Incident Description
The pilot in command was flying the airplane with a safety pilot onboard. After multiple approaches, when the landing gear was extended, only the nose landing gear extended. The main landing gear could not be extended. The pilot in command requested that the second pilot perform the gear up landing, citing the second pilot's greater experience.
Landing and Damage
Prior to touchdown, the propellers were feathered. The airplane touched down hard, resulting in the crushing of the lower aft fuselage.
Examination Findings
Examination of the hydraulic system revealed contamination in the system. According to the mechanic who worked on the airplane, the contamination caused the main gear uplock cylinder not to release and allow the gear to extend. The airplane is not equipped with an alternate gear extension system; therefore, if the hydraulic uplock valve cannot be released, the main gear cannot be extended.