Like every component on aircrafts, landing gear also has a service period. As the main fasteners of the landing gear like pintle pins are exposed to large loads, if maintenance is not carried out over time, it may break after a hard landing and an unsafe landing can occur. In addition, sensors that provide position indication of the landing gear can not produce senses due to pollution so the landing gear does not retract then the aircraft returns. This causes a cost loss for operators as well as reputational damage.
Basically, jacking is performed for operations such as landing gear replacement, shock absorber seal replacement or landing gear retraction-extension test after long-term parking. Shock absorber seal is damaged by the effect of dust accumulating on the shock absorber that causing oil leakage and decreasing the efficiency of the landing gear strut. From another point of view, performing an retraction- extension test after storage is to make sure that the landing gear will retract and extend properly on the first flight after long-term parking.
The aircrafts must be jacked to carry out all these necessary maintenance operations. Jacking is performed with three jacks, one under the nose and two under the wings. These jacks are generally powered by compressed air, as well as electric and hydraulic driven types. There is a locking nut on each jack gear. This locking nut keeps the gear stable in case the gear loses pressure suddenly. Three technicians in total, on each jack, turn this nut as the jack rises and keeps the gear secure. Apart from these three technicians, there should be four technicians on the ground and one in the cockpit for an healthy operation. Three of the other four technicians on the ground move the jacks and the other is in communication with the cockpit who is responsible for the synchronized jacking of the aircraft.
In addition to the old methods such as using spirit level in the forward or maindeck cargo section to raise the aircraft synchronously. It is ensured that the roll and pitch angles of the aircraft are controlled with ADIRS (Air Data/Inertial Reference System) of today’s aircraft. For example, a positive value of the roll angle shows that the right wing is down and a negative value of the pitch angle shows that the nose of the aircraft is down.