New EVS on Falcon 7X yields operational credits

 - May 16, 2011, 9:10 PM

The Dassault Falcon 7X is among the first business jets to benefit from the better quality of LCD imaging for the enhanced-vision system (EVS) that the manufacturer is now offering as an option on its head-up display (HUD). The system allows crews flying the large-cabin trijet to see more clearly at night and in foggy conditions.

In many cases, they even get operational credit, which means they can land in weather conditions that would be prohibitive for non-equipped aircraft. In short, they can get Category 2 minimums at a Category 1 airport. However, the EVS is not a cure-all against bad weather.

Dassault received U.S. FAA certification for its new EVS in October last year, three months after approval was granted by the European Aviation Safety Agency. EASA calls the system an EVS, while the FAA calls it an enhanced flight vision system (EFVS).

“It is the second EVS generation,” Dominique Chenevier, a Dassault test pilot, told AIN. The Falcon 2000 and 900 models already had a HUD EVS option available; however, they do not have an LCD display and do not offer operational credits.

The new system took four years to develop. CMC Electronics is supplying the cooled infrared sensor, which “sees” wavelengths between 1.2 and 5 microns. Airport lights emit wavelengths at approximately 1.5 microns and runway markings are visible at around 4.5 microns.

Rockwell Collins (Stand 7036) is in charge of the head-up display system–computer, projector and combiner. Dassault’s engineers have collaborated with their counterparts to develop a tailored product for the sensor and the HUD, and as is common with Dassault product development, pilot input was decisive.

Operational Credit

The new EVS is approved as a situational awareness aid for all the approaches for which the 7X is certified. However, the EVS is not approved for steep approaches–those having a glideslope angle greater than 4.5 degrees.

Using the EVS, the Falcon 7X crews can descend below the published approach minimums down to a height of 100 feet above the runway, compared to the usual 200- to 350-foot DHs, depending on the airport’s landing aids. At the usual DH, the pilot must see the runway with the EVS, otherwise he has to go around. He or she must keep the runway in sight through the EVS until the 100-foot DH is reached, at which point he/she must see it with natural vision.

In other words, on an airport fitted with a relatively modest Category 1 instrument landing system (ILS), the Falcon 7X can land as if it were a Category 2. These operational credits are still valid on some non-precision approaches, such as those without an ILS.

For European operators, the Falcon 7X’s EVS also gives an operational credit in runway visual range (RVR). “The crew can begin the approach with an RVR reduced by about one third below published minimums,” said Arnaud Paulmier, a Falcon customer support engineer.

Proliferating in Bizjets

Use of the EVS is becoming more widespread on business jets than on airliners because business aircraft more often land at airfields that have lower category instrument landing systems or even no precision guidance for approaches. Dassault has delivered a dozen Falcon 7Xs with this infrared system since November 2010. Some 80 percent of the aircraft delivered before then–about 80–will undergo retrofit. Clearly, the EVS option is very popular with operators.

However, crews still have to be persuaded to use it, a spokesman said. According to Dassault, a notable proportion of EVS units on the Falcon 900s and 2000s stayed in the “off” position.  Therefore, it concluded, not only do pilots have to be trained to use EVS, they also need to be encouraged to do so. Dassault is convinced that once they are used to it, pilots will not want to revert to their previous way of flying.

Test Flight

AIN was aboard an EVS demo flight in March, at night from the Istres flight-test center in southeast France to Chambéry. The latter airport is surrounded by hilly terrain, a populated area and a lake. With the EVS, we were able to perform a southbound approach and then circle to land on Runway 36 (northbound). The crew could not see as well as if it had been a clear day, but mountains, obstacles and the runway were easy to see. The procedure is normally prohibited at night because it involves visual flight at 900 feet above the city, but we were permitted to do so because the flight was in the “test” category.

“You do not fly in the EVS image; rather, the system comforts the pilot who uses landing aids like an ILS,” Chenevier explained. This is the “equivalent visual operations” concept, he said. If the additional information supplied by the EVS is consistent with the primary guidance when reaching minimums, the crew can carry on. Our night pattern went a little bit beyond this principle, as it really was a visual flight.

The EVS image is superimposed on the HUD’s combiner with conventional HUD symbology. It includes, for example, the velocity vector that shows the direction of the aircraft’s flightpath. The EVS’s field of view is 28 degrees in width and 26 degrees in height. An obvious requirement is that the EVS image must be perfectly overlaid with the real view, which was a major challenge for design engineers.

In terms of image quality, LCD technology provides a brighter display. The difference appears most evident during the day, with the display more easily readable. LCD technology enables one to see both the EVS image and the symbology, whatever the light conditions. The previous-generation EVS used cathode ray-tube HUDs, and the pilot sometimes had to choose between image and symbology.

However, Dassault’s pilots and engineers make it clear that the new system does have limitations because of the nature of IR technology. For example, the EVS can “see” through “young” fog–fog made of small droplets, but more mature fog, with larger droplets, cannot be tamed. This also is true of heavy rain.

Moreover, the system cannot “see” through clouds. This can be a benefit, however, in that the crew can better see towering clouds at night and thus anticipate turbulence. Paulmier noted that compared to seeing with the human eye, the EVS performs best in snow.

In short, the EVS is not an all-weather system–a factor that, in the late 1990s, deterred Dassault from following rival Gulfstream, which was then pioneering EVS use on business jets.

Training Challenges

EVS training for Falcon 7X pilots is a one-day session, and among the challenges, Paulmier said, is that the simulated EVS image is often “too beautiful.” This is one reason the French manufacturer believes in educating pilots about how to use the EVS, because while the system does improve safety, expectations should not be too high. For example, pilots must be taught how to take advantage of the EVS, while avoiding a “fascination” effect. Crew coordination must be maintained, Paulmier said.

Procedurally, the pilot in the left seat flies the aircraft using the HUD, whereas the right-seat pilot monitors the approach using head-down information. Paulmier explained that “specific procedures have been developed to ensure maximum crew coordination during the approach.” For example, he said, during an EVS approach when the left-seat pilot detects the approach lights or runway in the EVS, he or she calls out “EVS lights.” As the Pilot Flying, when reaching the minimums he will decide and announce whether to land or discontinue the approach. Further along in the approach, the first crewmember who sees the runway announces it. The crew then makes the final decision to land.

To get accustomed to the system, Dassault recommends flying with it in normal operations before using it for operational credits. “We also try to give our customers as much feedback as we can from our experience in development flights,” Paulmier said.

One limitation is the installation location. The HUD is installed in front of the left seat and the copilot has only a head-down EVS, which begs the question as to why the manufacturer would not offer dual EVSs on a pair of HUDs. This may be the next step, but two obstacles will have to be overcome. First, the price of the option–$455,000 for a single-HUD EVS–is probably too high. Second, to comply with the required level of redundancy, the entire avionics architecture would have to be reviewed.