There is no U.S. requirement to file the aircraft Mode S Code in Item 18. 6. SELCAL code (Item 18 SEL/) (a) Flights with HF radio and Selective Calling capability should include their 4-letter SELCAL code. Per the U.S. AIP, GEN 3.4, Paragraph 9, Selective Calling System (SELCAL) Facilities Available. (b) The SELCAL is a communication system that permits the selective calling of individual aircraft over radio-telephone channels from the ground station to properly equipped aircraft, to eliminate the need for the flight crew to constantly monitor the frequency in use. EXAMPLE- SEL/CLEF 7. Performance Category (Item 18 PER/) Include the appropriate single-letter Aircraft Approach Category as defined in the Pilot/Controller Glossary. EXAMPLE- PER/A TBL 4-20 Flight Routing Information Item International Flight Plan (FAA Form 7233-4) Equivalent Item on Domestic U.S. Requirements Domestic Flight Plan (FAA Form 7233-1) Departure Airport Item 13 Required Item 2 Departure Time Item 13 Required Item 1 Cruise Speed Item 15 Required Requested Altitude Item 15 Required Item 3 Route Item 15 Required Delay En Route Item 15, Item 18 DLE/ Required Destination Airport Item 16 Required Item 11 Total Estimated Elapsed Time Item 16 Required Item Item 16 Item 18 ALTN/ (Destination Alternate). If necessary RALT/ (En route Alternate); TALT/ No need to file for domestic U.S. flight Alternate Airport (Take-off Alternate) Estimated Elapsed Times Item 18 EET/ Include when filing flight plan with center other than departure center f. Instructions for Flight Routing Items 1. Departure Airport (Item 13, Item 18 DEP/) (a) Enter the departure airport. The airport should be identified using the four-letter location identifier from FAA Order JO 7350.9, Location Identifiers, or from ICAO Document 7910. FSS and FAA contracted flight plan filing services will allow up to 11 characters in the departure field. This will permit entry of non-ICAO identifier airports, and other fixes such as an intersection, fix/radial/distance, and latitude/longitude coordinates. Other electronic filing services may require a different format. NOTE- While user interfaces for flight plan filing are not specified, all flight plan filing services must adhere to the appropriate Interface Control Document upon transmission of the flight plan to the control facility. (b) When the intended departure airport (Item 13) is outside of domestic U.S. airspace, or if using the paper version of FAA Form 7233-4, or DoD equivalent, if the chosen flight plan filing service does not allow FAA Form 7233-4 - International Flight Plan Appendix 4-17