Avionics makers seek to break the 'sight barrier'
The crescent moon over Tucson does little to light up the black craggy terrain beyond the windscreen of N966E, 's specially modified Falcon 900EX, as we descend at 135 kt. toward the end of Runway 11 at the international airport one night in May.
On the primary flight display however is a new breed of 3-D synthetic vision that streamlines the task of visually lining up with the pictured runway, setting up the proper glideslope and flying down to the altitude where natural vision through the windscreen must take over. I flew the prototype system with Honeywell test pilots and engineers on May 13, departing Phoenix Deer Valley Airport at sunset for a series of nighttime approaches at the Tucson (Ariz.) International and Mesa Gateway airports.
Lighting up the approach inside the cockpit is a new “SmartView” cockpit display that Honeywell Aerospace is testing as part of a proof-of-concept program with thethis summer. The company has applied for a supplemental type certificate for SmartVision Lower Minimums (SVLM) as a software upgrade to its EASy 2 integrated avionics suite for the Falcon 900EX. EASy is a Dassault-specific version of Honeywell's Primus Epic integrated avionics suite.
The work puts Honeywell in a small but elite group of companies that are becoming the pathfinders for what will likely be a new generation of business aviation and airline cockpit guidance systems that make terminal area navigation more intuitive by marrying the visual compulsion of a conformal 3-D synthetic vision scene with validated guidance information and symbology of a traditional precision instrument approach.
SVLM, if eventually certified, will allow pilots for the first time to navigate within the confines of the synthetic scene down to as low as 150 ft. above the runway (also known as the decision height) with the visibility as low as 1,400 ft. That kind of capability today requires significant extra ground infrastructure or onboard equipment including head-up displays.
For synthetic vision, SVLM represents a fundamental shift from systems that are certified for situational awareness purposes only, meaning pilots primarily must rely on the more traditional but less intuitive needles and bars when it comes to flying instrument approaches down to the decision height (the lowest altitude to which the aircraft can descend before pilots must see the runway environment with the naked eye).
Key to taking a synthetic vision system from “situational awareness only” to a “supplemental” navigation tool, which allows pilots to fly and shoot instrument landings within the synthetic scene, will be coming up with a secondary, independent source of navigation information to validate the synthetic scene. Legacy synthetic vision systems use a single terrain-and-obstacle database for the 3-D rendering.
For operators, breaking the “sight barrier” appears to be win-win: less onboard equipment and maintenance, fewer training hours for pilots, more abbreviated and intuitive approaches, and nearly all-weather access to airports. For air navigation service providers, it promises to equate a lessening of airport infrastructure and runway lighting required, and all the associated maintenance.
For its part, the FAA has opened the door for the sea change to occur through certain regulatory hooks. Order 8400.13D, published in 2009, allows for “special authorization” Category 1 approaches down to 150-ft. decision height and 1,400-ft. runway visual range visibility for runways without touchdown zone and centerline lighting, infrastructure otherwise needed for instrument approach system (ILS) minimums below 200 ft. “The higher-performance capabilities of new and improved avionics have mitigated some of the performance requirements of the ground-based navigation equipment,” says the FAA. In order to prove out the higher-performance capabilities, companies can elect to include with their certification efforts a proof-of-concept demonstration with the FAA, an approach Honeywell is taking to gain the agency's input on the operational suitability and airworthiness of their design before completing development.
While several avionics companies, business jet airframers and even one airline are known to be seriously considering a proof-of-concept or other certification efforts for the synthetic aid, only Honeywell andto date are openly discussing their plans to gain lower landing minimums “credit” for synthetic vision tools. Both companies view lower landing minimums for synthetic vision as stepping-stones to a “fused” or “combined” vision system that will blend validated synthetic vision, passive forward-looking infrared sensors and active radar-based sensors to allow a pilot to fly an aircraft all the way to the ground and to the gate for the most part with the primary flight display or head-up display, in Rockwell Collins's case.
Creating navigation systems that simplify the gate-to-gate operation of an aircraft by eliminating the impacts of weather is a key step in the technology roadmap to “equivalent visual operations,” a next generation air transportation system (NextGen) goal. The idea is this: If pilots have the guidance and navigation tools onboard to always fly as if the weather is clear and the visibility unlimited, then instrument procedures can be simplified and airports are likely to operate with fewer delays even as traffic grows, the exception being for severe weather.
Today, there is a graduated scale (Cat. 1-3) of required onboard and ground-based infrastructure for landing in progressively lower cloud height and visibility minimums, with the costs, training and maintenance increasing as visibility and cloud height decrease. Cat. 1 approaches, with a 200-ft. minimum altitude and 1,800-2,400 ft. of “runway visual range” visibility, are the most numerous ground-based approaches in the U.S., with 1,283 approaches at 1,200 airports.
The “holy grail” for NextGen is to get lower landing credit for the fast-growing number of GPS-based approaches called lateral precision with vertical guidance (LPV) that today allow for no lower than 200-ft. minimums. There are already 3,098 LPV approaches at 1,553 airports in the U.S.
“There is growing accessibility into airports without the economic benefit [of lower minimums],” says Sandy Wyatt, Honeywell's project pilot for SVLM and the pilot-in-command of my demonstration flight. “SVLM will unlock that capability in a way that the average pilot can easily fly.”
Rockwell Collins is initially focused on unlocking synthetic vision capabilities on Cat. 1 instrument approaches by leveraging its certified Pro Line Fusion synthetic vision for the head-up display, a system that first went into service on theGlobal 5000 and 6000 in March 2012.
Matt Carrico, senior engineering manager of advanced concepts at Rockwell Collins, says testing of a prototype system on the company's Challenger 601 is already complete (for a customer he cannot identify) and certification activities with the FAA are underway.
Carrico says the certification process is “complicated” as certain elements of testing may not have to be shown since the company has already certified its head-up guidance system (without synthetic vision) for 150-ft. minimums and 1,400-ft. visibility via FAA Order 8400.13D for airline customers. The company is using system performance standards created by RTCA Special Committee 213 in 2011 (DO-315B) for reduced minimums to Cat. 1 ILS runways. RTCA plans to publish standards for reduced minimums for LPV approaches by the end of 2014.
“We believe we can get through the process in the next year or two,” he says of the timing. Beyond that, he says, the company will “likely” seek landing credit for LPV approaches. “Once we establish performance requirements, then we will evaluate which technologies and sets of technologies can get us further credit. It's premature to be picking those technologies just yet.”
The typical issue with the LPV approach in terms of synthetic vision for credit is that “you're using the same source for navigation and positioning,” says Sarah Barber, a principal engineering manager with Rockwell Collins and member of RTCA's Special Committee 213.
Honeywell is confident it has already come up with the necessary solutions for using SVLM on both the ILS and LPV approaches. The company officially started its one-month proof-of-concept project with the FAA's Long Beach, Calif., aircraft certification office on May 22 using N966E.
The pilot's interface to SVLM on the primary flight display is the Runway Approach Indicator, a suite of primary-flight-display cues that use first principles and visuals to help navigate to the runway end, and a “level of service” monitor to indicate the health of the SVLM system. Running in the background are five new monitors that validate the information and allow the synthetic scene to be used for navigation and lower minimums.
En route to Tucson International at 15,500 ft., we set up the Dassault flight-management system to fly the LPV approach to Runway 11 Left. The level-of-service monitor in the top right corner of the display has green text that lists the type of approach, the unique identifier for the approach, and a label that reads either “SVLM” or “NO SVLM.” In this case, “SVLM” was written in green text, meaning the approach was usable. An audible “No SVLM” or its accompanying text in an amber box in the level-of-service monitor means the approach must either be abandoned or flown as a normal ILS or LPV. Below the normal ILS or LPV minimums, the box turns red and pilots must fly the missed-approach procedure.
As Wyatt puts it, there are “five ways to make the SVLM go amber or red”—a fault in any of the five monitors. The runway-data-integrity monitor compares runway coordinates from two disparate databases to make sure the runway approach indicator box is correctly aligned to the runway; the altitude monitor compares barometric-, radio- and GPS-based altitude to protect against a bad barometric or GPS altitude; the missed-approach monitor identifies the missed-approach point by its distance from the runway rather than a barometric altitude; the approach-deviation monitor protects against crew flight technical errors, and the delta-position monitor compares the path along the ILS or LPV approach being flown with the aircraft's inertial reference system (IRS) baseline path.
The IRS reference path is key to Honeywell's approach to gaining lower minimums. With LPV and Cat. 1 approaches, the FAA allows for a 6-sec. lag between the time the ground or satellite-based approach guidance has a fault and becomes unusable to the time the aircraft must be alerted. For minimums lower than 200 ft. the FAA requires a 2-sec. notification time however, meaning LPV or Cat. 1 ILS beam data cannot be used. Honeywell solves the problem by decoupling the GPS data from the IRS after calibrating and monitoring the IRS system starting at about 4 nm from the runway end for period of 12-23 sec. After that time, the runway-approach-indicator guidance is based on the decoupled IRS output.
Although the autopilot system will continue to use the ILS or LPV data for its reference, the delta position monitor as an independent check will catch errors within the 2-sec. requirement and alert the pilot with a “NO SVLM” message.
Other elements of the display that are new or unique include a track-centered boresight, meaning the synthetic view is centered on the direction the aircraft is tracking versus the direction the nose is pointing (heading-centered). Though the EASy 2 flight deck nominally uses heading-centered synthetic vision, Honeywell has found that the track-centered method makes for a smoother presentation.
Nearing the airport, the runway approach indicator provides a very intuitive target to line up for the approach-and-sense motion, or flow, toward the runway end. It features a cyan box outlining the synthetic runway, and within 10 nm of the runway end it includes a four-light geometric precision-approach-path indicator (PAPI) at the front left-side of the box. When on the glideslope, the runway outline has the correct trapezoidal shape (see diagram, above) and PAPI shows two white lights to the left and two red lights to the right. Too high and all the lights go white; two low and all the PAPI lights are red.
At 10 nm from the runway end, a conformal lateral deviation indicator also appears in magenta intersecting a cyan line marking the approach path. A magenta aircraft icon shows the crab angle with respect to the course centerline.
Both features—the relative shape and location of the runway box and the PAPI—are familiar elements to pilots from their initial days in flight instruction, and were a very comfortable visual element for me on the pitch-black approach into Tucson. Pilots from their first days in the cockpit learn to roughly judge the proper vertical path for an approach by the outline shape of the runway, and to precisely trim the glidepath using the PAPI. It was no different in the Falcon, except that I had a visual image of the runway shape and the PAPI much farther from the runway than through the windscreen. With the validated position of the runway, I could place the flight-path marker on the end of the runway and be assured that is where the aircraft would end up. The flight-path marker, common on head-up display systems and legacy synthetic displays, is a predictor of where the aircraft will go based on its current dynamic state.
The system very quickly became comfortable to fly through four approaches into Tucson, with the transition between the primary flight display and the outside runway environment non-problematic at a 150 ft. decision height, or for that matter, down to 100 ft. What I could not evaluate on this night was the how the system would feel in actual instrument weather, or in a strong crosswind. Honeywell points out that the aircraft icon in the lateral guidance shows the pilot the direction where the runway will be located, and its tests in strong wind conditions have been non-problematic.
Tap the icon in the digital edition of AW&ST to fly along in a Falcon 900EX and see details of a new Honeywell synthetic vision-based avionics system, or go to AviationWeek.com/video