This February 2008 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Cessna 172RG. Injuries: None. Location: Chamblee, Ga. Aircraft damage: Substantial.
What reportedly happened: A CFI and the pilot-rated student were approaching to land on runway 20R. After completing the pre-landing checklist they checked the under-wing mirror and noticed that the main landing gear were not down and locked. They made every attempt to lower the gear but were unsuccessful. During landing the right main landing gear collapsed, buckling the right elevator.
Examination of the landing gear by an FAA inspector found the nose gear actuator O-ring cracked and leaking hydraulic fluid. All fluid had been exhausted.
Probable cause: A cracked nose gear actuator O-ring resulting in hydraulic fluid exhaustion, and collapse of the main gear.
For more information: NTSB.gov