I have gotten a number of e-mails asking if 12" Aircraft Registration numbers are required in the DC ADIZ. The answer is No. They are not required in the DC ADIZ This information comes directly from FAA headquarters, who provides guidance to the Flight Standards District Offices. 12-inch "N" numbers do not need to be displayed on aircraft operating in the New York and Washington, D.C. ADIZ. The FAA has confirmed that the portion of Part 99 that governs the operation of aircraft within an ADIZ requiring 12-inch "N" numbers does not apply to either the New York or Washington, D.C. ADIZ. Ed