Recently there has been lots of discussion about installation of external camera mounts, such as “GoPro” or NFlight” cameras and the question ask to the FAA is this considered a minor alteration as defined by Title 14 Code of Federal Regulation (14 CFR) part 43 Appendix A.
I think the proper answer to major or minor for this question is both yes and no depending on how it is installed. If the installation does not affect appreciable weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness then it would be a minor alteration.
However, if a mounting pad is permanently fix to the outside of the aircraft by riveting, screws, bolts or other structural attachment it may be a major alteration requiring a FAA field approval. However, if it is installed as the memo explains using “suction cups, or other temporary methods of attachments (not including permanent mechanical attachment to the aircraft), would not be considered a modification to the aircraft. These temporary attachments would not be subject to a regulator preview of 14 CFR part 43” according to the FAA memo dated March 13, 2014 form AFS-300 Aircraft Maintenance Division.
The memo goes on to state: “The use of these type attachments however are not supported by the FAA, and may (in the case of an in-flight detachment) lead to “careless operations” as provide for in 14 CFR sections 91.13 and 91.15.”
I have seen some installations installed in the cabin of small General Aviation (GA) aircraft using suction cups attached to a bar from side window to side window and this would be considered a minor alteration from what I saw. However, I have seen other installs where a mounting bracket was attached to a wing access panel using bolts and screws and this may fall in the category of a major alteration as it was permanently attached to the airframe with wires running through the wing to the cockpit. As previously stated because of the varying installations possibilities of this equipment determination is done on a case-by-case basis and made by the installer.
I have attached a copy of the FAA memo dated March 13, 2014, so you can read and draw your own conclusions if asked to perform an installation as the installer.