VOR Tracking with a Suspect Indication
You are outbound from the ABC VOR on the 315° radial, 22 DME, heading 320°M, TAS 100 kt, with wind 270°/20 kt. The CDI shows two dots left of centre. The DME display fluctuates between 22 and 27 nm, and the audio identification is too faint to read. ATC asks for your ETA at the 40 DME point on the same radial. You have a current chart, a magnetic compass, and a serviceable heading indicator. There is no GNSS on board. The controller is busy and has not offered a radar service. You must decide whether the VOR indication is usable, what heading to fly if it is, and what to do if the identification remains unreadable.
1. Assess whether the VOR/DME indication is usable for navigation and for the ETA request.
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I would not treat the indication as fully reliable. A fluctuating DME between 22 and 27 nm and an unreadable identification mean I cannot confirm that the receiver is locked onto the correct station, and I cannot rule out a flagged or false indication. The CDI deflection alone is not enough. Before using it, I would try to identify the station by Morse code, check the frequency against the chart, and cross-check the DME against a map feature or a second navaid. If the identification remains unreadable, I would treat the VOR as unusable and navigate by dead reckoning, while telling ATC that the navaid is suspect. I would not give an ETA based on a distance that is jumping by 5 nm.
2. If the VOR is eventually confirmed, calculate the heading to regain the 315° radial and the ETA to 40 DME.
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Track is 315°M. Wind 270°/20 kt: the crosswind component is 20 sin 45° = 14 kt from the left, and the headwind component is 20 cos 45° = 14 kt. Drift = (14/100) × 60 ≈ 8.4°, so crab left: heading ≈ 307°M. Groundspeed = 100 − 14 = 86 kt. The CDI shows two dots left, which means the selected course is to my left and I am right of the 315° radial. I would turn further left to intercept - about 20–30° left for a few minutes - then roll out on 307°M as the needle centres. From 22 DME to 40 DME is 18 nm. At 86 kt, time = 18/86 × 60 ≈ 12.6 minutes, so the ETA is about 13 minutes after the fix.
3. What would you tell ATC, and what would you do if the identification stays unreadable?
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I would tell ATC: “ABC VOR identification unreadable and DME fluctuating; unable to confirm the 40 DME estimate; navigating by dead reckoning, request position assistance if available.” That gives the controller accurate information without overstating the problem. If the identification remains unreadable, I would stop using the VOR for track guidance, fly a compass heading based on the chart and wind, and use time-and-distance checks against known features. I would not declare an emergency unless fuel, weather, or position uncertainty made it necessary. I would also consider requesting a radar vectors service if the controller can provide one, but I would not assume it is available.