Thanks for that Tinstaafl
You can find out how the 4000 ft filtering works
here
Basically on a Narrow Route brief from departure a/d to first waypoint and from last waypoint to arrival a/d you get everything from surface to FL120. For the remainder of the route you get +/- 4000 ft from the entered FL.
If you can't get what you want by manipulating the waypoints you will need to use the Route Briefing, which enables you to set upper and lower FL's but will give you the entire FIR.
As mere pilots we are not allowed to see the raw data from which the briefings are derived. However if you go to
the US Department of Defense NOTAM site and select Text Type "Raw" and put EGTT in as the ICAO identifier you will get the raw data, for example:-
B0172/03 NOTAMN
Q) EGTT/QAZCD/IV/NBO/E/000/020/5113N00136W005
A) EGTT
B) 0304190800
C) 0304271600
D) APR 19 20 AND 27 0800-1600
E) THRUXTON ATZ CLOSED DUE AD UNLICENCED
In the line starting Q) (the famous "Q Line") 000/020 is the effective height band as FL (sfc to 2000 ft)
Also locked in there is all sorts of information that would allow programs like NotamPlot and NotamPro to be really effective. You can find a Q Line decode
here
We're still lobbying to get this info released. NATS/AIS have no objection it's the CAA who are delaying a decision.
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24 Hrs seems to be the consensus for validity
Mike