By Jim Van Namee, CFII
Lolling about at Taos Regional Airport’s Vulture’s Row recently, I watched a visiting pilot perpetrate touch and goes; the first touchdown about halfway down the runway. This was followed by several more much closer to midway down the runway. Being an FAA Aviation Safety Counselor, this made me deliberate for a few moments and resolve to go forth and do the suitable safety counselor deed - write an article.
Taos has a 5800-foot runway, and, under ordinary conditions, most general aviation pilots can get away with hot, long landings on runways of comparable length at higher altitudes. But, my semi-learned mind nags, “Why?” What good is runway behind you? If you habitually accept landing well down the runway, one day the skills you need to put a wounded airplane down in a postage stamp-size field or short runway won’t be there to keep you from possible injury.
Your aerospace vehicle’s POH specifies landing speeds. Some speeds are given in a range; for example, 65-75 knots in some Cessna 182 manuals. Being good Americans we suppose more is better. So, we add 5 knots for Mom, 5 knots for the kids, etc. Some folks sense they are too near stall, so they’ve developed personal landing speeds.
Using time-honored Rules of Thumb, let’s look at the impact of higher landing speeds and higher density altitude on your landing distance. I’m going to use Taos Regional Airport (7091’ MSL with a 5800 feet runway) with an outside air temperature of 80 degrees. You are shooting the GPS approach to R/W 04 in a light rain shower; winds are 220 degrees at 7 knots. The 1972 POH for a 3000-pound Bonanza A36 specifies a flap down approach speed of 70 knots to achieve a normal landing distance of approximately 1800 feet. But, I’ll assume the examples below are being flown by a pilot who chooses to add 10 knots for Mom and a personal “comfort level” – can’t get too close to that power off, Vso stall speed of 52 knots.
For each knot of airspeed above POH final approach airspeed over the numbers, the touchdown point will be 100 feet further down the runway. Flying at 80 knots, your touchdown will be an additional 1000 feet further down the runway.
A tailwind of 10 percent of your approach speed will increase your landing distance by 20 percent. Often a downwind landing is selected at uncontrolled airports to save fuel and time if the wind is in the 5-7 knot range, or you’re coming in from an instrument approach and don’t want to circle to land. If you accept the 7-knot tailwind, then your landing distance will increase by another 20 percent, or an additional 360 feet.
A 10 percent change in airspeed will cause a 20 percent change in stopping distance. Flying at 80 knots, your stopping distance will increase 30 percent, or an additional 550 feet. You and your aerospace vehicle now have a stopping distance of 3710 feet from touchdown.
A one degree reduction in approach angle increases landing distance 13 percent. Let’s say you tend to fly a flat glide slope. Now you’ve added at least 480 feet to your landing distance for a total of 4190 feet. And, oh by the way, since the runway is wet, the landing distance may be increased by 50 percent making your rollout 6288 feet from touchdown (let’s hope you don’t add to that by hydroplaning). Whoops, even if you landed on the numbers, are a Beech test pilot who can meet the POH airspeeds and stop/landing distance; you’ve done gone and got busted. What’s the FAA and the insurance company gonna say? What are you gonna say? Most importantly, what are the local pilots hanging out in Vulture’s Row gonna say? I mean, this borders on awkwardness, mortification, maybe even shame.
A 1979 Cessna 172N POH shows only short field landing performance at Maximum Gross Weight. At Taos Regional, the plane would have a normal short field ground roll of approximately 700 feet at 60 knots. Applying all of the above situations with a pilot flying the airplane at 70 knots the ground roll would be 3460 feet. And that’s using the short field approach procedure. Not many of us can land on the exact end of the runway or meet the POH numbers set by a company test pilot in a new airplane.
So, could your modus operandi use some enrichment? Why not go out with a local flight instructor who is comfortable flying the book numbers in your type of plane and practice flying “on speed,” on glide-slope, and to a consistent spot not too far beyond the numbers. See what it’s like to make the first turn off without stressing the airplane.
Last, but certainly not least, for those of you in the lower provinces, never, I say again, NEVER get in an airplane with anyone who advises you to add 10 knots to your final approach speed when landing at high altitude airports (Hint – review TAS vs. IAS vs. DA). What's more, never acknowledge their counsel again. Run, don’t walk away, lest your brain become tainted with dumb dust.
Jim Van Namee, CFII and owner of Silver Eagle Aviation, LLC, operates at Taos Regional Airport (KSKX) in Taos, NM. He retired as a Naval Aviator with over 6000 flight hours and bunches of carrier landings. He is the New Mexico Pilots Association Director of Mountain Flying Instruction, and a Designated FAA Aviation Safety Counselor. He can be reached at email@example.com or 505-377-6786.