Figured Out Why I Can't Hear The Planes

[CanesFan95]

So I guess sometimes the tower transmits on more than 1 frequency at a time, but the pilots only talk back on one of those frequencies. Never realized this. Why on Earth would they do that? For the longest time, I've sat there bewildered wondering what the heck is wrong with the dang scanner?

 

[alcahuete]

They do that when positions are combined. If you're speaking about the tower, Ground combines with Local, Clearance Delivery (if there is one) combines with Ground. If there are multiple Local positions, they will often combine up to one, etc. This is especially true at night.

 

[scan18]

It is very common here in Hawaii where HCF center may have one controller covering 3 or 4 sectors at night when there is little traffic. So that controller will transmit on multiple frequencies covering those sectors. But obviously the aircraft will only be transmitting on one frequency for whatever sector they are in. That is why sometimes you will hear the controller say something like“change to my frequency 124.1” to the pilot when they cross into another sector, which means the controller is covering that sector also. And it lets the pilot know they will be speaking to the same person when they switch to the new freq.

 

[RichardKramer]

Here at Reading, PA airport the tower has a VHF/UHF freq; VHF 119.900 for civilian/military; UHF 288.300 for military. The controller will usually key up both VHF/UHF freqs; if you sit on the UHF freq you won't hear the civilian pilots talk back; same for a military aircraft on the UHF freq; if you sit on the VHF freq you won't hear the mil pilot talk back. This can even happen when you're scanning, you may miss one or the other pilots talk back depending what freq your scanner stops on.

 

[popnokick]

Here at Reading, PA airport the tower has a VHF/UHF freq; VHF 119.900 for civilian/military; UHF 288.300 for military. The controller will usually key up both VHF/UHF freqs; if you sit on the UHF freq you won't hear the civilian pilots talk back; same for a military aircraft on the UHF freq; if you sit on the VHF freq you won't hear the mil pilot talk back. This can even happen when you're scanning, you may miss one or the other pilots talk back depending what freq your scanner stops on.

I've observed this exactly as RichardKramer describes it when listening to NYC, Philadelphia, and Baltimore-Washington area airports / ATC.

 

[CanesFan95]

This was annoying for a long time. So this sounds like a dispatcher doing a multi-select on a trunking system. The risk is multi-tasking and you get 2+ pilots tryina talk to you at the same time on different frequencies. Then the tower person misses something important.

 

[Jay911]

Not anywhere near as much a problem as you think. I have done this in my emergency services dispatch job for the past 20+ years, and it's as I was trained by people who had 20 years in when I was the greenest rookie in the building. I'm also a firefighter, and if I hear a dispatcher say "01 Engine, go ahead" when 01 Engine never called them, and then "01 Engine, roger," a few seconds later, it tells me they're busy. I don't get on channel and say "hey hyuk dispatch yer talkin on the wrong channel", I know that they're talking on *many* channels at once to save time. Not only do they not have to pick the channel to respond on, but users of the channels know that the dispatcher is busy on another channel.

I multi-select all the channels I'm responsible for and then I can use my foot pedal to transmit, freeing up my "mousing hand" normally used to scroll and pick radio channels and xmit on them, for typing properly on the CAD, making things that much faster. I don't have to move the cursor on the radio and switch channels with every transmission, and can type a full remark with touch-typing quickly while the person is talking to me, rather than waiting, keying up with my one hand to "roger" them, and then waiting until I'm done that to type the reply.

ATCs and other air controllers may not be doing exactly the same thing. Like others have said, sometimes one controller is handling multiple zones or areas of responsibility, which is similar to my situation mentioned above, but other times, there may be multiple frequencies used for the same area. I don't know if America does it the same way my country does, but for example here civilian air is on one band and military is on another, but one controller will be handling both. So the controller will be talking on both VHF and UHF simultaneously, but the replies will come from only one band depending on who's answering him/her.

Lastly, on one of the things you mentioned in the post immediately above this one - nothing typically gets missed, or if it does, it's recognized immediately and the dispatcher/controller asks for the person to say their message again. Radio consoles mix all the voice traffic into a single stream of audio that is played into your headset - it's not like a scanner where only one signal can be heard at one time. Sometimes the console audio is advanced enough that you can route one signal to your left headphone and one to your right, or similar. In my center, and my experience, dispatchers are skilled enough to pick out 3 or 4 conversations going on at once. Not constantly, but if three people managed to key up at the same moment and say something to me, there's a good chance I would be able to recognize each transmission and understand what was being said. I wouldn't let them continue that for very long - lots of "stand by" would be applied while I untangled that bowl of spaghetti. But what I'm saying is, for one or two transmissions, if somebody blurted out something, it wouldn't be impossible to decipher what was said, and it'd be rare that something was missed. Even if it was, the person who didn't get a reply to whatever they said would 9 times out of 10 point that out and call again.

 

[chrismol1]

In my area there are a few tracon frequencies, not often used but you can hear the controller on the second freq multicasting, but the main freq is played over ATIS but there are additional towers sometimes for additional coverage in certain areas, used to be east and west freqs, and for when it gets congested they will tell planes to switch to another, happens frequently on the weekends with GA, GA goes on one and the airlines on the main freq. Splits up the atc workload. At night with the 1 controller they'll multicast on all of them

 

[GTR8000]

It's reasonable to assume that in the Tampa Bay area, ATC is transmitting on VHF and UHF simultaneously for commercial traffic out of TPA, and military traffic out of MacDill AFB. If you're only listening to VHF, then you'll hear the controller, but not the military aircraft on UHF. Having ATC on both frequencies simultaneously is done so that aircraft on either band have an awareness of what is going on in the airspace around them.

 

[CanesFan95]

Well, I've actually cought 'em on 2 VHF frequencies before, can't remember the frequencies. You can hear the pilots on one but not the other.

 

[ATCTech]

GTR8000, do none of the TRACONS or towers down there have cross-coupling (allowing the aircraft to hear each other on combined frequencies) in their voice switch equipment yet? As many of you have seen in my now old posts here we're 20 years past that being a "new" feature in our equipment Canada. I'm guessing the ARTCCs must have it by now for the en route frequencies?

 

[chrismol1]

Well, I've actually cought 'em on 2 VHF frequencies before, can't remember the frequencies. You can hear the pilots on one but not the other.

ahh okay its alright man hop on over to airnav pop in your airport and scroll down to
for Airport Communications for the freqs in the area, also not all of them might be used but there is a decent list there to get started on something

AirNav: Airport Information

 

[ATCTech]

Very quickly. here's my now 6 year old post on frequency cross-coupling in action here in Canada for those who may not know what I'm referring to. Moncton Centre sectors, simulcasts, and cross coupling

 

[alcahuete]

GTR8000, do none of the TRACONS or towers down there have cross-coupling (allowing the aircraft to hear each other on combined frequencies) in their voice switch equipment yet? As many of you have seen in my now old posts here we're 20 years past that being a "new" feature in our equipment Canada. I'm guessing the ARTCCs must have it by now for the en route frequencies?

Yes, cross coupling exists. There are a lot of technical limitations down here, unfortunately, because we're dealing with incredibly old equipment.

 

[spanky15805]

who's gonna' hold their breath for cross coupling?

 

[majoco]

At my local airport in the evening when it's fairly quiet, often approach, tower and ground control are paralleled - the aircraft still get told to change frequencies as usual and for the pilot there's no difference. He doesn't know they're paralleled other than recognising the controllers' voice.

 

[slayer816]

An example: The charts say ground is on 121.900. It may be an individual controller operating ground by him/herself. It may be the local controller running it combined with their frequency(ies). Depends on staffing and traffic, but someone that is controlling "ground" will always answer on 121.900 no matter what.

That's the idea all over the world. Some sectors are combined and uncombined constantly. Other sectors are only opened up if needed. A good example is monitoring approach sectors on LiveATC. Often you will hear the same controller broadcasting the same content at the same time on several channels but you will only hear the aircraft "talk back" on one. Also hearing the phrase "switch/change to my frequency xxxx" is an indicator. The controller informed the aircraft that he is controlling whatever sector he/she asked them to change to and you'll hear them again doing the same thing. Usually this is for transmitter coverage as some frequencies are transmitted from different locations.

For the controllers and air crew; not much changes. They speak, someone responds. To an uninvolved listener (us) it helps to understand the process to be able to better monitor the action.

 

[CanesFan95]

So do airports use directional antennas? This might explain other confusing things going on.

 

[alcahuete]

So do airports use directional antennas? This might explain other confusing things going on.

They don't. Approach and Centers use multiple radio sites for coverage, but towers are omnidirectional. They need to be able to hear everybody around the airport, not just in one direction.

 

[Ubbe]

So do airports use directional antennas? This might explain other confusing things going on.

I've never seen and have never heard of it. For the co-located sites in my area they use 2-stacked dipoles and on the tower it's verticals. For the companies own frequencies for crew and technical issues they have their own single dipole on the roof of their hangar. The controller crosspatch several frequencies daily. So if I have difficulties hearing an airplane it can be heard clearly on another frequency that rebroadcast both the controller and aircraft from the conversation at another frequency.

/Ubbe