The evolution of synthetic vision from pretty picture to tactical, practical tool for keeping schedules and boosting capacity is in a holding pattern, as regulators and the business aviation sector come to grips with the benefits versus the costs of having the capability.

Decisions by the likes of Bombardier, Dassault, Embraer and Gulfstream to proceed or mothball Synthetic Vision Guidance System (SVGS) technology could come later this year when the FAA completes and publishes guidance and policy on the equipment, and on performance, operations and certification of the system, information likely to be echoed by European regulators. That guidance will largely follow specifications crafted by the government and industry RTCA Special Committee 213 (SC213), although the FAA could make key changes that could alter the cost-benefit equation and give OEMs reason to scrap plans to deploy SVGS in the near term. SC213 develops minimum system performance and operational performance specifications for enhanced flight vision systems and synthetic vision systems, products that typically are adopted by the FAA and other regulators. An earlier version of SVGS guidance that SC213 sent to the FAA in 2011 was rejected, in part because industry had not yet tried out the technology in demonstration projects.

SVGS uses the basic elements of synthetic vision—a 3-D representation of terrain, obstacles and runways, combined with advanced guidance cues including a flight path vector, flight path angle and depiction of the runway—but adds multiple levels of verification to ensure that a runway and the approach to it are in the proper place, making SVGS a source for navigation information. Legacy synthetic vision systems were first approved by the FAA in 2006 as “situational awareness” tools for the primary flight display but were not considered usable for navigation.

With those assurances, a pilot using SVGS on a head-down or head-up display would be able to fly to the actual runway using a virtual depiction on the primary flight display or head-up display. The system would also provide “credit” in terms of lower approach minimums for Cat. 1 (Cat. 1) instrument approaches and GPS-based localizer performance with vertical guidance (LPV) approaches. The initial guidance will allow for a 150 ft. decision height (the point at which the crew must either have visual confirmation of the runway environment or perform a missed approach) with visibility as low as 1,400 ft. runway visual range (RVR), compared to the usual 200 ft. and 1,800-2,400 ft. minimums, respectively, for the two types of approaches. Minimums below 200 ft. generally require more airport infrastructure, including runway centerline lighting, and other safety equipment, elements that would be waived for the SVGS approaches.

The lower minimums are expected to provide more reliable access to thousands of runway ends that would otherwise require costly Cat. 2 or 3 instrument approach equipment, trained crews on board and more equipment on the ground. The FAA operates a total of 1,277 Cat. 1 ILS approaches at U.S. airports. Operators with head-up displays and specialized training can already get “special authorization” (SA) approvals to fly down to 150 ft. decision height minimums on 109 Cat. 1 and 29 Cat. 2 approaches in the U.S., but SVGS advocates are looking for much broader access. With SVGS, ideally that extra 50 ft. would be available to any aircraft with SVGS, whether head-up or head-down, at all 1,277 Cat. 1s as well as for the 914 LPV approaches that have a 200 ft. decision height (the FAA has a total of 3,534 LPVs, most with higher minimums).

Speaking at an SC213 meeting in Paris in mid-April, FAA representatives made clear that the agency would need to see adequate demand from the user community before committing the resources and manpower to make the necessary changes that would allow for SVGS across all Cat. 1 and LPV approaches.

“Our management is looking for a business case,” said an FAA representative at the meeting. “If we do this, what would be the cumulative effect on the [National Airspace] System? What would the benefit to the NAS be before they divvy up resources to address this task?”

The FAA explains that since the processes and charting for special authorization for Cat. 1 approaches (SA Cat. 1) at airports already exist, the impact on the agency to deploy more approaches for those runways would be relatively minor, assuming airport operators make a request for the approaches. 

For LPV, however, there are currently no charts or other processes in place to allow for lower minimum approaches. “The whole gamut of building an approach and charts—that’s a pretty large endeavor that is expensive and resource-intensive,” said the FAA representative. “So before the FAA would entertain getting behind that, in the near term, I think they would like to know if there’s an interest out there. If there are just a handful of operators who would do that, then it might not be a good cost-benefit. It might not really expand the capacity in the NAS. If there’s a lot of interest, and folks speak up and say we really want to do this, and can produce numbers and a business case and demonstrate that the taxpayer will benefit, then I think there will be more interest at the FAA headquarters level.”

With SVGS technology issues well in hand at their avionics providers—largely Honeywell and Rockwell Collins—business aircraft OEMs are now querying the sector for the level of interest. Honeywell says it is “too early” to announce an SVGS certification time frame, but says it has “strong interest” from several OEMs, particularly in the business aviation and regional jet market, with the commercial airline sector also showing “high” interest. “Although [airlines] have not yet equipped with synthetic vision systems (SVS), they view operational credit as a potential incentive to help their operators equip with the SVS safety technology,” says Honeywell. The company has already finished its SVGS testing campaign and transitioned the technology from its research team to its product group.

In 2013 Honeywell had applied for an FAA and European supplemental type certificate (STC) for SVGS as part of the EASy avionics suite in the Dassault Falcon 900, but only to allow the company to undertake a proof-of-concept test to demonstrate SVGS to OEM pilots and regulators. Honeywell has since abandoned the application for a standalone STC and is instead planning to certify SVGS as part of a broader software upgrade for its Primus Epic integrated cockpits at some point in the future.

The proof-of-concept phase involved flight testing in a Honeywell Falcon 900EX in May 2013 with nine pilots flying 64 approaches, primarily focusing on the behavior of five approach path monitors that Honeywell developed to ensure SVGS performance during an approach. The following month, 12 pilots tested the SVGS in simulated instrument weather conditions in a Boeing 777 “M-Cab” engineering simulator in Seattle, focusing on the transition from SVGS on a head-down display to the outside visual environment at various decision heights and visibility conditions. Data collection included flight technical error (FTE), which showed that pilots had no problem with the head-down to head-up transition and landing, says Thea Feyereisen, Honeywell Aerospace Engineering Fellow.

Specific to Honeywell’s approach to SVGS is a head-down display of the information, with a track-centered (versus heading-centered) synthetic vision display. The track-centered display results in a smooth presentation of the scene, particularly in turbulence. The company uses a “crabby symbol” cue to show the pilot the orientation of the runway with respect to the nose.

Rockwell Collins, which builds head-up guidance systems that can also display synthetic vision, is developing SVGS for the head-up display (as well as for the primary flight display), using a heading-centered synthetic scene. Bombardier is interested in certifying the company’s SVGS for the Global Express line of aircraft, although a flight-testing program is on hold at the moment while the airframer waits for the FAA guidance, company approvals and the latest SVGS software update from Rockwell Collins, provider of the Pro Line Fusion integrated Global Vision flight deck for the Global Express family. 

The Global Vision system, which has been delivered on about 300 aircraft, features synthetic vision on the head-up display, allowing authorized operators to descend to the 150 ft. decision height at SA Cat. 1 airports. Bombardier wants an SVGS that will be usable at all Cat. 1 runways, although it has not set a target date for the offering. The company last year demonstrated its version of SVGS to the FAA and others in a simulator, and is currently performing marketing surveys to find out how much demand there is for SVGS. Pending software delivery and company approval, officials plan to begin flight testing SVGS on a Global 5000 flight-test aircraft in 2016. A year ago, Rockwell Collins said it had expected to certify SVGS for Bombardier by September this year, a target that has now been pushed back. 

One of the problems with marketing SVGS to the business aviation sector is that the technology is probably most useful not as a means to an end for lower minimums, but as one element of a combined vision system (CVS). CVS fuses several vision inputs depending on the phase of flight: Pilots would use SVGS to get an aircraft down to 150-100 ft. decision height minimums and a 1,400-1,000 ft. RVR, respectively, at which point they would use an approved enhanced flight vision system (EFVS), with infrared, millimeter-wave radar or other technologies showing the scene on a head-up display, as a substitute for natural vision to fly down to the runway and taxi to the parking spot. 

With EFVS today, operators can get approach credit to descend to a 100 ft. decision height on a Cat. 1 runway, although the FAA is preparing final rules that will allow additional credit depending in part on the performance of the equipment. Companies continue to research CVS, but have not yet moved the capability into the product marketing arena.

Bombardier says the promise of CVS as the ultimate vision product makes SVGS by itself difficult sell to customers in the interim, and could force the company to offer the capability at no charge in return for operator feedback and lessons learned on the path to developing and deploying a CVS.

“We see SVGS as a step to CVS,” says one Bombardier engineer close to the development but not approved to speak on the company’s behalf. “What we’re all after is CVS.”

CVS as an end state is problematic for Honeywell, however, as its prototype is head-down on the primary flight display and as such does not meet the EFVS rules. Feyereisen says the company is trying to figure out “how to break through the HUD limitation” in the rules, including discussions with the FAA on certain hybrid modes that could allow the pilot-monitoring in a single-HUD aircraft to use CVS to better monitor an approach.