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January 14, 2013
FAA adopts jet NOx standards

As required by the Clean Air Act, the Federal Aviation Administration (FAA) has amended its regulations by adopting nitrogen oxide (NOx) air emissions standards and engine marking requirements promulgated by the EPA in June 2012 for jet engines on large commercial, passenger, and freighter aircraft.  FAA’s action took the form of a direct final rule without opportunity for public comment because the public had the opportunity to comment on EPA’s July 2011 proposal.  The FAA states that it is not adopting any standards or requirements different from those issued by the EPA.

Consistent with ICAO

The regulations affect aircraft turbofan and turbojet engines with rated thrusts greater than 26.7 kilonewtons (kN).  The EPA arranged its standards by tier, a numbering system that distinguishes levels of increased regulatory stringency.  This approach is consistent with the numeric identifier the International Civil Aviation Organization’s (ICAO) Committee on Aviation Environmental Protection (CAEP) uses to differentiate among standards.  For example, the standards that correspond to CAEP’s sixth meeting (CAEP/6) are identified by the EPA as Tier 6, while the standards that correspond to CAEP/8 are called Tier 8.  U.S. airlines and aircraft engine manufacturers have been meeting the international standards in advance of their impending adoption by the EPA and the FAA.

Tiers 6 and 8

The regulations establish two levels of increasingly stringent NOx emissions standards applicable to engines based on type certification date.  Newly certificated aircraft engines are those that receive a new type certificate after the effective date of the applicable standard.

  • Tier 6/CAEP 6 NOx standards.  The first set of standards is equivalent to the NOx limits established under CAEP/6.  This level was originally adopted by the ICAO and became internationally applicable after December 31, 2007.  Engine manufacturers have been producing engines that meet Tier 6 standards even though the standard and the marking designation had not yet been adopted in the United States.  Overall, Tier 6 represents an approximate 12 percent reduction in NOx emissions from Tier 4 standards, which were adopted by the ICAO in 2005 with an implementation date in 2008.  Under the EPA rule, the Tier 6 standard was effective for engines produced on and after July 18, 2012, unless otherwise covered by an exception or exemption.
  • Tier 8/CAEP/8 NOx standards are equivalent to the CAEP/8 NOx limits recommended by CAEP in February 2010 and applicable as ICAO standards and recommended practices in November 2011. The Tier 8 standards will be mandatory in the United States for engines for which the first individual production model is manufactured after December 31, 2013.  Overall, Tier 8 represents an approximate 15 percent reduction in NOx emissions from Tier 6.


FAA’s adopted standards include several exceptions.  For example, Tier 4 engines (and their derivatives) introduced before July 18, 2012, may continue to be produced through December 31, 2012, without further action by the manufacturer.  In addition, each engine manufacturer may produce up to six Tier 4-compliant engines with a date of manufacture on and after July 18, 2012, and before August 31, 2013, which do not meet the Tier 6 standards without further action by the manufacturer.  The final rule also allows for the production of a spare engine that is newly produced but meets the Tier 4 emissions standard under which it was certified rather than a more stringent standard that may be in place at the time of production.  A spare engine may not be installed in a new aircraft. 

FAA’s final action also includes test procedures based on ICAO’s Annex 16, Volume II.

FAA’s direct final rule covering aircraft gas turbine engines was published in the December 31, 2012, FR.