ATIS - Range

[fireflybob]

Can anyone tell me to what range and or altitude ATIS broadcasts are protected from adjacent stations?

Thanks for any help.

[hvogt]

ATIS is a VHF transmission. You can calculate the range as follows.

Range in NM = SQR(altitude) * 1.23

or

range in NM = SQR(FL) * 12

[fireflybob]

No that is not the question I am asking - sorry if it was not clear!

If I am flying (say) at 30,000 ft 100 nm from the station will I be within range of another ATIS broadcast on the same frequency which will interfere?

In other words at what maximum range and altitude am I guaranteed NOT to get interference from another ATIS broadcast?

[Spitoon]

IIRC the protected range of a transmitter is specified on the WT Act licence and/or ANO approval for the service being provided. For most comms services and navaids the DOC is usually shown in the AIP but this does not seem to be the case for ATIS. I think you will find each is different - partly because a smaller DOC may have to be accepted to get the frequency assignment. I suspect you'll be surprised at how small some are - at one international airport I worked at I think it was 15000ft and 25 miles although most crews would be able to report receiving it at 100+ miles out. All this is for an arrival ATIS - for a departure ATIS it's typically surface and 2 miles.

[BOAC]

Fireflybob- if you are experiencing ATIS 'blocking' please join me in contacting 'CHIRP' (http://www.chirp.co.uk/main/EmailReport/SubmitReport.asp) as we have recently managed to get the MAN ATIS put out on the 113.55 VOR as well to help. They have been most helpful.

In my opinion the recent frequency 'shuffle' has been very badly handled, resulting in several frequency 'overlays' which interfere with the need to brief arrivals in time IAW SOPs.

[chevvron]

Standard DOC for an arrival ATIS is 60nm/60,000ft; departure ATIS is a lot less, usually something like 10nm/10,000ft although most can't be heard at this range/height

[fireflybob]

Thanks for the replies!

chevvron, have you got a reference for those figures?

BOAC, the problem is with EMA ATIS which is same freq as CDG so cannot get the wx and runway till halfway down descent. It's not so much the wx thats the problem but the Rw in use when the wind could favour either runway which means less time for monitoring during descent if we have to rebrief and reprogram the FMC etc in accordance with company procedures.

[BOAC]

bob - you'll find tnose figures in the AIP for the relevant airfield if nowhere else, and ref EMA - that is what post#5 is all about! Contact CHIRP.

Les Francais have a habit of exceeding DOC output, going back (in my time, anyway) to the time when the LGW GE NDB was swamped by a Frenchie beacon miles away - and a quick handslap from ICAO (nudged by CHIRP again:ok: ) helped the Frenchies to find the volume control:)