Golden Eagle 421
Maintenance Powerplant; Maintenance Inspection Authority; Maintenance Airframe
Maintenance Avionics 4; Maintenance Inspector 20; Maintenance Lead Technician 22; Maintenance Technician 4
Training / Qualification; Troubleshooting; Situational Awareness
Aircraft Equipment Problem Critical
Aircraft Aircraft Damaged; General Maintenance Action
Procedure; Manuals; Human Factors; Equipment / Tooling; Aircraft
Aircraft had just had nose gear actuator replaced due to leaking. Original actuator was re-installed after overhaul by another repair facility. Original rod end was installed on actuator. Actuator was rigged according to Cessna Maintenance Manual (M/M). Gear was cycled numerous times (in excess of 20) as the right main gear actuator was discovered to be leaking after nose gear actuator was replaced. Right main gear actuator was replaced and rigged and gear cycled for function and leak checks as per Maintenance Manual. No faults were noted during gear cycles. Aircraft was released for service and was test flown by Maintenance personnel on two test flights one with owner/operator onboard as PIC. Aircraft was flown on multiple legs two days later with final landing at home base where the aircraft had a flat nose tire on landing and roll out. Aircraft was taxied from runway off to adjacent taxiway and recovered by the local Fixed Base Operator (FBO) with a Lektro Tug (strap and cradle type of system) and returned to owner's hangar. Maintenance was contacted and advised to change tire/tube as needed. Aircraft was jacked from nose [gear] only in storage hangar and nose tire assembly removed. Wheel and tire were inspected and [inner] tube was found to have a pinhole in sidewall. Wheel and tire showed no markings or damage and were assembled with a new tube and reinstalled on aircraft. Aircraft was towed to Maintenance facility for leak check of engines and was discovered to have a broken exhaust clamp which was replaced (no bearing on incident). Aircraft was towed back to storage hangar and pushed backwards into hangar with standard towbar and tug. On day of incident aircraft was removed from storage by local FBO and repositioned to ramp; being towed both in forward and backward direction with standard towbar and tug. Aircraft took off and had no abnormal indications from [landing] gear system as reported by owner/operator (sole occupant).On arrival in ZZZ; gear was cycled down and indicated three green lights and hydraulic system 'ON' light extinguishing at end of gear [extend] cycle as per normal operation. Pilot reported that on lowering nose to runway he felt a rumbling similar to the sound and feel of the flat tire experienced several days earlier and pulled the nose back off the runway and became airborne again for a short period. Aircraft settled back to runway and upon lowering the nose the second time the nose gear collapsed and the nose settled to the runway sliding to a stop. Aircraft was jacked and removed from runway.Examination of [landing] gear found the nose gear actuator rod end attaching the actuator to the gear drag leg had separated at the jam nut. Jam nut and safety lock and key were present and correct. Actuator was cycled and found to operate normally. Actuator was not disassembled at this time. Review of Service Difficulty reports found one instance of soft field conditions placing load on nose gear and allowing gear to collapse and also one condition of Tug Systems with straps used to pull aircraft up onto cradle to have damaged gear uplock hook not allowing gear to latch on hook and causing rod end to separate at next gear extension. Rod end may have been damaged from flat tire issue; as rod end is to be extended one turn further than slip fit according to rigging instructions and excessive loads may get transmitted back into rod from overcenter dragleg. Suggest that when aircraft with this type of gear locking system (overcenter drag leg with hydraulic cylinder holding pressure on overcenter mechanism) experiences any type of abnormal load (flat tire or load from towbar/tug) the rod end and attach point for both ends of actuator be inspected for cracks or movement.
Reporter stated when the Cessna 421C nose gear collapsed; the aircraft sustained a substantial amount of lower fuselage skin damage under the nose section. Propellers on both engines were bent and both engines required tear-down. All three landing gears had green lights. Down-lock position micro-switches are internal (inside) each landing gear actuator. Both ends of the actuator have threaded end caps that can be adjusted to help achieve a specific length; along with the rod end; to meet the installation requirements. The upper end cap of the actuator is attached to fuselage structure; and has an aluminum attachment that has been replaced with a steel type on certain series of Cessna 421 aircraft. He does not remember which type was on the incident aircraft. The lower end cap has an adjustable rod end with a jam nut that connects to the overcenter mechanism on the nose gear strut.Reporter stated the Cessna Maintenance Manual (M/M) does not give any specific reference to the number of threads that can be exposed from the end cap to meet the required actuator length for proper extension of the nose gear. The rod end holds overcenter force on the overcenter Mechanism from hydraulic pressure in the actuator. There is only .240 inches; or approximately one quarter of an inch of travel (movement) of the rod end that actually holds the gear in the down and locked position. A hard bounce; or even landing too fast; trying to force the aircraft down may damage the rod end and/or jar the overcenter mechanism from an overcenter position causing the nose gear to collapse. That's why he recommends inspecting both ends of the nose gear actuator and rod end attach points for cracks or movement after any type of abnormal load; including a flat tire or load from tow bar/tug.
A Maintenance Inspector recommends that whenever a Cessna 421 aircraft experiences any type of abnormal load from a flat tire; load from a tow bar and tug; or hard landing bounce; the rod end and attach points at both ends of the nose landing gear (NLG) hydraulic actuator be inspected for cracks or movement. NLG had collapsed on landing from a separated actuator rod end.