ID: nht76-4.15

DATE: 09/30/76

FROM: AUTHOR UNAVAILABLE; R. L. Carter; NHTSA

TO: Rockwell International

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Rockwell International's February 23, 1976, request for confirmation that the deactivation of automatic adjusters is acceptable during burnish procedures of Standard No. 121, Air Brake Systems, at the option of the manufacturer.

The procedure that you recommend is not permitted by any provision of Standard No. 121. The NHTSA would consider some provision to deal with the overadjustment of automatic adjusters upon receipt of technical data showing justification for such action. Based on consideration of the data received and a petition for amendment, the agency could commence a rulemaking proceeding in accordance with established procedures.

It should be noted that the option in FMVSS 105-75 that you describe requires that the automatic adjusters be deactivated for the entire test sequence, not just the burnish procedure.

Sincerely,

ATTACH.

February 23, 1976

National Highway Traffic Safety Administration Office of Crash Avoidance

Gentlemen:

Subject: Air Brakes - Automatic Adjusters

Rockwell International requests an interpretation of FMVSS #121 testing procedures as it relates to Rockwell cam and wedge brakes with automatic adjustment features.

Automatic adjusting air brakes are premium brakes having significant safety advantages in day to day operation. The automatic adjustment feature is offered on Rockwell cam and wedge brakes, single and dual actuated air and single and dual air/hydraulic units. The automatic adjusting feature enables vehicles to maintain their stopping capability when an otherwise manually adjusting brake would exceed available adjustment or "stroke." At the same time the automatic adjustment feature keeps brakes within a favorable operating range of the air chamber. This becomes more important with the improved brake performance required by FMVSS #121. It is noted that NHTSA has made proper allowance for automatic adjusting hydraulic brakes in the test procedures of FMVSS #105-75.

The accelerated brake burnishing required by FMVSS #121 results in rapid expansion of the brake drum and to a lesser extent brake lining, thereby preventing proper operation of the adjusters. It is, therefore, necessary to manually adjust the brakes for the test procedure.

Enclosed are copies of our recommended procedure for Rockwell International brakes with automatic adjusters when tested for FMVSS #121. It is requested that NHTSA review this procedure and advise that it is acceptable for testing under FMVSS #121. Secondly, it is requested that NHTSA allow for deactivation of automatic adjusters in the FMVSS #121 similar to the provisions of FMVSS #105-75 at the next opportunity.

Very truly yours,

ROCKWELL INTERNATIONAL, CORPORATION AUTOMOTIVE OPERATIONS;

William R. Rodger -- Vice President - Advanced Programs

Encls.

ID: nht76-4.16

DATE: 11/10/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Midland-Ross Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Midland-Ross' September 30, 1976, question whether the "method" specified by Compliance Testing, Inc., in its December 8, 1975, Technical Proposal for Solicitation NHTSA-6-A212 is consistent with the laboratory procedure contemplated by the NHTSA for its test contractors in evaluating the compliance of air-braked vehicles with Standard No. 121, Air Brake Systems. The NHTSA laboratory procedure for compliance contractors in the case of Standard No. 121 states in relevant part:

PROCEDURE:

A. Physically locate check valve or equivalent device.

B. Following manufacturer's recommendation, check the check valve or equivalent device for proper function without disconnecting any air line or fitting. Describe method and technique used.

The Compliance Testing, Inc. (CTI) solicitation was evaluated along with other proposals and has been accepted by the NHTSA. The "method" set forth by CTI as its intended course of action in evaluating the compliance of valves in accordance with the requirements of S5.1.2.3 will not appear in the manual produced for NHTSA compliance testing.

I would like to note in closing that this letter does not constitute an interpretation of the requirements of Standard No. 121. Although the laboratory procedure sets forth the method by which contractors satisfy NHTSA contracts, it does not mean that a vehicle need not meet the requirements of the standard when tested according to its terms by other methods.

MIDLAND-ROSS

September 8, 1976

Salvatore J. Nicolosi -- Office of Contracts and Procurement, National Highway Traffic Safety Administration

Gentlemen:

Subject: Laboratory Procedures for Air Brake Systems, Federal Motor Vehicle Safety Standard No. 121, Report #TP-121-00

Midland-Ross Corporation is a manufacturer of air brake actuation equipment for heavy duty trucks. We therefore manufacture components which are used by truck manufacturers for compliance with FMVSS 121. We are asking for interpretation of the requirements for check valves.

In the subject procedures, issued by the U.S. Department of Transportation, National Highway Traffic Safety Administration, Office of Standards Enforcement Motor Vehicle Programs, Section 1.3.2 states:

"This procedure must be followed by any contractor conducting FMVSS 121 tests for the National Highway Traffic Safety Administration."

Section 5.7 REQUIREMENT S5.1.2.3 -- SERVICE RESERVOIR SYSTEM AIR LOSS TEST states"

"Each service reservoir system shall be protected against loss of air pressure due to failure or leakage in the system between the service reservoir and the source of air pressure, by check valves or equivalent devices whose proper functioning can be checked without disconnecting any air line or fitting."

Under the same section PROCEDURE A and B:

"A. Physically locate check valve or equivalent devices.

B. Following the Manufacturer's recommendation, check the check valve or equivalent device for proper function without disconnecting any air line or fitting. Describe method and technique used." (Underscoring added.)

In the submission by Compliance Testing Inc., which we understand was accepted, the Contractor states:

"Method:

1. Build up air in system to maximum

2. Open bleed valve in supply tank

3. Monitor for 10 minutes pressure in primary and secondary tanks - no loss of air allowed"

We submit that on the surface this appears to be not in compliance with requirements of TP121.00 and we would like to have a clear interpretation of what the contractor plans to do with these valves in checking them for leakage. We submit that zero leakage is a physical impossibility and must be interpreted in terms of the accuracy of the equipment being used for measurement.

Further we submit that the contractor is obligated to test for compliance "following the Manufacturer's recommendation" which we in turn would consider to be the engineering specification for the appropriate valve.

We request that this question be clarified and the NHTSA position be stated so that erroneous claims of non-compliance can be avoided. An early response would be appreciated.

Sincerely,

M. J. Denholm -- Director of Engineering, Power Controls Div.

cc: J. Brewster, M-R; D. Gross, M-R; F. Nawalanic, M-R; A. Beier, IHC; R. MADISON

ID: nht76-4.17

DATE: 12/10/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Great Dane Trailers, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Great Dane Trailer's November 4, 1976, question whether the "controlled lockup" exception in S5.3.2 of Standard No. 121, Air Brake Systems, is available to a manufacturer who equips a "tri-axle" trailer suspension with one set of wheel speed sensors on the center axle (or, alternatively, on the front axle) and one antilock valve and logic module that meters air pressure to the two rearmost axles.

Your question appears to be similar to questions about tandem-axle suspensions that prompted an interpretation of the "controlled lockup" exception to the "no lockup" requirements of S5.3.1 and S5.3.2. A copy is enclosed for your information. You will note that the closing statement in the interpretation states that ". . . the controlled lockup exception is not dependent on the number or location of sensors used in an antilock installation." It is left to the manufacturer to decide what placement of the sensors will provide the best performance.

Sincerely,

Enclosure

Great Dane Trailers, Inc.

November 4, 1976

Thomas Herlihy Office of Chief Counsel National Highway Traffic Safety Administration

Subject: FMVSS 121-Air Brake Systems

Dear Mr. Herlihy:

In Section S5.3.2 of the 121 requirements, there are indications that anti-lock controls be applied to the two rearmost, nonliftable, nonsteerable axles. In the more recent interpretation, there are indications that if it is possible to predict which of the two axles will lock first during braking, sensors may be placed on this axle only; however, they both must be controlled.

My question involves a tri-axle unit. In this case, where must the sensors be used? By the first interpretation, controls need not be on the front axle of this suspension, only on the last two. Of these last two, the center axle will always lock before the rear axle, meaning that the control sensors should be installed on this center axle. However, in a tri-axle suspension, the front axle will lock first, the center axle will lock second and the rear axle will be the last to lock.

We would appreciate your early reply.

Sincerely,

Dudley E. DeWitt Manager/R & D

ID: nht76-4.18

DATE: 03/31/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Adams County

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your March 5, 1976, request for written permission to deactivate the "121 brake system" of a school bus manufactured from a Ford chassis with a Kelsey-Hayes antilock system.

From the description of the problems you have encounted with this vehicle, I assume that you do not intend to disconnect the entire "121 brake system", but only one or more antilock systems installed in satisfaction of the "no lockup" requirements of S5.3.1 of Standard No. 121, Air Brake Systems. The National Highway Traffic Safety Administration (NHTSA) has made a finding that early models of the antilock system supplied on transit and intercity buses is characterized by malfunction that warrants its deactivation until a correction is fully developed. This finding was not made with regard to the Kelsey-Hayes system that equips your vehicle.

Section 108(a)(2)(A) of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. @ 1397(a)(2)(a)) prohibits, with one exception, knowing disconnection of the antilock system by manufacturers, distributors, dealers, or repair businesses. A person that does not fall into those categories is not prohibited from disconnection of the system. Other State or Federal requirements, such as those of the Bureau of Motor Carrier Safety, may prohibit disconnection. In any case, the NHTSA urges that you not disconnect safety devices without consulting the vehicle manufacturer with regard to the safest configuration of the vehicle.

SINCERELY,

School District No. 12

MEMO NO: B-0093

DATE: MARCH 5, 1976

TO: CHIEF COUNCIL NATIONAL HIGHWAY TRAFFIC ADMINISTRATION

FROM: RON STACY SUPERVISOR OF TRANSPORTATION

RE: DE-ACTIVATE 121 BRAKES

A letter to Dr. Neil McCormick, (attached), telephone conversation with Brad Marks, "National Highway Safety Administration", Colorado, Dr. Steve Sacks, "National Highway Traffic Safety", Washington, D.C., explaining existing problems with the 121 brake, (Kelsey-Hayes, Ford Chassis).

December 1975, Kelsey-Hayes representative performed an inservice workshop. Problems still exist!

Refer, Fleet Maintenance Magazine, February 1976 issue, page 61. Washington Report; QUOTE: "NHTSA has also tentatively determined, at this writing, that virtually the only anti-lock system currently available for buses "is characterized by malfunction that warrants its deactivation on all vehicles on which it is installed while a correction is fully developed." UNQUOTE.

Request permission, in writing, to deactivate the 121 brake system, until such time corrections are complete.

Your cooperation and expedience is greatly appreciated.

RON STACY

School District No. 12 Adams County

TRANSPORTATION DEPARTMENT

MEMO NO: B-0085

DATE: NOVEMBER 13, 1975

TO: DR. NEIL MCCORMICK SUPERVISOR OF SUPPORTING SERVICES UNIT COLORADO DEPARTMENT OF EDUCATION

FROM: ROW STACY

REF: 121 BRAKES

1. Frequently one brake will grab at low speed.

2. Occasionally brakes will fade.

3. Occasionally all four wheels will lock-up on panic stop.

4. Occasionally brakes will fade completely: gradual stop, below 15 m.p.h.. Then, brakes will grab as if panic stop condition existed.

If I can be of further assistance, please do not hesitate to call.

ID: nht76-4.19

DATE: 02/12/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Hon. Robin Beard - H.O.R.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 29, 1976, question whether an owner of a vehicle manufactured to comply with Standard No. 121, Air Brake Systems may legally disconnect portions of the brake system after a vehicle has been delivered for use in his business.

Section 108(a)(2)(A) of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. @ 1397(a)(2)(A)) prohibits, with one exception, knowing disconnection of safety components by manufacturers, distributors, dealers, or repair businesses. Thus, there is no prohibition on disconnection by an owner of his own vehicle's system under the Traffic Safety Act. However, State statutes, or the regulations of the Bureau of Motor Carrier Safety may prohibit disconnection. In any case, the NHTSA urges that owners not disconnect safety devices without consultation with the vehicle manufacturer with regard to the safest configuration of the vehicle.

SINCERELY,

Congress of the United States House of Representatives

January 29, 1976

Robert L. Carter Associate Administrator Motor Vehicles Program U. S. Department of Transportation

I have been contacted by a constituent regarding the anti-skid devices on trucks and trailers.

I am informed by my constituent that he has encountered a great deal of expense due to the failure of these devices, such as damaged tires, tow bills, and time spent on repairs. My constituent would like to know if there would be a fine imposed or any type of penalty if these devices were disconnected.

I appreciate your checking on this matter and sending me a reply.

Robin Beard, M. C.

ID: nht76-4.2

DATE: 03/30/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Motor Coach Industries, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Motor Coach Industries' February 20, 1976, letter asking whether Standard No. 121, Air Brake Systems, requires the installation of parking brakes on all non-steerable axles of a bus, including a lightly-loaded axle, in satisfaction of the emergency braking provisions of S5.7.1. Once parking brakes are applied on the non-driving, lightly-loaded axle on some Motor Coach Industries (MCI) buses in cold, wet weather, the linings can freeze to the drums and "lock" the wheels so that they will not turn even after the parking brake is released. You suggest that parking brakes are inappropriate on a lightly-loaded axle, citing an interpretation of the standard that stated parking brakes are not required on an air-lift axle which lifts off the ground when the vehicle is parked.

MCI raised the same question of parking brake requirements for lightly-loaded axles in an April 17, 1972, letter requesting interpretation of the provision of S5.7.1 that requires automatic application of parking brakes. At the time, the NHTSA had just issued S5.7.1, expanding the methods for meeting performance levels for emergency braking performance. The question of whether parking brakes should be required on all axles under S5.7.1 was left open pending formal rulemaking.

What was not raised in MCI's April 1972 letter was whether both methods for meeting S5.7.1 performance levels necessitate parking brakes on all non-steerable axles. Section S5.7.1.2 permits reliance on retardation force capabilities of each non-steerable axle or, in the alternative, reliance on vehicle stopping capability using the vehicle's available parking brakes. In the second case, the NHTSA does not interpret S5.7.1 to require installation of parking brakes on an axle if it is not necessary to meet the stopping performance of S5.7.2.3 specified under S5.7.1.2. To the degree the language of S5.7.1 does not specifically address this method of satisfying the requirement, we regret that the agency's July 1972 response was not more clear.

An interpretative amendment of S5.7.1 would be appropriate in view of the difficulties that its misinterpretation has caused. However, in view of the short time remaining before the automatic application option will no longer be available, the NHTSA does not expect to undertake rulemaking to formalize this interpretation.

YOURS TRULY,

Motor Coach Industries, Inc.

February 20, 1976

Office of the Chief Counsel National Highway Traffic Safety Administration

SUBJECT: Tag Axle Parking Brake - MVSS 121 S 5.7.1.

Since March 1, 1975 Motor Coach Industries, Inc. of Pembina, N.D. had to add a parking brake (piggy back spring brake) to the tag axle wheels on MC-8 model coaches sold with the optional "Parking brake with automatic application" in order to comply to MVSS #121, S 5.7.1. The option for automatic application is a requirement for the States of New Jersey and Massachusetts and constitues about 20% of the MC-8 yearly production. One hundred and seventy five coaches have been equipped with this braking system since March 1, 1975. The addition of the piggy back parking brake is solely to meet the requirement of S 5.7.1 "parking brake on each axle, except steerable front axles" and is not needed to meet the parking brake performance.

During winter operation a problem has developed and quick action had to be taken to provide protection to the bus passengers due to possibility of tire fire. A copy of the Defect Information Report initiated by Motor Coach is attached for your review. A copy of a letter from a bus operator is also attached together with a picture of two damaged tires. In the letter of Mr. W. Owens of Capitol Bus Company, you will notice that a State trooper stopped the driver of bus CP 861 after noticing the wheels not turning.

M.C.I. is approaching NHTSA to obtain an interpretation of S5.7.1. which would differenciate between axle loading. Already an interpretation to the Dura Corporation ref - N40-30 (TWH) by your office states "the requirement for parking brake retardation force does not apply to an axle which is not on the ground when the parking brake system is activated." The tag axle wheels give a reading of 3,000 lbs per wheel at the ground level while the drive axle will carry to 11,000 lbs per duo wheel.

The parking brake retardation force is negligeable as the deterioration of the tire shows it. MCI has built 2,550 MC-7 model coaches and 1,500 MC-8 model coaches for the last 8 years without the need for parking brakes on the tag axle. We have a clear record as to the operation of the parking brake on our vehicles and do not understand the agency arbitrary requirement for a parking brake on each non-steerable front axle without consideration of axle loading. Our certification nameplate shows a G.A.W.R. of 22,000 lbs for the drive axle and a G.A.W.R. of 6,000 lbs. for the tag axle. This difference in axle rating on a same vehicle with the same tire size explains why the parking brake (DD3) on the drive axle will free under motion while the tag axle will drag along.

Effective September 1, 1976, MVSS 121 will prohibit the automatic application vs. a modulated control of the parking brake and no requirement for parking brakes on each non steerable front axle is maintained.

It is unfortunate to penalize the small number of coaches involved, to raise the cost of the vehicle without added return and to expose the bus operators to obvious danger.

George A. Hunt Engineering Manager

ID: nht76-4.20

DATE: 02/12/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: General Teamsters Local 959 - Alaska

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 29, 1976, questions whether an owner-operator of a vehicle manufactured to comply with Standard No. 121, Air Brake Systems, may legally disconnect portions of the brake system after a vehicle is delivered, or specify that the vehicle be delivered without certain portions of the brake system installed. Your members are asking about the antilock portion of the brake systems installed to meet the "no lockup" provisions of the standard (S5.3.1).

Two provisions of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. @ 1381 et seq.) are involved. Section 108(a)(1)(A) prohibits the sale of any vehicle unless it complies with all applicable safety standards that were in effect on the date of the vehicle's manufacture. This means that a member cannot purchase a newly-constructed tractor with portions of the brake system disconnected, if those portions are installed in compliance with the standard. The antilock portions of the system are, as far as I know, installed in compliance with the standard and therefore cannot be disconnected prior to sale.

Section 108(a)(2)(A) with which you are familiar prohibits, with one exception, knowing disconnection of the antilock system by manufacturers, distributors, dealers, or repair businesses. Thus, there is no prohibition on disconnection by an owner-operator of his own vehicle's system under the Traffic Safety Act. However, other State of Federal statutes, or the regulations of the Bureau of Motor Carrier Safety may prohibit disconnection. In any case, the NHTSA urges that you not disconnect safety devices without consultation with the vehicle manufacturer with regard to the safest configuration of the vehicle.

SINCERELY

General Teamsters Local 959 State of Alaska

January 29, 1976

Frank A. Berndt, Acting Chief Counsel U. S. Department of Transportation National Highway Traffic Safety Administration

Several of our members have obtained copies of your letter of September 29, 1975 to Mr. Joseph L. Casson, concerning Standard Number 121 and Section 108 (a) (2)(A) of the National Traffic and Motor Vehicle Safety Act. In that letter, you stated that manufacturers of air braked buses that conform to Standard Number 121 may instruct the owners of his products to disconnect the anti-lock system used to meet the Standard. For the period necessary to correct a safety-related defect in the system that may make its operation hazardous.

Several members of Local 959 either operate tractors or are in the process of obtaining newly built tractors. They have requested that I contact you to obtain your opinion on if they may disconnect the anti-lock system in the existing tractors, or not have an anti-lock system placed on their tractors which are presently being constructed. They are of the opinion that no anti-lock system currently on the market is safe. In other words, they wish to disconnect or not have placed on the newly constructed tractors any anti-lock system until the safety-related defects in the anti-lock system are corrected. If the anti-lock systems were disconnected, the defect report requirement of 49 CFR Part 573 and the defect notification requirements of 49 CFR Part 577 would be complied with.

Thanking you in advance for your attention to my request,

James A. Witt, General Counsel

CC: BILL SHANNON -- COPPER FREIGHT LINES

ID: nht76-4.21

DATE: 05/13/76

FROM: AUTHOR UNAVAILABLE; S. P. WOOD for F. Berndt; NHTSA

TO: Rome Engineering & Manufacturing Co.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Remco's April 26, 1976, question whether an exclusion from a safety standard based on the gross axle weight rating (GAWR) of an axle is met by using the rating of the axle beam by its manufacturer, or whether the truck or trailer manufacturer must also consider the load-bearing abilities of the wheels, rims, and hubs used with the axle beam.

Gross axle weight rating is defined in 49 CFR 571.3 to mean:

. . . the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tireground interfaces.

This definition means that the determination of GAWR is made by the vehicle manufacturer and that the axle beam rating of the component supplier cannot be the only basis for GAWR calculation. The GAWR is the value established at the tire-ground interfaces at each wheel position, and this means that the wheels, rims, hubs, and tires must be included in the determination. Thus, with regard to the exclusion from Standard No. 121, Air Brake Systems, until September 1, 1977, for any vehicle with an axle that has a GAWR of 24,000 pounds or more, the vehicle manufacturer must take into consideration each component on the axle as well as its attachment to the vehicle frame.

Sincerely,

ATTACH.

ROME ENGINEERING & MANUFACTURING CO.

April 26, 1976

TAD HERLIHY -- OFFICE OF CHIEF COUNSEL -- National Highway Safety Administration

Dear Sir:

We are in need of clarification of Motor Vehicle Safety Standard No. 121 as pertains to paragraph S3 of Part 571-S121-1, quote: "or that has a gross axle weight rating for any axle of 24,000 pounds or more."

Does this mean that a certification from the axle manufacturer that his product is rated at 24,000 pounds or more would exempt the trailer manufacturer from compliance with MVSS 121 or is it necessary to have a single axle as well as the tires, wheels, hubs, and rims on that axle rated at 24,000 pounds or more capacity before the exemption is valid?

We would appreciate an advisory opinion on this matter.

Thank you.

Very truly yours,

R. A. Plummer -- Vice President & General Manager

ID: nht76-4.22

DATE: 08/02/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: MOTAC Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Motac's June 24, 1976, request to know why a trailer with a flat cargo-carrying surface that is not more than 40 inches above the ground is considered a "heavy hauler trailer" (as defined in Standard No. 121, Air Brake Systems), while a trailer with an inclined cargo-carrying surface that is more than 40 inches above the ground over the fifth wheel attachment point is not considered a heavy hauler trailer. You also request confirmation that the period for exclusion of heavy hauler trailers from the standard has been extended to September 1, 1977.

At the time that the "heavy hauler trailer" exclusion was implemented, the agency considered and rejected the addition of trailers with inclined beds to the excluded category. I have enclosed a copy of the notice that implemented the exclusion, which states "The NHTSA has concluded that trailers with beds higher than 40 inches (including trailers whose beds are below 40 inches over the wheels but higher than 40 inches over the fifth wheel) can accommodate the new larger brake packages available at this time." Of course the exclusion was intended to and does apply to the traditional trailer with a gooseneck and a flat cargo-carrying surface that is not more than 40 inches above the ground. The "double-drop semi", the "stock drop frame flat-bed", and the "40'-0" single axle drop frame platform semi" you describe appear to qualify as heavy hauler trailers.

I have enclosed a copy of the amendment of Standard No. 121 that extends the date for exclusion of heavy hauler trailers to September 1, 1977.

Yours truly,

Enclosures

ATTACH.

June 24, 1976

Frank Berndt -- Acting Chief Counsel, DEPT. OF TRANSPORTATION

Subject: Clarification regarding installation of FMVSS-121 brakes on "Low Bed Heavy Hauler Trailers."

Dear Sir,

We would appreciate further clarification if FMVSS-121 brakes are required or are exempt on the Drop Frame Platform Semi-Trailer per our attached drawing SK-7229-W3. This Drop Frame Platform Semi-Trailer is also made with Tandem axles and a platform height of 39".

In accordance with my letter of Aug. 7, 1975 addressed to Mr. James B. Gregory and his reply "N40-30 of Sept. 8, 1975 (copies attached) I interpret that this type of trailer is exempt from the S-121 brakes as it complies to the definition of a Low Platform Heavy Hauler Trailer."

We also received from T.T.M.A., a copy of your letter, file No. N40-30 RFBPI (copies attached) with two sketches of similar type trailers, stating that they do not qualify for exemption of the S-121 brake system.

Since the greater majority of the load is carried on the main deck, which I interpret as the "Primary Cargo Carrying Surface" and only a small portion of the load can be carried on the gooseneck platform, I analyze that this complies with your definition of Low Platform Heavy Hauler Trailers.

Also please advise if your Docket No. 75-16, Notice 5 has become effective to extend the installation of the S-121 brake system on Heavy Hauler Trailers until Sept. 1, 1977 as I do not have a confirming copy in my files.

Yours very truly,

Jack A. Johnson -- Chief Engineer, MOTAC, INC.

Enc.

ID: nht76-4.23

DATE: 08/16/76

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Truck Equipment & Body Distributors Association

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your July 28, 1976, request for confirmation that a boat-carrying trailer which has a primary cargo-carrying surface less than 40 inches from the ground qualifies as a "Heavy hauler trailer", and that such trailers are not required to meet the requirements of Standard No. 121, Air Brake Systems, until September 1, 1977.

"Heavy hauler trailer" is defined in the standard as follows:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) Its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @ 393.106 of this title.

The boat-carrying trailer which you describe as having a bed height of 18 3/4 inches would qualify for exemption until September 1, 1977.

Yours truly,

ATTACH.

TRUCK EQUIPMENT & BODY

DISTRIBUTORS ASSOCIATION

July 28, 1976

Chief Counsel -- National Highway Traffic Safety Administration, Department of Transportation

Gentlemen:

We are writing on behalf of a member company who has received a large order for some boat trailers, per the enclosed photograph.

The trailer is 42 feet in overall length, and eight feet wide. The "primary carrying surface" is 18 3/4 inches high, although the gooseneck portion at the front of the trailer is 48 inches high and 79 inches long. The vehicle will be equipped with 12 1/4 inch by 5 inch air brakes.

We agree with our member that this unit is exempt from FMVSS 121, since it meets the definition of a "heavy-hauler trailer". However the member would appreciate your agreement just to be on the safe side.

Thank you for your assistance in this matter.

Sincerely,

THOMAS S. PIERATT/LW -- Executive Director

Enclosure:

[Graphics omitted]