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 Last issue, I pointed out that looming budget cutbacks may force us to take a serious look at modifying existing aircraft rather than buying new ones. My purpose was to make sure that the people writing the specifications for these mods would come with more realistic requirements for night-vision goggles, or NVGs, and forward-looking infrared, or FLIR, systems. This time, in the same vein, I want to address head-up displays. Before I get started on this, however, one final word on NVG systems. The switch I mentioned for turning the NVG-compatible cockpit lighting on and off should be a hands-on switch. The folks in our cockpit lighting lab have developed several options, the leading candidate being a switch on the underside of the throttle. It works smoothly and makes switching the appropriate lights on and off a completely subconscious act by the pilot. Now on to the head-up display, or HUD.
If you have been following my journalistic endeavors here in Code One, you know how I feel about HUDs. (Helmet-mounted displays, or HMDs, fall into the same category.) They are superior instruments for flying under instrument conditions. With this said, their acceptance has been unnecessarily delayed by the myopic attitudes of a few individuals who have not taken the time to understand the slightly different technique necessary to take advantage of their clear superiority. Strangely enough, although the edict remains on the books, to wit, "the HUD shall not be considered the primary flight reference," both the F-15E and the new C-17 have completely glass cockpits with none of the classic head-down flight instruments. Hummm.
I can't say that we haven't tried to change the situation. Working with the Instrument Flight Center at Randolph AFB, our human factors section has invented a superior means of displaying information to the pilot necessary for using the HUD as the primary flight reference. But when it came time to implement the changes, self-proclaimed experts stepped in and undid our efforts. So once again the powerfully uninformed are attempting to carry us head-long back into the dark ages.
These experts have failed to grasp the following: As soon as science can provide pilots with the sensor/computer combination to display a velocity vector (whether on a HUD, HMD, or a head-down display), you can radically improve your ability to control an aircraft on instruments. Until this fact sinks in, those ignoring it will continue to delay the acceptance of air excellent approach to flying when pilots are deprived of a visible horizon. I can't say it any plainer than that.
Perhaps a flashback will make things even clearer. Until the first true HUD became available, cockpit instruments were simply a continuation of efforts started by Gen. Jimmy Doolittle several decades ago when he guided his plane with needle, ball, and airspeed instruments.
Before HUDs became available, pilots had to control their planes under instrument conditions with what was described as control instruments (the attitude director indicator, or ADI, and the tachometer) and performance instruments (essentially, the rest of the cockpit). The plane was controlled by making the picture on the ADI agree with what was necessary to maintain that desired flight condition. But that was only the first step. Pilots had to check all of the performance instruments visually and then mentally integrate all this information to make sure that the airplane was truly doing what they wanted it to do.
A velocity vector display – whether it's on a HUD, an HMD, or a head-down, monochromatic or multicolor multifunction display – drastically simplifies this because it provides in one place both the control instrument aspect and the performance information. You control the airplane with the velocity vector and its relationship to the pitch ladder. At the same time, you receive nearly instantaneous feedback on most of the airplane's performance. As a result, the amount of information required from what used to be called performance instruments is drastically reduced.
With one quick look in a very narrow area around the velocity vector, you know immediately if you are maintaining level flight, climbing, diving, or turning. Again, all this information appears in one place. No need to look elsewhere. As a result, the velocity vector diminishes the importance of the airspeed, altitude, and heading. It eliminates the significance of vertical velocity entirely. You have no need to know the rate you are climbing or diving. All these rates have been converted into the angles they have been all along and then displayed directly. As a result, you can fly more precisely more safely, and more easily – all at the same time.
Here's a specific example. In the F-4, as I entered the glide slope in a GCA (that's short for ground-controlled approach; the ground controller is using a radar to help me land), I normally lowered the nose about one-eighth of a bar width on the ADI. At the same time, I made about a two percent reduction in power, tried to hold that picture on the ADI, and waited for the vertical velocity to settle down. With some luck, the vertical velocity ended up where I intended when I started the process, about 750 feet per minute rate of descent.
Even if I was successful the first time, if one and only one variable changed, I had to detect it first by integrating all the info from the performance instruments and then by trying to correct the situation by changing the picture on the ADI (usually with a power change as well) and hope, once again, that this was now what I needed. It seldom was.
 A velocity vector greatly simplifies the procedure. Let's assume I have done my homework and know the glide slope angle. (They are all published in the approach books.) When it comes time to enter the glide slope, I simply push the velocity vector down to that value. This is nominally a minus two and one-half degrees. From this point on, all I should ever hear from the controller is, "On glide path." The same is true of instrument landing systems, microwave landing systems, or even a self-contained radar, GPS, or DTS approach. (For those of you who have not been keeping up with your flying magazines, GPS stands for global positioning system and DTS for digital terrain system.) Notice that I didn't mention power, or airspeed, or vertical velocity.
In the F-4, I had to go through the mental gymnastics of combining ground speed and vertical velocity to maintain that two- and one-half-degree glide slope. With a HUD, I can see the results of those calculations directly without straining my brain. Within reasonable limits, all the other variables can change without having to change the position of the velocity vector at all. Consequently, my approach has to be easier and safer.
While I cannot completely ignore airspeed, it is no longer a key factor. In fact, if I already have the drift angle killed (that is, no further heading changes) before entering the glide slope, the HUD is the only place I have to look to ensure that the velocity vector is superimposed on the two and one-half degree down mark and to consider the angle-of-attack bracket (close to the velocity vector), which I've already checked against the airspeed.
Now, with an occasional glance at the altitude to see how I'm progressing toward decision height, I don't have to look anywhere else during the approach. Furthermore, because I'm using the HUD, I'm already looking through the canopy where the runway will appear. Hence, I'm the first to know when I break out of the clouds. This is not the case if I fly with my head down in the instruments.
I am not suggesting a cavalier approach to flying instruments. I do look at other information on the HUD. The point I'm trying to make is that I could accomplish the approach in exactly the manner described. Further, a velocity vector obviates the need to cram all the information into the HUD or in a head-down display that was spread over the entire panel in the past. The information is no longer required in the same format as it was before we had velocity vectors. Nor is all the information considered on the same level.
We should quit trying to make HUDs more complicated than they have to be. We should figure out what is truly needed, provide that – and nothing more.
As I said last time, if we are going to add new capabilities to the airplane or improve existing capabilities, we need to make sure that we give the operators the benefit of the doubt and understand what it is that we are trying to improve.
End of sermon. Again.
Check Six.
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