FAA Instrument Rating Airplane (IRA)Navigation SystemsMedium
A pilot performs a VOR ground checkpoint test at an airport where the published check radial is 174°. With the CDI centered and a FROM flag displayed, the OBS reads 179°. Per 14 CFR 91.171, is the VOR system airworthy for IFR flight?
- AYes, because the error is less than 10°
- BNo, because ground checkpoints require a TO indication, not FROM
- CNo, because the 5° error exceeds the ±4° tolerance for a ground checkpoint
- DYes, because ground checkpoints allow up to ±6° error
Show answer & explanationAnswer & explanation
Correct answer: C. No, because the 5° error exceeds the ±4° tolerance for a ground checkpoint
A designated ground checkpoint allows a maximum error of ±4°. Here the difference between the published radial (174°) and the indicated radial (179°) is 5°, which exceeds the allowable tolerance, so the equipment does not meet the required check and must not be used for IFR until repaired/recalibrated.
Why the other options are wrong
- A. 10° is not the applicable tolerance for any VOR check type.
- B. Ground checkpoints can be checked with either a TO or FROM indication, depending on facility orientation.
- D. ±6° tolerance applies to airborne checkpoints, not ground checkpoints.
VOR Ground Checkpoint
A designated point on an airport surface with a published radial used to verify VOR receiver accuracy; allowable error is ±4°.
- Ground checkpoint tolerance: ±4°
- Airborne checkpoint tolerance: ±6°
- Must be logged per 91.171 if used for IFR
Memory trick: 'Ground and dual: 4 is the rule; Airborne alone gets 6, that's the tool.'