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Federal Aviation Administration, DOT 

§ 121.173 

§ 121.171 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 associ-
ated with the approach end of the run-
way 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 center-
line of the specified area coincides with 
the centerline of the runway, beginning 
at the point where the obstruction 
clearance plane intersects the center-
line of the runway and proceeding to a 
point at least 1,500 feet from the begin-
ning point. Thereafter the centerline 
coincides with the takeoff path over 
the ground for the runway (in the case 
of takeoffs) or with the instrument ap-
proach 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 be-
yond 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 in-
creases uniformly to 500 feet on each 
side of the centerline at a point 1,500 
feet from the intersection of the ob-
struction clearance plane with the run-
way; thereafter it extends laterally 500 
feet on each side of the centerline. 

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

§ 121.173 General. 

(a) Except as provided in paragraph 

(c) of this section, each certificate 
holder operating a reciprocating-en-
gine-powered airplane shall comply 
with §§ 121.175 through 121.187. 

(b) Except as provided in paragraph 

(c) of this section, each certificate 
holder operating a turbine-engine-pow-
ered airplane shall comply with the ap-
plicable provisions of §§ 121.189 through 
121.197, except that when it operates— 

(1) A turbo-propeller-powered air-

plane type certificated after August 29, 
1959, but previously type certificated 
with the same number of reciprocating 
engines, the certificate holder may 
comply with §§ 121.175 through 121.187; 
or 

(2) Until December 20, 2010, a turbo- 

propeller-powered airplane described in 
§ 121.157(f), the certificate holder may 
comply with the applicable perform-
ance 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 §§ 121.199 through 
121.205 and any determination of com-
pliance must be based only on approved 
performance data. 

(d) The performance data in the Air-

plane Flight Manual applies in deter-
mining compliance with §§ 121.175 
through 121.197. Where conditions are 
different from those on which the per-
formance data is based, compliance is 
determined by interpolation or by com-
puting the effects of changes in the 
specific variables if the results of the 
interpolation or computations are sub-
stantially 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 air-
plane 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) 
after taking into account the tempera-
ture operating correction factors in the 
applicable Airplane Flight Manual. 

(f) The Administrator may authorize 

in the operations specifications devi-
ations from the requirements in the 
subpart if special circumstances make 
a literal observance of a requirement 
unnecessary for safety. 

(g) The ten-mile width specified in 

§§ 121.179 through 121.183 may be re-
duced to five miles, for not more than 
20 miles, when operating VFR or where