Ask the Captain: Are airport runways flat?

— -- Question: Are runways flat? From what I've noticed they are not. Also, some appear to have an angle or slope. Take for example San Jose Costa Rica International airport (SJO); even the terminal running parallel to the runway is on an angle. If you walk from gate 1 up to 21 it's an uphill walk. Is that normal? Some other runways appear to go up and down at different points.

— submitted by reader mguerra

Answer: No, runways are not flat. They are crowned to help drain water off the sides during rain, and often one end of a runway is higher or lower than the other. When preparing takeoff performance calculations, pilots include the slope of the runway. Taking off uphill causes performance degradation while downhill is a performance enhancement. Airplane flight manuals include the maximum runway slope allowed. A few runways have "humps" when a part of the runway will rise then descend. This makes for challenging landings.

Q: Captain, can you explain what the different signs we see out the window while we're taxiing to the runways denote? They seem to mark taxiways but I've always wondered about the different color-coding and whether it relates to specific runways or plane sizes, etc.

— joeduffus

A: Airport signs are carefully designed to help pilots determine their location. Runway signs are white on red backgrounds and are numbers; taxiways are yellow on black and are letters. There are other painted markings showing hold lines and the edge of the airport movement area.

The signs that are the most visible to passengers are taxiway signs showing different taxiways around the airport.

Here are some follow-up questions to a recent column about landings:

Q: Captain, I look forward to your columns! On the continuing subject of landings, I was wondering if there would be an advantage to having the wheels spin, possibly near the speed of landing, so that when the aircraft touches down, less rubber would be burnt.

—zspira98

Q: Some years ago, during one of our president's campaign to whip inflation (WIN), I sent in a suggestion aimed at reducing tire wear on airplanes. I suggested that the tires be fitted with a molded sidewall with slight protrusions in the form of "vanes" to catch the wind as the tires were lowered. This would start the tires spinning and thereby reduce the wear from "scuffing" until they got up to speed.

—a70ce61e0c0847d7

A: While the tires might wear slightly less, there would be a need to have the wheels spinning at the same speed to prevent an asymmetric side load from occurring during touchdown. The measuring and control of the wheel speed would add cost and complexity. I have never heard of an aircraft manufacturer that has considered adding this feature.

Readers, please leave your questions for John Cox here, and only leave comments about this week's column below.

John Cox is a retired airline captain with U.S. Airways and runs his own aviation safety consulting company, Safety Operating Systems.