### Question
How does the law define model year?


### Answer
Under *40 CFR § 87.1*, **model year** is defined as:

> the calendar year in which a nonroad engine is modified

#### Citation:
  - *40 CFR § 87.1*
  - Heading: **Title 40—Protection of Environment > PART 87—CONTROL OF AIR POLLUTION FROM AIRCRAFT AND AIRCRAFT ENGINES > PART 87—CONTROL OF AIR POLLUTION FROM AIRCRAFT AND AIRCRAFT ENGINES > Subpart A—General Provisions > CHAPTER I—ENVIRONMENTAL PROTECTION**

