FAA Instrument Rating Airplane (IRA)Navigation SystemsMedium
A pilot conducts a dual VOR receiver check by tuning both navigation receivers to the same VOR station and radial. Receiver 1 indicates the aircraft is on the 087° radial, and Receiver 2 indicates 093°. Per 14 CFR 91.171, does this system meet the requirement for IFR flight?
- AYes, because dual VOR checks have no specified tolerance
- BYes, because both receivers are within 10° of each other
- CNo, because dual VOR checks require identical readings
- DNo, because the 6° difference exceeds the maximum allowable difference of 4°
Show answer & explanationAnswer & explanation
Correct answer: D. No, because the 6° difference exceeds the maximum allowable difference of 4°
For a dual VOR check, the maximum permissible difference between the two indicated bearings is 4°. The difference here is 93° − 87° = 6°, which exceeds the allowable tolerance, so the system does not satisfy 14 CFR 91.171 and one or both receivers must be checked/repaired.
Why the other options are wrong
- A. 91.171 specifically requires a maximum 4° difference for dual checks.
- B. 10° is not the correct dual VOR tolerance.
- C. Exact identical readings are not required, only agreement within 4°.
Dual VOR Receiver Check
A method of checking VOR accuracy by comparing indications from two receivers tuned to the same station and radial; maximum allowable difference between them is 4°.
- Max difference allowed: 4°
- Tune both receivers to same VOR and radial
- Alternative to VOT or ground/airborne checkpoint checks
Memory trick: 'Two dials, four degrees, no more.'