The QC15 version is TSO'd. Because many operators require a TSO'd headset, Uflymic offered the TSO as an option. When I purchased mine, it wasn't available, but I sent it back for an inspection, paid the fee, and it was returned with a letter referencing the technical order, and stickers affixed to the mic and lead advising of the TSO reference. Nobody ever questioned my use of the headset, but I ensured it was compliant anyway.