ATC question

sigmanu499

New Member
Some time ago I was on a United flight flying from MEX to LAX. The cool thing about UAL is that you can listen to ATC on the in flight entertainment system. In the middle of the flight the pilots started asking Mazatlan center to deveate because of weather. ATC never responded, and the pilots keep on calling. After a few minutes the pilots just said, they were turning, with out any approval from ATC. Is this legal? I am insturment rated and have not heard about this. Well, obviously it is legal but why is it legal? Do the pilots just use TCAS to see other traffic or what?
 

seagull

Well-Known Member
Good point, in many parts of the world it's not a "center" like the U.S. In fact, most of the world you're talking to "radio" or "control", the former has no radar services, but limited air traffic services, the latter generally does have radar, but they may or may not actually use it for ATC purposes.

In any event, it's not unusual for the scenario you describe to occur. Technically it is using emergency authority, but in actual practice nobody worries about it.
 

sigmanu499

New Member
Thanks, I found it is actualy a center. I went online and found a web page done my the Mexican ATC union and it showed their facilities. They have 4 centers(Monterrey, Mazatlan, Mexico and Merida.) In reality the pictures looked more modern then in the US.

So, they pilots can fly around storms with out ATC approval. If this done in the US too? How, do they besure not to have a problem with other traffic?
 

seagull

Well-Known Member
Let's not misconstrue here. We are supposed to get a clearance before deviating, and so deviating without
a clearance is technically using our emergency authority. Having stated that, in actual practice
pilots will often make small deviations without a clearance, such that the turn won't be enough to be seen
on the radar anyway, or, in other countries where there is no radar at all.
 

triplec76

Well-Known Member
Its really good that you are asking questions and then thinking of questions to answer from the answers given to you. I drove my instructor nuts with this stuff for a long time, until I started realizing that there are many questions in aviation that cant be answered in a "black and white" way.

I think it would really depend on how much you need to deviate for weather. If its a small 10 or 20 degree turn for a smaller towering cumulus cloud, then it probably wouldnt present much of a problem (to answer your conflicting traffic question, if you can see the weather you need to avoid, you can probably see and avoid other traffic in your vacinity). If you need to deviate a hundred miles off course for weather (without ATC approval, in the US), then you will most likely have some explaining to do.

Bottom line is, in an emergency situation, do what it takes for the safety of the passengers, crew and aircraft.

EDIT: I also wanted to add that in the US (Chicago Center specifically, since most of my Center experience is with them), you will almost always get your deviation for weather avoidance. Even on the busiest days, Ive heard them approve every request they got. Although 15 minutes later they shut down their airspace to any more incoming traffic and placed everyone outside in a hold. I heard quite a few upset corporate pilots that day......
 

RiddlePilot

New Member
Seriously. When it comes down to either flying into a thunderstorm or deviating from a clearance when ATC isn't responding, the answer should be clear. You're PIC for a reason.
 
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