Some confusion exists as to what a pilot is supposed to do when a “Cleared as Filed” clearance is issued by ATC from an airport, but no Departure Procedure (DP) is assigned in the clearance. ATC at some airports may not issue a Departure Procedure as part of the clearance.
However, the pilot is expected to determine a way to safely depart the airport and join the enroute structure defined in the ATC clearance (or flight plan if “cleared as filed”). One way to accomplish this—and normally the safest way in IMC—is to fly the appropriate published Departure Procedure. If a textual DP has been established for the airport, it will be found in the front of the U.S. Terminal Procedures Publication under TAKE-OFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES. (Digital procedures are available at http://aeronav.faa.gov/index.asp?xml=aeronav/applications/d_tpp.)
If there is more than one Departure Procedure, the pilot should fly the one most appropriate to the route of flight. Absent specific departure instructions from ATC, the pilot may also elect to “climb on course,” but only if he/she has determined that adequate terrain and/or obstruction clearance can be maintained until reaching the minimum IFR altitude (MIA), or minimum enroute altitude (MEA.)
Weather conditions permitting, a pilot may request a “VFR climb” for the initial portion of the flight. While this will often expedite your departure clearance, note that this provision applies only to the vertical aspect of the ATC IFR clearance. The pilot is expected to follow the ground track as assigned, overflying the fixes or airways stated in the clearance. A “VFR climb” is not permission to deviate from the cleared route.
As part of your IFR preflight planning always familiarize yourself with the airport written and graphic departure procedures. You may not always be assigned one by ATC but you are expected to determine a safe departure method—a published DP is one way to accomplish that.
Following a published DP is also appropriate if you depart VFR expecting to pick up an IFR clearance en route, especially at night when terrain features, such as mountains, are not clearly visible – just remember to stay VFR until you have your IFR clearance.