Interpretation ID: nht75-5.8

DATE: 12/22/75

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: Blue Bird Body Company

TITLE: FMVSR INTERPRETATION

TEXT: This responds to Blue Bird Body Company's November 11, 1975, request for confirmation that a manufacturer's location of the seating reference point, as the term is defined in 49 CFR @ 571.3, may take into account nominal deflection of the seat and seat back cushions.

Blue Bird Body is correct that subparagraph (c) of the NHTSA's definition of seating reference point contemplates some deflection of seat cushions to simulate compression of padding material under the weight of a human torso and thigh. As noted in the preamble of the second proposal for a school bus seating standard (39 FR 27585, July 30, 1974), "It can be seen that the manufacturer's freedom to locate the point is sharply restricted by the definition which specifies that it actually simulate the position of the pivot center of the human torso and thigh, following SAE placement procedures."

Blue Bird Body's nominal seat and seat back cushion deflections appear to be reasonable, based on our understanding of the drawing you enclosed.

YOURS TRULY,

November 11, 1975

Richard Dyson Assistant Chief Council U. S. Dept. of Transportation NHTSA

As you might imagine, we are deeply involved in designing and developing school bus passenger seats to meet the proposed Docket 73-3, Notice 4, School Bus Passenger Seating and Crash Protection.

In several places this docket refers to "the seating reference point." This is a very important design dimension, since it becomes the basis for determining seat back height and seat spacing as required by this docket.

The purpose of this letter is to describe to you the manner in which we have defined our proposed seating reference point and to seek confirmation from you that this constitutes a valid seating reference point as required by Docket 73-3.

In Part 571.3 of the Federal Motor Vehicle Safety Standards, "seating reference point" is defined. Subparagraphs c and d under that definition state that the seating reference point simulates the position of the pivot center of the human torso and thigh and is the reference point employed to position the two dimensional templates described in the SAE recommended practice J-826, "Mannequins for Use in Defining Motor Vehicle Seating Accommodations" November, 1962. Subparagraph c seems to imply that nominal seat and back cushion deflections should be considered in defining the seating reference point. However, subparagraph d is not clear to us with regard to whether or not nominal seat and back cushion deflections should be considered. Please find enclosed a copy of our drawing 0756809 which shows our proposed seating reference point as defined by coordinates relative to the seat frame. Please note that this drawing is based on a nominal seat cushion deflection of 1/2" and a nominal back cushion deflection of 1/8". It is on this basis that we are proceeding with our seat design and development program.

Please review this drawing and make a determination if this is a valid way to define and describe the seating reference point, especially with regard to the nominal seat cushion and seat back cushion deflections.

Your early response will be appreciated since these dimensions are basic to our entire seat and vehicle development program.

W. G. Milby Staff Engineer

C: WILBUR RUMPH; JIM MOORMAN; BILL PIERCE

(Graphics omitted)

NOTES: 1. Seating reference point shown includes deflection of cushions. Nominal cushion deflection assume as 1/2" on seat cushion parallel to seat back, 1/8" on seat back parallel to seat cushion.

2. Seating reference point: See H-Point SAE J826 - Nov. 1962

C 1974 Nov. 1962

B (Illegible Words)

A (Illegible Words) corrected

INACTIVATES NOS. 0529933

BLUE BIRD BODY CO. FORT VALLEY. GEORGIA U.S.A.

(Illegible Words)

(Illegible Word) PADDED SEAT

(Illegible Words)

SIZE A

(Illegible)

BLUE BIRD

BODY COMPANY

DEAR MARTY THANKS FOR SHARING YOUR LETTER TO SENATOR DECONCINI WITH US. YOUR LETTER CORRECTLY SUMMARIZED THE CONFUSION CAUSED BY THE IMPACT OF THE NEW FEDERAL STANDARDS. EVERY BODY COMPANY HAS HAD TO INTERPRET THESE STANDARDS AND REACT ACCORDINGLY WITH LITTLE FURTHER HELP FROM ANY GOVT. AGENCY.

YOUR LAST PARAGRAPH REALLY SPOTLIGHTS THE MEAT OF THE MATTER. THESE QUESTIONS NEED TO BE ASKED AND ANSWERED. HOPEFULLY THE SENATOR AND OTHER WASHING REPS. WILL BEGIN TO ASK AND LOOK BEFORE THEY (Illegible Word)

THIS WILL SURELY GO DOWN AS A MOST UNUSUAL YEAR IN THE HISTORY OF THE SCHOOL BUS INDUSTRY. HOPEFULLY, WE WILL GET THRU IT AND THE FUTURE WILL MAKE MORE SENSE.

SINCERELY

JOSE