Unit load devices (ULD) come in several dimensions and are designed to fit the bellyhold of a jet plane, particularly wide-bodied aircraft. The number of containers that can be fitted is a function of the length of the cargo area and the sizes of the ULDs. The loading of ULDs is rather simple as it involves rolling in the container. Up to 32 such ULD can be loaded in a 747-400, while an A330 can hold 17. The number of ULDs an aircraft can hold is not absolute and varies according to the sizes used. ULDs offer several advantages:
- They use standardized sizes and equipment that fit in most commercial aircraft. The above photo shows ULDs of AKE type, which is a very common load unit compatible with a wide range of aircraft.
- Faster handling (loading and unloading) and tracking of the cargo.
The main drawback is that ULDs can only be used for air cargo operations and a transfer to another mode (trucking) requires consolidating or deconsolidating the loads carried.