14 C.F.R. § 137.31
Aircraft requirements
No person may operate an aircraft unless that aircraft—
(a) Meets the requirements of § 137.19(d); and
(b) Is equipped with a suitable and properly installed shoulder harness for use by each pilot.
No person may operate an aircraft unless that aircraft—
(a) Meets the requirements of § 137.19(d); and
(b) Is equipped with a suitable and properly installed shoulder harness for use by each pilot.