Flowman,
Thanks for your input.
LHR does not have a MINLINEUP. If it does, then I've not heard of it. Our taxi time is 16 minutes, apart from one runway where it's twenty minutes.
Scenario: XYZ123 calls at 1000 for a 1005 slot. He's not going to make it. We use the DSM to get a new slot via a DLY msg (entering in the new EOBT time of, 1005, which based on a taxi time of 16 minutes should get a slot no earlier than 1005 + 16 = 1021). The new slot is 1100. We send a REA msg. At 1015, a new slot comes through with 1025, which is not going to work if it's anything other than very quiet.
This happens so so often. Many of us now don't bother sending REAs if the slot is within 40 minutes, because we fear the improved slot will come through which leaves the a/c no chance of making it.
Is this only because the AFTN link is slow?