HUDs are standard now on the Boeing 787 and I’ll bet there’s less grumbling from F/O’s for one good reason: now there’s a HUD on their side as well in the 787. On the 737-800, the HUD is only on the captain’s side.
I’ll admit that I had my doubts too when I first started the transition from MD-80 captain to 737 captain. How could Flight Management computers, ILS antennas GPS and symbol generators reliably synthesize a runway display before my eyes despite clouds and weather obscuration? Worse, without any ground-based approach aids, how could the jet’s computers and satellite receivers pinpoint our position close enough to allow for safe descent and approach–completely in the blind?
I’ll also admit, like everyone else learning to use the HUD, I was swimming in symbology and information at first. Add to that the transition from traditional round dial displays on the MD-80 to the more advanced flat-panel displays on the Boeing Next Gen jets and you have a real spaghetti bowl of information swirling in front of you and in the case of the HUD, it’s all in ghostly monochromatic green, compared to the color-sorted original display on the instrument panel that is reproduced in the HUD:
But eventually, two things happen. First, you stop swimming in the symbology. Second, you learn after dozens of approaches in the clear as well as in the blind in weather that the system is reliable.
The first part, stopping the swimming is not as easy as it sounds but the trick is this: you have to embrace the theory of the flat panel display above that gives you a symmetry of information: airspeed tape on the left side, altitude tape on the right. Compare the two readouts between the photo of the information on the photo above, then on the HUD display above that. Note the markers indicating speed limits–we call it the “chain,” showing max speeds for configuration. That shifts as you change configuration–say, add or remove flaps.
On the instrument panel, you see the chain in a different color–up top on the HUD, it’s all ghostly green. So two things have to happen. First, you stop looking at colors and discipline yourself to see and heed shapes–but that’s not all. Second, you learn to not look at the side displays, but rather, incorporate shapes into your peripheral awareness. That is key: peripheral sense. keep both tapes, airspeed and altitude in your indirect awareness, alert for the shapes on each giving you cues to the restrictions. In the case of speed, it’s minimums and maximums (the “chains” counterpart on the low end is the “hook,” or stick shaker limit). In the case of altitude, same thing: level off or descent minimums, or climb level off points, or clean-up altitudes.
You don’t look “at” the HUD information, you look through it but incorporate the information as you go. I once counted all of the possible display symbology and counted nearly 60 pieces of information displayed. You could get lost trying to follow every piece of information, but the key is to just absorb whatever you can from the periphery as things change. Let’s put this into motion on an approach:
(note: the above is an embedded YouTube video. If your browser won’t animate it, just click here to watch)
Notice the slowly decreasing altitude on the righthand tape while the airspeed on the left remains stable. The radio altitude is counting down near the center–obviously that’s important and so that information is near center of your focus and incidentally, near the touchdown point. The compass rose below the display shows the course track, but the only thing you care about is alignment–again, you’re simply maintaining symmetry by keeping that peripheral information lined up.
This video is slightly different from the 737-800 I fly in that there’s no “flare” cue in this depiction: that’s simply the word “flare” that anunciate above a line that appears indicating where to put the nose for a smooth touchdown. Also, the word “idle” annunciates to suggest when to remove power as the autothrottles pull back for touchdown.
The dot in the center of the aircraft symbol is the desired path, the symbol surrounding it–if you’re successful at keeping them aligned–is the “flight path vector,” a symbol indicating where the aircraft is aimed despite the apparent orientation. That is, in a crosswind, you may be canted 20 to 30 degrees to one side or the other, but the FPV shows where you’re actually headed.
This video stops at touchdown, but the HUD does not: when you select detail level 2 or 3 and the ILS antenna supports it, the HUD gives you a runway remaining countdown and centerline steering information–which can be very useful in low-visibility landings and take-offs :
At my airline, we fly the HUD to the lowest minimum certified, as opposed to other Cat 3 certified aircraft that “autoland.” We never autoland–rather, with the aid of the HUD, the captain hand-flys every minimum visibility approach. Now that I have over a thousand hours in the 737-800 left seat, yes, I’m a “HUD cripple”–and I wouldn’t have it any other way.
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