Federal Aviation Administration, DOT

Section 121.173
way; thereafter it extends laterally 500
feet on each side of the centerline.

Subpart I - Airplane Performance
Operating Limitations

[Doc. No. 6258, 29 FR 19198, Dec. 31, 1964, as
amended by Amdt. 121-132, 41 FR 55475, Dec.
20, 1976]

SOURCE: Docket No. 6258, 29 FR 19198, Dec.
31, 1964; 30 FR 130, Jan. 7, 1965, unless otherwise noted.

Section 121.173

EDITORIAL NOTE: Nomenclature changes to
subpart I of part 121 appear at 60 FR 65928,
Dec. 20, 1995.

Section 121.171

General.

(a) Except as provided in paragraph
(c) of this section, each certificate
holder operating a reciprocating-engine-powered airplane shall comply
with SectionSection 121.175 through 121.187.
(b) Except as provided in paragraph
(c) of this section, each certificate
holder operating a turbine-engine-powered airplane shall comply with the applicable provisions of SectionSection 121.189 through
121.197, except that when it operates - 
(1) A turbo-propeller-powered airplane type certificated after August 29,
1959, but previously type certificated
with the same number of reciprocating
engines, the certificate holder may
comply with SectionSection 121.175 through 121.187;
or
(2) Until December 20, 2010, a turbopropeller-powered airplane described in
Section 121.157(f), the certificate holder may
comply with the applicable performance requirements of appendix K of
this part.
(c) Each certificate holder operating
a large nontransport category airplane
type certificated before January 1, 1965,
shall comply with SectionSection 121.199 through
121.205 and any determination of compliance must be based only on approved
performance data.
(d) The performance data in the Airplane Flight Manual applies in determining compliance with SectionSection 121.175
through 121.197. Where conditions are
different from those on which the performance data is based, compliance is
determined by interpolation or by computing the effects of changes in the
specific variables if the results of the
interpolation or computations are substantially as accurate as the results of
direct tests.
(e) Except as provided in paragraph
(c) of this section, no person may take
off a reciprocating-engine-powered airplane at a weight that is more than the
allowable weight for the runway being
used (determined under the runway
takeoff limitations of the operating
rules of 14 CFR part 121, subpart I)

Applicability.

(a) This subpart prescribes airplane
performance operating limitations for
all certificate holders.
(b) For purposes of this part, effective
length of the runway for landing means
the distance from the point at which
the obstruction clearance plane associated with the approach end of the runway intersects the centerline of the
runway to the far end thereof.
(c) For the purposes of this subpart,
obstruction clearance plane means a
plane sloping upward from the runway
at a slope of 1:20 to the horizontal, and
tangent to or clearing all obstructions
within a specified area surrounding the
runway as shown in a profile view of
that area. In the plan view, the centerline of the specified area coincides with
the centerline of the runway, beginning
at the point where the obstruction
clearance plane intersects the centerline of the runway and proceeding to a
point at least 1,500 feet from the beginning point. Thereafter the centerline
coincides with the takeoff path over
the ground for the runway (in the case
of takeoffs) or with the instrument approach counterpart (for landings), or,
where the applicable one of these paths
has not been established, it proceeds
consistent with turns of at least 4,000
foot radius until a point is reached beyond which the obstruction clearance
plane clears all obstructions. This area
extends laterally 200 feet on each side
of the centerline at the point where the
obstruction clearance plane intersects
the runway and continues at this width
to the end of the runway; then it increases uniformly to 500 feet on each
side of the centerline at a point 1,500
feet from the intersection of the obstruction clearance plane with the run-

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