ID: aiam1811

Dear Mr. Luce: Thank you for your response dated December 5, 1974, to ou certification information request (CIR 1177) letter dated November 4, 1974, pertaining to the Federal Motor Vehicle Safety Standard (FMVSS) No. 217, Bus Window Retention and Release,' failure.; The failure pertained to the bus not meeting the window retentio requirements (Section S5.1) when it was subjected to a compliance test conducted by a laboratory under contract to the National Highway Traffic Safety Administration (NHTSA).; Due to the disparity that exists between Blue Bird Body Company's tes results and those of the NHTSA, it is requested that the appropriate Blue Bird personnel participate in an informal technical meeting with NHTSA personnel on March 25, 1975. This meeting will be held at 10:00 a.m. in Room 3222, Trans Point Building,2100 Second Street, S.W.,Washington, D.C.; The following additional information will be required: 1. The number of buses modified to date as a result of the defec notification.; 2. Copy of the detail drawings or sketches and procedures to follow t accomplish the defect notification rework.; 3. Sample copy of the letters sent to the purchasers and th distributors or field representatives as a result of the defect notification.; 4. Specify at what point, in the buildup of the bus body, is the windo opening checked.; 5. The date when the bus body, Serial No. F25048, was assembled. 6. The date when the redesigned rubber extrusion was incorporated. Please advise by Monday, March 17, 1975, the names and titles of you representatives who will attend and whether the meeting date is satisfactory.; Should there be any questions concerning this letter, please refer the to Mr. Alfred Kazmierczak, a member of my staff, on telephone number 202-426-0826.; Sincerely, Francis Armstrong, Director, Office of Standard Enforcement, Motor Vehicle Programs;

ID: aiam5151

"Dear Mr. Radice: We have received your undated letter with respect t certification of aftermarket flashers. You understand that manufacturers of aftermarket turn signal flashers and hazard warning signal flashers must certify that the flashers comply with the applicable requirements of Federal Motor Vehicle Safety Standard No. 108 prior to sale. However, when a vehicle is equipped with a combination turn signal/hazard warning signal flasher, you ask whether the manufacturer of the replacement flasher must certify compliance with requirements for both flashers, or can certify the flasher to 'meet either the turn signal flasher or hazard warning signal flasher of FMVSS-108 but not both?' Paragraph S5.8.1 (formerly S5.7.1) of Standard No. 108 requires that each item of lighting equipment manufactured to replace any item of lighting equipment on any vehicle to which Standard No. 108 applies shall be designed to conform to Standard No. 108. Therefore, a combination turn signal/hazard warning signal flasher that is manufactured to replace a combination turn signal/hazard warning signal flasher must be designed to conform to requirements applicable to both turn signal flashers and hazard warning signal flashers. Paragraph S5.8.2 permits replacement lighting equipment to be labelled with the symbol DOT, constituting a certification of compliance to applicable Federal motor vehicle safety standards (although the manufacturer may certify by a label or tag affixed to the flasher or the container in which it is shipped). The 'applicable Federal motor vehicle safety standards' for a combination turn signal/hazard warning signal flasher are those portions of Standard No. 108 that specify requirements for turn signal flashers and hazard warning signal flashers. The manufacturer's certification must therefore cover both. I hope this explains the matter for you. Sincerely, John Womack Acting Chief Counsel";

ID: aiam1638

Dear Mr. Luce: The Office of Standards Enforcement (OSE) is in possession of a repor of a test conducted for the National Highway Traffic Safety Administration (NHTSA) which indicates that a Model CV-2901 bus manufactured by your company failed to meet the requirements of Federal Motor Vehicle Safety Standard (FMVSS) No. 217, Bus Window Retention and Release.' A copy of the Final Report is enclosed.; The potential noncompliance is summarized as follows: The bus did not comply with the window retention requirement (paragraph S5.1).; Pursuant to sections 112 and 108 (a)(2) of the National Traffic an Motor Vehicle Safety Act of 1966, Blue Bird Body Company is required to provide OSE, NHTSA, with the following information:; 1. The bus models and quantities manufactured by your company on an after September 1, 1973, that utilize the same window configuration as Model CV- 2901.; 2. The data used to certify your buses and the data obtained durin surveillance testing of the buses. This data should include actual test reports of testing done by or for your company.; 3. Information and data pertaining to investigations ad correctiv action you may have initiated as a result of the noncompliance indicated by this compliance test.; 4. Any other pertinent information you may wish to introduce. The Office of Standards Enforcement has received your defec notification dated October 1, 1974.; The requested information shall be submitted, in duplicate, to th National Highway Traffic Safety Administration, Motor Vehicle Programs, Office of Standards Enforcement, 2100 Second Street, S.W., Washington, D.C. 20590, within 20 days from the receipt of this letter.; Should there be any questions concerning this letter, please refer the to Mr. Alfred Kazmierczak, a member of my staff, telephone number 202-426- 0826.; Sincerely, Francis Armstrong, Director, Office of Standard Enforcement, Motor Vehicle Programs;

ID: aiam3300

Dear Mr. Murtha: This responds to your recent request for information on behalf of you constituent, Mr. Steve Zufall. Mr. Zufall is interested in the specifications applicable to the manufacture of propane tanks to be used in the conversion of gasoline-powered vehicles. He asked how to obtain 'numbers' to be listed on the tanks and mentioned the designation '4VA-240', which someone had discussed with him.; The enclosed discussion sets forth the implications under Federal la of converting gasoline-powered vehicles to use propane, as well as a general discussion of auxiliary fuel tanks. The applicable statutory authority is the National Traffic and Motor Vehicle Safety Act, as amended 1974 915 U.S.C. 1381, *et seq*.). The discussion first looks at the Federal Motor Vehicle Safety Standard (FMVSS) applicable to fuel systems and then at the defect responsibilities that might be involved. Next, a brief mention is made of the possibility of product liability suits.; There are no requirements under the Federal motor vehicle safet regulations that specify 'numbers' which must be stamped on propane gas tanks. The designation mentioned by Mr. Zufall, 4VA- 240', is actually '4BA-240' and refers to specifications under the Bureau of Motor Carrier Safety regulations relating to fuel systems on commercial vehicles or to tanks used for shipment of propane gas in interstate commerce. These regulations would not apply, however, to tanks or fuel systems on private vehicles. For further information regarding these regulations, Mr. Zufall should contact Mr. W. R. Fiste of the Bureau of Motor Carrier Safety (202-426-0033).; Sincerely, Frank Berndt, Chief Counsel

ID: aiam0702

Dear Mr. Douglas: This is in reply to your letter of May 2, 1972, in which you reques information relating to your responsibilities under the National Traffic and Motor Vehicle Safety Act of 1966 (the Act) and the Federal Motor Vehicle Safety Standards (FMVSS) and regulations issued thereunder.; Motor homes are not defined as such under the regulations. They fall i the category of multipurpose passenger vehicle and would be subject to all of the standards that apply to that type vehicle.; I am enclosing the following publications. The answers to you questions can be found therein:; >>>1. The Act 2. December 2, 1971, edition of the Federal Register - Recodification 3. Part 566 of Title 49 of the Code of Federal Regulations Manufacturer Identification; 4. Part 567 - Certification 5. Part 568 - Vehicles Manufactured in Two or More Stages 6. Part 573 - Defect Reports 7. Part 574 - Tire Identification 8. Notice of Publications Change<<< In the event you purchase an incomplete vehicle (chassis) fro Cadillac, they will furnish the documentation as required by part 568. In modifying the chassis you assume the role as an intermediate manufacturer and the recreational vehicle manufacturer becomes the final stage manufacturer. All terms are defined in Part 568.; Federal regulations concerning anti-pollution emission control device are not the responsibility of the Department of Transportation, but of the Environmental Protection Agency. A copy of your inquiry is being furnished to the Director, Division of Certification and Surveillance, Mobile Source Pollution Control Program, 2565 Plymouth Road, Ann Arbor, MI 48105. He will, I am sure, forward such information as he deems appropriate.; If you have further questions, I will be pleased to answer them. Sincerely, Francis Armstrong, Director, Office of Standard Enforcement, Motor Vehicle Programs;

ID: KenWeinstein

ID: 1984-3.29

TYPE: INTERPRETATION-NHTSA

DATE: 09/24/84

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Thomas D. Turner -- Manager, Engineering Services, Blue Bird Body Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your letter of August 15, 1984, concerning the application of Standard No. 301, Fuel System Integrity, to school buses with a gross vehicle weight rating of more than 10,000 pounds. You specifically asked about the effect on certification of adding auxiliary equipment to the fuel system. As explained below, you are correct in your understanding that the vehicle with any auxiliary equipment installed on it must be certified as complying with the standard.

You explained that you are receiving more requests for school buses equipped with auxiliary fuel-fired heaters and air conditioners. Those auxiliary devices would be connected to the fuel tank or line of the vehicle. You further explained that the typical auxiliary heating and air-conditioning include fuel powered units mounted to the outside of the chassis frame and/or the underside of the body and located between the outside of the chassis frame and the outside body sheetmetal, where it could be impacted by a moving barrier during the crash test required by Standard No. 301.

Standard No. 301 sets requirements for the integrity of the entire fuel system used in motor vehicles. If auxiliary fuel-powered equipment is installed in a vehicle before its sale to its first purchaser for purposes other than resale, the vehicle with the auxiliary equipment installed must be certified as complying with Standard No. 301.

You explained that because of the variety of different auxiliary fuel systems and the different sizes, types, and configurations of vehicle involved, you believe it is impracticable and economically prohibitive to conduct full scale crash tests. Therefore, you asked about alternative methods of determining compliance. As with all of the agency's standards, Standard No. 301 sets forth the test procedures that the agency will use to determine if a vehicle complies with the performance requirements of a standard. A manufacturer is not required to do crash testing to verify compliance; instead it may rely on such things as engineering analysis or computer simulations to establish that its vehicle conforms with the standard.

Section 108(b)(2) of the National Traffic and Motor Vehicle Safety Act requires a manufacturer to show that it has exercised due care in making its certification that the vehicle conforms with all applicable standards. Whether a manufacturer has exercised due care can only be made on a case-by-case basis. What constitutes "due care" in a particular case depends on all relevant facts, including such things as the limitations on current technology, the availability of test equipment, the size of the manufacturer and above all the diligence evidenced by the manufacturer. The agency would look to such things as the drawing, engineering instructions, and quality assurance procedures that you mentioned in order to make a determination of due care. Although an inspection by an independent laboratory is not required, the existence of such testing would be considered in determining whether a manufacturer has exercised due care.

Finally you asked if any manufacturers are currently relying on methods other than crash testing to determine whether their vehicles conform with our standard. Since manufacturers are required to self-certify their vehicles and are not required to receive any approval from this agency before making their certifications, I cannot answer your question. I note that in instances where there has been a question of whether a vehicle complies with Standard No. 301, manufacturers have provided crash test data to the agency to demonstrate their compliance with the standard.

If you have any further questions, please let me know.

Sincerely,

BLUE BIRD BODY COMPANY

August 15, 1984

OCC-1058

Frank Berndt Chief Counsel National Highway Traffic Safety Administration

Dear Mr. Berndt:

Blue Bird Body Company is a major manufacturer of school and non-school buses which are sold throughout the U.S. and Canada. For years, on non-school buses, we have offered air conditioning as a regular option and have provided auxiliary fuel fired heaters upon request on a temporary option basis. The market place has recently been expressing a need for these features on school buses. We have received requests for auxiliary fuel fired heaters from several northern states and Canadian provinces. The need for auxiliary heating capability is increasing with the increased popularity of diesel powered school buses, which have less heat available for heating and defrosting of the driver and passenger compartments.

The demand for air conditioning in school buses is naturally coming from the warmer climate states, particularly Florida, and is primarily for lift buses used in transporting the handicapped. These vehicles often travel long routes and the stops to load and unload passengers are often quite lengthy. As a result the students often spend a lot of time on the bus and many of the special students are more sensitive to excessive heat than non-handicapped students.

I have presented this background and brief explanation because we at Blue Bird, strongly believe that the need for auxiliary heating and air conditioning on school buses is real and justified, and has significant bearing on the safety and well being of the students being transported. In order to provide these needed features on new school buses in an efficient and cost effective manner, we as body manufacturers must be able to install available heating and air-conditioning units and systems at the factory, and certify the completed vehicle as meeting all applicable Federal Motor Vehicle Safety Standards. The typical and commonly available auxiliary heating systems and air conditioning systems include fuel powered units mounted to the outside of the chassis frame and/or the underside of the body and located between the outside of the chassis frame and the outside body sheetmetal, or skirt, as it is commonly called. With the variety of systems available that could be requested by the customer, the different sizes, types, and configurations of vehicles that are involved and the variety of possible mounting locations on each type vehicle, the combinations of equipment involved is potentially quite large. Our primary concern is with FMVSS 301-75 as it applies to school buses and auxiliary equipment provided on school buses that have their own fuel systems.

It is our understanding that FMVSS 301-75 as it applies to school buses with GVWR's of more than 10,000 pounds is a vehicle performance standard, and that the vehicle, including any and all auxiliary equipment installed on the vehicle, must meet FMVSS 301-75 requirements and be certified as meeting FMVSS 301-75. In other words, if we choose to manufacture and sell school buses with an auxiliary heater or air conditioner mounted in the skirt such that it could be impacted by the moving contoured barrier as specified in Section S6.5, we would need to be sure that the fuel system of the auxiliary heater or air conditioner would not cause the vehicle to exceed the fuel spillage requirements of S5.5 and be capable of documenting our compliance. We request your confirmation that the fuel system of an auxiliary heater or air conditioner installed on a new school bus is covered by FMVSS 301-75, and that there are no exemptions or interpretations that exclude such systems from the standard's requirements.

Due to the variety of systems and combinations discussed previously and the continual evolution of chassis, body and heater/air conditioner designs and manufacturing procedures, we feel it is impractical and economically prohibitive to conduct full scale vehicle crash tests. We, therefore, wish to pursue alternate methods of certification documentation. One particular system we have looked at is a skirt mounted air conditioner with a diesel engine. The diesel fuel system of the vehicle is certified as meeting FMVSS 301-75. The engine on the air conditioner shares the same fuel tank as the vehicle's engine and, thus, only the fuel lines, fuel pump, filler filter, and the air conditioner's engine itself pose a concern relating to FMVSS 301-75 compliance. Preliminary tests have shown the air conditioner fuel system contains only about 3 1/2 ounces of fuel and the fuel pump is controlled by an oil pressure switch on the air conditioner's engine. We feel that by locating the fuel pump and fuel filter inside the chassis frame where they are extremely well protected, and by using high quality flexible fuel lines carefully routed and supported to prevent them from being damaged, we can easily maintain assurance of compliance with FMVSS 301-75. On such a system, would the agency accept Engineering documentation in the form of drawings. Engineering instructions, and Quality Assurance procedures in lieu of actual crash test reports as a suitable basis for certification? Would it be necessary or desirable to have independent laboratory inspection and approval under such a method of certification? Are any manufacturers using this type of certification, and if so, could we be provided with examples of the documentation used?

Blue Bird Body Company believes in its motto that, "Your Children's Safety is Our Business". Blue Bird also believes in improving its products, providing the safest, most modern and most efficient products possible, and in meeting our customer's needs whenever possible. To this end we appreciate any assistance the agency can provide to enable us to offer auxiliary heaters and air conditioning on new school buses. I have taken the liberty of sending three copies of this letter to Mr. Francis Armstrong and to Mr. Ralph Hitchcock, since I feel input from both Enforcement and Rulemaking would be beneficial in addressing this issue.

Thank you very much for your consideration of this matter.

Thomas D. Turner Manager Engineering Services

c: FRANCIS ARMSTRONG (3) -- OFC. OF VEHICLE SAFETY COMPLIANCE; RALPH HITCHCOCK (3) -- OFC. OF VEHICLE SAFETY STDS.

ID: 86-5.34

TYPE: INTERPRETATION-NHTSA

DATE: 10/24/86

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Mr. H. Tsujishita

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your letter of July 15, 1986, asking three interpretation questions concerning Federal Motor Vehicle Safety Standards Nos. 101, Controls and Displays, and 108, Lamps, Reflective Devices, and Associated Equipment. The answers to your questions are provided below.

By way of background information, the National Highway Traffic Safety Administration does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, it is the responsibility of the manufacturer to ensure that its motor vehicles or equipment comply with applicable standards. The following represents our opinion based on the information provided in your letter.

Your first question concerns the visibility requirements for the upper beam telltale (indicator). As noted by your letter, section S5.3.3 of Standard No. 101 provides that the light intensity of each telltale shall be such that, when activated, that telltale and its identification are visible to the driver under all daytime and nighttime conditions. The upper beam telltale is one of the telltales subject to that requirement. You note, however, that section S4.5.2 of Standard No. 108 requires a high beam indicator that conforms to SAE Recommended Practice J564a (except that the signal color need not be red). J564a provides that the upper beam indicator should be "plainly visible to drivers of all heights under normal driving conditions when headlights are required." Based on this provision, you suggest that the upper beam telltale is not required to be visible to the driver under the daytime conditions when headlamps are not needed. As discussed below, your understanding is incorrect.

The difference between these two requirements is not so great as you suggest. The reference to "normal driving conditions" in J564a includes a variety of non-nighttime conditions (e.g., driving at dusk or dawn, and driving in daytime rainstorms) when headlamp use may be required by the States. To the extent that Standard No. 101 requires the telltale to be visible under daylight driving conditions not covered by Standard No. 108, manufacturers must meet the broader requirement. Manufacturers are required to meet all applicable safety standards. We note that while Standards Nos. 101 and 108 each cover upper beam telltales and specify different requirements, it is possible to meet the requirements of both standards simultaneously.

You stated that under daylight conditions the upper beam cannot dazzle oncoming drivers and that there is therefore no need to inform the driver that the upper beam is on. While there may be less need for this telltale during daylight than at night, Standard No. 101 reflects our belief that there is still a need and requires that the telltale be visible under all daytime and nighttime conditions (if the upper beams are actually on).

Your second question concerns the upper beam telltale minimum area requirement. SAE Recommended Practice J564a, which, as noted above, is referenced by section S4.5.2 of Standard No. 108, provides that the upper beam indicator should consist of a "light, with a minimum area equivalent to that of a 3/16 in. diameter circle." You asked how this requirement would apply to two designs.

In the first design, the outline of the telltale symbol would lighten while the area within and around the telltale symbol would not. You suggested that the framed area, i.e., the area within the telltale that is framed by the outline but not lighted itself, can be counted into the minimum area requirement. As discussed below, that is incorrect. In the second design, the telltale symbol would be superimposed on a rectangle. In this case, the entire area within the rectangle would lighten, except for that covered by the symbol itself. You suggested that the lighted area other than that covered by the symbol can be counted toward the minimum area requirement. As discussed below, that is correct.

In referencing SAE Recommended Practice J564a, Standard No. 108 requires that the upper beam indicator must consist of a light, and also specifies the minimum area for that light. It does not specify the shape of the light. If the light is a simple circle which is lighted in its entirety (with the identification required by Standard No. 101 placed adjacent to the circle), that lighted circle must be at least 3/16 inch in diameter. If the light is some other shape, such as the shape of the upper beam symbol or a rectangle in which only part of the area is lighted, the total area which is lighted must be at least as large as the area of a 3/16 inch circle. Thus, in the case of the first design discussed above, only the outline area (i.e., the blue lighted area) of the upper beam symbol can be counted toward the minimum area requirement. The unlighted interior part (i.e., the black area) of the symbol cannot be counted toward the minimum area requirement. In the case of the second design discussed above, the entire (blue) area within the rectangle that lightens can be counted toward the minimum area requirement. However, that part of the rectangle which does not lighten, i.e., the (white) part covered by the symbol, cannot be counted.

Your third question concerns Standard No. 101's illumination requirements for a side marker lamp control that is incorporated into the master lighting switch. As suggested by your letter and as discussed below, illumination is not required if the identifying symbol for the side marker lamps is marked on the master lighting switch.

While Table 1 of Standard No. 101 requires that side marker lamp controls be identified with the side marker lamp control symbol and that such identification be illuminated, it also provides that separate identification is not required if controlled by the master lighting switch. Thus, for side marker lamp controls that are incorporated into the master lighting switch, use of the side maker lamp control symbol is voluntary. Since such identification is not required by Standard No. 101, it is our opinion that the standard does not require manufacturers to illuminate such identification if they choose to provide it voluntarily.

SINCERELY,

AGENDA 4-b DAIHATSU MOTOR CO., LTD.

Erika Z. Jones Chief Counsel Office of the Chief Counsel National Highway Traffic Safety Administration

Dear Ms. Jones:

Additionally to the questions which we sent by letter date Feb. 18, 1986, would you please kindly answer the questions with regard to the interpretation of FMVSS Nos. 101 and 108 as described on the following pages?

H. Tsujishita Chief Co-ordinator of Technical Administration Dept. Head Office

ENC.

1. FMVSS Nos. 108 & 101; Highbeam Indicator Visibility requirement

Paragraph S5.3.3 of FMVSS No. 101 provides that each tell-tale and its identification shall be visible to the driver under all daytime and night time conditions. According to this provision, highbeam tell-tale shall be visible even under daytime condition.

On the other hand, paragraph S4.5.2. of FMVSS No. 108 requires a highbeam indicator which conforms to SAE J564a on each vehicle, and SAE J564a provides that the highbeam indicator shall be plainly visible to the driver under normal driving conditions when head lights are required. That means, under daytime conditions whenhead lights are not required, the highbeam indicator is not needed to be plainly visible.

We believe that the purpose of the highbeam indicator is essentially to indicate the driver that the upper beam of the head lamps are on to prevent the opposite driver from being dazzled by passing each other with the upper beam on. Under the daytime condition, as the upper beam can not dazzle the opposite driver any longer, and there is no need to indicate the driver trat the upper beam is on.

Therefore we believe that the high beam indicator (tell-tale) is not required to be visible to the driver under the daytime conditions when head lights are not needed.

Is our understanding right?

2. FMVSS No. 108; Highbeam Indicator Minimum Area Requirement

As stated above, S4.5.2 of FMVSS No. 108 requires a highbeam indicator which conforms to SAE J564a on each vehicle, and SAE J564a provides that the highbeam indicator shall have a minimum area equivalent to that of a 3/16 in. diameter circle.

A. In case that only the frame of the tell-tale will be lighten

We believe the framed area can be counted into the minimum area requirement.

B. In case that the background of the tell-tale will be lighten

We believe the entire shaded area can be counted into the minimum area requirement.

If our understanding is wrong, please explain in the above requirement in detail.

(Graphics omitted)

3. FMVSS No. 101; Side Marker Lamp Control Illumination

Table 1 of FMVSS No. 101 requires that the identification of side marker lamp control shall be illuminated when the head lamps are on, and it also provides in its footnote that separate identification (for the side marker lamp control) are not required if the side marker lamp are controlled by the master lighting switch. In case that the side marker lamps are are controlled by the master lighting switch and the identifing symbol for the side marker lamps is marked on the switch voluntarily by the manufacturer, we believe that the illumination for the side marker lamp control is not required, because the side marker lamp control which is combined into the master lighting switch is easily identifiable.

Is our understanding right?

ID: Sens_a_brake003065

Mr. Gregory Gibb
Edge International Limited
PO Box 5682
Frankton, Hamilton
New Zealand

Dear Mr. Gibb:

This responds to your inquiry regarding the regulations applicable to a trailer brake system that relies on a combination of air and hydraulics. You asked if a system manufactured by your company, the "Sens-a-Brake" system, would be classified as an air brake system under Federal Motor Vehicle Safety Standard (FMVSS) No. 121, Air brake systems. As explained below, the "Sens-a-Brake" system would be defined as an air-over-hydraulic brake subsystem, and therefore would be an airbrake system under FMVSS No. 121.

I am pleased to have this opportunity to explain our regulations to you. FMVSS No. 121 specifies performance requirements for trucks, buses and trailers equipped with air brake systems. S4 of the standard defines "air brake system" as follows:

Air brake system means a system that uses air as a medium for transmitting pressure or force from the driver control to the service brake, including an air-over-hydraulic brake subsystem, but does not include a system that uses compressed air or vacuum only to assist the driver in applying muscular force to hydraulic or mechanical components. (Emphasis added.)

S4 of the standard defines "air-over-hydraulic brake subsystem" as:

[A] subsystem of the air brake system that uses compressed air to transmit a force from the driver control to a hydraulic brake system to actuate the service brakes.

In your letter you explained that the "Sens-a-Brake" system consists of an electronic brake controller and an air compressor mounted on a trailer, which supplies air for the application of the trailers braking mechanism. Your companys web site states that the electric brake controller incorporates a "pressure sensitive film that enables accurate measurement of the force being applied to the towing vehicles brake pedal."The website further explains that this pad attaches directly to the brake pedal of the tow vehicle. The pedal controller then modulates the air pressure supplied by the air compressor based on the pressure applied to the brake by the vehicle driver. The air pressure then transmits a force to the mechanism used to apply or release the hydraulic trailer brakes.

Based on the description you provided in your letter and the information on your companys website, the "Sens-a-Brake" system comes within definition of "air-over-hydraulic brake subsystem." The "Sens-a-Brake" system transmits a force applied by a vehicle driver to the brake pedal, first through an electrical signal and then through compressed air, to a hydraulic brake system. While the system does not use air as the initial means for transmitting force from the driver control to the hydraulic system, compressed air is used in the system to transmit force from the driver control. Therefore, the "Sens-a-Brake" system would be an "air-over-hydraulic system," which is regulated as an air brake system under FMVSS No. 121.

In your letter, you referenced a previous interpretation letter the agency issued to Mr. Tom Brunson, in which the agency concluded that a system with some similarities to the "Sens-a-Brake" system was not an air brake system (April 4, 2000). However, the system addressed by the letter to Mr. Brunson had one significant difference; the air pressure in that system was controlled primarily through an inertial controller mounted on the back of the tow vehicle. The system in the Brunson letter permitted a driver to control braking through a dash-mounted switch, but the switch was not intended to modulate the pressure applied to the brake mechanism. The primary control for actuating the air compressor in the Brunson letter system was the inertial controller mounted on the rear of the tow vehicle and not the vehicle driver. In contrast, the "Sens-a-Brake" system relies on force generated at the driver control (the force applied to the brake pedal pad) to modulate the application of compressed air to a hydraulic brake.

Similarly, in an October 22, 2001 letter to Mr. Gary Rudnik the agency concluded that a trailer brake system was not an air brake system under FMVSS No. 121 if a trailers brakes activated as a result of the tow vehicles brake lamps illuminating (copy enclosed). Under the system described in the Rudnick letter, the brake pedal would function solely as an on-off switch for the trailer braking system, with the trailers brakes being activated upon illumination of the tow vehicles brake lamps when the driver pressed the tow vehicles brake pedal. However, the system would not transmit force applied by the driver via air to modulate the brakes; the brake pedal merely served as an on-off switch for the trailer braking system. Again in contrast, the "Sens-a-Brake" system relies on force applied to the brake pedal to modulate the application of compressed air to a hydraulic brake.

Thus, if a system were to modulate the amount of air pressure applied to a hydraulic trailer brake mechanism in relation to force applied to a driver control, then that system would be an air brake system. If, however, a driver control were merely to function as an on-off switch, then that system would not be an air brake system under FMVSS No. 121.

We note that when the agency incorporated the definition of "air-over-hydraulic brake subsystem" into FMVSS No. 121, we did not anticipate its application to light duty trailers. At that time, the agency indicated that air-over-hydraulic brake subsystems were installed exclusively on single-unit vehicles with a gross vehicle weight rating greater than 19,500 pounds (See 60 Federal Register 36741; July 18, 1995; copy enclosed). Unless the standard were amended through the rulemaking process, the Sens-a-Brake system is an air brake system under FMVSS No. 121. If you have any further questions, please contact Mr. Chris Calamita, of my staff at (202) 366-2992

Sincerely,

Jacqueline Glassman
Chief Counsel

Enclosures
ref:121
d.6/25/04

ID: 16-1289 (GM hazard innovative) -- 28 Apr 16 rsy