DAL191 wrote on Dec 12^th, 2009 at 1:15pm:

With enough trying and patience I haqe been able to enter, activate and execute almost all flight plans. NATW and the lastest one NATX have me completely stumped.  It makes no difference if I Line Select it to the left or right side, I still receive NOT IN DATA BASE. The navigation data base which came with the 767-300 Base is the one dated March-April 2009. Does anyone know what might be the problem? Thank you.

Yes.  You cannot enter NATA NATB NATC or NAT-anything into the FMC.  You need to go to the referenced sites that publish what the current tracks (NATs) are for the day.

On that site, it will say:
A PIKIL 57/20 58/30 59/40 58/50 PORGY HO
EAST LVLS NIL
WEST LVLS 310 320 330 340 350 360 370 380 390
(EAST LVLS NIL with the altitudes only listed in the WEST LVLS means that this NAT is westbound only)

This means that NATA is a current option, and is defined by the waypoints (what you enter into the FMC) PIKIL, Lat/Lon 57/20, 58/30, 59/40, 58/50, waypoint PORGY, and NDB HO.

Entrys to your FMC should be as follows:
Beginning of route up to NATx (where x is whatever letter is in the plan)
PIKIL
58/30
59/40
58/50
PORGY
HO
End of route after NATx

Be careful.  Sometimes plans found online (this one for today's KLM652) will read like this:
JFK PUT TUSKY N63B VIXUN NATT 53/30 NATT DOGAL NATT BABAN UN544 DEVOL

You see NATT in several places.  Check the site for the current NATs and you'll see this:
T VIXUN LOGSU 49/50 51/40 53/30 54/20 DOGAL BABAN
EAST LVLS 320 330 340 350 360 370 380 390 400
WEST LVLS NIL

As you can see, the NATT placeholder only omits a couple waypoints in the plan.  Basically, if you see a plan with several instances of a NAT, ignore the middle fixes and insert the NAT from the first instance to the last instance.  It'll all match up in the end.

Kyle