§91.171

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§ 91.171 VOR equipment check for IFR operations.

(a) No person may operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment of that aircraft—

(1) Is maintained, checked, and inspected 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 section.

(b) Except as provided in paragraph (c) of this section, each person conducting a VOR check under paragraph (a)(2) of this section shall—

(1) Use, at the airport of intended departure, 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 maximum permissible indicated bearing error is plus or minus 4 degrees); or
(2) Use, at the airport of intended departure, a point on the airport surface designated as a VOR system checkpoint by the Administrator, or, outside the United States, by an appropriate authority (the maximum permissible bearing error is plus or minus 4 degrees);
(3) If neither a test signal nor a designated checkpoint on the surface is available, use an airborne checkpoint designated by the Administrator or, outside the United States, by an appropriate authority (the maximum permissible 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 variation between the published radial and the indicated bearing is 6 degrees).

(c) If dual system VOR (units independent 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 section. 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 paragraph (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 radiated by a repair station, as specified in paragraph (b)(1) of this section, is used, an entry must be made in the aircraft log or other record by the repair station certificate holder or the certificate holder's representative certifying to the bearing transmitted by the repair station for the check and the date of transmission.

Part §91 Subpart B — Flight Rules
§91.101 Applicability • §91.103 Preflight • §91.105 Crewmembers at stations • §91.107 Seatbelts • §91.109 Flight instruction • §91.111 Near other aircraft
§91.113 Right-of-way • §91.115 Right-of-way on water • §91.117 Speed Limits • §91.119 Minimum altitudes • §91.121 Altimeter • §91.123 ATC instructions • §91.125 Light signals
§91.126 Class G • §91.127 Class E • §91.129 Class D • §91.130 Class C • §91.131 Class B • §91.133 Restricted areas • §91.135 Class A
§91.137 TFRs • §91.138 Hawaiian TFRs • §91.139 Emergency traffic • §91.141 Presidential TFRs • §91.143 Space ops • §91.144 High barometric pressure
§91.145 Air shows & and sporting events • §91.146 Charity flights • §91.147 Paying-passenger flights
§91.151 VFR Fuel reserves • §91.153 VFR flight plans • §91.155 VFR weather minimums • §91.157 Special VFR • §91.159 VFR cruising altitude • §91.161 DC ADIZ
§91.167 IFR Fuel reserves • §91.169 IFR flight plans • §91.171 VOR test • §91.173 ATC clearances • §91.175 IFR Takeoffs and landing
§91.177 IFR Minimum altitudes • §91.179 IFR cruising altitudes • §91.180 RVSM • §91.181 Course flown • §91.183 IFR comm. • §91.185 IFR radio failure
§91.187 Malfunctions in IFR • §91.189 Cat II & III ops. • §91.191 Cat II & III manual • §91.193 Certain Cat II ops.