The landing gear on a semi-trailer serves several important applications in the transportation and logistics industry:

1. Support and Stability: When a semi-trailer is not coupled to a truck tractor, such as during loading, unloading, or when parked at a warehouse or distribution center, the landing gear provides essential support and stability. It prevents the trailer from tipping over or resting on its suspension components.

2. Loading and Unloading: The landing gear allows the trailer to be detached from the tractor and leveled to facilitate loading and unloading operations. This is particularly important when the trailer needs to remain stationary for extended periods.

3. Parking: When trailers are parked for storage or temporary use, the landing gear supports the weight of the trailer and prevents unnecessary wear on the suspension system. This also allows the trailer to be parked on uneven surfaces without affecting its stability.

4. Maintenance: The landing gear enables easy access to the underside of the trailer for routine maintenance and repairs. By raising the trailer off the ground, technicians can inspect and service components such as brakes, axles, and electrical systems more safely and effectively.

5. Adjustment: During coupling with a truck tractor, the landing gear allows for adjustment to ensure proper alignment and height between the trailer's kingpin and the fifth wheel on the tractor. This ensures a secure connection and smooth operation while driving.

6. Emergency Situations: In the event of a mechanical failure or an accident that renders the trailer immobile, the landing gear provides a means to stabilize the trailer until assistance arrives or repairs can be made.

Overall, the application of semi-trailer landing gear is critical for ensuring operational efficiency, safety, and maintenance in the transportation and logistics industry. Properly functioning landing gear enhances the overall functionality and longevity of semi-trailers while supporting efficient loading, unloading, and parking operations.