It's around 11:00 PM, and you need to get home. Your Piper Archer is IFR legal, but your IFR currency has lapsed. The non-towered airport you are departing from has mountains surrounding it, and you've never flown out of it at night before.
You find yourself pondering Instrument Departure Procedures. As you probably already know, these come in two flavors.
1. Obstacle departure procedures (ODPs)
Per the AIM, ODPs provide obstacle clearance "via the least onerous route from the terminal area to the appropriate en route structure." In other words, awesome! You have a way to get out of town without hitting something protruding from the ground.
2. Standard instrument departures (SIDs)
SIDs, on the other hand, are "air traffic control (ATC) procedures printed for pilot/controller use in graphic form to provide obstruction clearance and a transition from the terminal area to the appropriate en route structure." They're another option.
Unfortunately, you have few options tonight because of your lack of IFR currency. Or do you?
ODPs may be flown without ATC permission unless another SID is assigned. But that's only for IFR flights. Tonight, you'll be VFR all the way, which precludes using a SID.
But those words about being able to fly an ODP without requiring ATC permission start to gnaw at you because maybe this will be a safe way to exit the area, which is surrounded by obstacles.
So, you read the fine print on the ODP for your airport and see the letters VCOA. Digging back further into your IFR brain, you remember what that means: visual climb over airport, a series of climbing turns performed in safe proximity of the airport to an "at-or-above altitude," after which a pilot may proceed in IMC to the en route structure, "route to a fix that may include a climb-in-holding pattern to reach the MEA/MIA for the en route portion of their IFR flight."
And there's that IFR word again... but it's an ODP, and the nagging word keeps nagging. "ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC," followed by another passage in the AIM that says "Pilots operating under 14 CFR Part 91 are strongly encouraged to file and fly a DP at night, during marginal Visual Meteorological Conditions (VMC) and Instrument Meteorological Conditions (IMC), when one is available."