Accident Overview
On the morning of Friday 19 April 2002, a pilot was engaged in spreading superphosphate on a hill-country property south-east of Masterton, New Zealand. Operations had commenced at 0735 hours after the pilot and loader driver flew to the airstrip from Masterton. Topdressing proceeded normally for two hours, including a refuel and break from 0935 to 1000 hours. During the break, the pilot conducted a full pre-flight inspection. The loader driver noted the first takeoff after the break at 1001 hours; that sortie was completed normally. However, the aircraft became overdue on the second sortie.
Looking towards the area being worked, the loader driver saw a column of black smoke and immediately telephoned the company chief pilot, who was operating another aircraft nearby. The chief pilot had already seen the smoke and flew across to investigate. He saw the aircraft burning fiercely on the shoulder of a ridge and contacted emergency services. He briefly considered landing by the accident site but decided against it and returned to the airstrip to pick up the loader driver. They flew back to the site but saw no sign of the pilot, so returned to Masterton.
Witness Accounts
The farmer whose property was being topdressed was working on the eastern side of the valley. While the aircraft was on its last run, he saw an object fall from it and "flutter" to the ground. He initially thought it might be a superphosphate bag. Two fencing contractors working nearby also saw an object fall from the aircraft; shortly afterward, one remarked that the aircraft "had no tail." They watched it climb and "veer to the left" before striking the ground near the top of the ridge at the southern end of the valley. The aircraft caught fire on impact.
The farmer, though he did not see the impact due to intervening terrain, realized something was wrong and drove his four-wheel motorcycle to the site, taking about three minutes. On arrival, he found the center section of the aircraft well ablaze and could not see the pilot despite getting as close as the left wingtip. He reported several explosions during the fire. Once the fire subsided, he saw the pilot's body in the wreckage.
Another farmer on the ridge to the west witnessed the impact. He estimated that about 10 seconds elapsed between impact and the first sign of fire, and had expected to see the pilot jump clear.
The falling object was later found to be the tail fin (vertical stabilizer), which had landed in a clearing 870 m from the crash site, near where the fencing contractors had been working.
Investigation Findings
The accident occurred in daylight at 1013 hours NZST, 12 km south-south-east of Masterton, at an elevation of 1240 feet (grid reference 260-T26-370116, latitude S 41° 04.36', longitude E 175° 42.05').
Investigators concluded that the pilot was appropriately licensed, experienced, and fit for the flights. The aircraft had been operating normally up to the time of the accident. An undetected fatigue crack or series of cracks had been propagating in the forward area of the tail fin for some time. These cracks developed to a point where the remaining structure could not accommodate normal flight loads, causing the fin to separate from the aircraft.
The departure of the fin likely resulted in uncommanded yawing and pitching effects, with accompanying control feedback and unusual sounds. The rudder became lodged in the tailplane upper surface, potentially restricting elevator control, though the extent and duration of any restriction could not be determined. The resultant impact with terrain may have been an attempt by the pilot to carry out an immediate forced landing, or may have resulted from the limited control available. The impact and subsequent fire were not survivable.
The fatigue cracking originated from cuts in the skin made when the leading-edge abrasion strip was being trimmed in situ. It was not determined when and by whom the cuts were made; however, measures have been taken to prevent a recurrence.