What are the US flight planning regulations for an alternate airport?
It is important to point out that what follows only applies to flying under §91. Operations under §135 have a different set of requirements for alternates than those specified here in §91.169. Your question includes the general-aviation tag, which is poorly defined (at no fault of your own); the tag description given on this site includes all civil aviation other than §121 airline flights, but many definitions exclude charter, or even all §135 flying. In what follows I will assume flight operations conducted exclusively under §91.

Q1:
Yes, that is correct. An alternate is always required on the flight plan unless—among other things—the first airport of intended landing has an instrument approach prescribed under §97 or otherwise authorized.
Weather conditions also determine that exception.

Q2:
This is mostly true, but needs some corrections and clarifications.

There is no requirement for the airport to have weather reporting or forecast based at or provided specifically for that airport. The regulation merely requires &quot;appropriate weather reports or weather forecasts&quot;. This could include weather information such as Area Forecasts or even TAFs or METARS for nearby airports.

Yes, this is accurate.

Yes, this is true when understood within the programing–type flowchart logic you use. However, just to be clear, lack of an IAP alone does not disqualify the airport as an alternate—see #2 and §91.169(c)(2).

No, not necessarily. AIM 1-1-18(b)(5)(c) clarifies that operators with non-WAAS equipped GPS systems can plan to use a GPS approach at either their destination or the alternate, but not both:



(c) For flight planning purposes, TSO­C129() and TSO­C196()-equipped users (GPS users) whose navigation systems have fault detection and exclusion (FDE) capability, who perform a preflight RAIM prediction for the approach integrity at the airport where the RNAV (GPS) approach will be flown, and have proper knowledge and any required training and/or approval to conduct a GPS-­based IAP, may file based on a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the alternate airport, pilots may plan for:
(1) Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
(2) LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approved barometric vertical navigation (baro­VNAV) equipment;
(3) RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baro­VNAV equipment and the pilot has verified required navigation performance (RNP) availability through an approved prediction program.

Note: TSO­C129 and TSO­C196 are the non-WAAS TSOs (as opposed to the WAAS TSOs: TSO-C145 and TSO-C146)

Yes, this is seen in AIM 1-1-18(b)(3)(b):


Ground-based facilities necessary for these routes must be operational.


Yes, this is true.

Yes, though I would say equal to or greater.



Q3:
Yes, the filed alternate—and the approach used to qualify it—are for legal filing purposes. In the actual flight, another appropriate approach, deviation airport, or approach at the deviation airport can be selected as needed.