FAA Instrument Flight Instructor (FII)IFR Procedures and ApproachesEasy
A pilot performs a VOR receiver accuracy check using a VOT (VOR Test Signal) prior to an IFR flight. What is the maximum permissible bearing error under 14 CFR 91.171?
- A±2 degrees
- B±6 degrees
- C±4 degrees
- D±10 degrees
Show answer & explanationAnswer & explanation
Correct answer: C. ±4 degrees
14 CFR 91.171 permits a maximum of ±4 degrees error when using a VOT or a certified VOR ground checkpoint, and ±6 degrees for an airborne checkpoint or dual-VOR cross-check comparison.
Why the other options are wrong
- A. ±2 degrees is tighter than any regulatory tolerance.
- B. ±6 degrees applies to airborne checkpoints, not VOT checks.
- D. ±10 degrees exceeds all allowable VOR check tolerances.
VOR Receiver Accuracy Check (91.171)
Regulatory requirement to check VOR receiver accuracy within the preceding 30 days before flight under IFR using VOR navigation.
- VOT or ground checkpoint: ±4° tolerance
- Airborne checkpoint: ±6° tolerance
- Dual VOR cross-check: ±4° difference between the two indications
- Pilot must log date, place, bearing error, and signature
Memory trick: 'VOT gets 4, air gets 6' — ground checks are tighter