The most common certification standards for ULDs are the Technical Standards Orders (TSOs), which are set by the FAA and EASA.
We work to the requirements set out in ETSO C90 by EASA. This European Technical Standard Order covers all aspects of a standard ULD, from design, testing and production to operations, repair and maintenance. As long as we comply with all the applicable parts, you have an airworthy ULD and not simply a metal box.
There are occasions when a ULD does not meet the TSO standard. Perhaps because it needs to carry a certain type of cargo or be loaded onto a specific type of aircraft. In cases like these, we have to get a Supplemental Type Certificate (STC). VRR is actually authorised by EASA to issue STCs, which is how we manage to get even customised ULDs certified.