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In the comments on this answer an interesting assertion was made, that you never have a situation in the US where there is no possible alternate airport. Assuming that:

  • you're flying an aircraft that is normally flown for commercial reasons,
  • you're flying to an airport that normally allows flights to land,
  • you're flying from an airport in the US to another airport in the US,
  • and you're following the regulation that you have to have enough fuel to get to your destination, then fly to your alternate, then stay in the air for another 45 minutes

is there any combination of aircraft and airports where no alternate landing airport would be possible?

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  • $\begingroup$ I can guess an A380 or concorde will have a more limited set of options $\endgroup$ – ratchet freak Jul 11 '14 at 8:19
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    $\begingroup$ @ratchet yes, but that's a regulation. The question seems to be asking if you can construct a hypothetical flight plan ignoring such regulations. That's why I don't understand what the question is asking. $\endgroup$ – RedGrittyBrick Jul 11 '14 at 10:55
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    $\begingroup$ Either that, or he's asking if there's an airport within the US that cannot legally be used because of said regulation (no alternate reachable). If there is, I'm guessing Alaska and some limited range aircraft. $\endgroup$ – falstro Jul 11 '14 at 10:58
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    $\begingroup$ @ratchetfreak, that regulation was what I meant. I'll edit the question to reflect that. $\endgroup$ – Joe Jul 11 '14 at 16:11
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    $\begingroup$ I'm not sure if the space shuttle was flown "for commercial reasons" but it comes to mind as an aircraft that wouldn't be able to make it to an alternate. $\endgroup$ – Steve V. Jul 11 '14 at 21:48
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For larger aircraft, likely no. Worst case they can carry enough fuel to return to their origin. If range does became an issue (e.g. Atlanta -> Anchorage) you would just schedule a technical stop somewhere like Yellowknife. Alaska has a ton of small airfields so short-range aircraft would have many alternatives. Wether the alternate has any services is another question.

As the question asks about US airports only, mainland -> Hawaii would be a possibility. Hawaiian Air's 717 planes already need extra tanks in the fuselage to get to the mainland, so a return flight would be weather-dependent. If you take off from Seattle and several airports close for bad weather after you pass the no-return point your options are rather limited. If the weather is bad enough to close every airport in the islands then channeling Sullenberger won't help much. Unlikely any sane pilot would take off with that kind of forecast, and Hawaii's weather is usually pretty good.

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    $\begingroup$ Mainland-to-Hawaii is about the only (US) case I can think of where there may be no alternate possible (and even then only in rare situations where all the islands are hit by lousy weather - Hilo and Honolulu are about 180 miles apart which should be well within diversion range for something like runway fouling). $\endgroup$ – voretaq7 Jul 11 '14 at 16:09

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