Just as all IFR flights require an alternate airport when the destination falls below certain weather requirements, commercial and charter operations must specify a departure alternate in certain cases.
In many cases, our departure alternate would be a return to the same airport we just left.
There might be no perfect option: There's a good departure alternate 20 minutes away, but opposite your planned direction of flight.
It's also your call as to when you bother with a departure alternate at all.
The next step after getting a plan for a departure alternate is deciding how much to prepare the cockpit for executing that plan.
As airports continue to be turned into shopping malls, selecting a departure alternate is becoming more important and challenging, especially in area where large bodies of water or mountains mean no airports for a long ways around half the compass, and a large area of fog or line of thunderstorms could rule out airports that otherwise be available.
As sure as Murphy's Law exists--and there are those who claim Murphy was an optimist--the time you do boogie off into the clag with no usable departure alternate will be when the forecast thin, broken layer will become 4000 feet of overcast with more ice in it than your airplane can climb through.
There is no provision to load an approach procedure for your departure airport or a departure alternate
, nor can you load a destination alternate approach.
Making a safe diversion to a departure alternate airport requires organization.
But assuming the pilot was qualified and the airplane capable of shedding the ice it was encountering, your next thought might be a conscious decision to focus on the back-up instrumentation when responding to the attitude indictor failure, and to execute a known plan to divert back to the departure airport or to a nearby departure alternate.
If you do elect a departure alternate
, share it with ATC by noting it in the flight plan remarks.
If weather is above minimums," Dewhirst suggests, "set up for the approach" for the departure airport or a nearby departure alternate