Date: 201308
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: FBO
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Cruise
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Main Gear
Component problem: Design; Malfunctioning
Reporter organization: FBO
Reporter function: Instructor
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Human factors: Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: While in the ZZZ practice area with my commercial student; our left main gear failed to fully extend. We ran the Emergency Gear Down Checklist; utilizing the hand pump. It still failed to extend. We raised the gear and lowered it again; but the left main again failed to fully extend; remaining about half way down. In fact; it did not retract before trying to extend it again. I feared that the left gear wasn't getting hydraulic pressure. I crawled onto the floor near the rudder pedals and checked the hydraulic reservoir. It was full. So then we ran the Manual Gear Extension Checklist again and pumped the gear down using the manual override handle. The right main and nose gears came down and locked. The left gear remained in its half down position. So then I went into the back seat of the aircraft to get a better look at the half down gear. The tire was wet all over. I suspected it most likely from hydraulic fluid spraying out from a broken line each time the hydraulic pump was actuated. I decided that I didn't want to risk any more fluid loss by actuating the gear (and compromising the ability to lower and lock the other gear by depleting all ofa the fluid) so for the moment decided to leave it in its present position. The next checklist to run in the aircraft manual was the 'Gear Up Landing'. I decided that I wanted to exhaust all other possible solutions to extend the gear before considering the possibility of an intentional gear up landing. They only other idea I could think of was a textbook example I had heard of that involved opening up the door; reaching outside the aircraft; and pulling the gear up. We contacted ZZZ Tower to alert them of our situation and have them call our mechanics to see if they could provide any other ideas that we had not thought of. We proceeded inbound to overfly the airport in order to get better radio reception with our mechanics and Chief Pilot. After troubleshooting; the only idea they could come up with was the textbook example mentioned above. So; not wanting to risk injury to people on the ground by potential objects exiting the aircraft after opening the door; we proceeded to head back out over the Ocean. My student and I switched seats. I had him fly the aircraft from the right seat; and I settled in to the left seat. He slowed the aircraft to 60 KTS at 4;000 FT; allowing plenty of altitude to recover if we entered into an inadvertent stall. I took off my shoes so they wouldn't fall out into the ocean below. I fastened my seat belt; opened the door; turned around; put my feet and legs outside; and stretched. They wouldn't reach. So; I came back in and decided I'd have to try to reach the gear with my arm. I opened the door; turned around; and tried to reach; but couldn't. I came back in and realized that any forward facing solution was not going to work. I turned around backwards; fashioned a makeshift harness to hold me in; lowered and reclined the seat to its full aft and down position; opened the door; reached out again; and was able to reach the gear this time. But I didn't have the strength to pull it all the way into its locked position with one arm. So next I reached out with both hands; grabbed the gear; and then pulled it forward. Then I needed to flex the gear upwards with my forearms while still pulling backward with my biceps. I heard and felt a 'click'. My student confirmed that we had a 'Green' down and locked light. We called the Tower to come in for landing. I conducted the landing. It was on speed; on glide path; on centerline; and smooth. On rollout we had no braking control on the left side. I immediately advised Tower; 'negative braking;' so they wouldn't launch an aircraft for departure from the intersecting runway. I maintained centerline through the nose wheel steering and slowly decelerated the aircraft using only the right brake--with a hard pull to the right from the differential braking at high speed. Finally we came to a standstill; shut down the engine; and were towed into the ramp. Upon inspection by Maintenance; it was discovered that the pivot axle had sheared--most likely a manufacturing defect during the forging process. That is why the [left main] gear would neither extend nor retract. It's also the reason why the brake system was affected even though the gear and brake hydraulic systems are separate and independent. There is a hole through the two pieces that normally match up perfectly providing a conduit for the brake fluid. The only thing I would have changed is to have insisted on landing on Runway 30 (the longest of the runways) instead of Runway 25R. The city of ZZZ Operations and the Tower had requested us 'NOT' to land on Runway 30 so we would not disable it and cause airliners to have to circle to land on 25R if we would have experienced a catastrophe. That was not my concern if I really felt the gear would have collapsed (I would have definitely insisted on Runway 30); however; since it was down and locked; I had no fear of that and acquiesced to their request. There was no way to have known that an independent; unrelated system was affected. It would have been better to have landed on Runway 30 with the subsequent braking problem.

Callback: Reporter stated the retractable landing gear system on the Cessna-172RG is electrically commanded and hydraulically actuated. There is no 'Free-Fall' to a 'Down' and 'Locked' position. All three positions nose; left and right landing gears must be hydraulically actuated to the 'Down' and 'Locked' position. If an electrical failure occurs; the Manual Hand Pump can be used. But if there is a loss of hydraulic fluid; there would be no way to extend or retract the landing gears. The nose and right gear operated OK; but the left gear would not move even with the Manual Hydraulic Pump.Reporter stated both Main Landing Gears (MLGs) rotate as they cycle up or down. When Gear 'Down' was initiated the left MLG pivot axle sheared and although the gear started to fall from its own weight; the airloads limited the forward movement of the gear to the 'Locked' position. Separate; independent hydraulic lines for the landing gear and brake end (connect) to the pivot axle fitting. Instead of having a hydraulic brake line going to the brake; a forged or machined hole in the pivot axle and landing gear are aligned and allows hydraulic brake fluid pressure to flow down to the brake. When the pivot axle sheared the holes became misaligned. That was the source of the fluid on the tire and wheel when he first noticed the left gear would not fully extend. Reporter stated Cessna stopped production of C-172RG retractable gears in 1986. The current Owner replaced the left pivot axle fitting and also had the right pivot axle removed and sent out for Non-Destructive Testing (NDT). He knows of other similar pivot axle failures that have occurred. An FAA Airworthiness Directive (A/D) had been issued some years ago to perform inspections of the pivot axle.



Synopsis: A Flight Instructor describes his efforts to reach out and physically pull the Left Main Landing Gear (MLG) forward into a 'Down and Locked' position; while his commercial Student flew their Cessna C-172RG aircraft. The Left MLG Pivot Axle had sheared preventing hydraulic extension of the gear. The left brake also failed to operate on landing.