TM  1-1520-240-10 3-3-22            (7) Observe the CDU display. The display indi- cated the GPS test mode status as of one of the follow- ing. GPS TEST: IN PROCESS GPS TEST: NOT RUN GPS TEST: PASSED GPS TEST: FAILED g.  Procedure   for   Displaying   GPS   Key   and  GPS Space Vehicle Status. (1) Set the DISPLAY switch to XTK/TKE/KEY. (2) Set the MODE switch to LAT/LONG (MGRS may also be used). (3) The display indicates GPS daily key status, time remaining on the currently entered keys and how many Space Vehicles (SV) are currently being used by the GPS. KEY STATUS TIME REMARKS DK OK Days or hours still available on key GPS daily key in use and verified. DK NO * No GPS daily key available DK IN * GPS daily key available but not verified. 3-3-50.  Preflight Procedures. a.  Data Required Prior to DGNS Turn-on The following initial data must be entered by the pilot after system turn-on and initialization, unless previously en- tered data is satisfactory: Datums  of  operation,  when  using  MGRS  coordinates. This data may be part of the data load if preprogrammed. In combined or GPS mode the GPS provides preset posi- tion. If Doppler only mode is selected MGRS coordinates of present position - zone area, easting and northing; latitude/longitude coordinates may also be used to input present position. This data may be part of the data load if preprogrammed. Variation of present position to the nearest one-tenth of a degree. Coordinates of desired destinations 00 through 99. It is not necessary to enter all destinations in the same coor- dinate system. This data may be part of the data load if preprogrammed. Variation of destinations to the nearest one-tenth of a degree. Crypto-Key variables necessary to enable the GPS re- ceiver to operate in Y code are entered via remote fill data only and not via the CDU keyboard. NOTE Destinations   are   entered   manually   when steering information is required to a destina- tion that was not in the set of data loaded via the data loader, or it is desired to update pres- ent position by overflying a destination, or a present position variation computation is de- sired. (See CDU operation). If a present posi- tion  variation  update  is  desired,  destination variation must be entered. The operator may enter one or more destination variations; it is not necessary for all destinations to have as- sociated variations entered and also not nec- essary to enter all destinations in any case, but variations must be entered AFTER des- tination coordinates are entered. The Doppler outputs true heading and accepts magnetic heading from gyromagnetic heading reference. If accu- rate magnetic variations are not applied, then navigation accuracy will be affected. b.  System Initialization (1) Enter GPS mode “M”. NOTE You must select GPS mode “M” during initial- ization. If “Y” mode is selected before Crypto- Key variables are loaded the system will lock- up forever. You must select GPS mode “M” during initial- ization. If “Y” mode is selected before Crypto- Key variables are loaded the system will lock- up forever. (2) Perform self test (para d. below). (3) Perform download (para c. below) of data loader cartridge if necessary, or manually enter datum, destinations, magnetic variations, and present position (para. f or g. below). (4) Load   Crypto-Key   variables   (unless   pre- viously loaded and still valid) necessary for operation of the GPS in Y mode. NOTE It is necessary to wait at least 12 minutes for key validation when new keys have been en- tered, or collection of almanac data when set has  no  previous  almanac  data.  During  this time the GPS operating mode must be M and uninterrupted. After this time the GPS operat- ing mode may be switched to Y. Observe the GPS Key status and number of SVs tracked after switching to Y mode. If the SV number goes to zero repeat this procedure. The Key status  shall  switch  from  DK  IN  to  DK  OK sometime during the 12 minutes. (5) Check datum of operation, if MGRS is being used.