Altitude treasure hunt

Karen, a commercial pilot from Utah, asks: “Where on an airport is the “official” altitude measured? Is it the ramp, the terminal, the beacon tower, the middle of the runway? If so, which runway? I was on the ramp at Hemphill County Airport (KHHF), in Canadian, Texas, the other day and the terminal is on a hill overlooking everything and it got me to wondering.”

I confess that I never thought about where the official altitude of the field is measured from until you asked, nor do I recall any instructor ever teaching me about this back in the day.

But once you brought it up, I can think of dozens of airports that are far from flat. And I, too, have been to KHHF, with its uphill hike to the pilot relief station. And it’s the only airport that I’ve ever visited that has a subterranean tornado shelter!

Not that I was there during a tornado or anything, but finding the answer to your question initiated a whirlwind of activity.

I started with what we in the flight-training biz like to call the “Pee-hack,” the Pilot’s Handbook of Aeronautical Knowledge. I like the PHAK because it’s thorough and well written — generally in something pretty close to plain English.

As it also has 39 pages of information on airports and airport ops, I figured I’d quickly have the answer to your question and I was worrying about how I’d fill up the rest of the space in today’s column. That wasn’t to be.

I diligently searched through the chapter, and then thumbed through the rest of the book to get an answer to your question. No joy.

With a groan, I turned to the AIM, which back in my day was the Airman’s Information Manual, but is now the more politically correct Aeronautical Information Manual.

I confess, I’m not a fan of the AIM, either then or now, except when I’m suffering from insomnia. Still, I reviewed every section I thought might have our hidden gem, including the sections on airport markings, airport ops, and even the section on setting altimeters, thinking that there might be some reference to the benefits and risks of using the official airport elevation as a baseline setting if your Kollsman window is funky.

After three very sound nights of sleep, I can report no joy. Well, I enjoyed the rest, but you know what I mean. No joy on finding the answer to your question.

Of course, that doesn’t mean it isn’t buried somewhere in the sections I reviewed. There are a lot of words in those chapters. If I missed it, feel free to flame my tail in comments.

Next, where you are probably supposed to look first, I turned to the FARs, which rather than put me to sleep, tend to give me a headache. The FARs are written by lawyers and the amount of double speak, double negatives, and triple confusion makes them nearly unfathomable without two legal pads and a package of sticky notes.

You would have no reason to know this, but airport laws are in part 153, which is not exactly the gold mine of airport information that you’d expect. The part largely covers noise issues, funding issues, and inspector access issues.

Once again, no joy.

Moving on, I turned to the little-known Aeronautical Chart User’s Guide, a wonderful book for learning about rare and bizarre symbols and notations that appear on charts. Like all FAA pubs, it suffers from having a poor index, so I braced myself for poring over the pages with many poured cups of coffee (having no fear of the excess coffee keeping me up all night because I could always read the AIM to counteract the caffeine).

But much to my surprise, the answer was on page 16, in the section on airport chart symbols: “The elevation of an airport is the highest point on the usable portion of the landing areas.” In other words, the highest point of any of the runways.

OK. Now we know. But then I began to wonder…What’s the authority for that? If it’s not in the FARs, and it’s not in the AIM, where did it come from?

So, I whipped out the local Chart Supplement — the artist formally known as the Airport Facilities Directory — and found the same information right up front, in the chart legend, item 11. About this time, it occurred to me that I’d been focusing on airport altitude, not airport “elevation.”

I brought up an electronic version of the AIM and did a word search for “airport elevation,” and it turns out the subject is in the AIM, after all. It’s in the frickin’ Pilot/Controller Glossary. On page 623. Sheesh. 

But still no joy on a source for this little gem.

It was time to look beyond the FAA to understand the FAA. I broke out Richie Lengel’s visually chaotic, but fabulously indexed, Everything Explained for the Professional Pilot, and quickly found myself at the source of the Nile, as it were.

Lengel had the same information, but he also included a reference: Advisory Circular AC 150/5300-13A. It’s titled “Airport Design,” and it’s issued by the Airport Engineering Division of the FAA. I didn’t even know the FAA had an Airport Engineering Division, but of course it makes sense that it does. According to the FAA’s website, the division is made up of 17 people, most of whom are civil and electrical engineers of various flavors.

The AC is 308 pages long, but, thankfully, what I was after was on page 3 in the definitions section, which just repeats what we already learned. 

As a side note, the official Lat/Long of an airport is NOT where the elevation of the field is measured. Instead, the charted location of an airport, per the Chart Supplement, is the approximant geometric center of all its usable runway surfaces.

And unlike runway numbers, which sometimes change with magnetic drift, once this center point is first calculated, it forever stays the same as the official heart of the airport — even if expansion or the closing of runways makes the difference between the true geometric center and the recorded center start to look like the difference between the geographic and magnetic north poles.

William E. Dubois is a commercial pilot, ground instructor, and is now unlikely to ever forget where the elevation of an airport is measured from.