Q.    ​What are the actual FAA requirements regarding how long AD DFP's (dirty fingerprints) are kept. If the AD has repetitive  inspections are all DFP's kept or just the most current compliance?
A. ​The term “DFPs” is something the Europeans originated.  Our FARs don’t mention it at all. As far as ADs are concerned, we require “appropriate
entries be made into the aircraft records” which is like you say, clear as mud.  The rule doesn’t get any more specific than that, which means that copies
are acceptable if the originals are lost or destroyed or otherwise unavailable. For repetitive ADs, it is not necessary to keep records of
superseded maintenance. Most of these rules are addressed in FAR 91. 417 and AC 39-7D, but they do not get as specific as your question is asking.
​Q.    How long does a U.S. Export Certificate of Airworthiness remain valid?
​A.    It never expires, although some countries have special requirements in their bilateral agreements with the US that state that they will not accept an Export Certificate of Airworthiness if it is more than 60 days old or if the airplane has flown more than 50 hours since it was issued.  Be sure to check the bilateral agreements found on the FAA website at www.faa.gov.  They are found in Advisory Circular 21-2.
Q.    When exporting an airplane, does it have to remain on the US registry until the Export Certificate of Airworthiness is issued?  In other words, when may the exporter request the airplane to be deregistered from the US registry?
​A.    If there are no more flights to be made while under the current US registration number, and there is no more work to be accomplished requiring an FAA mechanic or IA to make their appropriate logbook entries or 337s, etc., then the aircraft may be deregistered after that point.