An aft centre of gravity (CoG) position contributed to the crash of a Sling 4 at Caloundra last year, according to an Australian Transport Safety Bureau (ATSB) report released today.
Sling VH-BEG was on approach to Caloundra's runway 05 on 12 August last year when it crashed during a left turn on late final. All four passengers on board were seriously injured and the aircraft complelely destroyed.
The pilot reported being distracted by parachutists and was concerned they could drift into the path of the plane. During the distraction the pilot allowed the aircraft to become too high and drift to the right of the runway centreline.
"The pilot then reduced power to idle and commenced a forward slip to attempt to increase the approach angle and regain the desired approach path," the ATSB investigation report states. "As the aircraft approached the runway 05 threshold, he stopped the forward slip and began a left turn toward the threshold.
"During the left turn, the aircraft aerodynamically stalled and the aircraft rolled to the left. Almost immediately, the left wing tip struck the ground and the aircraft collided with terrain."
Investigators estimated the weight of the aircraft at only 1 kg less than the MTOW of 920 kg, but that the CoG was outside the envelope for the entire flight. The pilot reported using the standard passenger weight of 77 kg each rather than the actual weights and that he used the aircraft's Electronic Flight Instrumentation System (EFIS) to calculate the CoG position.
The ATSB noted that the 77-kg method should not be used for aircraft with less than seven seats.
"The flight was conducted with the centre of gravity aft of the rear limit," the ATSB investigators concluded. "This had the effect of making the aircraft less stable and more susceptible to an aerodynamic stall. This also made recovery from a stall more difficult.
"After detecting that the aircraft had deviated from the desired flight path, the pilot attempted to continue the approach by manoeuvring the aircraft at low level and low speed. The aircraft was loaded outside of the permissible centre of gravity range, and the manoeuvring further reduced the remaining margins of controllable flight until the aircraft stalled and control was lost."
The full investigation report is on the ATSB website.