The briefer sends a flight plan to the host computer at the  ARTCC (Center). After processing the flight plan, the  computer sends flight strips to the tower, to the radar facility  that handles the departure route, and to the Center controller  whose sector the flight first enters.  Figure 2-6  shows a typical  strip. These strips are delivered approximately 30 minutes  prior to the proposed departure time. Strips are delivered to  en route facilities 30 minutes before the flight is expected to  enter their airspace. If a flight plan is not opened, it will “time  out” 2 hours after the proposed departure time. When departing an airport in Class G airspace, a pilot receives  an IFR clearance from the FSS by radio or telephone. It  contains either a clearance void time, in which case an aircraft  must be airborne prior to that time, or a release time. Pilots  should not take off prior to the release time. Pilots can help  the controller by stating how soon they expect to be airborne.  If the void time is, for example, 10 minutes past the hour and  an aircraft is airborne at exactly 10 minutes past the hour,  the clearance is void—a pilot must take off prior to the void  time. A specific void time may be requested when filing a  flight plan. Several controllers in the tower cab are involved in handling  an instrument flight. Where there is a dedicated clearance  delivery position, that frequency is found in the A/FD and  on the instrument approach chart for the departure airport.  Where there is no clearance delivery position, the ground  controller performs this function. At the busiest airports, pre- taxi clearance is required; the frequency for pre-taxi clearance  can be found in the A/FD. Taxi clearance should be requested  not more than 10 minutes before proposed taxi time. It is recommended that pilots read their IFR clearance back to  the clearance delivery controller. Instrument clearances can  be overwhelming when attempting to copy them verbatim,  but they follow a format that allows a pilot to be prepared  when responding “Ready to copy.” The format is: clearance  limit (usually the destination airport); route, including any  departure procedure; initial altitude; frequency (for departure  The last clearance received supersedes all previous clearances.  For example, if the DP says “Climb and maintain 2,000 feet,  expect higher in 6 miles,” but upon contacting the departure  controller a new clearance is received: “Climb and maintain  8,000 feet,” the 2,000 feet restriction has been canceled. This  rule applies in both terminal and Center airspace. Pilots are required to have either the text of a departure  procedure (DP) or a graphic representation (if one is  available), and should review it before accepting a clearance.  This is another reason to find out ahead of time which DP is  in use. If the DP includes an altitude or a departure control  frequency, those items are not included in the clearance. As the controller reads the clearance, check it against what  is already written down; if there is a change, draw a line  through that item and write in the changed item. Chances  are the changes are minimal, and most of the clearance is  copied before keying the microphone. Still, it is worthwhile  to develop clearance shorthand to decrease the verbiage that  must be copied (see Appendix 1). Assume an IFR flight plan has been filed from Seattle,  Washington to Sacramento, California via V-23 at 7,000  feet. Traffic is taking off to the north from Seattle-Tacoma  (Sea-Tac) airport and, by monitoring the clearance delivery  frequency, a pilot can determine the departure procedure  being assigned to southbound flights. The clearance limit  is the destination airport, so write “SAC” after the letter C.  Write “SEATTLE TWO – V23” after R for Route because  departure control issued this departure to other flights. Write  “70” after the A, the departure control frequency printed on  the approach charts for Sea-Tac after F, and leave the space  after the letter T blank—the transponder code is generated by  computer and can seldom be determined in advance. Then,  call clearance delivery and report “Ready to copy.” control); and transponder code. With the exception of the  transponder code, a pilot knows most of these items before  engine start. One technique for clearance copying is writing  C-R-A-F-T. ATC Towers Altitude—37,000 feet  Destination—Minneapolis  Departure point—San Diego Call sign—Northwest 196 Figure 2-6.  Flight strip. 2-5