Occurrence
On 9 August 2018, a Quest Kodiak 100 aircraft, registered P2-NTZ, operated by New Tribes Mission (NTM), conducted a flight from Goroka, Eastern Highlands Province, to the newly built Mibu airstrip in Madang Province, Papua New Guinea. The purpose was the first landing at the new strip. The aircraft carried two pilots, one as pilot in command (PIC) and an observer. During the landing roll at approximately 23:32 UTC, the nose wheel sank into a soft patch on the strip surface. The aircraft stopped abruptly, and the nose-wheel fork fractured on both sides of the oleo attachment plate, causing the nose-wheel and fork assembly to separate from the oleo. The pilots, the sole occupants, were not injured.
Aircraft Damage
As the fork separated, the nose of the aircraft dropped and dug into the soft ground until the bottom of the engine cowling contacted the surface. The engine and propeller, under significant power, sustained substantial damage from impact with the ground. Damage included the nose landing gear, propeller, engine, and cowling.
Previous Landing
The pilots reported that earlier that day they received a strip report indicating the airstrip was dry and suitable. Upon arrival, the PIC conducted an aerial inspection and saw no standing water, mud, or cracks. They performed two circuits with go-arounds for approach planning. The first landing and subsequent takeoff were successful, but the pilots noted two soft spots during the landing roll that caused quick deceleration, requiring extra power to maintain momentum. The takeoff from that landing was normal. During the second landing roll, the nose wheel sank and became bogged.
Maintenance History
On 2 June 2018, Quest Aircraft issued Mandatory Services Bulletin SB18-01 for inspection of the nose landing gear fork (Type A, P/N 100-410-7001) on serial numbers 100-0001 through 100-0217. Aircraft P2-NTZ (S/N 100-0118) fell within that range. NTM maintenance records showed a non-destructive testing (NDT) inspection was performed on 20 June 2018 in accordance with Field Services Instruction FSI-147. During the accident, the fork fractured as described in FSI-147.
Investigation Findings
The AIC sent the fractured fork to the Australian Transport Safety Bureau (ATSB) for materials failure analysis. The ATSB report stated that stress cracks developed near bolted holes, characteristic of overstress concentration areas. Fracture morphology indicated overstress in every instance, with mostly brittle fractures and some ductile features. No evidence of pre-existing damage was found. The presence of fluorescent dye penetrant indicated prior NDT compliance with the service bulletin. The AIC determined that during the second landing roll, the nose wheel sank into soft ground, causing sudden impact overstress loads that fractured the fork.
Safety Action
The Rural Airstrips Agency (RAA) reviewed its internal procedures for producing technical airstrip reports after the accident. Procedures were amended to incorporate geological and civil engineering input and to ensure clear, concise recommendations for the general aviation public.