Mechanical component: repair or overhaul?


Air Support - Aircraft component Maintenance ballscrew Technical paper

As most components installed on commercial aircraft, mechanical components are not subjected to periodic maintenance. Generally, they are only removed and shipped to the PART 145 repair shop in the event of a failure.

Let us concentrate more particularly on components which include mechanisms lubricated with grease:

  • Ball screw => ex : thrust reverser actuator
  • Gears => ex : flap actuators, electric motors, reducers, gearboxes, etc.
  • Bearing => ex : everywhere !

Despite the use of high performance greases, aging and temperature changes inevitably lead to a rise of their viscosity, which could end up transforming them into a thick paste of particularly poor fluidity.

It is not unusual to receive in our workshops, components as various as windshield-wiper motors or "VBV actuators" whose rotating mechanisms are almost, or even completely, blocked by the presence of this paste.

The problem has to do with the fact that, in the absence of fluidity of grease, the resistive torque is such that the driving mechanism can be seriously damaged.

For example, in the case of a wiper motor, the electric motor is frequently burnt, while in other mechanical devices, the drive shaft can be twisted, or even broken.

In other cases, gears or intermediate connecting parts can be damaged, because they are not intended to undergo high rotating torques.

Thus, the aging of grease can induce important failures, requiring the replacement of expensive parts during repair.

It is why we recommend a strict follow-up of all components concerned, in order to submit them to a periodic maintenance (overhaul) which, if it is carried out regularly, will require only the inexpensive replacement of grease and seals.

We roughly note that a component whose grease has not been replaced for 18 to 24 months can present these risks of failure.

Therefore, an overhaul every 4000 to 5000 flight hours seems appropriate.

For more details, contact us!