4 point restraints

Thanks, Larry.

Thanks for the info, Bruce.
Ken

The FAA has acknowledged the value of shoulder harnesses by allowing their installation as a "minor change" per AC 23-17C. No STC or field approval req'd.
As a safety improvement, any shoulder harness should be acceptable. The harness could be attached to a right angled bar the length of Frame F. The front of the bar becomes a doubler for Frame F, a minor alteration as long as holes are drilled only into the doubler and not into the Frame. How the doubler
is attached to Frame F is between you and your mechanic.

I agree that the 4-point is a better system. Thanks for the feedback, John.
Ken

Yes, the 337 is the form for an FAA "field approval" which is necessary for a major alteration. A 337 would also be filed for the STC but does not need FAA approval because the STC is already approved data. Your mechanic should be well versed with this.

I'm pursuing the four point because I feel it's a better restrain system, allowing better protection from lateral impacts, i.e. catching a wing and subsequently spinning as well as better for straight ahead impact. The three point is better than nothing though.