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14 CFR Ch. I (1–1–19 Edition)

§ 91.173

of radio navigation unless the VOR
equipment of that aircraft—

(1) Is maintained, checked, and in-

spected under an approved procedure;
or

(2) Has been operationally checked

within the preceding 30 days, and was
found to be within the limits of the
permissible indicated bearing error set
forth in paragraph (b) or (c) of this sec-
tion.

(b) Except as provided in paragraph

(1) Use, at the airport of intended de-

parture, an FAA-operated or approved
test signal or a test signal radiated by
a certificated and appropriately rated
radio repair station or, outside the
United States, a test signal operated or
approved by an appropriate authority
to check the VOR equipment (the max-
imum permissible indicated bearing
error is plus or minus 4 degrees); or

(2) Use, at the airport of intended de-

parture, a point on the airport surface
designated as a VOR system check-
point by the Administrator, or, outside
the United States, by an appropriate
authority (the maximum permissible
bearing error is plus or minus 4 de-
grees);

(3) If neither a test signal nor a des-

ignated checkpoint on the surface is
available, use an airborne checkpoint
designated by the Administrator or,
outside the United States, by an appro-
priate authority (the maximum per-
missible bearing error is plus or minus
6 degrees); or

(4) If no check signal or point is

available, while in flight—

(i) Select a VOR radial that lies

along the centerline of an established
VOR airway;

(ii) Select a prominent ground point

along the selected radial preferably
more than 20 nautical miles from the
VOR ground facility and maneuver the
aircraft directly over the point at a
reasonably low altitude; and

(iii) Note the VOR bearing indicated

by the receiver when over the ground
point (the maximum permissible vari-
ation between the published radial and
the indicated bearing is 6 degrees).

pendent of each other except for the

antenna) is installed in the aircraft,
the person checking the equipment
may check one system against the
other in place of the check procedures
specified in paragraph (b) of this sec-
tion. Both systems shall be tuned to
the same VOR ground facility and note
the indicated bearings to that station.
The maximum permissible variation
between the two indicated bearings is 4
degrees.

(d) Each person making the VOR

operational check, as specified in para-
graph (b) or (c) of this section, shall
enter the date, place, bearing error,
and sign the aircraft log or other
record. In addition, if a test signal ra-
diated by a repair station, as specified
in paragraph (b)(1) of this section, is
used, an entry must be made in the air-
craft log or other record by the repair
station certificate holder or the certifi-
cate holder’s representative certifying
to the bearing transmitted by the re-
pair station for the check and the date
of transmission.

(Approved by the Office of Management and
Budget under control number 2120–0005)

§ 91.173

ATC clearance and flight plan

required.

No person may operate an aircraft in

controlled airspace under IFR unless
that person has—

(a) Filed an IFR flight plan; and
(b) Received an appropriate ATC

clearance.

§ 91.175

Takeoff and landing under

IFR.

(a)

Instrument approaches to civil air-

ports.

Unless otherwise authorized by

the FAA, when it is necessary to use an
instrument approach to a civil airport,
each person operating an aircraft must
use a standard instrument approach
procedure prescribed in part 97 of this
chapter for that airport. This para-
graph does not apply to United States
military aircraft.

(b)

Authorized DA/DH or MDA.

For the

purpose of this section, when the ap-
proach procedure being used provides
for and requires the use of a DA/DH or
MDA, the authorized DA/DH or MDA is
the highest of the following:

(1) The DA/DH or MDA prescribed by

the approach procedure.

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