Honeywell’s experimental head-down solution
combines infrared and computerized vision
with traditional PFD symbology. Some early
tests are encouraging, but can the new system
replace HUDs in the cockpit?
(January 2012) The question that was being debated around the halls of NBAA 2011 the other week was about as technical and geeky as it gets: When flying a very low approach, lower even than a decision height of 200 feet, where is the proper place for your “head,” that is, your eyes and your attention, to be? Should it be down, looking at the primary flight display, and then out, looking for the runway environment at decision height, or should your eyes simply be up and outside the airplane all the time?
At first blush, it sounds as though it’s a no-brainer. Why would the pilot be looking down when the runway is out there if he doesn’t have to be? Then again, unless the airplane is equipped with a head-up display, the pilot has to be looking down a good part of the time. Quantifying how much time is spent up and how much time is spent down is not an easy task. Proficient instrument pilots are skilled at monitoring two instruments simultaneously while peeking at a third, and the layouts of PFDs make it easier to see even more than that without shifting focus. I’ve long felt that the way we teach instrument students to scan is a poor imitation of the way we actually take in the flight instrument data and make sense of it, but one does have to start somewhere. The theory behind the HUD is that, by using it, the pilot has everything in the main field of view. There is still a scan going on, though it is a compact, fluid and efficient one, to be sure.
If the whole head-up versus head-down argument sounds purely academic to you, you’re right in a way and wrong in a different, more important way.
Best of Both Worlds?
Honeywell has been working on very cool technology that it calls combined vision, which blends an enhanced vision picture (an infrared look at what’s actually out there) into the center of synthetic vision (a computer-generated view of what the system knows is out there, including terrain and runway environment) on the primary flight display. With combined vision, the pilot uses HUD-style symbology as viewed on the PFD to fly down to minimums.
Today that’s still 200 feet, because the experimental technology gets no credit for lower than that, yet. If and when Honeywell gets certification for the combined vision system and if it gets credit for lower minimums, as can be the case with a HUD, the technique would remain the same.
Once you’ve arrived at minimums, you simply look up to find the runway and land, or, failing that, you initiate the missed approach.
The question is this: When you’re down to very low clearance over the ground and moving at a good clip over it with things happening fast, is the pilot who has to pop his or her head up at that last moment to find the runway at any kind of performance disadvantage compared with the pilot who is looking through the HUD the whole time? The answer seems as though it would be obvious, that the pilot staring at the runway through the HUD would be in better shape to turn the approach into a successful landing. But much to Honeywell’s delight, that seems not to be the case.
