Jmacaula wrote: It just seemed bizarre to me, because most airports or airlines have a designated alternate of a major airport (I assume most smaller ones don't have adequate mechanic or emergency crew ). Hence why if you are heading north from say JFK, it is almost a given your secondary airport is BOS just because it is a major airport. I know even if you are something like 60miles from Halifax, the routing is still Boston even though Moncton is like a 2 hour drive away from Halifax and offers most the same abilities.
You are talking about an alternate in case there is bad weather or closure at the destination airport, but when something happens en route, the pilots want to know the location of the nearest runway that can handle their plane, they don't even think about maintenance or available equipment.
To echo and clarify several other posts above, the secondary or "alternate" airport is a NON-EMERGENCY arrival airport designated for a diversion if the primary arrival airport is unavailable. It has nothing to do with a diversion airport in an in-flight emergency.
Also:
The alternate is specifically related to the arrival airport, and would probably be something like Orlando, Ft. Lauderdale, or Tampa, in the case mentioned in the initial post. If you are in the middle of a ten-hour flight, your alternate is nowhere near where you are. The pilot does not even necessarily have to divert to the alternate airport -- he may divert to any airport he wishes, emergency or not, as long as he is legal in doing so (note: an actual emergency pretty much makes everything legal.). The reason for the alternate is to determine how much fuel the pilot must legally have on board, based on his calculations PRIOR to departure. Once airborne, there is no specific requirement to have a certain minimum amount of fuel remaining upon landing. But the flight plan filed prior to departure does require a certain minimum amount of fuel to be on board when the aircraft departs. Obviously, there are buffers built into the legal calculations that require more fuel on board than the pilot calculates to be the exact amount of fuel used for the entire flight, and the pilot will often add even more fuel at his discretion if he expects that he may need to maneuver around bad weather, lengthening the duration of the flight.
Alternates will often be odd, but they will include consideration for the airline's needs in servicing and repositioning the aircraft, as well as passenger handling. An emergency divert will be the closest suitable airport at the time the decision is made to divert, although some things that seem like they should be are not always emergencies, and a situation that requires a divert for mechanical failure or other reasons might not be to the nearest suitable airport, depending on the pilot's judgment and often (in the case of a non-imminent crash-type emergency) after consultation with a company dispatcher or maintenance specialist over the radio.
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