Email from FAAST on Jan 21 2021
Major Changes to Experimental Aircraft
Notice Number: NOTC1658
The purpose of this notice is to remind owners/operators of experimental certificates for exhibition, air racing, operating amateur-built aircraft, or operating light-sport aircraft (LSA) of the need to notify their servicing Flight Standards District Office (FSDO) of major changes made to the aircraft that affect performance and/or controllability.
A few instances of major changes [as defined by 14 CFR§ 21.93(a)] to experimental aircraft have surfaced recently. Most of these major changes were performed on experimental aircraft that have already completed the Phase I flight evaluation, had their performance parameters documented in the aircraft log as required by the Phase I operating limitations, and are now flying per the Phase II operating limitations. Subsequent major changes appreciably affected performance and/or controllability, and must be properly tested in a controlled environment as stated in 14 CFR § 91.319(b). In other words, the owner/operator/modifier should have notified the servicing Flight Standards District Office of the major change so that the operating limitations could be amended and the aircraft placed back into Phase I operations. The specific instructions for notifying the FSDO are contained in paragraphs 22 and 23 of the current operating limitations for any aircraft with experimental certificates.
Boise FSDO (208)387-4000
Casper FSDO (800)325-5785
Helena FSDO (406)449-5270
Portland FSDO (503)615-3200
Salt Lake FSDO (801)257-5020
Seattle FSDO (206)231-3828
Spokane FSDO (509)532-2340