[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR21.93]

[Page 128-129]
 
                     TITLE 14--AERONAUTICS AND SPACE
 
CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
 
PART 21--CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS--Table of Contents
 
                 Subpart D--Changes to Type Certificates
 
Sec. 21.93  Classification of changes in type design.

    (a) In addition to changes in type design specified in paragraph (b) 
of this section, changes in type design are classified as minor and 
major. A ``minor change'' is one that has no appreciable effect on the 
weight, balance, structural strength, reliability, operational 
characteristics, or other characteristics affecting the airworthiness of 
the product. All other changes are ``major changes'' (except as provided 
in paragraph (b) of this section).
    (b) For the purpose of complying with Part 36 of this chapter, and 
except as provided in paragraphs (b)(2), (b)(3), and (b)(4) of this 
section, any voluntary change in the type design of an aircraft that may 
increase the noise levels of that aircraft is an ``acoustical change'' 
(in addition to being a minor or major change as classified in paragraph 
(a) of this section) for the following aircraft:

[[Page 129]]

    (1) Transport category large airplanes.
    (2) Jet (Turbojet powered) airplanes (regardless of category). For 
airplanes to which this paragraph applies, ``acoustical changes'' do not 
include changes in type design that are limited to one of the following-
-
    (i) Gear down flight with one or more retractable landing gear down 
during the entire flight, or
    (ii) Spare engine and nacelle carriage external to the skin of the 
airplane (and return of the pylon or other external mount), or
    (iii) Time-limited engine and/or nacelle changes, where the change 
in type design specifies that the airplane may not be operated for a 
period of more than 90 days unless compliance with the applicable 
acoustical change provisions of Part 36 of this chapter is shown for 
that change in type design.
    (3) Propeller driven commuter category and small airplanes in the 
primary, normal, utility, acrobatic, transport, and restricted 
categories, except for airplanes that are:
    (i) Designated for ``agricultural aircraft operations'' (as defined 
in Sec. 137.3 of this chapter, effective January 1, 1966) to which 
Sec. 36.1583 of this chapter does not apply, or
    (ii) Designated for dispensing fire fighting materials to which 
Sec. 36.1583 of this chapter does not apply, or
    (iii) U.S. registered, and that had flight time prior to January 1, 
1955 or
    (iv) Land configured aircraft reconfigured with floats or skis. This 
reconfiguration does not permit further exception from the requirements 
of this section upon any acoustical change not enumerated in 
Sec. 21.93(b).
    (4) Helicopters except:
    (i) Those helicopters that are designated exclusively:
    (A) For ``agricultural aircraft operations'', as defined in 
Sec. 137.3 of this chapter, as effective on January 1, 1966;
    (B) For dispensing fire fighting materials; or
    (C) For carrying external loads, as defined in Sec. 133.1(b) of this 
chapter, as effective on December 20, 1976.
    (ii) Those helicopters modified by installation or removal of 
external equipment. For purposes of this paragraph, ``external 
equipment'' means any instrument, mechanism, part, apparatus, 
appurtenance, or accessory that is attached to, or extends from, the 
helicopter exterior but is not used nor is intended to be used in 
operating or controlling a helicopter in flight and is not part of an 
airframe or engine. An ``acoustical change'' does not include:
    (A) Addition or removal of external equipment;
    (B) Changes in the airframe made to accommodate the addition or 
removal of external equipment, to provide for an external load attaching 
means, to facilitate the use of external equipment or external loads, or 
to facilitate the safe operation of the helicopter with external 
equipment mounted to, or external loads carried by, the helicopter;
    (C) Reconfiguration of the helicopter by the addition or removal of 
floats and skis;
    (D) Flight with one or more doors and/or windows removed or in an 
open position; or
    (E) Any changes in the operational limitations placed on the 
helicopter as a consequence of the addition or removal of external 
equipment, floats, and skis, or flight operations with doors and/or 
windows removed or in an open position.
    (c) For purposes of complying with part 34 of this chapter, any 
voluntary change in the type design of the airplane or engine which may 
increase fuel venting or exhaust emissions is an ``emissions change.''

[Amdt. 21-27, 34 FR 18363]

    Editorial Note: For Federal Register citations affecting Sec. 21.93, 
see the List of CFR Sections Affected, which appears in the Finding Aids 
section of the printed volume and on GPO Access.