There have been a number of questions regarding the new UN number for engines, UN 3528 in Class 3 when engines are shipped to, from or within the US and the application of US State variation USG-13 for the limit of 25 kg in a cargo compartment on passenger aircraft.
Currently UN 3528 is subject to the 25 kg limit and as engines must be declared by the weight of the actual engine, then the 25 kg will be exceeded. However, until 31 March 2017 shippers can still ship engines as UN 3166, see the note under Special Provision A208 and Note 2 under 22.214.171.124.1, Step 5. UN 3166 is excepted from the 25 kg limit.
The US DOT draft final rule HM-215N was to bring UN 3528 into the 25 kg exception in 49 CFR but this proposal has been withdrawn by Executive Order from the US new administration. Until 31 March 2017, subject engines can be shipped under UN 3166 Class 9 however, it is uncertain what will be the case after 1 April 2017.
Within the US, UN 3166 is the only number so that it is not an issue for US domestic transportation. US DOT PHMSA will be considering what options are to move forward with the harmonization of 49 CR to the international regulations. As more information become available, we will post it on this website.