Runways can’t always be perfectly smooth

Question: I have noticed that runways are not perfectly level at some airports. A retired pilot friend of mine said that some even have humps in them. Why are the runways not perfectly flat, and does this pose any problems during landings and takeoffs?

— Tom Page Answer: Some runways are more challenging because of the slope and humps. The slope is included in performance calculations for takeoff and landing, as it can affect acceleration and deceleration. Humps can cause “firm” landings if the pilots are not aware of them or if they miscalculate the touchdown point.

Runways are rarely the same elevation at each end, so in many cases the question is the amount of slope. There is also a need to keep taxiways at a reasonable slope, and there may be differences in elevation on a different axis. Airport designers must make compromises for efficiency and cost.

Q: Why does the plane bounce while taxiing ? Are the runways/taxiways always bumpy? Do the plane’s shocks not absorb it?

— Roman Grizzell, Franklin, Tenn.

A: The struts (shock absorbers) are designed to take the loads during landing. This makes them a bit stiffer than a car. Plus weight is distributed differently during taxi, making bouncing more likely. And many taxiways are not perfectly smooth, causing extra motion when taxiing on them.

Q: Recently I flew from Portland to Chicago. Just after takeoff, the pilot announced we needed to return to the airport because we scraped our tail on the runway. We were in a 757. Is this common?

— Joe, Chicago

A: No, it is not common but does happen. Many modern jet airliners have long fuselages, making the tail more vulnerable to scraping at certain angles.

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