The pilot reported that during the takeoff initial climb, after the landing gear was retracted, the landing gear’s hydraulic pump electric motor continued to run, even though the landing gear appeared to be fully retracted, as viewed in the landing gear mirror.
He then attempted to extend the landing gear normally, but the landing gear would not indicate down and locked. Subsequently, for over an hour, he attempted to manually extend the landing gear, using the emergency manual gear extension hand pump, but he could see in the mirror that the landing gear was only partially extended.
During the subsequent emergency landing at the airport in Palm Springs, California, the main landing gear collapsed and the Cessna 177 skidded to a stop on the runway. The right stabilator sustained substantial damage.
A post-accident examination revealed that the landing gear system was empty of hydraulic fluid. After the system was serviced with hydraulic fluid and operated, a leak was found at the nose gear actuator due to the failure of a shaft seal.
The tests revealed that the landing gear extension process could not be completed, and the manual landing gear pump did not have sufficient fluid remaining to extend all three landing gear. The airplane logbooks revealed no records of service to the nose gear actuator and shaft seal and each were the original manufactured parts.
Probable cause: The failure of a shaft seal at the nose gear retraction/extension actuator, which resulted in a loss of hydraulic fluid and a main landing gear collapse during landing.
NTSB Identification: GAA16CA074
This November 2015 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.
This is why retractables cost more to insure.
Jim Macklin says
Preflight inspection should look closely at landing gear actuators for signs of leakage. Hydraulic fluid is dyed red and leakage will show the color or dirt caked on and near the actuators.
Electro-hydraulic pumps are controlled by pressure switches that turn the pump off when the pressure reaches a certain point. The numbers will vary but gear operation might required 800 psi and the pump will shut off when a microswitch open when the gear is either full down or full up. Often there are no actual uplocks, pressure in the system holds the gear up against the switch. When the fluid cools or if there is a leak, the pump will run a second or two to snug the gear up.
Some airplanes may have a timer that limits the time the pump can run, usually 2 or 3 times the gear cycle time.
In some airplanes the gear will free fall and lock without any pump pressure required. Some designs require hydraulic pressure to complete the extension cycle. Some airplanes require hydraulic pressure to release mechanical uplocks.
Any proper complex airplane checkout should involve a complete understanding of the particular airplane and how its gear system works. Getting an A&P to explain if the CFI can’t answer your questions completely.
Actually looking at the fluid level in the hydraulic system is just as important as looking at the fuel quantity or tread remaining on each tire.
Glenn Swiatek says
Flight aware registration page shows the plane was delivered in 1974.
If those seals were original manufacture, they exceeded design requirements by, likely, 4x years. Or more.
My guess is all the seals will be replaced again in 3.