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Runway Slope
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Beware of the Insidious Incline
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 By Mike Magnell
How many runways in the world do you think are perfectly level? I mean really flat, with both ends the exact same elevation, and no dips or rises in between. Surprise! The answer is none. All runways have slope, some a lot and others only a little, but they all have some degree of slope. There are even those like Tijuana International airport’s single runway, which in addition to slope, contains so many dips that it looks like a stretched out roller coaster as you commence the takeoff roll.
I am a product of General Aviation, and as I progressed up through the rating ranks of Private to ATP, I don’t recall runway slope being a focus point of any GA training curriculum. In fact, my first real encounter with it was as a young 26-year-old Bush Pilot in Alaska, and then again as a 30-year-old new-hire Flight Engineer (Second Officer) on the stretched B727-200 for Western Airlines out of Los Angeles.
As a young Bush Pilot in Northwest Alaska on the Seward Peninsula during the early 1970s, I had to deal with two very short runways that had a significant amount of slope. What I quickly learned was that landing down hill and trying to takeoff up hill generally did not work out too well. Of course, that statement depends on many variables such as, how much slope, runway length, prevailing wind conditions, and the surrounding terrain involved.
One of those Alaska runways was located at Hannum Creek, where my wife’s family has a Summer Mining Camp. The strip was only 900 feet long and not much above MSL elevation, but it had a considerable slope as it ran parallel to a cold bubbly creek, nestled in a very tiny draw, surrounded by wind disturbing hills on all sides, with no really good clear straight in approach from any direction. My first landing there was in a Helio Courier, which is a CSTOL aircraft and a super short field landing machine. The light wind at the time favored a down slope landing, and not knowing any better, that is exactly what I did. The results were amazing to me, because even in the empty Helio, with only myself in it, I used just about all of that 900 foot strip getting down and stopped. After that, I always landed the other way there – up slope, and made my takeoffs down slope.
The other runway in Alaska was located at Serpentine Hot Springs, and is today still only 1,100 feet long. It too has a similar slope, though it sits in a bigger valley than Hannum with a much better approach. However, it is definitely a one way in and the opposite way out strip, because of slope and rising terrain. If one tries to takeoff up slope at Serpentine, they better be in an empty Turbine Powered Pilatus Porter, because the terrain rises into some rather distinct and nasty looking hills in not too far of a distance, and those pugnacious little hills have swallowed up a few planes that didn’t pay attention to the laws of physics. The deceiving thing about both Hannum and Serpentine is, to the pilot’s naked eye, the slope and surrounding terrain look a bit nebulous and not all that threatening, but beware — they are surely dangerous. And there lies the major problem about runway slope. It is very difficult to put into proper perspective with just the naked eye.
My next indelible encounter with runway slope was on a more, shall we say, professional basis, than the Alaska seat of the pants bush flying experience. I was a new-hire Second Officer in 1976 for Western Airlines on the B727 and getting ready for takeoff at the old mile high Denver Stapleton Airport (elevation 5,280). Part of my job as Second Officer was to prepare a takeoff and landing data card for the pilots. While I was preparing the takeoff card at Denver this particular day, I happen to notice that the Maximum Gross Takeoff Weight (MGTW) was different by several thousand pounds for the same runway, depending on which way you decided to takeoff. There were no obstacles on this selected runway in either direction, so slope at that altitude was the only variable. I had been schooled in runway slope during my Flight Engineer performance training, but for some reason sitting there at Denver, getting ready for that takeoff and looking at Western’s runway data charts and seeing the striking effect slope had on MGTW from an otherwise benign looking runway, really drove the point about runway slope home to me much better than sitting in the classroom ever could.
In the Southwestern USA we have an eclectic group of runways, many of which are at high elevations, and runway slope has a much more profound effect on an aircraft’s performance when trying to takeoff in high density altitude situations as opposed to sea level departures.
Take Big Bear Airport at Big Bear Lake in the San Bernardino Mountains of Southern California for example. It sits at an elevation of 6,750 feet, the runway is relatively long at 5,850 feet, and to the naked eye it looks completely level. However, taking off to the east on runway 8 will offer you a bit of an up slope to overcome, and also at the east end of the runway is a group of tall and not so inviting pine trees. Departing to the east there on a hot day into the wind could be interesting if your aircraft is challengingly loaded. You can expect a down draft coming up on the leeward wind side of those trees right after getting airborne off of the runway, and as a result you may run out of climb performance and start sharing the same real estate with those pernicious looking trees right in front of you. If the wind is around 7 to maybe even 10 knots out of the east at Big Bear, I will probably launch downhill and downwind to the west on runway 26, straight out over the lake with no obstacles to miss and no potential down drifts to deal with.
There are a lot of other airports we could discuss, all with there own set of individual circumstances and idiosyncrasies, but they all have one thing in common, slope – no matter how flat the runway may appear. The point I am trying to make here is that GA pilots should include runway slope into their preflight planning equation, especially at high altitude airports, because it is definitely a piece of the aircraft performance puzzle.
Finding runway slope data during your preflight planning is not too difficult. Most airfield diagrams, such as those found in Flight Guide, include slope data for each runway. As an alternative, a quick call to the Airport Manager’s office of your destination airport will rapidly yield runway slope information. I have queried many an airport manager about runway slope, and always got a friendly and accurate answer. In fact, I was at Leadville, Colorado (elevation 9,927) recently for the first time, and while there asked Dan Jensen, the Airport Manager, what the runway slope was. He immediately and amicably replied, “The south end is nine feet lower than the north end.” He didn’t even have to look it up!
When flying GA aircraft I like to think of runway slope in conjunction with the prevailing wind, and ask myself if one enhances the other or mitigates it. In some extreme bush situations, like what I encountered in Alaska, runway slope can be so copious that it is the sole consideration for your takeoff and landing decisions. However, a gentle, insidious slope can present an even greater challenge to your ability to choose the safest runway.
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