# How to interpret ATIS ground communication

Let's say I have the following ground communication from ATIS:

> Gillespie tower information Charlie,
> Time 1547 zulu, wind 250 at 20
> Visibility 7, Ceiling 1000 overcast
> Temperature 18 / Dewpoint 14
> Altimeter 30.90
> Localizer Delta approach in use, landing and departing runway 27R and 27L.
> Advice on initial contact, you have information Charlie


I more or less important the important bits but I don't understand the nuances.

What I understand:

1. "Charlie" means I have to listen to the weather report for time-period Charlie (since there are alpha, bravo, charlie, delta weather reports, corresponding to 4 time periods during the day).
2. 1747 means 5:47 pm.
3. Wind at 270 degrees at 10 mph
4. Temperature 18 is 18 degrees Celsius
5. Set altimeter to 30.01 as that is the pressure altitude on the field
6. "Advice on initial contact, you have information charlie" means when I talk to ground for requesting taxi to runway or something, I notify ground that I have "information charlie"

Questions:

1. What is the relation between zulu time and PDT time. Given zulu is universal, how do I convert between local time zones?
2. With the visibility numbers, is higher better or worse?
3. With dewpoint numbers, is higher better or worse?
4. What is localizer delta approach in use? Is "localizer delta" the name of some kind of jet?
5. What does it mean when it says "landing and departing runway 27R and 27L?

Some of these questions might be really obvious to most, but I am a new student pilot in training for my PPL, so it's still a bit new to me.

• This may be useful for many of your questions: aviation.stackexchange.com/questions/25231/… Jul 10, 2021 at 5:18
• @BillLynch I must have missed that question. I'll update my post Jul 10, 2021 at 6:16

Understanding:

1. The ATIS letter codes state which ‘version’ of the ATIS you are listening to, which can be communicated in a simple way to ensure you are up to date. The letter / version advances when either a significant change occurs in the weather or routinely as per the airfield regulations (such as every hour). ATC can ask if you’ve copied information C and you respond yes or no, simple.

2. Yes. 24h clock.

3. Nautical miles per hour. Not statute (regular) miles per hour.

4. Yes

5. That is the altimeter setting for correct density altitude at your field. Pressure altitude would be from an altimeter setting of 29.92.

6. Correct, as per 1.

Questions:

1. UTC is PDT + 7. Google it.

2. Visibility is measured in statute (“regular”) miles in North America and metres everywhere else. Bigger is better and you will learn what the minimum required visibility is for visual flight.

3. Dew point is a temperature measured in degrees Celsius. We can use this to predict a rough altitude where cloud will start to form and also for performance considerations as linked by other members. The number itself is important (in more than just a “bigger or smaller is better” way) but the gap between it and the OAT is also important. You should learn about this on your road to your PPL

4. This message is stating the primary instrument approach that is in use. A localiser is a type of instrument approach and delta is the variant of it. These can be found in the terminal approach plates for the airfield. You’ll learn about these when you start your instrument rating training.

5. Some airports have preferential runways for departure and arrival to help traffic flow or to avoid certain parts of the airspace for noise or terrain reasons. So to aid forward planning, the ATIS will tell you which runways to expect for departure and arrival. In this case both 27L and 27R are being used for both departures and arrivals.

• Of interest, the -D suffix in the name of the LOC-D approach at SEE indicates that it is a circling-only approach (no straight-in minima are published). Given that the suffix is -D one would expect there to be at least three other such circling-only approaches to SEE (A, B, and C), but in fact the LOC-D is the only one. Strange. Jul 10, 2021 at 20:01