I'm thinking if adding a "Y" type shoulder harness in a pre 9/14/69 normal category aircraft. In table 9-1 I see the minimum static test load of 704 pounds. Is the shoulder harness static test load (0.4)x(704)x 1/cos angle ?
How was the number 704 derived? 9 x 170lbs = 1,530lbs and 0.4 x 1,530 = 612 lbs
AC 23-17C replaced AC-23-17B says same thing.
"The FAA does not encourage the approval of retrofit shoulder harness installations as
minor changes. The preferred methods of approval are STC or field approval.
However, the FAA should not forbid the approval of a retrofit shoulder harness
installation as a minor change in: 1) the front seats of those small airplanes
manufactured before July 19, 1978, and 2) in other seats of those small airplanes
manufactured before December 13, 1986.
A retrofit shoulder harness installation may receive approval as a minor change in
these small airplanes if:
The installation requires no change of the structure (such as welding or drilling
holes).
The certification basis of the airplane is either 14 CFR, part 23 before Amendment
23-20, part 3 of the CAR, or a predecessor regulation.
In addition, a minor change installation should follow the guidance for hardware,
restraint angles, and attachment locations provided in the following:
AC 43.13-2A, “Acceptable Methods, Techniques, and Practices Aircraft Alterations.”
AC 21-34, “Shoulder Harness-Safety Belt Installations.”
AC 23-4, “Static Strength Substantiation of Attachment Points for Occupant Restraint
System Installations.”
105
AC 23-17B 04/12/05
Installations approved as a minor change may not provide the occupant with the
protection required either by regulation (CAR 3.386) or 14 CFR, part 23, § 23.561).
However, a properly installed retrofit shoulder harness installation is a safety
improvement over occupant restraint by seat belt alone."
......blah, blah,blah,.......
"We conclude from these rules that if a shoulder harness is not required equipment,
it is not essential to the safe operation of the airplane. Therefore, CAR 3.652 and
§ 23.1301, before Amendment 23-20, should not be used as a basis to prohibit
shoulder harness installation by minor change. "