To perform a selective enforcement audit with respect to drag area for tractors, use the reference method specified in §1037.525; we may instead require you to use the same method you used for certification. The following provisions apply instead of 40 CFR 1068.420 for a selective enforcement audit with respect to drag area:

(a) Determine whether or not a tractor fails to meet standards as follows:

(1) We will select a vehicle configuration for testing. Perform a coastdown measurement with the vehicle in its production configuration according to §1037.528. Instead of the process described in §1037.528(h)(12), determine your test result as described in this paragraph (a). You must have an equal number of runs in each direction.

(2) Measure a yaw curve for your test vehicle using your alternate method according to §1037.525(b)(3). You do not need to test at the coastdown effective. You may use a previously established yaw curve from your certification testing if it is available.

(3) Using this yaw curve, perform a regression using values of drag area, CdAalt, and yaw angle, ψalt, to determine the air-direction correction coefficients, a0, a1, a2, a3, and a4, for the following equation:

(4) Adjust the drag area value from each coastdown run, CdArun, from the yaw angle of each run, ψrun, to ±4.5° to represent a wind-averaged drag area value, CdAwa by applying Eq. 1037.305-1 as follows:

(5) Perform additional coastdown measurements until you reach a pass or fail decision under this paragraph (a).

(6) Calculate statistical values to characterize cumulative test results at least once per day based on an equal number of coastdown runs in each direction. Determine the wind-averaged drag area value for the test CdAwa by averaging all CdAwa-run values for all days of testing. Determine the upper and lower bounds of the drag area value, CdAwa-bounded, expressed to two decimal places, using a confidence interval as follows:

(7) Compliance is determined based on the values of CdAwa-upper and CdAwa-lower relative to the adjusted bin boundary. For purposes of this section, the upper limit of a bin is expressed as the specified value plus 0.05 to account for rounding. For example, for a bin including values of 5.5-5.9 m2, being above the upper limit means exceeding 5.95. The vehicle reaches a pass or fail decision relative to the adjusted bin boundary based on one of the following criteria:

(i) The vehicle passes if CdAwa-upper is less than or equal to the upper limit of the bin to which you certified the vehicle.

(ii) The vehicle fails if CdAwa-lower is greater than the upper limit of the bin to which you certified the vehicle.

(iii) The vehicle passes if you perform 100 coastdown runs and CdAwa-upper is greater than and CdAwa-lower is lower than the upper limit of the bin to which you certified the vehicle.

(iv) The vehicle fails if you choose to stop testing before reaching a final determination under this paragraph (a)(7).

(b) If you reach a pass decision on the first test vehicle, the emission family passes the SEA and you may stop testing. If you reach a fail decision on the first test vehicle, repeat the testing described in paragraph (a) of this section for two additional vehicles of the same configuration, or of a different configuration that we specify. Continue testing two additional vehicles for each failing vehicle until you reach a pass or fail decision for the family based on one of the following criteria:

(1) The emission family passes if at any point more than 50 percent of the vehicles have reached a pass decision.

(2) The emission family fails if six vehicles reach a fail decision.

(3) The emission family passes if you test 11 vehicles with five or fewer vehicles reaching a fail decision.

(4) The emission family fails if you choose to stop testing before reaching a final determination under this paragraph (b).

(c) We may suspend a certificate of conformity as described in 40 CFR 1068.430 if your emission family fails an SEA, subject to the following provisions:

(1) We may reinstate a suspended certificate if you revise Falt-aero or make other changes to your testing methodology to properly correlate your testing to the reference method specified in §1037.525.

(2) We may require you to apply any adjustments and corrections determined under paragraph (c)(1) of this section to your other emission families in any future application for certification.

(d) If we test some of your vehicles in addition to your testing, we may decide not to include your test results as official data for those vehicles if there is substantial disagreement between your testing and our testing. We will reinstate your data as valid if you show us that we made an error and your data are correct. If we perform testing, we may choose to stop testing after any number of tests and not determine a failure.

(e) If we rely on our test data instead of yours, we will notify you in writing of our decision and the reasons we believe your facility is not appropriate for doing the tests we require under this paragraph (b). You may request in writing that we consider your test results from the same facility for future testing if you show us that you have made changes to resolve the problem.

(f) We may allow you to perform additional replicate tests with a given vehicle or to test additional vehicles, consistent with good engineering judgment.

(g) You must assign the appropriate CdA bin for your compliance demonstration at the end of the model year for every configuration you tested that failed under this section.