(i)
Designatedfor ”agricultural aircraftoperations” (asde.nedinSec.137.3 of this chapter, e.ective January 1, 1966) to which Sec. 36.1583 of this chapter does not apply, or

(ii)
Designated for dispensing .re .ghting materials to which Sec. 36.1583 of this chapter does not apply, or

(iii) U.S. registered, and that had .ight time prior to January 1, 1955 or
(iv) Land con.gured aircraft recon.gured with .oats or skis. This recon.-guration does not permit further exception from the requirements of the 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 de.ned in Sec. 137.3 of this chapter, as e.ective on January 1, 1966;
(B)
for dispensing .re .ghting materials; or

(C)
for carryingexternalloads, asde.nedinSec.133.1(b) ofthis chapter, as e.ective on December 20, 1976.

(ii) Those helicopters modi.ed by installation or removal of external equip-ment. For purposes of this paragraph, ”external equipment” means any instrument, mechanism,part, apparatus, appurtenance, or accessory that it attached to, or extends from, the helicopter exterior but is not used norisintended tobeusedinoperating orcontrolling ahelicopterin .ight andisnotpartof anairframeorengine.An ”acoustical change” doesnot include :
(A)
addition or removal of external equipment;

(B)
changesin the airframe made to accommodate the addition or remo-val of external equipment, to provide for an external load attaching means, tofacilitate the use of external equipment or externalloads, or to facilitate the safe operation of the helicopter with external equip-ment mounted to, or external loads carried by, the helicopter;

(C)
recon.guration of the helicopter by the addition or removal of .oats and skis;

(D)
.ight with one or moredoors and/or windows removed orin an open position; or

(E)
any changesin the operationallimitationsplaced on thehelicopter as a consequence ofthe addition or removal of external equipment, .oats, and skis, or .ight operations with doors and/or windows removed or in an open position.

(c)
Forpurposes of complying withpart34 of this chapter, any voluntary changeinthe type design of the airplane or engine which may increase fuel venting or exhaust emissions is an ”emissions change.”

Amdt. 21-81, E.. 8/7/2002
FAR 21.95 : Approval of minor changes in type design.
Minor changes in a type design may be approved under a method acceptable to the Administrator before submitting to the Administrator any substantiating or descriptive data.
FAR 21.97 : Approval of major changes in type design.
(a)
[In the case of a major change in type design, the applicant must submit substan-tiating data and necessary descriptive data for inclusion in the type design.

(b)
Approval of a major change in the type design of an aircraft engine is limited to the speci.c engine con.guration upon which the change is made unless the applicant identi.esin the necessarydescriptivedataforinclusionin the typedesign the other con.gurations of the same engine type for which approval is requested and shows that the change is compatible with the other con.gurations.]

Amdt. 21-40, E.. 10/31/74
′
Elodie Roux. Septembre 2003
Subpart D–Changes to Type Certi.cates
FAR21.99 :[Requireddesign changes.]
(a)
When an Airworthiness Directive is issued under Part 39 the holder of the type certi.cate for the product concerned must–

(1)
If the Administrator .nds that design changes are necessary to correct the unsafe condition of the product, and upon his request, submit appropriate design changes for approval; and
　
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