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7 Answers

Who has the final say in determining airport distances?

Asked by: 2455 views , ,
FAA Regulations, Flight Instructor

I need help with measuring airport distances, any my particular problem is measuring the distance between S50 and KCLS. Using a plotter, or Foreflight, the straight line distance comes to 50NM between the centers of the airport symbols. When I put the lat/long coordinates from the Chart Supplements, using FAA's distance calculator in this website: https://oeaaa.faa.gov/oeaaa/external/gisTools/gisAction.jsp?action=showDistanceCalculationToolForm, the total distance is a bit short of 50NM (49.8). Airnav.com and Safelog give similar distances. So who is correct? 

I have posted the same question to Seattle FSDO and currently waiting for a reply. Perhaps this is a question that has been answered before.

Thanks

Christian

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7 Answers



  1. Russ Roslewski on Jul 23, 2020

    The DPE.

    Not being trite here. The only person that really matters is the person who is going to determine whether or not you meet the requirements when you show up to the checkride. Well, you need to convince your CFI also, since you need their sign-off.

    The is no “official source” of distances. However, the OEAAA tool, or any geodetic calculator (calculates distances applying the curvature of the earth) would be the most accurate.

    I would say that if you show up to the checkride and the examiner asks, the obvious way for them to check it is using either a plotter (if you’re using paper charts), or the EFB program itself (if using an EFB). So if that method used shows it as less than 50 nm, it doesn’t count.

    But why bother risking it? Can you just fly to TDO instead? It’s 56 nm.

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  2. cyoedhana on Jul 23, 2020

    Hi Russ,

    Thanks for the answer. I ended up flying your suggested route to KTDO then KCLS. Cheapest avgas within 50NM from S50 so far is at KCLS.

    Unfortunately, S50-KCLS is one of the three problematic distances that I have encountered. There is S50-KOTH (249.6NM), and S50-KRBG (249.9NM). Both of their distances show up as 250NM on Foreflight. For commercial long cross-country, I have been recommending KRNT as the starting point of the flight. It is just tempting to simplify the route if I can argue that S50-KRBG is 250NM.

    Thanks,

    Christian

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  3. Mark Kolber on Jul 29, 2020

    I’m sorry Christian, but…

    I see questions like yours all the time and I have difficulty understanding them. It’s completely beyond to me why one would *want* to cut it that close when there are other options so close by. Don’t you like flying?

    In your original example, the difference between KCLS (49.9 NM according to SkyVector) and KTDO (56.4 nm) as a destination, inn a 152 cruising at only 90 KTS, is a whopping 9 minutes. Less if you fly anything faster.

    On the long cross country, what’s so bad about repositioning to RNT as the starting point or, for that matter, including a touch & go at 16S either on the way down or on the way back?

    Is the problem needing to save 12 minutes worth of fuel?

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  4. cyoedhana on Jul 29, 2020

    Well Mark, I have no personal problem logging an extra 0.2hr. Its good for the logbook. But I have seen S50->KCLS->KRBG->S50 route used to fulfil 61.129(a)(4)(i). On Foreflight, this route should work, because KRGB->S50 distance is given as exactly 250nm. Then there is the hair-splitting 249.9nm give by AirNav.

    I just can’t help wandering if the route is a potential checkride buster. Per Russ’ input, it should not be hard to convince a DPE that 249.9 looks like 250 on a plotter. But you never know. Hence the question.

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  5. Mark Kolber on Jul 30, 2020

    That’s my point exactly. Why mess around with a potential checkride buster when an extra 0.2 hours buys certainty.

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  6. Gary S. on Aug 11, 2020

    Splitting hairs on a round-robin? Hmmmm

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  7. Mackey on Oct 10, 2020

    GREATER than 50 miles…..

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