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6 Answers

Navigation test question

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Private Pilot

An airplane flies on a certain latitude from a point on longitude W176 to a point on longitude E175. What is the direction of the flight?
The answer is that the plane indeed flies from the west to the east, but the direction is nonetheless westward. I don't understand why. Can someone explain?

 

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6 Answers



  1. John D Collins on Feb 03, 2024

    It is kind of a trick question. Longitudes are measured in degrees east or west of the prime meridian that runs pole to pole through Greenwich in the UK with a value of zero longitude. The highest west value is +180 and is measured in degrees west of the prime meridian, The highest east value is -180 and is measured in degrees east of the prime meridian, So in effect +180 and -180 are the same longitude, just measured from opposite directions from the prime meridian. If the international date line was a straight line in the Pacific, that is where east 180 would equal west 180.

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  2. Oren on Feb 04, 2024

    Sorry I still don’t get it. Why do you say it’s westward, when you’re flying from the West to the East?

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  3. John D Collins on Feb 04, 2024

    To circumnavigate around the earth east to west (or west to east), there are 360 degrees of longitude. Going east of the prime meridian, the direction is specified as east longitude starting at the prime meridian at 00 E and continuing half way around the globe at 180 E. The longitudes starting from London area in the direction of Europe’s then the mid east, then Asia, then the Pacific. Going westward from the prime meridian, longitudes go the other way starting at 00 W and end half way around the world to 180 W. 180 E and 180 W are the same longitude in the Pacific.So going west from 176 W to 180 W one would go from 176 W to 177 W to 178 W to 179 W to 180 W, which is also 180 E. Continuing to 175 E one would have to go to 179 E, 178 E, 177 E, 176 E to 175 E. Take out a globe or Google earth and check it out.

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  4. Oren on Feb 04, 2024

    I understand that. So what you are saying is that if I am flying from W176 to E175, I’d fly first to 177W, 178W… all the way to 18OW. Meaning that that the nose of the plane will point westward.? But then 180W is 180E. I’d be flying to 179E, then 178E, etc.. The nose then points to the East.

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  5. Jeff Baum on Feb 04, 2024

    Let’s try this…

    If you are in the Western Hemisphere and fly west the Lines of Longitude numbers increase, until reaching 180° meridian. If you are in the Eastern Hemisphere and fly west the Lines of Longitude numbers decrease until you reach the 0° meridian. All lines of Longitude are referenced East or West from the “Prime Meridian” also called the “Greenwich Meridian” which is 0°. Since there are 360°s in a circle and you are dividing East/West (right/left) there can only be 180°s in each half. Thus the designation 45° East Longitude or 172° West Longitude. You won’t find a Longitude above 180° (such as 193° West Longitude) on a navigational chart.

    Now, consider these flights…

    If you fly from Moscow (UUEE 37.5° East Longitude) to Paris France (LFPG 2° East Longitude), you are flying WEST and the Longitudes are getting smaller.

    If you fly from Paris France (LFPG 2° East Longitude) to New York (KJFK 73° West Longitude) you are flying West and the Longitudes get smaller… UNTIL you reach the 0° meridian…you move from the Eastern Hemisphere with East Longitudes into the Western Hemisphere with West Longitudes. Now the Lines of Longitude are getting bigger as you fly away from the 0° meridian and you have not made a turn. You are still flying West.

    If you fly from New York (KJFK 73 West Longitude) to Los Angeles (KLAX 118° West Longitude) you are still flying West and the Longitudes are getting bigger.

    If you fly from Honolulu Hawaii (PHNL 175° West Longitude) to Tokyo/Narita (RJAA 140° EAST Longitude) you are STILL flying WEST and the Longitudes are getting bigger… UNTIL… you cross the 180° meridian… You move back from the Western Hemisphere with West Longitudes into the Eastern Hemisphere with East Longitudes. Now having passed the 180° meridian the Longitudes are getting smaller, but you have NOT made a turn, you are STILL flying WEST.

    Find a world globe or map. Find LAX. Next find Tokyo Japan. About half way between the two you will find the 180° meridian (The International Date Line runs about the 180° meridian). Note that the Lines of Longitude either side of the 180° meridian are labeled East or West. You must fly west to get from KLAX to RJAA. If you start out flying West until you get to the 180° Longitude and then start flying East, you’ll end up back at LAX.

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  6. Oren on Feb 05, 2024

    Now I get it! Thank you so much!

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