Airworthiness Requirements for Modified Homebuilts

I have read FAA regs for what repairs/mods require a new airworthiness inspection. I am not clear if my modifications require a DAR inspection for new airworthiness or is an A&P/IA inspection enough? I have a Wagabond Traveler that I modified as follows:
1. Engine Accessory mods: New STC starter and alternator. (I assume this does not constitute engine mod for airworthiness)
2. Landing Gear Mod: Replaced original builder-mod spring steel gear with Grove aluminum gear (Repaired fuselage tube damage and installed pads on lower longerons by welding)
3. Replaced 30% of fuselage fabric after removing for inspection.

Do any of these changes void the original airworthiness so long as done per FAA AC standards and have A&P sign offs?

Your original operating limitations will tell you what to do. Major modifications require you to NOTIFY the FAA in the specimen operating limitations that most aircraft have incorporated in their specific limitations. You don't need a DAR or any particular inspection.


(19) After incorporating a major change as described in § 21.93, the aircraft owner is required
to reestablish compliance with § 91.319(b) and notify the geographically responsible FSDO of the
location of the proposed test area. The aircraft owner must obtain concurrence from the FSDO
as to the suitability of the proposed test area. If the major change includes installing a different
type of engine (reciprocating to turbine) or a change of a fixed-pitch from or to a controllable propeller,
the aircraft owner must fill out a revised Form 8130-6 to update the aircraft’s file in the FAA
Aircraft Registry. All operations must be conducted under day VFR conditions in a sparsely populated
area. The aircraft must remain in flight test for a minimum of 5 hours. The FSDO may require
additional time (more than 5 hours) depending on the extent of the modification. Persons nonessential
to the flight must not be carried. The aircraft owner must make a detailed logbook entry describing the
change before the test flight. Following satisfactory completion of the required number of flight hours
in the flight test area, the pilot must certify in the records that the aircraft has been shown to comply
with § 91.319(b). Compliance with § 91.319(b) must be recorded in the aircraft records with the
following, or a similarly worded, statement: “I certify that the prescribed flight test hours have been
completed and the aircraft is controllable throughout its normal range of speeds and throughout
all maneuvers to be executed, has no hazardous characteristics or design features, and is safe for
operation. The following aircraft operating data has been demonstrated during the flight testing:
speeds Vso ______, Vx ______, and Vy ______, and the weight ______, and CG location ______ at
which they were obtained.”

To add to the above:

§21.93 Classification of changes in type design.

(a) In addition to changes in type design specified in paragraph (b) of this section, changes in type design are classified as minor and major. A “minor change” is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product. All other changes are “major changes”...

1 and 3 are probably OK, but a new landing gear would probably be considered a "major change."

My experience with this has been that I just make a call to the FSDO and ask for an Airworthiness Inspector. They will ask for a written description of the work, which I usually have already written up and will email to the inspector while we speak. Typical response to a major mod such as change to a different HP engine, replacing tail with redesigned tail, addition of flaps, structural changes, etc, is to assign a 5 hour (or longer) fight test period, and will send me a letter to document the same.

As previously stated by Dana and FlyingRon, follow your operating limitations. 1 & 3 are simple log entries. #2 would require a call to your local FSDO. If in doubt, give FSDO a call and ask.

-Cub Builder

I replaced my prop last year with a different make/model.

All I had to do was make an appointment with my local FSDO, and show them my log entries and a written request outlining my desired flight test area.

I was given a 5 hour back-into-Phase 1 flight test period; after the 5 hr, it's just a re-certification by me that everything has been completed and that new stall speeds / W&B / CG have been computed.

You were welcome to make an appointment, but all you have to do is send them a post card.

Thank you all for such detailed and thoughtful responses. I was dreading the effort that might be involved, but you made it clear that I just have to put one foot in front of the other, one step at a time! (Just watch WHERE you step!) Thank You.

The repairs don't need A&P sign off. The repairs done by owner are signed off by owner.
The A & P does the condition inspection and annual condition sign off.

You can get help from your A&P for these repairs and modifications. But don't ask him to sign for your repairs and modifications.