The two men, partners in an earthmoving business, were flying to Canterbury's Mount Algidus Station for work.
Judge Farnan said heavy cloud coverage in the Lindis Pass area at the time of the crash meant the defendant's decision to fly down through the cloud exposed Mr Edwards to hazard.
She accepted the prosecution's argument Sarginson had failed to carry out a proper weight and balance calculation for the aircraft, questioning whether he had even carried out "mental'' calculations.
Estimates by prosecution witnesses that the aircraft weighed 690kg at takeoff, well over the maximum allowed weight of about 620kg, were credible.
The aircraft was still "significantly overloaded and out of balance'' at the time of the crash, she said.
Sarginson's conduct was reckless as to the risk of serious injury or death, both in his capacity as a director of the company and as a worker, and she convicted him on two charges under the Health and Safety at Work Act.
Her finding meant she did not need to consider two other charges under the Act, nor a charge under the Civil Aviation Act.
However, the trial did not resolve the issue of whether the crash directly caused Edwards' death.
That is despite the pre-trial admission of facts stating it was the result of "... high energy impact injuries to his chest and pelvis causing multiple fractures to his ribs and pelvis''.
The issue will be a factor in determining the amount of reparation Sarginson will be ordered to pay to Edwards' family.
Judge Farnan remanded Sarginson at large until April 29, and his counsel, Colin Withnall QC, must file a submission on the issue by April 8.
The trial started in August, and continued intermittently in Queenstown and Invercargill District Courts over 20 days until January.
