FAA Instrument Rating Airplane (IRA)Navigation SystemsEasy
A pilot performs a VOT (VOR Test facility) check by tuning the VOT frequency and centering the CDI needle with a FROM indication showing on the OBS at 004°. Per 14 CFR 91.171, is this VOR check satisfactory?
- AYes, because the reading is within 4° of 0°
- BNo, because a VOT check requires a TO indication, not FROM
- CYes, but only if the aircraft is airborne during the check
- DNo, because the reading must be exactly 0°
Show answer & explanationAnswer & explanation
Correct answer: A. Yes, because the reading is within 4° of 0°
14 CFR 91.171 allows a maximum error of ±4° for a VOT check when the CDI is centered with a FROM flag showing 0° (or a TO flag showing 180°). A reading of 004° is exactly at, but within, the allowable 4° tolerance, so the check is satisfactory.
Why the other options are wrong
- B. A VOT check is valid with either a FROM/0° or TO/180° indication.
- C. VOT checks are ground checks performed on the ramp, not airborne.
- D. The regulation allows up to 4° of error, not a perfect 0°.
VOT Check Tolerance
A VOT (VOR Test) check verifies VOR receiver accuracy by tuning a test facility signal; the CDI should center with a FROM indication at 0° (or TO at 180°) within ±4°.
- VOT tolerance is ±4°
- FROM flag should read 0°, TO flag should read 180°
- Must be logged in aircraft records per 91.171
Memory trick: 'VOT: Zero degrees, Four is the fence.'