40 CFR 91.116 - Certification procedure
(a) The manufacturer must select, from each engine family, a test engine of a configuration that the manufacturer deems to be most likely to exceed the Family Emission Limit (FEL).
(b) At the manufacturer's option, the criterion for selecting the worst case engine may be that engine configuration which has the highest weighted brake-specific fuel consumption over the appropriate engine test cycle.
Title 40 published on 2013-07-01
no entries appear in the Federal Register after this date.