Documentation of Email from EPA to OMB on Interagency Comments for Aircraft 

Engine Emission Standards Draft NPRM

May 3, 2011

From: Matt Spears/AA/USEPA/US

To: "Frey, Nathan J." <Nathan_J._Frey@omb.eop.gov>

Date: 05/03/2011 01:46 PM

Subject: Clarification of EPA's postilion on aircraft NOx NPRM exemption provisions

Hi Nathan,

I wanted to provide you with a clarification regarding EPA's position related to our proposed NOx production cutoff 

exemption provisions in the aircraft engine NOx NPRM.

As you know, EPA does not agree with a specific provision in ICAO's guidance (ETM) that specifies a general 

maximum number of exemptions of 75 exemptions per engine type certificate for the CAEP/6 NOx standard 

production cutoff. Up until now, our position has been to accept the number "75" but substitute the basis of "per 

engine type certificate" with "per manufacturer" or equivalently with "per type certificate holder."

Among our reasons for not accepting the specific ICAO guidance provision is that we find the ETM limit of 75 per type 

certificate could potentially be used to inappropriately exempt a large number of engines for new production aircraft. 

We are also concerned that specifically identifying an exemption provision that is too generous could create an 

expectation that potential future exemption provisions would be equally generous, even if not warranted by data or 

policy considerations. These concerns are largely based primarily on our in-depth discussions with the engine 

manufacturers, which concluded that the need for exemptions would likely involve one or two models with the number 

of justifiable exempt engines being much less 75 in total. 

We understand that FAA has objected to EPA proposing this difference from ICAO guidance, even though we assert 

that if we justify why such a provision is inappropriate it would be within our authority to propose provisions that differ 

from such non-mandatory guidance. In our earlier summary document to you, we elaborated upon why we believe 

we have the discretion to adopt parts of ICAO's guidance and not others.

We continue to oppose the specific ICAO guidance provision of a general maximum of 75 exemptions per engine 

type certificate. However, we have reconsidered a more appropriate exemption allowance that helps address the 

concerns stated above. Specifically, we will not propose a substitute number or a substitute basis. Rather, we will 

indicate that we propose to adopt the remainder of the ETM guidance on exemptions, less the provision of a 

maximum of 75 per type certificate. In its place, we propose to retain the current exemption provision as embodied in 

part 87.7(c), which states that each application for exemption would be evaluated on a case-by-case basis, based on 

the information provided by the applicant. We would then determine an appropriate maximum number of exemptions, 

if any, without considering the ICAO guidance provision of a general maximum of 75 per type certificate.

Please let me know if you would like any further clarification on EPA's position.

Regards,

Matthew W Spears

U.S. Environmental Protection Agency

Mail Code: ASD1

2000 Traverwood Drive

Ann Arbor, MI 48105, USA