49 CFR § 175.88

A unit load device may not be loaded on an aircraft unless the device has been inspected and found to be free from any evidence of leakage from, or damage to, any package containing hazardous materials.

A package containing hazardous materials marked “THIS SIDE UP” or “THIS END UP”, or with arrows to indicate the proper orientation of the package, must be stored and loaded aboard an aircraft in accordance with such markings. A package without orientation markings containing liquid hazardous materials must be stored and loaded with top closure facing upward.

Packages containing hazardous materials must be:

Secured in an aircraft in a manner that will prevent any shifting or change in the orientation of the packages;

Protected from being damaged, including by the shifting of baggage, mail, stores, or other cargo;

Loaded so that accidental damage is not caused through dragging or mishandling; and

When containing Class 7 (radioactive) materials, secured in a manner that ensures that the separation requirements of §§ 175.701 and 175.702 will be maintained at all times during flight.