SAND POINT, AK, USA
N125FG
PIPER PA-18-150
THE PILOT REPORTED HE HAD LANDED THE 29' TUNDRA TIRE EQUIPPED TAIL WHEEL AIRPLANE ON THE HARD SURFACED RUNWAY AND WAS SLOWING TO TAXI SPEED WHEN THE AIRPLANE SUDDENLY VEERED TO THE RIGHT. HE APPLIED FULL LEFT BRAKE AND RUDDER, BUT WAS UNABLE TO STRAIGHTEN THE AIRPLANE BEFORE THE LEFT MAIN LANDING GEAR COLLAPSED. SUBSEQUENT EXAMINATION OF THE TAILWHEEL STEERING MECHANISM FOUND THE ANTI-CASTORING LIMITS WERE BELOW THE MANUFACTURER'S RECOMMENDED BREAK FREE FORCE, WHICH ALLOWED THE AIRPLANE TO TURN FASTER AND MORE FREELY TO THE RIGHT THAN COMMANDED BY THE RUDDER CONTROL INPUTS. CONVERSATIONS WITH PILOTS WHO HAVE EXTENSIVE EXPERIENCE WITH TUNDRA TIRES DISCLOSED THAT AIRPLANES SO EQUIPPED ARE MUCH MORE DIFFICULT TO HANDLE ON HARD SURFACED RUNWAYS THAN AIRPLANES WITH CONVENTIONAL TIRES.
On June 2, 1995, about 1940 Alaska daylight time, a Piper PA-18- 150 airplane, N125FG, equipped with 29" tundra tires, received substantial damage while landing on runway 31 at Sand Point Airport, Sand Point, Alaska. Neither the airline transport certificated pilot, or the sole passenger aboard were injured. The 14 CFR Part 91 flight was operated by the State of Alaska's Department of Fish and Game. The purpose of the flight was to return a State of Alaska employee to his work station at Sand Point. The flight operated in visual meteorological conditions, and had departed Port Moller, Alaska, about 1900. The pilot reported that prior to landing, he noted the wind as approximately 5 to 7 knots, straight down the runway. He said in an interview with the NTSB investigator-in-charge (IIC) on June 8, 1995, that he had considered landing in the gravel alongside of the runway because of the better handling qualities of the tundra tires in gravel as compared to those of a hard surfaced runway, but he elected to land on the runway because of the favorable wind and other factors. During the landing roll, he reported the airplane veered to the right. He said he applied hard left brake, full left rudder, and full power. The airplane began to slowly respond to the left, but prior to becoming straight, the left main gear collapsed. Postaccident conversations with the Chief Pilot/Mechanic for the Department of Fish and Game disclosed that he had discovered no obvious anomalies with the accident airplane's wheels or brakes. He did discover the anti-castoring break free limits of the steerable tailwheel was set below the limit recommended by the manufacturer. He said that as a result, the tailwheel would freely castor to the right at a lower than normal load force, which would make it very difficult to control the airplane once it started going to the right. The Chief Pilot is a certificated Airframe and Powerplant mechanic with inspection authorization (IA). The NTSB IIC also spoke with the accident pilot, the Chief Pilot, and other pilots who have extensive experience in landing airplanes equipped with tundra tires. All of the pilots indicated that airplanes equipped with tundra tires are much more difficult to land on hard surfaced runways than gravel or sand. They commented that soft landing surfaces are much more forgiving, and allow the larger tires to move and slide more readily than if they were on a hard surface.
The premature castoring of the tailwheel steering mechanism. A factor associated the accident is the added degree of difficulty in handling airplanes equipped with oversize 'tundra' tires.
Source: NTSB Aviation Accident Database
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