There are two possible explanations.
1. Cargo loading that cause the aircraft to tip backwards. If you load the tail before you load the front, you can tip the airplane over. This happens quite often, but I’m not sure it’s the case, here.
2. Aircraft mechanics making a hydraulic repair and failing to put in the landing gear down locks. When they’re checking hydraulic operation, mechanics will actually raise the gear handle in the cockpit. On the 747 400, it’s a big mechanical handle if you raise the gear handle in the cockpit with the hydraulic systems pressured, you can check for hydraulic leaks on newly installed landing gear actuators. However, you must install the down locks, pins that prevent movement, on each gear.
I suspect they were troubleshooting hydraulics, and did not put the full set of pins in the body gear.
For the record on the 747, the rear most main landing gear trucks are referred to as “body gear”. The two forward trucks, which are normal in this photo, are known as the “wing gear”.
In this photo, the wing gear are normal, but it appears the body gear has been partially retracted.
