictures and improved gray-shade presentation in bright ambient light, which is important for viewing images supplied by EVS sensors, said Collins.

Using technology similar to a digital media projector, an LCD HUD eliminates the high-intensity CRTs in today’s systems, which are heavy, bulky and hot-running and require high-voltage power supplies. Prices for LCD-based head-up displays from the major manufacturers are expected to remain about the same as those for current CRT-derived equipment, but this new standard for HUD image projection will create possibilities for improved EVS images, perhaps blended from a variety of infrared and millimeter-wave radar sensors. Such a HUD package would create new possibilities for operations in low visibility, thereby improving safety and possibly extending additional operational credits to operators.

Thales recently delivered the world’s first LCD HUD to Airbus for flight testing aboard an A340-600. Embraer and Collins are developing a dual LCD head-up guidance system for the Embraer 190 under a $60 million contract from launch customer JetBlue Airways, and Boeing has selected Collins to supply the dual LCD HUD in the 787.

Gulfstream and Bombardier so far are the first business jet makers to have certified HUD-based enhanced-vision systems, in Gulfstream’s case the Kollsman infrared sensor system certified in a variety of the Savannah, Ga. company’s long-range jets and in Bombardier’s case a recently certified system developed by CMC Electronics and Thales. Dassault and Boeing Business Jets are also working on HUD-based EVS concepts, while Cessna is developing EVS for head-down displays.

Advanced Vision and Sensor Fusion

The FAA recently adopted rules allowing the use of HUD-based EVS for descent below published minimums on straight-in instrument approaches. The regulations let pilots continue straight-in Category I and nonprecision approaches below decision height or minimum descent altitude to 100 feet above touchdown zone elevation, at which point they need to be able to see the runway or approach lights unaided to be legal to land.

Experts believe that lower takeoff and landing minimums resulting from enhanced-vision systems are only the beginning of the benefits new types of advanced vision technology can bring to business aviation. That’s because SVS presentations, which have evolved into slick, video-game-like systems on the primary flight displays (designed to replace the traditional blue-over-brown portrayal of the artificial horizon with a virtual world complete with terrain, obstacles and even other aircraft and airport vehicles) are also expected to be applied to HUDs.

Honeywell and Rockwell Collins are both pursuing fused EVS and SVS image technology, but only Rockwell Collins has been demonstrating concepts that redraw digitized maps of the earth’s topography to create a virtual SVS world on a HUD.

Last summer, test pilots from NASA and Gulfstream flew a GV equipped with an experimental Rockwell Collins synthetic-vision system to explore some of the latest techniques for SVS/EVS blending. Fitted with a combination of head-up displays, a new type of multi-scan weather radar, special sensors, a voice-recognition system and cockpit displays with computer-generated images of the terrain, the GV used in the trials was a veritable flying laboratory.

Pilots shot a series of instrument approaches to NASA’s Wallops Flight Facility in Virginia using only SVS for visual guidance. Gulfstream senior production test pilot Chip King served as the pilot-in-command and flew with NASA-designated pilot Mike Norman, who evaluated the SVS. With his side of the cockpit windshield intentionally blocked, Norman flew approaches to minimums using the computer-generated graphical information displayed on an LCD monitor and on the HUD without any trouble, Rockwell Collins reported.

Next on the drawing board for HUD-based EVS is millimeter-wave radar, which is a promising technology to supplement infrared EVS, if it can be produced at a low enough cost. Although the image produced by a millimeter-wave radar isn’t as crisp as infrared, it has the advantage of being able to see through clouds. Fusion of infrared sensors tuned to various wavelengths and a millimeter-wave radar acting as a third, active sensor could provide a more complete view of the world ahead of the aircraft.

BAE Systems and NASA demonstrated such a system earlier this year in NASA’s Boeing 757 testbed at the Wallops Test Center. During one of the flights conducted by a pair of uninitiated Air Force pilots, a truck was parked on the end of the runway and the view ahead was intentionally blocked by a screen placed in front of the windshield.

While the Air Force pilots complained about the “noise” that the millimeter-wave radar created on the HUD (saying it looked like snow on a tv screen), both agreed it was similar to making a landing on a dark night and that they could easily “see” the truck. When all three sensors were combined into a single EVS image, the pilots said the picture was much better.

Rockwell Collins is also continuing to work with NASA and the Air Force on HUD-based synthetic vision, which creates a view of the world manufactured from a terrain database. The idea is to create a wire-mesh-type grid that draws hills and mountains but does not obstruct vision ahead. Making sure that the grid conforms precisely with what exists in the real world is the biggest challenge for developers.

“The accuracy of the sensors is a big issue, certainly in heading,” said Peter Howells, systems engineering manager for Rockwell Collins. “Accuracy in position will come with the use of GPS, but a bigger concern is precise alignment using inertial reference systems, which allow us to accurately represent the outside world.”

Other techniques for creating a synthetic view on the HUD are currently being explored, Howells added, one being the use of computer processing to correlate the real view from the EVS to the vision being shown on the SVS, allowing the computer to correct the synthetic image as needed.

Honeywell’s approach has been to focus on bringing EVS to the HUD and SVS to head-down primary flight displays. The avionics maker has tested an SVS for the PFD, but at this point it has no plans to apply the technology to a HUD.

“We see a great benefit in having EVS overlaid on a head-up display and having SVS on a head-down display,” said Honeywell’s Cundiff. “There are some things you’ve got to go solve if you try putting synthetic vision on a HUD. For example, how do you make the SVS image really match what a pilot sees out the window? If you’re trying to overlay terrain on top of terrain that really exists, they had better match perfectly. On a head-down display it doesn’t necessarily have to be conformal to anything, but on a HUD it has to match exactly to the terrain that’s out there.”

Surface Guidance Systems

In the future, fully integrated surface guidance systems will be needed to safely and efficiently guide airplanes on large airports, especially in poor weather and at night.

Rockwell Collins has been honing its SVS concept for the past several years, leveraging the technology from its HUD development group in Portland, Ore., to design a system capable of providing pilots with a variety of on-airport cues.

Using an onboard high-accuracy airport surface map database coupled with one-meter position accuracy from an airport differential GPS or LAAS station, HUD systems developed by Collins in the future will display a graphical overlay of the runway or taxiway ahead, precisely aligned with the proper perspective of the flight deck.

Runway and taxiway edge lights would be overlaid with their graphic equivalents, with their centerlines clearly displayed.

Upcoming turns, including high-speed turnoffs, would be alerted well in advance, with distances to go and current taxi speed versus maximum speed for the turn shown prominently, and the turns themselves accurately depicted as the aircraft proceeds around them. Tracking around a turn will be aided by a “future trend line,” familiar to pilots currently flying electronic HSIs.

Finally, should the crew be uncertain about the aircraft’s position, they could switch the HGS display to show a plan view of the airport’s runways and taxiways.

“One of the challenges is whether you can create a system that communicates with the flight management computer to create a taxi path on the HUD that would show you how to get from where you are on the airport to where you need to go,” said Howells, adding that Rockwell Collins is working on that, too.