FAA Instrument Flight Instructor (FII)Instruments and SystemsMedium
A pilot performs a VOR receiver accuracy check using a VOT signal at the airport. After centering the CDI, the OBS reads 358° and the TO/FROM indicator displays 'FROM.' Is this receiver within the tolerance allowed by 14 CFR 91.171?
- ANo, because the OBS must read exactly 000° for a VOT check
- BYes, but only if the error is verified against a second VOR receiver
- CNo, because the TO/FROM flag should show 'TO' during a VOT check
- DYes, because the error is within the ±4° tolerance allowed for a VOT check
Show answer & explanationAnswer & explanation
Correct answer: D. Yes, because the error is within the ±4° tolerance allowed for a VOT check
During a VOT check, centering the CDI with a FROM indication should occur at 0° (or a TO indication at 180°), with a maximum permissible bearing error of ±4°. Here, 358° is only 2° off from 0°, which is well within tolerance, so the receiver is airworthy for IFR use.
Why the other options are wrong
- A. The tolerance allows up to ±4° deviation, not an exact reading.
- B. A VOT check does not require cross-checking against a second receiver; that's for the dual-receiver method.
- C. FROM at 0° is the correct indication for a VOT check, not TO.
VOR Accuracy Check — VOT Method
A ground check using a VOR Test Facility (VOT) signal to verify VOR receiver accuracy per 14 CFR 91.171.
- Tolerance is ±4° for a VOT check
- CDI centers with FROM at 0° or TO at 180°
- Must be logged with date, place, and error in aircraft records
Memory trick: VOT = Very-Okay-Tolerance, up to 4 degrees.