NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
Before the accident flight, the commercial pilot had conducted three flights, during which parachutists were successfully dropped. After each flight, he returned the empty airplane to a dry grass airstrip (1,950 ft long) and conducted full-stop landings. Because the temperature was over 90° with high humidity, the pilot requested that his manifests allow only up to 14 parachutists and a longer time between shutdowns to ensure sufficient time for adequate engine cooling before the next flight. The pilot reported that pop-up rain showers had been passing north and south of his base airport throughout the morning but that they never came closer than 10 to 15 miles.
While preparing for the accident flight, the pilot noted that clouds were over the intended drop zone but that there was no rain and that the clouds were moving away from the northern edge of the drop zone, so the pilot decided that it was worth attempting the flight. While climbing through 4,000 ft, an air traffic controller advised the pilot that light-to-moderate precipitation was in the area. The pilot continued to climb toward the drop zone, and the flight encountered light rain. The pilot advised the 14 parachutists that they were returning to land because of the weather.
The approach was a stabilized, power-on approach, which was much flatter than the previous approaches with an empty airplane. The pilot used flaps incrementally to 30° (full flaps), initiated a flare over the threshold, and touched down at 65 knots. He used full-reverse propeller and retracted the flaps during the landing roll. When the pilot started to apply the brakes, he discovered that the braking action was null. The grass runway was wet because of a recent rain shower. Because of the hot temperature, humidity, full load of parachutists, and trees at the end of the runway, the pilot decided not to attempt a go-around. The pilot held full aft on the control yoke for aerodynamic braking, stayed in full-reverse propeller, and braked as much as possible without locking the wheels up. Just before coming to a complete stop (about 5 to 10 mph), the airplane rolled into a ditch before a road beyond the departure end of the runway, which resulted in substantial damage to the empennage.
According to the airplane manufacturer, the applicable Pilot’s Operating Handbook (POH) tables did not provide distances for landing on wet grass runways. However, for landing on dry grass runways, 40% distance was added to the normal landing roll distance chart figures. The pilot reported that the airplane weighed 8,010 lbs, and the nearest weather reporting station to the accident site, located at an airport about 16 miles to the north, reported that the temperature was 30°C at the time of the accident. According to the POH chart, the minimum required landing distance would have been about 2,265 ft. The published length of the runway was 1,950 ft.
The closest airport had an available runway that was 5,507 ft long, which would have been well within the safe stopping distance for the fully loaded airplane. The pilot’s decision to land the fully loaded airplane on the wet grass runway that had insufficient length for the landing led to the runway overrun. If he had chosen to land at the nearby airport that had sufficient length for the landing, the accident may have been avoided.