FAA Instrument Flight Instructor (FII)Instrument RegulationsMedium
A CFII is briefing a client on VOR receiver accuracy checks required by 91.171 before IFR flight. The client plans to use a VOT (VOR Test) signal to check the receiver. What is the maximum permissible error for this type of check?
- APlus or minus 8 degrees
- BPlus or minus 2 degrees
- CPlus or minus 4 degrees
- DPlus or minus 6 degrees
Show answer & explanationAnswer & explanation
Correct answer: C. Plus or minus 4 degrees
91.171(b)(1) specifies that when using a VOT, the course deviation indicator must center with the OBS set to 0 degrees with a TO/FROM indication of FROM, within plus or minus 4 degrees. This differs from the airborne checkpoint tolerance of plus or minus 6 degrees.
Why the other options are wrong
- A. Exceeds all permissible tolerances under 91.171.
- B. Tighter than any regulatory tolerance specified in 91.171.
- D. This is the tolerance for a designated airborne checkpoint, not a VOT.
VOR Equipment Check (91.171)
Before IFR flight, a pilot must have checked VOR accuracy within the preceding 30 days using one of several approved methods, each with a specified tolerance.
- VOT check: ±4 degrees.
- Certificated ground checkpoint: ±4 degrees.
- Certificated airborne checkpoint: ±6 degrees.
- Dual VOR receiver check: ±4 degrees difference between the two.
Memory trick: 'VOT and Ground are tight at 4, Air is loose at 6.'