Exactly why the autopilot disengaged (an event recorded by
avionics) in the midst of a right turn to avoid weather ahead remains
unknown. Investigators noted that Bramlage had activated propeller
de-icing and inertial separator during the climb, but not the de-icing
boots. The autopilot disengaged while the aircraft was banked about 25
degrees right, in instrument meteorological conditions, and Bramlage
attempted to troubleshoot the autopilot as the bank angle increased to
50 degrees and the aircraft began to descend.

The bank angle increased to between 75 and 100 degrees as the
aircraft descended rapidly from 25,000 feet in the final seconds of the
flight. After descending about 10,000 feet and reaching 338 knots—about
175 knots above maneuvering speed—“the pilot likely applied either
abrupt or full aft elevator control input, resulting in overstress
fracture of both wings,” the NTSB summary states.

Investigators estimate, based on logbook and aircraft data, that
Bramlage had logged about 755 hours total time, the vast majority of it
in piston singles (NTSB study of the pilot’s logbook revealed
record-keeping errors) before launching on the flight home from the
Bahamas. By the time he launched his final flight, Bramlage had flown
about 38 hours in the Pilatus, investigators estimate. He had not logged
any actual instrument time in the seven years before buying the Pilatus
and obtaining training that included an instrument proficiency check.

Investigators
subpoenaed a student who trained with Bramlage. While this pilot, a
retired airline captain, had high praise for the training program and
instructors, and was reluctant to criticize Bramlage’s competence, “when
asked if he thought based on his experience that the accident pilot was
behind the airplane, he said he would have to say yes.”

Bramlage told another pilot, who flies a PC-12/45, that it took a
long time to perform tasks “because he does the checklist twice.”
Bramlage asked that pilot questions about use of the inertial separator
prior to departure on the accident flight.

Investigators found no evidence that mechanical failure contributed
to the crash. The NTSB ruled Nov. 24 that the probable cause of the
crash was: “The failure of the pilot to maintain control of the airplane
while climbing to cruise altitude in instrument meteorological
conditions (IMC) following disconnect of the autopilot. The reason for
the autopilot disconnect could not be determined during post-accident
testing. Contributing to the accident was the pilot's lack of experience
in high-performance, turbo-propeller airplanes and in IMC.” 
demands on the pilot. probably somewhat less
than the Lancair due to a lower stall speed and precictable stall
characturistics.