Interpretation ID: nht80-2.41

DATE: 05/30/80

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. R. W. Hildebrandt Group Director, Engineering Heavy Vehicle Systems Group The Bendix Corporation 901 Cleveland Street Elyria, Ohio 44035

Dear Mr. Hildebrandt:

This responds to your April 8, 1980, letter asking for an interpretation of section 5.2.1.1 of Standard No. 121, Air Brake Systems. In particular, you ask whether your system complies with the provisions of that section which require that vehicles have a reservoir capable of releasing the parking brakes in the event of an emergency failure of the service brake system. You indicate that your system is in compliance with the intent of this section but may not be in technical compliance with the actual requirements. Nonetheless, you believe that your system complies based upon a letter of interpretation made by the agency to Berg Manufacturing Company dated August 27, 1979.

The August letter to Berg to which you refer in your letter was conditioned upon our reading of the facts as stated by Berg in their letter. That letter as it applied to section 5.2.1.1 was not an interpretation of the standard, but rather an assessment by the agency as to whether we believed that time and based upon the given facts, we stated to Berg that we felt that their system would comply.

The agency has always been reluctant to issue such letters, because it is impossible to determine compliance based up a manufacturer's description of its vehicles or from vehicle drawings. It is necessary for the agency to conduct tests to be certain whether a vehicle will comply. Accordingly, the agency always indicates in its letters that any assessment of compliance is contingent upon the description made in the manufacturer's letter, and that our opinions only reflect our engineering expertise and in no way bind the agency should we test the vehicle and find a noncompliance. In fact, we have frequently indicated to manufacturers that these letters are of little or no value to them.

Subsequent to the issuance of the Berg letter, the agency has received a clearer picture of how the Berg system operates. We have notified that company that their system does not comply with the requirements of the standard. Berg has indicated to the agency that they consider their system to be as good as any that is in complete compliance with the standard and has petitioned the agency to amend the standard in a way that would permit their system. The agency is now looking into the Berg request. We suggest that you closely follow that rulemaking action.

With respect to your system, it appears that it too would not comply with the technical requirements of the standard, because your system does not have a reservoir capable of releasing the parking brakes in the event of service brake failure. Although the agency appreciates your argument that your system meets the intent of the standard for the release of parking brakes when the service brake system fails, nonetheless the standard is specific in its requirement that a reservoir be provided that is capable of releasing the parking brakes. We cannot by interpretation remove the reservoir requirement. Our rulemaking effort with respect to the Berg petition will address the question of whether the reservoir requirement remains necessary in the standard.

Sincerely,

Frank Berndt Chief Counsel

Office of Chief Counsel National Highway Traffic Safety Administration 400 Seventh Street, S.W. Washington, D.C. 20590

April 8, 1980

Subject: Request for Confirmation - Federal Motor Vehicle Safety Standard No. 121; Air Brake Systems; Section 5.2.1.1

Gentlemen:

The Bendix Corporation, Heavy Vehicle Systems Group (Bendix) respectfully requests from the National Highway Traffic Safety Administration (NHTSA) confirmation of Bendix' conclusion that the trailer air brake reservoir system as set forth in Attachment A satisfies the intent and is in compliance with Section S5.2.1.1 of Federal Motor Vehicle Safety Standard No. 121 (FMVSS 121). Bendix' conclusion of compliance is based upon the NHTSA August 27, 1979 interpretation issued to Berg Manufacturing Company (Berg) (Attachment B), and Laboratory Procedures for Federal Motor Vehicle Safety Standard No. 121; TP-121-02, Test Data, page 47 (Attachment C).

The Bendix' trailer reservoir system, shown and described herein; utilizes standard industry accepted components to provide trailer service, emergency and parking brake capabilities. The air applied emergency vapability of this Bendix system is equal to or better than that required by FMVSS 121. Service air for trailer parking is applied through the relay emergency valve. In the event of a reduction in pressure of the service reservoir, spring applied braking would be a secondary means of braking for parking and emergency. The emergency parking brake is applied when the trailer supply line pressure is vented to atmosphere, and released when this line is pressurized to approximately 55 psi. Supply line pressurization for release of the trailer parking brake is unaffected by any single failure in the trailer's service brake system.

The submitted Bendix trailer reservoir system has parking brake release capability as stated in Section S5.2.1.1 of the Standard. Bendix supports the intent of Section S5.2.1.1.1 which promotes highway safety by requiring the towed vehicles parking brakes to have the capability of being released from the towing vehicle in the event of a trailer service system loss of pressure.

A trailer reservoir for the storage of air pressure used to release the parking brakes in event of a service failure per section S5.2.1.1 is redundant, as utilization of the stored pressure requires pressurization of the trailer supply line. In the Bendix' system, if a failure occurs in the service air system, such as a failure of the reservoir, air pressure used for release of the spring applied brakes is provided by the trailer supply line which is pressurized by the air system of the towing vehicle when charging the trailer.

After reviewing the NHTSA interpretation of August 27, 1979 (Attachment B) and the Laboratory procedure TP-121-02 (Attachment C) Bendix has concluded that a trailer brake system which provides parking brake release when the trailer supply line is pressurized is in compliance with S5.2.1.1.

A similar Bendix' trailer reservoir system, having anti-lock capability was submitted to the NHTSA with our letter of September 14, 1977 (Attachment D) petitioning for a revision of Section S5.2.1.1.

Bendix hereby respectfully requests concurrence from with the NHTSA that the Bendix trailer air brake reservoir system, discussed herein, complies with S5.2.1.1 of FMVSS 121. We would be pleased to discuss these Bendix systems in more detail at your convenience.

Very truly yours,

R. W. Hildebrandt Group Director, Engineering

RWH:mnr

Attachments Omitted.