Q15, from the same FAQ (I'm a slow reader
):
Q15. How should I file a plan for a flight landing outside the UK FIR – do I need an EET for the FIR boundary? And will the system recognise an ICAO airport code outside the UK FIR?
A15. Yes, you need to use an EET for the FIR boundary otherwise the system will not recognise that the airfield you wish to fly to is outside the UK and will therefore reject your flight plan for an unknown location.
For example, the route field must contain an FIR crossing point ie 5127N00038W and field 18 must contain the EET to that point ie EET/5127N00038W0026
The system being used by Atlas does not accept all the options for flight planning detailed in CAP694 (The UK Flight planning Guide) and will only accept an 11 character lat/long or a range and bearing from a three letter beacon. So, a five character boundary point for example cannot be used.