Interpretation ID: nht92-5.28

DATE: July 7, 1992

FROM: Paul Jackson Rice -- Chief Counsel, NHTSA

TO: Michael Love -- Manager, Compliance Porsche Cars North America, Inc.

TITLE: None

ATTACHMT: Attached to letter dated 6/10/92 from Michael Love to Paul J. Rice (OCC 7401)

TEXT:

This responds to your letter of June 10,1992, requesting concurrence by this Office in your interpretation of the requirements of Standard No. 108 for the location of center highmounted stop lamps (CHMSL). Your letter was occasioned by mine of April 27, 1992, with respect to the design presented in your letter of April 3.

To summarize our earlier correspondence, Porsche wishes to install a CHMSL on the movable spoiler of its 911 Carrera, a configuration previously approved by this Office providing that all photometric and visibility requirements are met. However, S5.3.1.8 of Standard No. 108 requires that "If the lamp is mounted below the rear window, no portion of the lens shall be lower than 6 inches below the rear window on convertibles, or 3 inches on other passenger cars." Although Porsche's intended CHMSL meets this requirement with the spoiler in the extended position (when the car reaches 45 to 55 mph and slows to 9 to 12 mph), at other times, when the spoiler is lowered, the center lamp would be 7.5 inches below the window on the coupe, and 9.5 inches for the convertible. Because the CHMSL on the Carerra would not meet the locational requirements from a state of rest up to a minimum of 45 mph, we informed you that this design would not conform to Standard No. 108.

In your latest letter, you present the possibility of equipping the Porsche with two separate CHMSLs. The CHMSL discussed in your April letter, located at the trailing edge of the spoiler, would be activated when the spoiler had risen 35% from its at-rest position, and be deactivated at the time the spoiler lowers to 35%, from the at-rest position. The second CHMSL, located on the spoiler where it abuts the vehicle body and mounted at a complying height, would be activated when the vehicle is at rest, and when the spoiler is at heights less than 35% from the at-rest position, generally at times that the other CHMSL is deactivated. You expect that all photometric and height requirements of Standard No. 108 will be met in switching from one lamp to another while the spoiler is moving, though it might be necessary to have both lamps functioning together for a short period of time in order to fulfill photometric requirements.

A manufacturer's certification of compliance to the CHMSL requirements of Standard No. 108 is based upon the normal operation of motor vehicle equipment. The additional CHMSL you posit would appear to fulfill these requirements when the vehicle is at rest, and in low speed operation. Thus, for certification purposes, we regard this CHMSL as the one for which certification is supplied.

However, it appears that the spoiler in rising may affect the photometric conformance of the certification CHMSL. Under S5.3.1.1, when a part of a vehicle prevents a stop lamp from meeting its photometric output at any

applicable group of test points, any auxiliary stop lamp that meets these requirements may be provided. We interpret this as allowing the non-certification CHMSL to perform as a surrogate to the certification CHMSL at the point that conformance of the certification CHMSL is affected.

You have raised the possibility that it will be necessary to have both CHMSLs operating simultaneously for a short period of time in order to fulfill photometric requirements. While the meaning of this statement is not exactly clear, for purposes of this interpretation, it would appear to mean that simultaneous operation of both lamps might occur briefly when the rising spoiler masks the certification CHMSL at the same time the non-certification CHMSL is operating at a height below the minimum specified by Standard No. 108. Although in the past we have encouraged disabling of interior mounted CHMSLs when new ones are added to fixed spoilers, so that a vehicle will not be equipped with two permanent simultaneously operating CHMSLs, the situation here appears to differ. Under the circumstances outlined above, it does not appear that a noncompliance with Standard No. 108 would be created.

If our understanding is not correct, we would be willing to discuss the matter further.