Interpretation ID: nht74-2.15

DATE: 03/20/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Kelsey-Hayes Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your February 1, 1974, request for interpretation of the language "maximum temperature of 500 +/- 50 degrees F" appearing in S6.1.8.1 of Standard No. 121, Air brake systems, 49 CFR 571.121.

The language is intended to specify a temperature range within which to conduct the burnishing procedure in the event brake applications cause the hottest brake on a vehicle to reach 500 degrees F. The word "maximum" is inappropriate and will be deleted in an upcoming notice responding to petitions that raised the same point.

Yours truly,

ATTACH.

KELSEY-HAYES COMPANY

February 1, 1974

National Highway Traffic Safety Administration, U. S. Department of Transportation,

Attention: Lawrence Schneider -- Chief Counsel

RE: Request for Interpretation FMVSS-121; Air Brake Systems Docket 73-13; Notice 3 @ 6.1.8.1 Brake Burnish Procedure

Gentlemen:

We would appreciate an interpretation of the following sentence which appears in the above cited section of Standard 121:

"If during any of the brake applications specified in Table IV, the hottest brake reaches 500 degrees F, make the remainder of the 500 applications from that speed except that a higher or lower speed shall be used as necessary to maintain a maximum temperature of 500 degrees F +/- 50 degrees F."

We believe the meaning of this sentence to be that the temperature of a brake may not exceed 550 degrees F at any time during a brake application and that the speed limitations specified in Table IV may be waived to maintain the temperature below 550 degrees F only if the temperature of the hottest brake reaches 500 degrees during any stop.

We are puzzled by the words ". . . maintain a maximum of 500 degrees F +/- 50 degrees F", as the tolerance appears to be inappropriate if our interpretation is correct. Conversely, if the intent is to limit the temperature range to 500 degrees F +/- 50 degrees F once a temperature of 500 degrees F is reached, the word "maximum" is inappropriate.

A prompt reply would be very much appreciated.

Very truly yours,

John F. McCuen -- Attorney

cc: W. T. Birge; D. Renner