OK.

"Mode C and Mode S transponders always send the altitude that would be indicated if 1013.2 hPa were set on the subscale which, at touchdown, will be QNE."

Wonder why they specify 'at touchdown?' QNE is QNE, whether it's at touchdown or any other phase of flight.

From MATS Part 1:

"During conditions of exceptionally low atmospheric pressure it is not possible to set QFE or QNH on some aircraft altimeters. In these circumstances an aerodrome or runway QNE can be requested. The QNE is the reading in feet on an altimeter with the sub-scale set to 1013.2 hPa when the aircraft is at aerodrome or touchdown elevation."

So to summarise for the less gifted eg me.....is an accurate readout of height agl available to ATC at the big boy airports?

At Luton it is, as long as you entered the QNH into the ATM properly!

Did wonder once why the inbound was below the level of the airfield at 2 miles. The pressure was high and the QNH had dropped out and de-faulted to 1013.

Wouldn't that give you height AMSL, not AGL ?

Might well be the same at some airports, but the last time I visited Luton I could have sworn it was on top of a hill. :O

Correct, it always shows the altitude above sea level. Fortunately as Luton is 500 ft up its an easy number to subtract for my poor brain!

Ok, now you are pissing me off. Any chance of an intelligent response?

No.

That's in answer to your original question, by the way:

I'll leave it to you to decide whether it constitutes an intelligent response. :O

To explain, ATC see height above sea level, not height above ground level. But then any self-respecting airfield controller is going to know the height AMSL of their airfield and the surrounding area, so as LB says, it's easy enough to do the calculation if necessary.

No ? Save your breath then. Goodbye.

Give me strength. :ugh:

I joined this forum because of the acars messages from af447. I have no affinity with commercial aviation. I found other things of interest. You have convinced me I have out stayed my welcome. Your strength is irrelevant. I wont be back on this forum.

Bet he never flies from Luton again...