Welcome Guest. Sign in or Signup

2 Answers

Interpreting the WCA (-) and (+) values

Asked by: 925 views General Aviation

Dear CFIs

Do I understand correctly?

If the Variation and Deviation are written as 10°E, it is the same as +10° and you subtract the value.

If the Variation and Deviation are written as 10°W, it is the same as -10° and you add the value.

Correct?

And how about WCA figures? When written as e.g. -012 how should this be interpreted?

Many thanks!

Regards, Ben

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

2 Answers

  1. Best Answer


    Bryan on Jan 17, 2023

    For magnetic variation, you want to look at page 16-7 in the Pilot’s Handbook of Aeronautical Knowledge:

    If the variation is shown as “9° E,” this means that MN is 9° east of TN. If a TC of 360° is to be flown, 9° must be subtracted from 360°, which results in a magnetic heading of 351°. To fly east, a magnetic course of 081° (090° – 9°) would be flown. To fly south, the magnetic course would be
    171° (180° – 9°). To fly west, it would be 261° (270° – 9°). To fly a TH of 060°, a magnetic course of 051° (060° – 9°) would be flown. Remember, if variation is west, add; if east, subtract. One method for remembering whether to add or subtract variation is the phrase “east is least (subtract) and west is best (add).”

    For magnetic deviation, the card will only give you the values for every 30 degrees or so. If your calculated heading is between those, you have to interpolate. Using figure 16-12 from the PHAK, if your calculated heading were 015°, the compass card says 0° for N and 28° for 30°. So you would fly 014°–the middle of the two marks. Deviation does not have exact math–it’s interpolation.

    Finally, for wind, think of how you calculated the wind correction angle–you had to know both the direction you wanted to fly and the direction of the wind. If you’re using the slide style E6B, if your dot is to the left of your course, you correct left which will ALWAYS be subtracting the appropriate correction from your heading. If your dot is to the right, you correct right which will ALWAYS be adding the correction to your heading.

    Based on your last two posts, it appears to me that you are trying to ram these three concepts together in your mind. Don’t. The reason for each of these three calculations is different and that affects how the corrections must be applied. If they could be simplified into a single action through some memory trick or mathematical formula, it would have been done years ago. Take it one step at a time every time and you’ll be fine. Mush them together and you’ll make mistakes.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  2. Benni2000 on Jan 17, 2023

    Many thanks Bryan! Much appreciated.

    I am studying the Navigation Theory GS and then attempting the sample questions.

    Some of the terms and concepts in the exams are nowhere in the course material. Hence these 🙂

    0 Votes Thumb up 0 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.