Dehavilland DHC 3T N928RK accident near Iliamna, Alaska

Probable cause

The pilot's decision to depart in dark night, visual meteorological conditions over water, which resulted in his subsequent spatial disorientation and loss of airplane control. Contributing to the accident was the pilot's failure to determine the airplane's actual preflight weight and balance and center of gravity (CG), which led to the airplane being loaded and operated outside of the weight and CG limits and to a subsequent aerodynamic stall.

NTSB analysis

The airline transport pilot and nine passengers departed in a float-equipped airplane in dark night, visual meteorological conditions on a 14 Code of Federal Regulations Part 91 other work use flight from a fishing lodge to a remote fishing location. The pilot reported that, before the flight departed, the front and center fuel tanks were filled, and the aft fuel tank had "residual" fuel. He did not weigh the cargo nor did he document any weight and balance calculations. When asked how he calculated the airplane's weight and balance before departure, the pilot said he "guesstimated" it.

According to a witness, after liftoff, the airplane began to climb and then descended, and the floats subsequently struck the water's surface. The airplane then became airborne again and veered right, but he lost sight of it behind an area of rising terrain. The pilot reported that he heard a noise from the left side of the airplane shortly after liftoff, which was likely the floats impacting the water. According to the automatic dependent surveillance-broadcast data, the airplane then began a gradual right turn before reaching a maximum altitude of 175 ft above the water. The airplane then descended toward the water's surface, flew low over the water and terrain, and then climbed briefly again before it impacted terrain. The pilot stated that he did not know that the airplane touched the water's surface after the initial liftoff or that the airplane then turned right.

Impact signatures were consistent with a right-wing-low attitude at impact. The entire airplane was accounted for at the wreckage site. Disassembly and examination of the engine and propeller revealed that both were operating during impact. Examination of the airframe and flight control systems found no preimpact malfunctions or failures that would have precluded normal operation.

A postaccident weight and balance study using the passenger weights, weighed cargo, and fuel load showed that the airplane exceeded its maximum gross weight of 8,367 lbs by about 508.6 lbs and that the center of gravity (CG) was 4.08 inches aft of the aft CG limit. Data from the airplane's automatic dependent surveillance-broadcast (ADS-B) showed that the airplane was at or below the stall speeds listed in the airplane flight manual during both the initial and second climbs. The ADS-B data show that, because the pilot failed to determine the airplane's actual preflight weight and CG and loaded and operated outside of the weight and CG limits, the airplane did not attain a proper airspeed to climb, and it experienced an aerodynamic stall.

The pilot departed during dark night conditions over water and was relying on external visual cues and not the airplane's instrumentation to control the airplane. There were insufficient external cues available to the pilot to reliably control the airplane, and he was likely experiencing spatial disorientation after takeoff and the subsequent maneuvering.

Text from the NTSB. Open the NTSB docket for ANC15FA071 for the full record.