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Instrument Rating

Flying along an airway 50 miles from the VOR station you’re tracking to, you look up from your Dean Koontz novel and see a CDI needle deflection just shy of full. How far off the airway are you? a. One mile b. Over two miles but still in protected airspace c. Four miles and flying on the edge d. More than four miles and trolling for mountains 2. Flying that same airway, still 50 miles from the fix, same needle deflection, but you’re using an older IFR-certified GPS to drive your CDI. How far off are you now? a. One mile b. About two miles c. Almost five miles d. Depends on how close you are to the station 3. Same place, same CDI, but with that WAAS upgrade that was supposed to cost $1500 and actually set you back five grand. Now how far off are you? a. One mile b. About two miles c. Almost five miles d. Depends on how close you are to the station 4. You’ve checked your VORs per the regulations and they look fine. What’s the maximum amount they could be off? a. Four degrees b. Six degrees c. a or b d. There’s really no way to tell 5. Suppose your VOR test showed the number-one CDI was two degrees off and now it’s time to shoot an ILS. You should assume your CDI for the localizer is: a. Two degrees off b. Between 0.5 and 1 degree off c. Spot on d. You can’t tell using a VOR test

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4 Answers

  1. Kris Kortokrax on Oct 25, 2013

    What is the purpose of this exercise?

    Consider that if you check one VOR against the other in flight that they must be within 4 degrees of each other. If the first one is 6 degrees off the desired radial and the second one shows a 4 degree difference from the first, then the second could be 10 degrees off and both would pass the test.

    The test has no bearing on localizer accuracy. That’s why it is labeled a VOR test.

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  2. John D Collins on Oct 26, 2013

    First question, assuming your VOR is accurate and the CDI selection is set accurately, you will be approximately 4 SM off the centerline.

    Second question, assuming the CDI is accurate and RAIM is acceptable, you are close to 5 NM off centerline.

    Third question, assuming the CDI is accurate and the WAAS integrity is acceptable, you are close to 2 NM off the centerline.

    Fourth question, the VOR accuracy is not relevant to the Localizer accuracy. Neither is the angular width of the localizer able to be determined other than at the threshold where it should be +/- 350 feet. A longer runway will have a narrower localizer angle for full scale deflection (FSD) and a shorter runway a wider angle. Since the FSD is calibrated to be +/- 350 feet at the threshold a longer runway has the localizer further away from the threshold than a shorter runway, so the FSD angle varies.

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  3. lion on Oct 26, 2013

    Kris & John..thank u for the answers. I am not sure of the answrs but I think the the first one is not 4 but around 8 nm off course because the question says that the CDI is almost full deflection. Since one degree off course put us 1 nm off course when we are 60 nm and around .8 nm when we are 50 nm of the vor. Then 10 degrees (full def) times 8 is 8 nm off course. By the way, i found these questions online without anwers in the IFR magazine. They said the answers on page 13 but i could not find that page.

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  4. Lion on Oct 27, 2013

    I agree with John on his answer to the the second question.

    In case of a GPS, full deflected needle represents 5 NM when the GPS is in the en route mode ( > 30 NM of the VOR).

    “….When used with a GPS it shows actual distance left or right of the programmed course-line. Sensitivity is usually programmable or automatically switched, but 5 nautical miles deviation at full scale is typical for en route operations…”

    Ref: http://en.wikipedia.org/wiki/Course_deviation_indicator

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