173.151—Exceptions for Class 4.

[Amdt. 173-224, 55 FR 52634, Dec. 21, 1990, as amended by Amdt. 173-231, 57 FR 52940, Nov. 5, 1992; Amdt. 173-234, 58 FR 51532, Oct. 1, 1993; Amdt. 173-255, 61 FR 50626, Sept. 26, 1996; 69 FR 76156, Dec. 20, 2004; 70 FR 34398, June 14, 2005; 71 FR 14602, Mar. 22, 2006; 72 FR 55692, Oct. 1, 2007]