Interpretation ID: nht92-6.12

DATE: June 10, 1992

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

TO: Paul Jackson Rice -- Chief Counsel, NHTSA

TITLE: Re: Request for Interpretation - FMVSS 108

ATTACHMT: Attached to letter dated 7/7/92 from Paul J. Rice to Michael Love (A39; Std. 108)

TEXT:

On April 3, 1992, I wrote to you requesting an interpretation of FMVSS 108 regarding center high mounted stop lamps. Your interpretation of the regulations with regard to our proposed design was not consistent with our interpretation. Therefore, we have come up with an alternate design which we believe will be consistent with your interpretation. Since this new design raises several questions, we are requesting another interpretation. The attached document contains that request.

Please contact me at 702/348-3198 if you should have any questions.

Attachment

PORSCHE REQUEST FOR INTERPRETATION

Porsche is considering a new design of center high mounted stop lamp (CHMSL) for its 911 Carrera model. In order to accommodate a moveable rear spoiler, the CHMSL would consist of two separate lamps: Lamp A would be mounted on the front edge of the moveable spoiler; Lamp B would be mounted on the rear edge of the moveable spoiler. Both lamps are on the center line of the car. This dual light system would function as follows:

From 0 to 50+/-5mph the spoiler would be in the down position. The CHMSL Lamp A would function (when the brakes were engaged). CHMSL Lamp B would not function.

At 5O+/-5mph when the spoiler is rising, Lamp A would function until the spoiler is approximately 35% up. At this point Lamp B would begin functioning and Lamp A would be disabled.

Above 50+/-5mph the spoiler would be in the up position and Lamp B would function (when the brakes were engaged).

As the speed drops below 5O+/-5mph the Spoiler would remain in the up position until approximately 9+/-3mph and Lamp B would function.

At 9+/-3mph when the spoiler is lowering, Lamp B would function until the spoiler reached the 35% up position. At this point Lamp A would begin functioning and Lamp B would be disabled.

With this design we expect that all photometric and height requirements of FMVSS 108 will be met with switching from Lamp A to Lamp B while the spoiler is moving. It is possible that it will be necessary to have both Lamp A and Lamp B functioning together for a short period of time in order to fulfill photometric requirements.

We have identified the following issues and request NHTSA's views on them:

The switching from Lamp A to Lamp B does not violate the "steady burning" requirement of FMVSS 108.

There is no problem with having two separate CHMSLs as long as they fulfill the requirements of FMVSS 108 while they are capable of functioning, either separately or together.

Having Lamp B drop below the height requirement of FMVSS 108 is not a problem if it is not capable of functioning while below that level (i.e.: If it is no longer capable of functioning (lighting), then it is no longer a lamp by definition).