Prior to reassembly rinse the filter in new hydraulic fluid to ensure no cleaning solution residue remains. The filters are located on the belly, almost directly under the external hydraulic service connectors. We think not, but a lot of L39 owners are doing just that. During our field trips to customer location, some owners are reporting that they are feeling a lot of vibrations during the take off or landing, and are assuming they have a bad shimmy damper. In 99.9 percent of the cases, we find its the nose tire that is old, side wall cracked, and not able to return to its round shape after a short taxi period, especially if the aircraft has been parked for several weeks.
Some owners say that they have already installed a new set of tires .
The problem are tires having a service life time for 10 years including storage under defined climatic conditions. During that time the tires are losing a part of their flexibility , that's normal and calculated for a total time of 10 years and not yet dangerous. But if tires are unused and exceed the time and than get loads on the L-39 the fatigue of flexibility goes much faster than normal. It starts with small surface cracks around the tire , not on the running surface, but on the tire side walls. The bigger cracks appearing around mintage of Serial Number or Tire Brand , say areas where additional marks was put in the tire wall surface.