Date: 201306
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Night
Aircraft: Citation Excel (C560XL)
Operator: Fractional
Operating under: Part 135
Flight phase: Parked
Aircraft component: Main Gear
Component problem: Design; Malfunctioning
Reporter organization: Fractional
Reporter function: Lead Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant; Maintenance Inspection Authority
Human factors: Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Maintenance
When detected: Routine Inspection
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: CE-560XL aircraft with high cycles. I was assigned as a Lead Technician to two aircraft: Aircraft X; a CE-560XL which was in inspection and Aircraft Y; another CE560XL that had just had an inspection. However; on the previous night; during the Post Maintenance Flight Control Check of aircraft Y; a discrepancy was found with the aileron/rudder interconnect. This was troubleshot and the new part was installed and I completed the reinspection of the installation. Later that night [early morning] when Mechanic A was starting the Post Check he informed me that the left-hand (L/H) main gear was sitting on the main tire. I went over and verified that this was the case and then noticed that the R/H main gear oleo had also collapsed but not completely; still having about one inch of [gear] barrel showing. There was no evidence of hydraulic fluid leakage on the floor or the [main gear] struts; but the tires showed evidence of chemical burn; indicative of Skydrol coming into contact with the rubber.  We jacked Aircraft Y and upon further inspection for damage; (because the aircraft had been moved outside for engine runs and not knowing when the oleos collapsed); found that the L/H main tire had worn through the paint [on the main gear] and had started to polish the base metal of the gear. We attempted a full service of the oleo I.A.W. CE560XL Maintenance Manual (M/M) 12-14-00 which turned out unsuccessful. The oleo started to leak fluid out of the top seals intermittently. At this point I had the mechanics A and B stop and created two discrepancies items on the Work Order and then ordered two new oleos and hardware for the left and right gear.My concern is that when the L/H oleo collapsed; it allowed the main gear casting to come into contact with the tire. If this were to happen in flight before landing; [then] during taxi it could cause a catastrophic failure of the tire resulting in damage to the aircraft and possible injury or death to the occupants.  [Recommend] some form of a mechanical/physical type of safeguard to prevent the gear from coming into contact with the tire if the oleo were to collapse; maybe some kind of internal stop.

Callback: Reporter stated Cessna uses a trailing link type landing gear with three parts: the main landing gear (MLG) casting; a trailing link and an oleo strut on the aft side that attaches to the lower trailing link. A knob on the outboard side of the lower trailing link had contacted the inboard side of the single main tire on the left main landing gear (MLG). The CE-560 XL was in for one of the Maintenance Phase Checks and part of that involves servicing the MLG oleo struts. Strut servicing procedures include releasing the nitrogen head pressure in the oleo and completely flushing the Skydrol hydraulic fluid three times from the oleo strut. The oleo is then refilled with Skydrol fluid to a specific level which should allow the oleo piston to have approximately half an inch of chrome extension showing; before pressurized nitrogen is added. The half inch extension is a cushion to keep sufficient distance between the knob on the trailing Link and the main tire if the nitrogen should bleed off.Reporter stated he suspects that both left and right main gear oleos had started to collapse after the oleo struts were fully serviced with Skydrol and nitrogen and the CE-560 had been pushed out for engine runs. He and Mechanic A had found the collapsed oleos after the aircraft was pulled back into the hangar for continued maintenance. That's why no leaks were noted on the hangar floor. Maintenance believes the oleo strut inner seals had rolled; resulting in the loss of nitrogen and Skydrol. Attempts to re-service both oleos were not successful because Skydrol would leak out when added. The MLG oleos are life limited components that are changed after a certain number of cycles; but he does not know what the cycles were for the two oleos that had collapsed. His company has issued a maintenance alert regarding the oleos. No information from engineering yet; if changes in maintenance procedures or oleo seals will occur for similar MLGs. Mechanics are not allowed to file Service Difficulty Reports (SDR); only Engineering can. He has thirty plus years of maintenance experience.



Synopsis: A Lead Aircraft Maintenance Technician reports the left-hand (L/H) main landing gear (MLG) oleo strut on a CE-560XL aircraft had collapsed; allowing the L/H MLG casting to come in contact with the single main gear tire. The right MLG oleo had also collapsed. Reporter expressed concern for a catastrophic failure of the single main tire and aircraft safety.