(a) Use test results from two engines each quarter to calculate the required sample size for the model year for each engine family.
(b) Early in each calendar quarter, randomly select and test two engines from the end of the assembly line for each engine family.
(c) Calculate the required sample size for each engine family. Separately calculate this figure for HC + NOX and CO. The required sample size is the greater of these calculated values. Use the following equation:
N = Required sample size for the model year.
t95 = 95% confidence coefficient, which depends on the number of tests completed, n, as specified in the table in paragraph (c)(1) of this section. It defines 95% confidence intervals for a one-tail distribution.
σ = Test sample standard deviation (see paragraph (c)(2) of this section).
x = Mean of emission test results of the sample.
STD = Emission standard.
(1) Determine the 95% confidence coefficient, t95, from the following table:
(2) Calculate the standard deviation, σ, for the test sample using the following formula:
Xi = Emission test result for an individual engine.
n = The number of tests completed in an engine family.
(d) Use final deteriorated test results to calculate the variables in the equations in paragraph (c) of this section (see § 1048.315(a)).
(e) After each new test, recalculate the required sample size using the updated mean values, standard deviations, and the appropriate 95-percent confidence coefficient.
(f) Distribute the remaining tests evenly throughout the rest of the year. You may need to adjust your schedule for selecting engines if the required sample size changes. If your scheduled quarterly testing for the remainder of the model year is sufficient to meet the calculated sample size, you may wait until the next quarter to do additional testing. Continue to randomly select engines from each engine family.
(g) Continue testing until one of the following things happens:
(1) After completing the minimum number of tests required in paragraph (b) of this section, the number of tests completed in an engine family, n, is greater than the required sample size, N, and the sample mean, x, is less than or equal to the emission standard. For example, if N = 5.1 after the fifth test, the sample-size calculation does not allow you to stop testing.
(2) The engine family does not comply according to § 1048.315.
(3) You test 30 engines from the engine family.
(4) You test one percent of your projected annual U.S.-directed production volume for the engine family, rounded to the nearest whole number. Do not count an engine under this paragraph (g)(4) if it fails to meet an applicable emission standard. You may stop testing after you test one percent of your production volume even if you have not tested the number of engines specified in paragraph (b) of this section. For example, if projected volume is 475 engines, test two engines in each of the first two quarters and one engine in the third quarter to fulfill your testing requirements under this section for that engine family.
(5) You choose to declare that the engine family does not comply with the requirements of this subpart.
(h) If the sample-size calculation allows you to stop testing for one pollutant but not another, you must continue measuring emission levels of all pollutants for any additional tests required under this section. However, you need not continue making the calculations specified in this subpart for the pollutant for which testing is not required. This paragraph (h) does not affect the number of tests required under this section, the required calculations in § 1048.315, or the remedial steps required under § 1048.320.
(i) You may elect to test more randomly chosen engines than we require under this section. Include these engines in the sample-size calculations.
30 + 1.70
[67 FR 68347, Nov. 8, 2002, as amended at 70 FR 40475, July 13, 2005; 73 FR 59237, Oct. 8, 2008]