The Alternates group on the Plan screen allows you to optionally specify up to four alternate airports for the flight in question.
The Alternates group is extendable to reveal a Route dropdown and Maximum Flight Level (MFL) field for each alternate.
The alternate dropdown for each alternate contains all alternates available for the destination.
You can enter an alternate into the box that is not offered by the dropdown list, but the inputted alternate station will not be populated in the dropdown list. This is also true for a blank alternate field (no alternate).
When you enter an additional alternate in the alternate dropdown that is not originally from the list and then leave the focus, the entry is validated for a valid ICAO. If it is valid, the route choices from destination to this alternate (if they exist) are populated in the route dropdown list. The maximum flight level box remains empty.
If you blank out an alternate from the alternate dropdown, the Route dropdown and Maximum Flight Level field are reset to empty.
Among the four alternates, if there are any blank alternates, the non-blank alternates are, upon compute, moved up so that any blank alternates are at the end of the list.
The order of the alternates is the same as they are listed in FOMS Menu 110 (Airport Alternates program).
When you manually change the order of the alternate by setting the station name in the alternate dropdown, the Route choice dropdown and Maximum Flight Level field will move along.
Let’s assume that initially you made route choices and maximum flight levels for KSJC and KSMF.
Now, you want to trade the position of the two alternates that you set before. Change the 1st alternate from KSJC to KSMF by picking from the alternate dropdown.
Change the 2nd alternate from KSMF to KSJC by picking from the alternate dropdown.
As seen here, when changing alternate station names, the value choices of route choice and MFL will go along with it if they have been input under this alternate station. This behavior will be the same for user added alternate.
The fields in the Alternates group are described below.