Probable cause
The failure of the engine-driven hydraulic pump due to the installation of improper cap screws, which resulted in a gap in the pump housing, a subsequent hydraulic leak, and the landing gear collapsing.
NTSB analysis
The private pilot was conducting a personal, cross-country flight. He reported that he attempted to lower the retractable landing gear during a visual approach; however, the right main landing gear (MLG) did not fully extend. He attempted to manually pump the landing gear down with the emergency hand pump, but it was very difficult to move, and after several pumps, it would not move at all. Upon landing, the right MLG collapsed and the airplane impacted the ground, which resulted in substantial damage to the right horizontal stabilizer and elevator. Postaccident examination and tests revealed that, when the MLG system was tested using the airplane’s engine-driven hydraulic pump, fluid started leaking from a gap in the pump’s diaphragm seal between the front plate assembly and the rear housing assembly, and the MLG would not extend. Subsequently, the MLG system was tested with an external hydraulic pump, and it functioned properly. The two front plate cap screws on the side of the leaking pump gap were loose, had only three or four threads engaged with the rear assembly, and had insufficient shank length. The corresponding rear housing internal threads were sheared.
Due to the installation of cap screws with insufficient shank length, fewer threads were engaged when the screws were tightened. The insufficient length of the shanks likely led to excessive force being applied on the engaged threads when the cap screws were installed, the threads being damaged, and a gap in the pump housing to develop, which allowed fluid to leak from the pump when it was pressurized. The hydraulic leak prevented the right MLG from fully extending and resulted in it collapsing upon landing.
Text from the NTSB. Open the NTSB docket for ANC18LA043 for the full record.
Event
- Date
- Jun 1, 2018
- Type
- Accident
- Place
- Ramona, California
- Nearest airport
- Ramona (RNM)
- Highest injury
- None
- Weather
- Visual (VMC)
- Light
- Day
Cessna 210
- N-number
- N9410M
- Category
- Airplane
- Year built
- 1970
- Damage
- Substantial
- Operating rule
- Part 91 (general aviation)
- Purpose of flight
- Personal
From the NTSB aviation accident database: N-registered aircraft, events since 2008, data through Oct 28, 2026. The file is published monthly, so the latest weeks are incomplete and recent records can change. The official source is the NTSB aviation investigation search. CheckAero is independent and not affiliated with the NTSB.