Runway Number Recipricals (sp)

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HPNFlyGirl

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I know there is a formula that tells you how to find the reciprical of a runway, but I am not sure what it is. Say if you had runways 03/21 how would you find out that 03 is 21 and if it was 21 how the runway was 03.

Also would an air traffic controller ask you to fly the reciprical of what you were flying?
 
HPNFlyGirl said:
I know there is a formula that tells you how to find the reciprical of a runway, but I am not sure what it is. Say if you had runways 03/21 how would you find out that 03 is 21 and if it was 21 how the runway was 03.

Also would an air traffic controller ask you to fly the reciprical of what you were flying?
Click to expand...

Shifting two between the left and right digits works for most cases.

Say runway 24. take the two away from the left digit, and add to the right digit: 06.

Runway 15: take two away from the right digit, add it to the left digit: 33
 
HPNFlyGirl said:
Thank you Bill...now is there an instance where this would not work?
Click to expand...

There are supposedly two pairs that this will not work on, but dang if I can remember them. It wouldn't take too long to go around the compass and do every reciprical pair.
 
Basically, add or subtract 18 as appropriate. If less than 18, add, else subtract.
 
Bill Jennings said:
There are supposedly two pairs that this will not work on, but dang if I can remember them. It wouldn't take too long to go around the compass and do every reciprical pair.
Click to expand...
19/01 is one of 'em
 
The easiest way to do a not so easy math problem in your head is to approach it as more than one easy math problem. With reciprical headings, you really want to add or subtract 180 degrees. It is easier to add or subtract 200 degrees (340 - 200 = 140) but we know that isn't correct because we added or subtracted 20 too much so we correct it by subtracting or adding back 20 degrees (140 + 20 = 160) which is the recip heading for 340. Because of going beyound 0/360 degrees sometimes you have to add 200 and subtract 20, other times you have to subtract 200 and add 20. That is exactly what the add 2 to one number and subtract 2 from the other (or vice versa) is doing. Of course, if you are in a plane, the quickest and easiest is simply to look at you DG or OBS. Recipricals are always on opposite sides of the dial. Find the number that you want the recip of and then look straight across the dial for its recip.

There is a similar approach to converting Celcius to Fahrenheit in your head. Most people can't do 9/5s in their head but they can double a number. Doubling a number and then subtracting 1/10 of the result is the same as 9/5 so take 15 deg. C, double it (30), subtract 1/10 (30-3=27). now you still have to add the 27 to 32 to get degrees F. If that is too difficult, then add it to 30 and then add 2 more. (=59F)
 
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If I need a recipricol, I tend to just get it off of the unused CDI. Set the runway heading or whatever I have at the top, read the recipricol at the bottom. Keeps me from being distracted doing math in my head, not that it's all that hard to add or subtract 18.
 
Bill Jennings said:
Shifting two between the left and right digits works for most cases.

Say runway 24. take the two away from the left digit, and add to the right digit: 06.

Runway 15: take two away from the right digit, add it to the left digit: 33
Click to expand...
May be it is just me that seems overly complicated and an obtuse solution. Oposite unway headings will alwys be 180 degrees apart (unless there are some odd ball curved runways around). So if the runway is 19 degrees or higher subtract 18, if it is less than or equal to 18 add 18.
 
HPNFlyGirl said:
I know there is a formula that tells you how to find the reciprical of a runway, but I am not sure what it is. Say if you had runways 03/21 how would you find out that 03 is 21 and if it was 21 how the runway was 03.
Click to expand...
The easiest way for the numerically challenged is to spot one of the headings on your DG and then draw (in your mind) a line directly across to the other side... that heading is your answer.

-Skip
 
Skip Miller said:
The easiest way for the numerically challenged is to spot one of the headings on your DG and then draw (in your mind) a line directly across to the other side... that heading is your answer.

-Skip
Click to expand...
Or place a pencil across the DG.
 
The recip is always 180 degrees off - so add or subtract 18. (01-18, add, 19-36, subtract)
 
HPNFlyGirl said:
I know there is a formula that tells you how to find the reciprical of a runway, but I am not sure what it is. Say if you had runways 03/21 how would you find out that 03 is 21 and if it was 21 how the runway was 03.

Also would an air traffic controller ask you to fly the reciprical of what you were flying?
Click to expand...
Like the others have said, the easiest way to figure out the reciprical is to add or subtract 18. (01-18, add, 19-36, subtract) (Since the reciprical is always 180 degrees off.) That's they way I do it and it can be done all in your head.

Once you land on enough runways though, you get to know the recipricals without having to think.

I don't quite know what you mean by your second question, Brook. If you're asking if a controller would instruct you to: "N12345, fly your reciprical heading" then the answer is no. If he said to you "N12345, make a 180 degree turn [heading XXX]" then the answer is yes.

Hope this helps,
Jason
 
For recip hdg I do it how Bo said. For T* conversions I do it how Graueradler said. It's easy after the first few times.
 
The tricks have you adding 20 and subtracting 2, or vice-versa subtracting 20 and adding 2, which amazingly, is the same thing as adding or subtracting 18. :rolleyes:
 
Maybe Sporty's can come up with a "Runway Reciprical Calculator"...they can list it next to the "Am I Going To Enter The Cloud Spotter Thingy" and the "Altitude Reminder Clicker".

Greg
182RG
 
ggroves said:
Maybe Sporty's can come up with a "Runway Reciprical Calculator"...they can list it next to the "Am I Going To Enter The Cloud Spotter Thingy" and the "Altitude Reminder Clicker".

Greg
182RG
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At $19.95, they'd be a bargain. :rolleyes: :D
 
I do a "sum of the numbers" kind of thing using the leading 2 digits...

HDG/RCP
030/210 ... 0+3 = 2+1
060/240 ... 0+6 = 2+4
090/270 ... 0+9 = 2+7
120/300 ... 1+2 = 3+0
150/330 ... 1+5 = 3+3
 
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ah, the old "9's" trick.....good for finding transposed numbers in spreadsheets, too...when the sum of the digits of a variance equals 9 (or some multiple) the error is usually due to transposed numbers in an entry... works in this case because 18 (reciprocal heading) is an integer multiple of 9

gkainz said:
I do a "sum of the numbers" kind of thing using the leading 2 digits...

HDG/RCP
030/210 ... 0+3 = 2+1
060/240 ... 0+6 = 2+4
090/270 ... 0+9 = 2+7
120/300 ... 1+2 = 3+0
150/330 ... 1+5 = 3+3
Click to expand...
 
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gkainz said:
I do a "sum of the numbers" kind of thing using the leading 2 digits...

HDG/RCP
030/210 ... 0+3 = 2+1
060/240 ... 0+6 = 2+4
090/270 ... 0+9 = 2+7
120/300 ... 1+2 = 3+0
150/330 ... 1+5 = 3+3
Click to expand...

190/010 ... 1+9 = 0+1 ?????
 
lancefisher said:
190/010 ... 1+9 = 0+1 ?????
Click to expand...
Apply slight dislexia here and it looks just fine... :D sort makes sense if you think 1+9 is 10 and 010 is RWY 10 ...
 
you guys are making it all way too hard. just visualize the compass. it's not tough. now, remembering which way to turn, is tough! visualizing where the 45 is off of a right pattern runway 5, is tough. but not the reciprocals.
 
You'll get to where you just know the numbers.. No big deal.

As far as which way to turn..for the pattern.. I draw a picture in my head of a top-down view of the airport..After awhile it'll get easy.
At least 95% of my flying has been at controlled airports. If I am going into an uncontrolled airport I usually just:

1.) Announce straight in approach every mile from 25 miles out.

2.) Say AT LEAST four times: "Any traffic in the area please advise."
 
Yeah, I don't even consciously do math anymore, I just know. Eventually, you will fly to enough airports and from looking at diagrams you will just know that it's 3/21 or 7/25 or 17/35 without thinking about it. But really, just use Jesse's method. It's a can't fail.
 
gkainz said:
I do a "sum of the numbers" kind of thing using the leading 2 digits...

HDG/RCP
030/210 ... 0+3 = 2+1
060/240 ... 0+6 = 2+4
090/270 ... 0+9 = 2+7
120/300 ... 1+2 = 3+0
150/330 ... 1+5 = 3+3
Click to expand...

Yeppers - That's what I do.
 
Glad the thread came back, several things gnawed at me.....

If you are using an unused CDI, both of mine have a pointer at the bottom of the dial. Set the bearing on the top and read the reciprocal from the pointer on the bottom. Normal usage is if you are on an inbound heading, Position reporting to ATC will use the outbound radial. Just read it off the bottom.

Second, why the importance of the question? If you have planned/prepared correctly, you have an airport diagram available to you. It gives all the runway numbers.
 
jangell said:
If I am going into an uncontrolled airport I usually just:

1.) Announce straight in approach every mile from 25 miles out.

2.) Say AT LEAST four times: "Any traffic in the area please advise."
Click to expand...

roflmao!!!

we really thought about doing this at gastons, just to see what you all would do, but decided we wanted to keep you as friends until at least the end of the weekend :)
 
tonycondon said:
roflmao!!!

we really thought about doing this at gastons, just to see what you all would do, but decided we wanted to keep you as friends until at least the end of the weekend :)
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You only thought those metal cases had poker chips in them!!!:hairraise:
 
haha ed, and thanks for changing your avatar, it made me feel even more guilty about surfing POA all day at work.
 
tonycondon said:
roflmao!!!

we really thought about doing this at gastons, just to see what you all would do, but decided we wanted to keep you as friends until at least the end of the weekend :)
Click to expand...

That's OK, Lance Flynn did it on departure. :D
 
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