Preflight and Initial Flight
Before departure, hydraulic fluid was added to the landing gear hydraulic system. During takeoff, the landing gear retracted without incident, and the flight proceeded to a practice area for airwork.
Landing Gear Failure
After completing initial airwork, the pilot attempted to extend the landing gear before performing additional maneuvers. The gear failed to extend. The emergency checklist was followed but did not resolve the issue. The flight returned to the departure airport.
Attempts to Extend Gear
Upon return, the flight crew contacted dispatch in an attempt to lower the landing gear, but these efforts were unsuccessful. Additionally, the certified flight instructor (CFI) attempted to manually extend the main landing gear but was unable to do so.
Landing and Collapse
The aircraft landed with the nose landing gear extended and the main landing gear in trail. At touchdown, the main landing gear collapsed.
Post-Incident Examination
An FAA Airworthiness inspector examined the airplane and found the hand pump suction line assembly (part number 2480001-23) was damaged, with hydraulic fluid covering the area. The line was retained for further examination by the NTSB Materials Laboratory.
The laboratory examination revealed at least eight transverse cuts in the tube section of the line adjacent to the end ferrule. One cut directly adjacent to the end ferrule penetrated the wall thickness and was slightly less than 0.03 inch wide. The sides of that cut were straight into the tube, but the bottom had a curved surface progressing to a sharp bottom. The other cuts did not penetrate the wall thickness. Loss of metal at the cut locations appeared to be primarily from metal flow rather than from grinding or cutting. There was no evidence that the edges of the ferrule or B-nut created the cuts in the tubing.