Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 20; Flight Crew Total 4100; Flight Crew Type 250
Communication Breakdown
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Other / Unknown
Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Human Factors
Landing gear recently serviced re: uplock switch.  Preflight indicated hydraulic fluid not full; noticed in sight glass. Notified mechanic who affirmed it was full and probably overfilled.  Possible bubble at sight glass.  Went on word of mechanic and after further preflight departed on an instrument training flight ZZZ-ZZZ1.  Upon gear retraction at takeoff; the uplocks released and [gear] failed to retract further; hanging in the 'wasp leg' position.  Having the instrument student continue flying the aircraft; recycled the gear...little movement observed in the mirrors owner had installed under each wing.  Contacted ATC that we needed to troubleshoot a landing gear issue while holding over ZZZ2.  For the next 45 minutes we (instrument student and myself) communicated with the aircraft's owner on the ground via text messaging initially; followed by radio on a discrete frequency while he was in contact with the mechanic. Recycled the gear several times with very little movement and initiated the emergency gear extension procedures using the hand pump. Upon pulling out the handle all the way to the extension; the handle would not move up or down as it seemed 'locked.'  At that point recycled the gear handle several times noticing a fair amount of movement in the landing gear (reference mirrors) indicating there was some hydraulic fluid in the system.  Student reached for the handle and was able to release it with a firm upwards movement and we were able to further pump the gear down to confirm locked. Declared an emergency and preceeded to land [returned to] ZZZ with a runway flyby for the Tower to visually confirm landing gear extension; most noticeably the nose gear.  Landed uneventfully on 18R and taxied to FBO. Aircraft was put up jacks for a landing gear checks about an hour later confirming fluid was low; most likely due to the aircraft was connected to the hydraulic 'mule' after it's servicing and the fluid drained out.  Several swings of the landing gear during the course of the next 30 minutes on jacks confirmed there was no mechanical concerns.  A test flight was completed later that evening indicating no extension or retraction issues.
Reporter stated the Cessna C-210 had a Continental IO-520 Six cylinder engine. There are only two lights in the cockpit for the landing gears: an Amber light for gear 'in-transit;' meaning anything not 'locked' and a Green light for 'Down' and 'Locked' for all three gears. He did a runway 'Flyby' just to confirm the nose gear was showing down since he did not have a mirror mounted on the aircraft to view the nose gear. Reporter stated the low Hydraulic fluid was most likely caused by the Hydraulic mule equipment being positioned lower than the aircraft's service connection. Although initially the hydraulic quantity was probably 'full' or over serviced; gravity allowed the hydraulic fluid to flow back into the mule unnoticed; prior to Mechanic disconnecting the hydraulic service line.
A Flight Instructor describes the efforts of a student pilot and himself to manually extend the landing gears on a Cessna C210 aircraft after takeoff when all three gears failed to fully retract. Landing gears were hanging in the 'Wasp Leg' position.  Low Hydraulic fluid quantity was a contributor.