Among avionics manufacturers, there are two philosophies at work, the so-called “head-up, head-down” debate. This has devolved into cockpits equipped with head-up displays (HUD) and those with traditional head-down displays (flat-panel LCD pilot flight and multifunction displays) and no HUD. Head-up means the pilot can continue looking out the windshield while viewing flight guidance information on the HUD, through touchdown. Head-down means viewing information on the instrument panel, then looking through the windshield during touchdown. Both methods have proved safe, although avionics manufacturers claim benefits for their particular approach. HUD currently offers some credit on weather minimums, while head-down displays with synthetic vision haven’t yet been certified for minimums reductions, although manufacturers and an industry committee are working on that.
Rockwell Collins, which bought Head-Up Guidance (HGS) system manufacturer Flight Dynamics of Portland, Ore., in April 1999, is gearing up to spread the HUD philosophy further, into aircraft as small as single-engine turboprops and light to midsize jets. The company’s existing HGS-6000 series HUDs are too large for anything smaller than a super-midsize jet. So last year, Rockwell Collins introduced the HGS-3500 compact HUD, which combines elements of the larger HUD into a smaller lightweight package. The HGS-3500 will cost about one-fifth as much as the HGS-6000 series and should be certified in 2014 or 2015.
Flying with a HUD provides key safety benefits, according to Rockwell Collins. It lets one pilot use the HUD to make performance callouts during the takeoff, which allows the other pilot (who is flying the airplane) to focus on the view outside. Other features include advisory assistance for tailstrike avoidance during takeoff and landing, angle-of-attack exceedance prevention, rollout lateral guidance based on localizer data, Tcas corrective action guidance, runway remaining, deceleration rate, wind-shear guidance and unusual-attitude depiction and guidance. All this while the pilot is looking outside, focusing on infinity while at the same time seeing a clear view of the HUD symbology.
The growing proliferation of HUDs means pilots will need to learn how to use the devices effectively. And there is a benefit to learning HUD symbology, because avionics manufacturers are increasingly adapting that symbology, especially the flight-path vector or symbol, in their head-down displays. The Honeywell Primus Apex flight deck in the Pilatus PC-12 NG, for example, features a sophisticated implementation of the flight-path symbol adapted from the Primus Epic systems used in larger aircraft such as the Gulfstream G450 and G550.
To help the aviation media understand HUD and its benefits, Rockwell Collins held a HUD training session at its Portland factory in mid-April. The session consisted of an explanation of HUD philosophy, features and symbology as well as a discussion of safety and operational issues with not only Rockwell Collins experts but also Perry Solmonson, Horizon Air director of flight standards and training, and Doug Perrill, director of aviation for Portland-based Falcon operator B2 Flight. We were each then treated to a session in the Portland facility’s engineering simulator, which replicates a Boeing 757 with a HUD. Rick Theriault, principal engineering manager systems and flight controls for Rockwell Collins Head-Up Guidance Systems, was our instructor.
One of the highlights of the training was a demonstration of a feature available on the Rockwell Collins Pro Line Fusion flight deck, which is now certified and operating on the Bombardier Global 5000 and 6000 (as the Vision flight deck). The Fusion/Vision flight deck allows the display of enhanced-vision imagery from an infrared sensor or synthetic vision (also displayed head-down) on the HUD. The enhanced and synthetic vision images can be combined in the simulator, but this is not a feature yet available in Fusion-equipped airplanes. The pilot can switch between normal, enhanced, synthetic or combined vision on the HUD using a button on the control wheel. For certain types of moisture-laden cloud that enhanced vision can’t see through, it’s handy to be able to pull up the synthetic vision or the combined vision view to see the terrain near the aircraft. This was demonstrated to us in the simulator with a cloudy night approach into Innsbruck Airport in Austria. Of course, in a two-pilot airplane, one pilot can watch the enhanced vision view through the HUD while the other monitors the synthetic view on the head-down display or on a second HUD, if so equipped.
The HUD consolidates a lot of information in a small space, a so-called combiner screen that flips down in front of the pilot’s view through the windshield. The pilot is able to focus on infinity instead of on the combiner itself, but is also able to see and interpret what is playing on the combiner while looking outside. I found that it didn’t take long to get used to letting my eyes focus outside but also being able to see the HUD symbology.
During the normal takeoff, Theriault pointed out how the flight-path vector (FPV) grows little landing gear legs, to indicate that the airplane is on the ground. Pressing the go-around button on the throttle sets up the HUD to provide guidance during the takeoff, including ground-roll yaw using the localizer signal shown by a guidance cue (a small solid dot) inside the hollow FPV. The guidance cue is basically the flight director on the HUD. After rotation, Theriault had me pull the nose up until the boresight (the aircraft symbol on a normal attitude indicator) sat on the dashed 15-degree pitch target. Selecting heading and altitude modes made the guidance cue command a level-off and the proper heading to level the wings. As Theriault put it, “The task, just as always, is to keep the flight path vector on top of the guidance cue.”
After demonstrating the normal takeoff, Theriault had me depart in 300 RVR visibility. Staying straight on the runway was easy, using the guidance cue, and the HUD helped me make a smooth takeoff. Where the HUD really helps, he explained, “is in the unlikely event of something going wrong; it’s going to give you all the information you need to get back to the localizer and maintain your intended trajectory and free up some of that mental bandwidth.”
The guidance cue really helps when the engine fails before V1. Simply use the rudder to keep the cue in the right place, cut the remaining engine’s power and get on the brakes. The altitude scale at this point changes to a runway-remaining scale. The pointer on the scale shows how much runway will be left at the current rate of braking. Not enough cushion? Add more braking (if possible). We did this at 300 RVR, so when I got the airplane stopped, we had 1,500 feet of runway left, according to the scale on the HUD. When the simulator operator dialed the visibility back up, we could see that, indeed, we were right in the touchdown zone for the opposite runway.
Unusual Attitude and Stall
The Rockwell Collins HUD has a feature I’m not sure I like. Once the airplane exceeds 65 degrees of bank, the display reverts to a simple ADI-like format, without the speed and altitude tapes or conformal symbology, just sky and ground and a little g meter. The regular HUD display elements “are likely to be very dynamic and distracting,” Theriault explained. I would prefer something with some arrows on it, telling the pilot the best way to turn.
“We have thought about it,” said Theriault. “It’s probably something we’re going to come up with soon, for loss of control. In the initial development, the pilots we were working with at the time wanted to see just an indication of where the sky is, where the ground is and allow them whatever it takes to regain control of the aircraft.”
During the unusual-attitude exercise I found no difficulty in knowing which way to turn to right the airplane (probably because I was the one who put it into the 90-degree bank followed by a nose-low attitude). Recovery was easier using the g meter to keep from exceeding the two-g limit.
A handy angle-of-attack margin indicator (Theriault calls it a picnic bench) appears on the HUD to show where stickshaker will occur. I could easily see the margin between stickshaker and our current attitude by looking at the distance between the picnic bench and the FPV. Stalling the simulated 757 was just a matter of slowing down (at 22,000 feet) and slowly pulling the yoke aft to get the FPV to touch the picnic bench. I got us into a secondary stall during the recovery because I didn’t pitch the nose down quickly enough.
A Tcas resolution advisory is simple on the HUD: just fly to a fly-to box, which is more prominent than the guidance cue. “All you have to do,” Theriault said, “is smoothly pitch up into that fly-to box, do what you need to do with power to maintain airspeed and stay in that box until the resolution advisory goes away.” The box then disappears, and since we were shooting an approach, a push of the go-around button put us on track for another try. “The beauty of [the TCAS advisory],” he said, “is not only does it tell you what to do with your hands and your feet and what you need to do with the energy management parameters presented on the HUD, but while you’re doing all that, you’re head-up, eyes out, able to scan for traffic the entire time.”
Theriault had me fly VMC and IMC approaches. A neat HUD feature is that it displays a three-degree glideslope reference line. All I had to do on the VMC approach was to fly toward the runway until the reference line was positioned next to the PAPI (just beyond the end of the runway). Then I used the flight controls to position the FPV right on top of the reference line, and that made for a stabilized approach.
At about 100 feet, a horizontal dashed line shows up underneath the FPV, and all I had to do was follow that line with the FPV as the line rose gently, telling me exactly how to flare. “That’s going to give you a touchdown with a sink rate of about two feet per second,” Theriault said. “A nice repeatable touchdown sink rate.” He pointed out that the glideslope reference line is particularly useful during a night approach to a runway without any PAPI or VASI guidance.
We shot the ILS approach to Runway 10R at Portland International Airport, first in Category I conditions (200-foot decision height, 1,800 feet RVR) then tried one set to Category IIIB (50-foot DH and 660 feet RVR). After that, Theriault asked for the weather to be dialed down to zero-zero (this was an exercise, not something a pilot would do in real life).
For the Category III approach, a little more flying precision is required, and the flare guidance is embodied in the regular guidance cue, all the way to touchdown. After touchdown, the same takeoff symbology told me how to stay straight on the runway.
I was able to get us on the runway during the zero-zero landing, which we verified by dialing up the visibility after landing. I found that being new to flying a HUD, I didn’t feel like I was looking outside as much as I was paying attention to the HUD itself. But at the same time, I do know that my vision was taking in the outside world when (and if) it appeared in the simulated windshield. It’s hard to explain exactly what I was seeing and perceiving, but obviously the HUD system does work.
Watching the demo (I didn’t fly this one) of the approach into Innsbruck was interesting because the city is surrounded by high mountains and the approach is next to “fairly daunting terrain,” Theriault said, “and we’re going to be flying below the mountaintops.” In the synthetic vision mode, I could easily see the runway and an extended centerline, plus a gridline as well as texturing of the terrain to give an idea of distances and relative motion. The enhanced-vision sensor picks up the approach lights, so by toggling on the combined vision view I could easily see the terrain (via synthetic vision) plus the runway environment. Looking out the windshield, I could see nothing but inky clouds.
Horizon Air pilots spend about two days in initial HUD training and about one to one-and-a-half days for recurrent, but some of this is integrated with their normal training events, according to Perry Solmonson, director of flight standards and training. One of the key benefits of using HUDs in the airline’s fleet of Bombardier Q400s is the ability to eliminate costly diversions. “I can attach money value to the time spent if we have to divert,” he said. With HUD, if a localizer is qualified to Category III (even if the ILS is only a Category I), the HUD-equipped Horizon Q400 pilots can fly an approach with weather as low as 150 feet DH and 1,400 feet RVR.
Doug Perrill, the director of aviation who flies a Falcon 2000EX, uses the HUD 100 percent of the time, he said. He and the other pilot who flies the 2000EX plan to obtain certification for Category II and III operations, to take advantage of the lower minimums available at Portland International Airport. “What does HGS give us?” he asked. “The one common denominator is called path. It gives us a path to where we’re going. And it’s in real-world terms.”