Both the U.S. FAA’s NextGen program and Europe’s Single European Sky Air Traffic Management (ATM) Research (SESAR) Joint Undertaking aim to increase air traffic efficiency through more optimal routing/fuel burn and emissions reduction, while increasing safety and capacity. A key to increasing capacity is to minimize the effect of weather on flight operations.
For decades, air carriers have been looking for comprehensive solutions to low-visibility conditions to enhance operational capabilities independent of airport facilities. To incorporate the advancing technology and capabilities, the FAA and European Aviation Safety Agency (EASA) continue to update the aircraft and ground equipage requirements, pilot training, and procedures necessary to achieve lower minimums under instrument flight rules.
For instance, in 2007 Federal Aviation Regulation (FAR) 91.175 was revised to include a means to go below the authorized decision height (DH) or minimum decision altitude (MDA) using an Enhanced Flight Vision System (EFVS). The instrument flight rules under 91.175 enable the pilot to use an electronic device to see the runway environment as compared to the traditional requirements that a pilot must see the runway out the window with the naked eye. The intended runway must be “distinctly visible and identifiable” to go below DH or MDA.
Currently, the FAA has only certified aircraft installed with a HUD (head-up display) to meet these regulations. A study by a team of engineers from Honeywell provides evidence for an equivalency of performance of a head-down, primary flight display with synthetic vision (SV) and Enhanced Vision (EV)—a Combined Vision System (CVS)—to the performance with a HUD with IR imagery. If certified, the CVS would enable pilots flying with an aircraft equipped with a sensor but not with a HUD to visually acquire the necessary cues to land in lower-visibility conditions.
The Honeywell team began with a prototype version of the currently certified synthetic vision display. The prototype included enhancements in the orientation of the display and was shown to enhance the primary flight display (PFD) stability and reduce workload. Using a blended altitude solution with multiple sensor sources improved accuracy and fault tolerance and enabled enhanced runway approach symbology to be created.
The team was tasked with the integration of the IR image with the synthetic vision display that was acceptable to pilots and facilitated their performance in the approach and landing phase of flight. After encouraging findings from an initial empirical study in the laboratory revealing advantages of the head-down display location for the detection of the approach lights, the team went to flight test to further enhance the CVS features.
The first series of flight tests of the CVS prototype system took place in a Cessna Citation Sovereign aircraft in June 2010. The experimental installation featured a Kollsman EVSII camera on the top of the aircraft nose in a forward storage compartment. The IR image from the camera was integrated onto the synthetic vision display on the primary flight display on the left side.
The objective was to evaluate the system performance in flight in both visual meteorological conditions (VMCs) and instrument meteorological conditions (IMCs) in the Phoenix, AZ, area and the California coast. The integration included symbology improvements to declutter elements of the display to optimize the detection of the approach lighting system, the development of the colorized IR (infrared) imagery to improve the integration into the synthetic vision system (SVS) background, and the creation of a semi-transparent sky portion of the image to improve the pilot’s awareness of the synthetic terrain in low-visibility conditions. The CVS was driven by a ruggedized flight test desktop computer located in the aft cabin. The single desktop flight computer was used to render combined SVS/EVS images, acquire real-time video streams, acquire flight and FMS data from the aircraft data bus, and record and analyze all the relevant flight test data and video data.
The local flights originated from Phoenix Deer Valley (KDVT) to Prescott or Williams Gateway and then returned to KDVT. These local flights were used primarily to optimize the display color scale, improve the IR integration image quality over a variety of weather and terrain conditions, and to optimize primary flight and flight director guidance symbology for their dynamics, size, shape, and usability. The goal was to ensure that the overall behavior of the prototype display could meet the demanding requirements for pilots to perform critical approach and landing performance evaluations.
The flights in the California area were conducted in low-visibility conditions of marine fog. Pilots flew low approaches to 30 to 50 ft above the runway. The pilot flying responded with “lights,” and the response time was recorded and compared to when the pilot not flying saw the lights looking out the window. The findings indicated a statistically significant average of 30-ft advantage of use of IR over the naked eye in marine weather conditions with fog, rain, and clouds. The pilot flying with the CVS stayed head-down until 100 ft above the runway and then glanced up and made a subjective decision of whether he was appropriately configured to land and could comfortably complete a successful landing.
A second series of flight tests was conducted on the Sovereign in October 2010. The goals were to improve the IR coloring, make modifications to the flight director dynamics, and integrate the hybrid IRS for improved accuracy of the aircraft position to better align the IR imagery with the synthetic vision terrain. Three Honeywell flight test pilots flew over 20 h in both day and night VMC. Findings indicated significant improvements in the IR alignment and usability of the flight director.
The final series of flight tests took place over a two-week period in December 2010 on the East Coast of the U.S. on a Honeywell-owned G450 aircraft equipped with a certified Kollsman EVS camera and a Honeywell HUD 2020 display. The objective of the flight tests was to capture objective and subjective performance data while flying with the certified Enhanced Vision System on the HUD and the head-down CVS. The research question was whether the prototype CVS display could support the pilot’s approach and landing task as well as the certified EVS system that offers the pilot operational landing credit in low-visibility conditions. A variety of weather conditions, including low visibility and strong crosswinds, were found on ILS approaches at six different airports.
The research findings revealed pilot performance equivalency when the pilots flew with the IR imagery on the head-up EFVS and the head-down CVS display. On each approach, all pilots were able to strictly conform to the necessary flight criteria and maintained a stable approach through touchdown and rollout. The lateral and vertical tracking errors in both the CVS and HUD conditions met the established criteria for approach and landing in weather minima as established by the FAA.
The subjective ratings mirrored the objective data indicating that both displays clearly supported the pilots’ tasks of verification of the runway environment and their transition to the actual runway for landing. Workload ratings indicated that both display formats allowed the pilot to maintain low workload levels even in low-visibility conditions and on high-workload approaches with crosswinds.
It is quite promising that the CVS display faired equally well as the certified HUD with such limited practice, especially since the pilots were highly practiced with the HUD, which is used on a regular basis on the G450. Clearly, the CVS adds performance benefits by priming the pilot with the picture of the environment prior to breakout and provides a means for a stable approach through the use of the path-centered display.
This article is based on SAE International tech paper 2011-01-2525 by Patricia May Ververs, Gang He, John Suddreth, Rob Odgers, Jary Engels, Ivan Wyatt, Keith Hughes, Christopher Hamblin, and Thea Feyereisen of Honeywell International Inc.