Interpretation ID: nht92-1.35

DATE: 12/07/92

FROM: PAUL JACKSON RICE -- CHIEF COUNSEL, NHTSA

TO: MARK V. SCHWARTZ -- ACCOUNT EXECUTIVE, ENTRAN DEVICES, INC.

ATTACHMT: ATTACHED TO LETTER DATED 10-28-92 FROM MARK V. SCHWARTZ TO PAUL J. RICE (OCC 7927)

TEXT: This responds to your October 28, 1992 letter, asking me to reconsider my September 29, 1992 letter to you interpreting 49 CFR Part 572, Anthropomorphic Test Dummies. More specifically, my September 29, 1992 letter addressed the requirement in @ 572.36(g) that the thorax and knee impactor accelerometers in the Hybrid III test dummy "shall have the dimensions and characteristics of Endevco Model 7231c or equivalent."

You had asked if one of your company's accelerometer models would be deemed "equivalent," within the meaning of @ 572.36(g), to the specified make and model accelerometer. I stated that Part 572 sets forth the specifications with which test dummies must comply if those test dummies are to be used in this agency's compliance testing. I further stated that the agency has always used the specified make and model accelerometer in the compliance testing conducted to date. Thus, it has not been necessary for the agency to make any determination of which accelerometers, if any, are "equivalent" to the specified accelerometer for agency compliance testing purposes. Until the agency makes a determination about equivalent accelerometers, I indicated that the matter is one to be worked out between your company and prospective users of your company's accelerometers. I also indicated that NHTSA will not review the use of any particular accelerometers in certification testing, including your company's accelerometers, unless the test results indicate a problem or problems caused by those accelerometers.

In your October 28, 1992 follow-up letter, you expressed that you were "extremely disappointed" with my September 29 letter. You stated that "[though] your letter states that users of accelerometers are free to define equivalence, the reality is that they will take no unnecessary course of action that varies from your compliance testing." You said that you had spoken with "technical decision makers" at Chrysler, Ford, and GM and all three indicated that they would not use an accelerometer for development and certification work, when a different accelerometer must be used in NHTSA's compliance testing. Accordingly, you again asked that the agency state whether a model of accelerometer manufactured by Entran is equivalent to the make and model of accelerometer specified for use in compliance testing.

In order to make a determination of which accelerometer models are "equivalent" to the make and model of accelerometer currently specified for use in compliance testing, NHTSA must conduct an analysis to identify the attributes that will ensure that an accelerometer measures results in the relevant crash environment that are equivalent to the results that would be measured in that crash environment by the currently specified accelerometer. This analysis would require an expenditure of agency time and resources, although the amount of the expenditure is currently not known. These expenditures would not benefit the agency's compliance testing efforts, since the currently specified accelerometer is readily available, nor would the expenditures contribute generally toward the agency's safety mission. Accordingly, the agency cannot justify the expenditure of resources needed to make an analysis of the equivalence issue at this time.

However, accelerometer manufacturers and other interested parties are free to make their own analyses of equivalence, using their resources. The interested parties may present their analyses of equivalence to potential users of a non-specified accelerometer, in order to demonstrate to the potential user that the non-specified accelerometer will be found equivalent to the specified accelerometer when NHTSA makes its determination of equivalence. If the potential user is convinced by such demonstration, that party can then use the non-specified accelerometer in its testing.

In my previous letter to you, I stated that NHTSA will not review the use of any particular accelerometers in certification testing, unless the test results indicate a problem or problems caused by those accelerometers. This statement was included in that letter to make clear to all parties that the absence of a NHTSA determination of equivalence for a particular accelerometer model does not represent some sort of negative finding by the agency with respect to the performance or capabilities of that particular accelerometer. This statement has apparently served that purpose. For instance, it has come to our attention that Chrysler and General Motors have procured significant numbers of Entran accelerometers for use in vehicle crash tests. Thus, it appears that vehicle manufacturers and other potential users correctly understand the meaning of the current specification in Part 572 for one particular accelerometer model, and that the specification of one particular accelerometer model in Part 572 does not pose any insuperable obstacle to the use of other, non-specified accelerometer models for testing other than NHTSA's certification testing. There is, therefore, no compelling need for NHTSA to use its resources to conduct an analysis of accelerometer equivalence.