Printed headline: HUDs Heading Up
A new generation of head-up displays (HUD) is emerging, with some of the most cutting-edge technologies since Sextant Avionique introduced the first commercial HUD for the Dassault Mercure in 1975.
Next-gen HUDs, in combination with enhanced visual technologies, are enabling pilots to access more airports under the most limited runway visual range (RVR) and low-ceiling conditions. At the same time, head-mounted displays (HMD), now in development for commercial and business aircraft pilots, could upend the concept of a fixed-screen installation by the windscreen.
As operator demand for head-up displays and vision systems has grown, OEMs and avionics suppliers are increasing the availability of HUDs and their functionality, according to Grant Blythe, principal marketing manager for head-up guidance and vision systems at Collins Aerospace. One example he cites is the Boeing 787, which includes dual Collins head-up guidance systems (HGS) as standard equipment rather than as an option.
“Additionally, we’ve seen a shift toward demand for dual HUD solutions rather than single—captain’s side [left- seat] only—HUD installations,” he explains, as operators see the benefit of such a system and want both pilots to have access to it. Collins offers dual HGS solutions for the Boeing 737 and 777X, Airbus A220 and Embraer E-Jets in addition to the 787.
Along with forward fit on these current-production aircraft, Collins Aerospace offers HGS for retrofit on a range of aircraft, from light corporate and regional turboprops to the largest widebody jets. This could become more critical if regulatory authorities mandate HUDs. “The biggest example of this is China, where the civil aviation authority has published a road map that mandates 100% of Chinese-registered air transport aircraft to be equipped with HUDs by 2025,” he says. “Also, nearly 90 airports have had exclusive approaches approved for HUD operators, allowing improved low-visibility capability, while avoiding a huge amount of airport expansion work.”
While making HUDs applicable to more aircraft types, the trend is toward smaller units. For example, Collins’ HGS-3500 compact HUD, says Blythe, uses waveguide optics, a cutting-edge technology that removes the overhead projector, permitting HUDs for flight decks that are too space-constrained for a conventional HUD.
“At least for now, waveguide does sacrifice some optical performance in order to achieve similarity to the size and weight of just the combiner from a conventional projection HUD,” Blythe explains. “Collins is working to improve the technology to match the full performance of projection HUDs offered on large flight decks in the future.”
Another area of rapid advancement in technology has been in vision systems. For those, Blythe reports that Collins now offers enhanced flight vision system (EFVS), synthetic vision system (SVS) and combined vision system (CVS) capabilities integrated with its HGS. “These features take the base symbology of a head-up display and add real-time infrared and computer-generated video to provide pilots with a ‘visual equivalent view’ of the outside world in any conditions,” says Blythe. “The visibility advantage offered by the EFVS allows airlines to operate in conditions as low as 1,000-ft. runway visibility range (RVR) at airports and runways that only support Category 1 approaches.”
Cat. 1 is an instrument approach with a minimum descent altitude, decision altitude or decision height not lower than 200 ft. and with visibility not less than one-half a statute mile or an RVR of at least 1,800 ft. However, the RVR minimum could be higher, depending on the unique characteristics and ground infrastructure for the approach.
Blythe says Collins is also evaluating potential advanced features using automatic dependent surveillance-broadcast (ADS-B) information, including some that would assist in maintaining separation or support low-visibility taxi operations. “We believe any new features must earn their place on our HUDs. Since a critical function of a Collins head-up display is that pilots must see through it, we only want to display new symbols if it provides the pilot with actionable information.”
Brian Ast, senior aviation systems and human factors engineer for Olathe, Kansas-based Garmin, cites a dual trend with HUDs: more applications to larger aircraft coupled with reduced size for use on a larger number of aircraft types. As an example, he mentions Garmin’s GHD 2100 for Cessna’s new Citation Longitude business jet.
The GHD 2100, Ast explains, is a projection-type HUD incorporating a high-resolution glass combiner display—which shows the projected image in front of the pilot—and a slim, self-contained projection unit installed above the pilot’s head. “It is made as small as possible so the pilot’s headroom is not restricted,” he notes. “The smaller size of the projector, and its lighter weight, enables the system to be used in smaller cockpits, which was a key driver in the design of the GHD 2100.”
Among the new HUD’s significant advantages, Ast notes, is its ability to display “dynamically more relevant information” to the pilot during various phases of flight. “What you don’t want to do is clutter the image on the HUD with a lot of information that might not be relevant to what the pilot needs at any given point,” he says.
Stephane Bertheau, regional marketing manager for avionics products at Thales, reports that the Paris-headquartered company offers its digital head-up display system (D-HUDS) as an optional forward-fit product on the Airbus A320, A330, A350 and A380. While installation constraints make HUD products more practical for forward fit, retrofit of D-HUDS is possible through an Airbus service bulletin.
Airbus aircraft equipped with D-HUDS are certified to approach runways under Cat. 1 or Cat. 2 conditions using HUD guidance. “Using HUD is a great operational improvement allowing decrease of decision height or runway visual range but not enough to reach zero visibility and zero ceiling,” says Bertheau. “Thales and Airbus are working together to merge HUD, synthetic vision and multispectral infrared cameras to offer combined vision systems to operators.” At the same time, he adds, Thales is working to implement features to extend current HUD technology such as colored and 3D symbology.
Thales is also developing an HMD product it calls Topmax. As he explains, an HMD addresses the main drawback of HUDs when installed as a retrofit—usually wiring and mechanical changes. “Topmax is a full-color HMD, with a 360-deg. field of view with all the capabilities of a HUD, including synthetic vision systems and enhanced vision systems,” he says.
Bertheau says installation of the supporting infrastructure could be done during three overnight stays. The product is slated for availability starting in 2020 for any aircraft type, with installation by supplemental type certificate, although Thales is in discussions with airframe OEMs to offer Topmax through a service bulletin upgrade as well.
“We are convinced that this product will be a game changer for vision systems on existing aircraft, although we don’t believe there will be a [total] transition from HUD to HMD,” remarks Bertheau. “What we see is HUD for line-fit, HMD for retrofit.”
Universal Avionics is also in the process of certifying what it says will be the first fully functional HMD specifically for the commercial airline forward and retrofit markets.
SkyLens, as the HMD is called, was developed by Elbit Systems, which acquired Tucson, Arizona-based Universal Avionics in 2018. The lightweight system is incorporated into a head-mounted, high-transparency visor.
“We see a lot of potential for SkyLens in the airline market as it will enable pilots to fly approaches down to the ground in almost all weather conditions, opening access to airports that would normally require a flight to be diverted or canceled due to poor visibility,” says Scott Campbell, Universal Avionics director for airline and military sales.
SkyLens incorporates Elbit’s ClearVision EFVS. The symbology and images are projected onto a high-transparency visor, providing see-through video under day, night and all-weather conditions. For the pilot, SkyLens provides a 180-deg., left or right view of the synthetic vision system imagery without having to remain in a specific sitting position to view a standard cockpit-installed HUD.
“We tailor the symbology of the SkyLens HMD to match the existing instrumentation on the aircraft,” Campbell says. “Our interface to the existing avionics will be to ‘listen’ and replicate their modes and annunciations on the head-down display avionics, only now displayed head-out.”
No modifications to the aircraft’s existing avionics infrastructure are required because SkyLens plugs into a connector unit installed in the cockpit in close proximity to the pilot’s seat. The connector unit is the link between SkyLens and the ClearVision computer, which can be located in the avionics bay or the cabin. The computer takes in the EVS imagery from the EVS camera, which is installed inside the radome, with a window looking outside.
Initial certification of SkyLens is imminent, initially on the ATR 42/72 regional turboprop family. However, Campbell explains that a single-aisle jet of some type will follow next.
Despite these advances in HUD designs, Garmin’s Ast suggests there are still two issues the industry must tackle. “One is getting HUDs in front of more people. Not having a HUD as part of your flight deck has tremendous safety implications,” he stresses. “Then, from the technology side, there is a need to go toward lighter, smaller, cheaper systems and [to make] them more adaptable for installation on more than one aircraft type.”