Questions about real live ATC

I’ve been listening to a lot lately, and I’ve been hearing some things that I haven’t heard yet. Since there are quite a few pilots on this community, I thought that it would be a good idea to ask some questions that I have.
Here they are…

  1. What is the (I might spell it wrong) the altimeter? Example, i’ll hear an ATC giving an aircraft instructions, and they’ll say some thing like altimeter 29.38. What does this mean? And what is it’s purpose?

  2. When an aircraft contacts ground (out bound from an airport) they’ll say that they have “Information India” or “Information whiskey” I know that India means “I”, and whiskey means “W”, but what does “Information I” or “Information W” mean?

  3. This is kind of off topic, but what do IFR, and VFR stand for?

  4. What is the clearance frequency used for? And when is it used?

  5. What are the ramp frequencies used for, and when are they used?

I’ll Probably have more questions in the future, but that’s all I have for now!


Air pressure, helps the pilots really understand what’s their actual altitude.

“Information Alpha” etc means which ATIS information they have.

IFR means instrument flight rules while VFR means visual flight rules.




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@Tyler_Shelton may be able to explain the best, since he’s a real life ATC controller.

I won’t throw in my 2 cents, best leave it to those who do the job

It sounds like your fellow community members covered most of it, but I’ll clarify on a few! :)

1.) In simple terms, the altimeter calibrates the aircrafts altitude. As the barometric pressure changes, so does the altimeter. It is important the pilot has entered the correct values on their altimeter so they’re showing the correct altitude. Imagine how important this is when there is low visibility and the pilot believes he is still at 500ft, but in all actuality he is about to hit the ground.

2.) The “code” correlates to the current ATIS code. Prior to contacting ground or any receiving facility, the pilot will check the ATIS to find all pertinent and current information pertaining to that airfield. By reciting the correct ATIS code, the controller knows the aircraft has the most current ATIS that is being broadcasting.

3.) IFR and VFR simply describe the weather conditions and type of flight.

IFR weather: Ceiling below 1000ft/Visibility less than 3SM
VFR weather: Ceiling at or above 1000ft/Visibility at or above 3SM

Along with weather also comes how aircraft will classify themselves during the flight. If an aircraft is flying VFR, they’re proceeding to their destination visually, providing their own separation by the basic VFR means of “see and avoid”. If an aircraft is flying IFR, they’re receiving all instruction while airborne from ATC, to include vectors, altitudes, etc. The weather does not need to be IFR to be flying IFR.

4.) Clearance Delivery is used by pilots to receive important information from ATC prior to contacting ground. Before any flight the pilots must file a flight plan with ATC. ATC then scrutinizes the pilot requests and approves or amends the request based on traffic volumes, weather, destination conditions, etc. They then read the clearance to the pilot with information like route of flight, squawk, altitude to expect, departure frequency, and many others.

5.) Ramp frequencies are often times used to request a pushback at bigger airports where ground does not manage the individual ramps. A ramp controller will approve a pushback and taxi up to but not beyond the ramp hold line. From there the aircraft will request taxi instructions to a departure runway. Each airport is different. Where I work the ramp frequency is used to communicate with airfield operations vehicle and many other airfield agencies.

Feel free to continue the thread or PM if you ever have questions. Don’t forget and are your best friend for some of the basic aviation procedures. I’ve learned a lot there even outside of my formal training!


What different types of aircraft are considered “Heavy”, “Super”, and neither Heavy, nor Super?

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And everything else has no prefix?

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But, the “Medium” aircrafts don’t have the prefix “Medium” when talking on ATC, right?

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Ok! Thanks!

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Another Question:
I listen to KBOS a lot, and sometimes: while an aircraft is taxing, the aircraft will call the ATC and say “(Callsign) is approaching spot 7” or something like that. I don’t know if this is just a KBOS thing, or not, but can anyone tell me what this means?

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No medium announcements. Heavy is a wake vortex category - typically Boeing 757 and above.

Are you sure? I’ve heard the ATC refer to plenty of A330’s as “Heavy”
Are 767’s, and A330’s Heavy?

Sometimes pilots will only use the heavy prefix upon contacting a frequency, and then disregard it once the controller establishes contact. I hear it at Heathrow all the time.
I guess it just helps keep the messages as short as possible when busy. According to ICAO, both the A330 and 767 are heavy aircraft.

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This is a little off-topic, but isn’t it illegal for the public to listen to ATC in England?

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