Unpaved runways call for additional research
One of the notes commonly found alongside landing-distance charts in pilot’s operating handbooks gives the pilot a way to calculate how much extra runway you would use when landing on an unpaved surface. It takes 1,295 feet to bring a 1986 Cessna 172 over the hedges and to a stop at sea level on dry, level pavement using a short-field technique when the temperature is 20 degrees Celsius. It will take 1,542 feet to accomplish the same task on a “dry grass runway,” according to the aircraft’s POH.
How much extra length is required on a wet grass runway?
That’s anybody’s guess. But it doesn’t stop people from experimenting, sometimes unaware, sometimes from necessity—and on occasion, both. We learn about the experiments when something goes wrong, and it’s a good reminder of a common but hidden hazard that looms large at this time of year.
By April, spring is well-sprung in many places. In others, the battle of the seasons is still going back and forth. Checking notams about temporary runway closures and getting firsthand updates on rapidly changing conditions at potential destinations are good ideas, followed by a careful low pass to see for yourself, especially if the seasonal thaw is under way. Temperatures fluctuating above and below freezing in early spring can make a runway that was usable in the early morning a treacherous mess by noon. If the airport you plan to visit—say, for a grass-strip practice flight—is near home and just an attractive possible practice strip, drive over and walk the runway before flying there. If it’s far away, be sure to get a time stamp on any condition reports you receive, whether the formal kind or a casual observer’s report. Even then, stay skeptical.
What if the runway is known to be firm, but it rained there last night? A wet grass runway isn’t always a no-go—but if your flight runs into other kinds of trouble, it could be the final link in an accident chain.
That’s what happened on April 30, 2011, in Suchez, Georgia, when a flight’s troubles began with a balked landing and were compounded by shifting winds and wet grass.
The pilot of a Cessna 172M overflew the Suchez airstrip to check the windsock, and decided to land on Runway 2, a 2,000-foot-long grass runway. The airplane was too high on final, and the pilot went around. Then he tried the approach again. The airplane “touched down at a point 800 to 1,000 feet from the approach end of the runway at 90 mph; that was about 20 mph faster than normal,” said a National Transportation Safety Board accident report. The pilot “later stated that at touchdown the wind shifted. After touchdown on the wet grass, he applied the brakes, but the airplane would not stop. Because he was too far down the runway to perform a go-around, he continued on the ground with the brakes applied. The airplane traveled off the end of the runway where the right wing collided with a fence. The airplane then traveled through a ditch and came to rest upright in a field.”
The NTSB report added that “marks on the runway revealed the airplane touched down about 800 feet before the departure end of the runway.” It said the probable accident causes include the pilot’s decision not to go around, and excessive speed.
You say that you checked with Flight Service, which confirmed that the runway you plan to land on was used on the day of your flight, and that you overflew the runway at 500 feet, and it looked good?
It’s your call. But despite all that legwork, a flight still turned out badly on April 9, 2011, for a pilot in Talkeetna, Alaska, who landed a Piper PA-22 on a snow-covered unattended gravel strip that appeared firm but had a hidden slushy spot, causing the aircraft to nose over.
The NTSB report filled in an important blank about the strip, noting that the pilot “was unaware that the airstrip was used primarily by ski-equipped airplanes during the winter.” It assigned as the accident’s probable cause “the pilot’s selection of a soft, slushy runway for landing, resulting in a noseover.”
When evaluating a possible landing site before you head out for a spring flight, make sure you know who uses the place, and with what kind of equipment. That may give you some important clues about what to expect. Then brief yourself on the emergency procedures you would follow there to complete the preflight picture of your proposed flight.
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