[Federal Register Volume 64, Number 225 (Tuesday, November 23, 1999)]
[Rules and Regulations]
[Pages 65655-65656]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-30502]



 ========================================================================
 Rules and Regulations
                                                 Federal Register
 ________________________________________________________________________
 
 This section of the FEDERAL REGISTER contains regulatory documents 
 having general applicability and legal effect, most of which are keyed 
 to and codified in the Code of Federal Regulations, which is published 
 under 50 titles pursuant to 44 U.S.C. 1510.
 
 The Code of Federal Regulations is sold by the Superintendent of Documents. 
 Prices of new books are listed in the first FEDERAL REGISTER issue of each 
 week.
 
 ========================================================================
 

  Federal Register / Vol. 64, No. 225 / Tuesday, November 23, 1999 / 
Rules and Regulations  

[[Page 65655]]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 21


Applicability of 90-Day Rule for Intermixed Airplane Engines and/
or Nacelles

AGENCY: Federal Aviation Administration, DOT.

ACTION: Statement of policy.

-----------------------------------------------------------------------

SUMMARY: This document clarifies the continued applicability of the 90-
day limit for certain changes in airplane type designs after the final 
compliance date requiring an all Stage 3 fleet in the contiguous United 
States. The Federal Aviation Administration (FAA) has received numerous 
inquiries regarding the use of the 90-day limit after December 31, 
1999. This document provides guidance to operators that need to use 
that provision of the airplane type certification regulations, 
including the limits of its use.

FOR FURTHER INFORMATION CONTACT:
Mr. Thomas Connor, Manager, Noise Division (AEE-100), Office of 
Environment and Energy, FAA, 800 Independence Avenue, SW., Washington, 
DC 20591; telephone (202) 267-8933, fax (202) 267-5594.

SUPPLEMENTARY INFORMATION:

Background

    In 1980, the Air Transport Association of America (ATA) petitioned 
the FAA on behalf of its member operators for an exemption from 14 CFR 
21.93(b), and for a corresponding rule change that would allow 
unlimited intermix of airplane engines and/or nacelles that do not 
conform to specified noise levels. On January 26, 1981, the FAA 
published a Notice of Proposed Rulemaking (NPRM) (46 FR 8347), 
proposing to amend the definition of ``acoustical change'' in the 
aircraft noise certification rules as it applies to turbojet engine-
powered, large transport category airplanes. The NPRM proposed 
permitting the temporary installation and use (intermix) of airplane 
engines having different noise levels, provided that the affected 
airplane is brought back into conformance with an acoustically 
certificated configuration for that airplane type within 90 days of the 
initial change.
    The final rule revising Sec. 21.93(b)(2)(iii) was published on 
January 7, 1982 (47 FR 756). The regulation provided relief to 
operators and manufacturers without resulting in a significant noise 
impact by allowing the unlimited intermix of engines and/or nacelles 
for maintenance purposes for up to a period of 90 days without 
triggering the acoustical change requirement of Sec. 21.93. The change 
did not affect any other applicable requirements for certification of 
type design or airworthiness, or for operating the affected airplanes.
    The Stage 3 transition regulations contained in 14 CFR part 91 were 
promulgated in 1991 to implement the Airport Noise and Capacity Act of 
1990. The law requires that after December 31, 1999, no person may 
operate to or from any airport in the contiguous United States any 
airplane with a maximum certificated weight of more than 75,000 pounds 
unless that airplane has been shown to comply with Stage 3 noise 
levels. The FAA issued a notice in the Federal Register (64 FR 51430, 
September 23, 1999) and has sent several letters to operators reminding 
them of the prohibition against the operation of Stage 2 airplanes 
after December 31, 1999.
    Since the law places a ban on the operation of Stage 2 airplanes 
after December 31, 1999, several operators have inquired whether the 
relief provided in Sec. 21.93(b)(2)(iii) will continue to be available, 
or if the State 3 transition requirements eliminate that option for 
airplanes operated in the contiguous United States.
    Essentially, Sec. 21.93(b)(2)(iii) allows an operator to operate a 
turbojet powered airplane with a mix of engines (for which compliance 
with the acoustical change provisions of 14 CFR part 36 have not been 
shown) for a period not to exceed 90 days. In a typical case, the 
operator of a multi-engine Stage 3 airplane would use this provision to 
install one Stage 2 engine while the Stage 3 engine is in repair. 
Another common situation occurs when a Stage 3 engine incurs a minor 
damage that changes its noise characteristics and can continue safe 
operation, but cannot be immediately repaired. Thus, the regulation 
refers to ``time-limited engine and/or nacelle changes.'' The rule 
allows the intermix without the configuration being considered an 
``acoustical change'' that would otherwise invoke considerable 
certification requirements.
    When the FAA changed the rule in 1981, it determined that these 
occasional changes would not have a substantial impact on overall 
airplane operating noise levels if the use was limited to 90 days. The 
first 90 days of such a configuration is not considered an acoustical 
change; over 90 days, an operator must demonstrate that the intermix 
meets the acoustical change provision of 14 CFR part 36, or it must 
bring the airplane into compliance with an acoustically certificated 
configuration for that airplane type.
    The 1981 rule change also specifically noted that the 90-day 
allowance was intended for maintenance purposes (47 FR 758). Recently, 
the FAA has received information that some operators may be using this 
provision to maximize the size of their operating fleets--essentially, 
operators may not have a sufficient number of engines to maintain their 
entire fleets in Stage 3 configuration. To remedy the situation, 
operators may be trading out Stage 2 and Stage 3 engines every 90 days 
or so and ``invoking'' Sec. 21.93(b)(2)(iii) to maintain their status 
as having Stage 3 compliant aircraft. This situation came to the 
attention of the FAA when operators inquired whether they would be able 
to continue this practice after the December 31, 1999, compliance 
deadline.
    The FAA stresses that the Sec. 21.93(b)(2)(iii) provision was 
designed to assist operators with unplanned engine damage or 
maintenance events. The rule was never intended to be used to 
demonstrate ``paper-only'' compliance with Stage 3 noise requirements 
on a continuing basis, either before or after the statutory final 
compliance date. While the FAA considered removing the 90-day allowance 
to prevent these ``musical engine'' activities, the agency also

[[Page 65656]]

realized the value of the provision for its intended purposes and the 
substantial workload that would be generated for both the agency and 
the operators if the provision were removed.
    Accordingly, the FAA has determined that the 90-day period allowed 
by Sec. 21.93(b)(2)(iii) will continue to be available after December 
31, 1999. The affected operators are reminded that the 90-day period 
provision is only valid for maintenance purposes. Those airplanes using 
intermixed engines and/or nacelles will continue to be considered Stage 
3 for compliance purposes as long as the reason for the configuration 
is maintenance-related. The FAA warns operators that the swapping of 
engines between airplanes will be closely monitored. If, for example, 
an engine is removed from a Stage 3 configured airplane, and replaced 
with an intermix engine operated under Sec. 21.93(b)(2)(iii), careful 
attention will be paid by the FAA to the status of the removed engine. 
If the removed engine is reinstalled on a different airplane, the FAA 
will monitor whether any required maintenance or repair was first 
accomplished, as stated by the agency when the rule was adopted.
    If operators are found to be abusing Sec. 21.93(b)(2)(iii) in order 
to meet Stage 3 compliance requirements, operators will face 
enforcement action and the agency will consider removing the allowance 
or requiring prior approval for its use. A chronic lack of spare 
engines or a determination that an operator does not have sufficient 
engines available to operate a Stage 3 fleet at one time is not 
considered an acceptable reason for using Sec. 21.93(b)(2)(iii).
    Operators may use Sec. 21.93(b)(2)(iii) to intermix engines only 
when maintenance must be performed on an engine and no conforming 
engine for the configuration is available. Engine removals that invoke 
Sec. 21.93(b)(2)(iii) will be carefully monitored by the FAA.

    Issued in Washington, DC on November 17, 1999.
James D. Erickson,
Director of Environment and Energy.
[FR Doc. 99-30502 Filed 11-22-99; 8:45 am]
BILLING CODE 4910-13-M