I See Fourteen Lights

There might be fog or mist present when I depart tomorrow from an uncontrolled aerodrome. The minimum allowable visibility for my departure is half a statute mile, so I need to be able to determine how far I can see along the runway, without a tower, a flight service specialist or an electronic runway visual range (RVR) measurement. I'll have to count runway lights.

I haven't done this in a while--you don't get fog much in the summer--so I had to double check some numbers. I found then in A Quick Reference: Airfield Standards from the US FAA. (Nice little reference. I intend to read it through in its entirety sometime, maybe while waiting for fog). It confirms for me that the lights along the runway edge are spaced 200' apart. There are six thousand feet in a nautical mile, but for some reason ground visibility is measured in statute miles, which contain only 5280 feet apiece. (I had to look that number up, too). That means that I need to be able to see half of that, or 2640' feet along the runway to meet the half-mile minimum visibility. And at this point I realize "well duh: if there is an RVR then a half mile is RVR 2600." So I'm on track. This means that if I pull onto the runway even with one set of runway lights (they are aligned with each other on each edge of the runway) I need to be able to count 2600 divided by 200, or thirteen more pairs of them, stretching away into the foggy gloom, in order to be legal. I'm happy to ignore the extra 40' because RVR values do, and because I'm looking along the hypotenuse of the triangle whose base is on the runway edge, and surely I'll pick up another forty feet there.

Whom am I kidding? This is Cockpit Conversation. We don't make assumptions about trigonometry here, we do trigonometry. The base of the triangle runs from my position at the first runway edge light, to the fourteenth runway light, and is 2600' long. Assume I'm in the middle of a runway, standard width 200', making the height of the triangle 100'. The measurement of the hypotenuse is therefore sqrt((2600 x 2600)+(100 x 100)) = 2602. So no, actually, there is almost no difference between the distance from the first runway light to the fourteenth, and the distance from my eye to the fourteenth light. That's a very skinny triangle. My assumption is wrong. So if I wanted to be a nerd, I could park thirty-eight feet back from the first pair of runway lights. But generally I want to go flying.

In order to save Americans time telling me that the RVR for half a mile is 2400, I'll confirm that in Canada and the other countries I checked researching this post, the RVR for half a mile is 2600. I don't know why Americans use 2400, and neither do the people in this thread on the subject. I especially like the way that the person who initially answers the question there doesn't notice that RVR 2400 for a half mile doesn't add up, until the student points it out. Another thing I expect American commenters to want to tell me today is that "if you have to count runway lights on short final, you should go missed." That's becase their landings are legally restricted by visibility. But Canadian landings are governed only by decision height or MDA. If the runway is visible at DH/MDA, a landing is authorized for us. Our plates have an "advisory visibility" which we can use to calculate whether we expect to be visual at minimums, but its value does not affect our legality to put the airplane on the runway. Once we are past the FAF, the RVR does not restrict us. We do have something called an approach ban which can stop us from legally attempting an approach in terrible visibility, but that's a whole 'nother topic.

That Horrible Moment When ...

... you land at some little GA airport in the afternoon, because it happened to have a runway long enough, and it was equidistant from the various places you thought you might be asked to go the next day, and then you get a phone call at o-dark-hundred, and during flight planning you ask yourself, "Does the aerodrome have lighting?"

It did. But with fall just around the corner, I'd better start checking that.

Keeping It Between the Lights

About ten years ago a crew landed a Boeing 737 at Edmonton International in the fog and snow, and touched down beside the runway instead of on it. They got the airplane back on the runway after taking out a sign and a bunch of lights, and no one was hurt. The poor pilots had been up for almost twenty-four hours by the time it happened.

I feel so badly for them. I've landed at Edmonton International at night, and there are a lot of lights. When you land on a northern, snow-covered runway you find the rows of lights or reflectors and you land between them. You can't see the runway. It's exactly the same black and then reflective white as the area outside the runway. You just flare and hope the information you got on the depth of the snow and how packed it is was correct.

I think I did a similar thing when I was a commercial student, landing on a grass field. It was an actual field, just your standard chunk of turf in between the farm roads. There was a windbreak of poplar trees planted along one side, and then a line of tires showing the edge of the area they considered the runway. Presumably the "runway" side was more packed down from landing aircraft, more frequently mowed, and checked for rocks, mole hills, and the like. The CFS entry for the airport didn't mention the tires and I think I may have landed on the wrong side of them. I don't even remember--that's how un-serious my incident was. It could have been bad had the ground been soft or the grass really long and hiding obstacles on the "bad" side. I just remember that someone later told me which was the correct side. Obviously it wasn't an international airport, and before someone put the tires there I'm sure folks just landed all over.

Last time I landed at CYEG it was night, and the end of my working day. The controller asked me to turn a five mile final, but not knowing the local night time landmarks well it was difficult for me to choose a bearing that would set me up for that. I could easily turn final five miles from the airport, but I didn't have a waypoint set for the threshold of the runway, and single pilot at night, and tired in descent for a runway is a really bad place to start calculating a lat and long based off runway information, or perhaps there was a waypoint on a GPS plate, and then programming a lat and long out of a book into the GPS. Normally for that sort of thing you can use the runway as a yardstick and just mentally extend it to where you need to join, but the layout of runways at the International there combined with the angle I was approaching from made it tricky. So I did that thing that is free and safe and doesn't require me to take my eyes off the instruments or the scenery: I asked the controller a question similar to, "does this look good for where you want me to intercept final?" I probably threw in the word "unfamiliar," as well. The controller has a radar screen that shows the runways, and my blip, and he has tools that can show my extended track and distance, but he probably doesn't need them as his job is to look at blips and know whether they will conflict. It definitely made me look less cool. I couldn't pretend to be a completely fearless pilot utterly blasé in the face of any danger. But it saved me a couple of minutes in the air, because the controller told me I was free to fly direct to the threshold. And who wants a pilot inured to danger when you can have one who gets you there safely?

This is in no means intended to imply that the 737 crew wouldn't have had their incident had they asked for help. I was only trying to point out that on a beautiful visibility night a pilot who is a lot less tired can get confused. The visibility was terrible for these guys and they must have been exhausted. The upside is that their company changed the procedures after that, so crews no longer risked having to do that night landing after being up for a full day.