FAA Sport Pilot Airplane (SPA)Airspace and NavigationHard
A pilot wants to fly directly inbound to a VOR station on the 360° radial (a magnetic heading of approximately 360°). Instead of setting the OBS to 180°, the pilot mistakenly sets it to 360° and observes a 'FROM' flag with the CDI deflected to the right. If the pilot turns right to center the needle, what will result?
- AThe aircraft will correctly intercept and track inbound on the 360° radial to the station
- BThe VOR receiver will require recalibration since a 'FROM' flag cannot appear with a right deflection
- CThe aircraft will move farther from the desired course due to reverse sensing caused by the incorrect OBS setting
- DThe CDI will center exactly as the aircraft passes over the station
Show answer & explanationAnswer & explanation
Correct answer: C. The aircraft will move farther from the desired course due to reverse sensing caused by the incorrect OBS setting
Reverse sensing occurs when the OBS is set to the reciprocal of the course being flown. With the OBS set to 360° while flying south to intercept the 360° radial inbound (heading roughly 180°), CDI corrections are backwards: turning toward the needle actually moves the aircraft farther off course rather than toward it.
Why the other options are wrong
- A. Reverse sensing means the standard correction technique will not work correctly here.
- B. A 'FROM' flag with any needle deflection is a normal indication and doesn't indicate malfunction.
- D. The CDI centering location is unaffected by sensing direction, but tracking to get there will be reversed.
VOR Reverse Sensing
An indication error that occurs when the OBS is set to the reciprocal of the course being flown, causing CDI corrections to work backwards.
- Occurs when flying with the tail toward the selected course
- Turning toward the needle moves the aircraft away from the desired track
- Avoided by setting the OBS to match the direction of flight (course, not reciprocal)
- Common trap when tracking radials inbound versus outbound
Memory trick: 'Reverse sensing = your instrument is lying backwards, so turn AWAY from the needle instead'