As a bystander watching with interest can I make a quick comment.
Fireflybob said:
If I am inbound (on a Flight Level) I will be passed QNH when cleared to descend to an altitude and this ... requires a mandatory readback
In this circumstance I assume that you would have already listened to the current ATIS, containing the QNH, prior to contacting the APP controller; you may even have been asked to indicate which version you are working with upon first contact.
No explicit QNH readback would be required until you are instructed to descend to altitude since you will not need to
USE the current QNH information until that time.
Jumbo Driver said:
...why we are asked to acknowledge both the ATIS letter and also to repeat the QNH, which is itself an essential and integral part of the ATIS that we are implicitly acknowledging as having copied and understood
I agree that you are acknowledging receipt of the current ATIS, as is the arriving pilot contacting an Approach unit for the first time.
However, controllers need to be assured that departures are working to the same datum as other inbound traffic that has been required to readback the QNH upon descent to altitude.
If you will; you are 'climbing' to field elevation and need to be informed and acknowledge explicit receipt of that information.
Both situations attempt to trap human factor errors (1012/1021) on the communication side.
Jumbo Driver said:
Only in the case where QNH does change from the acknowledged ATIS letter should it need to be mentioned (by you) - and then, of course, it will be read back.
As another poster pointed out; updates once you are talking to GMC or AIR would be transmitted as a broadcast, trusting that you are concentrating upon the job at hand.
Sorry to intrude.
