FlyerTalk Forums - View Single Post - The Consolidated "Interesting Things Heard on Channel 9" Thread [Merged]
Old Sep 24, 05, 7:29 pm
  #7  
PLTHOO
 
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Even Nerdier Additions

Originally Posted by spotwelder
Hi, to be even more nerdy...

The ATIS is often recorded on a navigation aid frequency such as the VOR used for holding. This means that the approaching aircraft will be able to receive the information without having to tune an extra radio for the task, but one that the crew would have to tune anyway.

The ATIS is usually updated twice an hour, commonly at minutes 20 and 50 past the hour. Special ATIS updates are recorded when certain weather changes meet the critieria published in ICAO Annex 3 and 11. Also, whenever runway directions are changed or other pertinent information changes. Some airports have departure ATIS messages and a separate arrival ATIS message.

It is usual for the approach controller to ensure that the inbound ATIS letter has been received correctly but an arriving aircraft may not have to confirm the ATIS letter to tower. Same for departures, ground usually do the check and leave tower free.

Just as a minor point, if the whole ATIS message has changed, and the changes are significant such that the controller wants the pilots to listen to it all, then the pilots will not "change" to the ATIS frequency. They will remain with radio box "A" with the air traffic controller and use box "B" to tune the ATIS (or the navigation aid).

PS, for the list of geeks, you could have added air traffic controllers and accident investigators

Happy landings

Spottie

The ATIS is often on a dedicated frequency specific to the airport, which aircraft will always check prior to calling for departure clearance when on the ground, or will check when on the arrival sequence. Whenever the aircraft calls for departure clearance, taxi clearnace, or switches to one of the many arrival frequencies on the approach, he will announce what ATIS they have by letter. Additionally, the letters used are usually divided into groups for many airports in the same area---such as SFO will have A-E, OAK will have F-I, etc.

The information usually dedicated to VOR frequencies is special weather announcements such as convective sigments (big weather) and just the ID info for the particular NAVAID.

As far as switching between radios, etc the heavy metal flown by the airlines will have multiple radios usually with the FO or Captain (whoever is not flying the leg) check the ATIS info during the arrival/pushback checklist.......not really a major concern on number of radios, etc.

The arriving aircraft will be switched between multiple arrival frequencies as they are passed into different sectors on the arrival, then on to an approach controller, and finally to tower when on the formal approach. Usually the tower controller will indicate the current ATIS because the flight crew most likely listened to it on the first part of the arrival (sometimes 30+ minutes ago). Sometimes in windy/stormy conditions you can also hear aircraft request wind checks and updated ATIS info so they have updated info.

The frequency of ATIS updates are completely dependent on the airfield....the big ones will sometimes have AWOS or ASOS (Automatic Weather Observation Station) and will be a male computer voice that transmits the most current observation on the field. Another fun part to identifying if the ATIS is current is listening to the time given in Zulu-----it sometimes takes time to catch on. Another interesting experience on CH.9 is listening to info and ATIS on international flights---Asis is always interesting.

If you are really an airport geek and want to know what runway is being used....the airports will frequently have 800 numbers or local numbers where you can call the ATIS or AWOS and hear it over the phone---so you can get an idea what conditions are when there. The info is usually found in Flightguide or Jepp approach charts.
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