What happened
On 21 January 2020, a Cessna 208B EX, registration PK-SNP, operated by PT. Smart Cakrawala Aviation, was performing an unscheduled cargo and passenger flight from Timika to Kenyam Airstrip, Papua. The flight carried two pilots and 12 passengers.
During the final approach to runway 22, the Pilot Monitoring (PM) instructed the Pilot Flying (PF) to maintain a speed between 70 and 84 knots and to pitch down. Shortly after, the aircraft's stall warning activated, followed by an Enhanced Ground Proximity Warning System (EGPWS) "MINIMUM" callout. Despite further instructions to pitch down and reduce power to idle, a second stall warning occurred. The aircraft touched down approximately 150 meters before the start of the runway, with the tail section impacting the ground first, followed by the main landing gear. The aircraft then bounced to the right, striking the ground outside the pavement with the right landing gear before the crew recovered the aircraft to the centerline.
There were no injuries among the occupants, though the aircraft sustained damage to the landing gear struts, wheel sidewalls, cargo pods, and the tail section.
The investigation
The investigation focused on the aircraft's configuration and the accuracy of the pre-flight weight and balance calculations. Investigators found that the aircraft was equipped with an Aircraft Payload Extender (APE) system and a STOL system, which added weight to the airframe. However, the operator had not updated the aircraft's empty weight records to account for these modifications.
Furthermore, the investigation identified significant discrepancies in how weight was calculated. The weight and balance form used a mix of kilograms for passengers/cargo and pounds for fuel/aircraft weight. Additionally, the operator used a simplified conversion factor of 1 kg = 2.2 lbs, rather than the more precise 1 kg = 2.2046 lbs required by the manual. These errors resulted in a calculated takeoff weight that was lower than the actual weight, meaning the aircraft was operating beyond its certified limitations.
Findings
- The aircraft's empty weight was not updated to include the weight of the installed APE and cargo pod systems.
- Inaccurate weight and balance calculations were caused by using inconsistent weight units (kg and lbs) within the same form.
- The use of an imprecise conversion factor (1 kg = 2.2 lbs) led to an underestimation of the actual aircraft weight.
- Recalculations confirmed that the actual ramp and takeoff weights exceeded the aircraft's structural limitations.
- The flight crew experienced stall warnings and EGPWS alerts during the final approach due to the aircraft's heavy state.