look at the key on the bottom of the map for D216 and it tells you!
In operational hours call salisbury oprerations on 122.75
I can't find that bit....and last I heard, Hereford was not near Salisbury! (I suspect you're refering to 126
)
I just checked 216 on the AIS web site and there is not much info about it. I suspect it is something to do with the SAS so probably not a good idea to bust it. Many of the ones down south have a phone number which you can phone beforehand to check whether they are hot or cold....if cold you can go right through them. Otherwise there is a freq you can call for a crossing service or info service....but this mysterious 216 doesn't seem to have much info about it...:
Definition
Country code EG
Type Danger
Designation 216
Multi Code
Name CREDENHILL
Lower Limit
Unit Indicator Lower Limit
Upper Limit
Unit Indicator Upper Limit
Area Code EUR
Controlling Agency
Activation Information
Time Code
NOTAM
Time Indicator
Description
Time of Operation 1
Time of Operation 2
Time of Operation 3
Time of Operation 4
Time of Operation 5
Time of Operation 6
Time of Operation 7
So sorry, can't be much help.