FAA Instrument Rating Airplane (IRA)Regulations and CurrencyMedium
An aircraft's dual VOR receivers are checked against each other on the ground per 14 CFR 91.171. What is the maximum allowable difference in indicated bearing between the two receivers for the check to be considered satisfactory?
- A6 degrees
- B8 degrees
- C2 degrees
- D4 degrees
Show answer & explanationAnswer & explanation
Correct answer: D. 4 degrees
14 CFR 91.171 allows a dual VOR check where both receivers are tuned to the same VOR facility and the indicated bearings compared; the maximum permissible difference between the two indications is 4 degrees.
Why the other options are wrong
- A. 6 degrees is the tolerance for airborne checkpoints or ground checks using a designated radial, not the dual check.
- B. 8 degrees exceeds any allowable VOR check tolerance.
- C. 2 degrees is not the specified tolerance for any VOR check method.
VOR Equipment Check (91.171)
IFR flight under VOR navigation requires the VOR system be checked within the preceding 30 days using an approved method with specified tolerances.
- VOT or ground checkpoint: ±4° tolerance
- Airborne checkpoint or designated radial: ±6° tolerance
- Dual VOR receiver comparison: max 4° difference between receivers
Memory trick: 'Ground=4, Air=6, Dual diff=4' — remember the tolerance triangle.