On Final: Limitations

On Final: Limitations

On Final: Limitations

Sitting at an elevation of 4,830 ft, the runway at Sedona, Ariz., has a 1.83 percent slope, which requires careful consideration to ensure adequate runway is available for given aircraft weight and weather.

In junior high, I used to walk to school every day. It was uphill both ways. At least so I thought. When I tell my grandkids this story they just look confused. “Didn’t they have Uber back then Poppy?”

But the slope of the runway is much more important to airplanes. During the summer, Larry King and I planned a gross weight departure from Colorado Springs (KCOS) on a 25-degree C day in his Citation M2. We figured 11,022 feet of runway (35L) would be plenty. But after plugging in the parameters into Cessna’s handy performance calculator, we were wrong. The software said we would have to offload 700 pounds of stuff in order to legally depart. And we would still need every foot of the runway to do so.

“What’s wrong with this stupid calculator,” I moaned. After much wrangling with the numbers, we realized that the runway slope for 35L at 1.2 percent was the culprit. Just a few hundred yards away was the 13,501-foot 35R with a slope of only 0.62 percent. Plugging in the data showed us that the reduced slope would allow us to depart at gross weight and we would need only 9,600 feet to do it.

Slope is important.

I found this out again recently during a visit to Sedona, Arizona (KSEZ). Sitting at 4,830 feet MSL and 500 feet above the town on a large mesa, the airport is often referred to as the “aircraft carrier of the desert.” It is truly spectacular, surrounded by dramatic red rock outcroppings. The airport’s location creates its own local weather as the mountains absorb heat during the day and generate significant winds at night and early morning.

We departed Dallas in the Mustang at 0815 in order to arrive before the daily landing turbulence. The approach was fairly routine even with both PAPI’s NOTAM’ed out of service. The hardest part was focusing on the flying instead of the incredible terrain surrounding the airport.

When it came time to depart, I had some thinking to do. The winds were forecast to be out of the northeast at 10 knots, favoring runway 03. The only obstacle departure procedure however, was to the southwest off runway 21. Should I depart with a 10-knot tailwind? That’s not something I would normally do, but here is where the runway slope came in. The handy Cessna calculator said I could depart on 03 into the wind and use about 4,300 feet or depart with a 10-knot tailwind on 21 and use 4,100 feet. Again, all due to the runway slope of 1.83 percent.

On the morning of departure, Mother Nature made the decision for us with winds from the northeast gusting to 17 knots, exceeding takeoff limitations. The young line person operating the pickup truck with the tow bar didn’t understand why we needed to be turned around facing the wind for our engine start. “It’s all about limitations,” I said.

Runway 03 it would be.

Years ago, before performance calculators, we often just guessed the outcome of winds and weather. Today, we don’t have to.

Fly safe.

About the Author

Leave a Reply