Monday, July 20, 2015

"My Frequency" Confession

When flying IFR, a pilot "reads back" that is repeats back all the instructions we receive from air traffic control, to demonstrate that we have heard and accept the instruction, and to give the controller a chance to notice if we have heard incorrectly, or if the controller misspoke. It gets a little silly sometimes: the pilot asks for a particular clearance, the controller clears them for it, and the pilot reads it back again, but it prevents us from descending to five thousand when it's only safe down to nine thousand. When I say pilots talk to "air traffic control," we are only sometimes speaking to someone who can look out the window of a tower and see us. We're usually speaking to someone who can see an electronic blip on a computer screen, generated in response to radar return and transponder code information from our aircraft. We may even be talking to someone who merely has a copy of our flight plan and has keep track of aircraft based on our position reports, in an area with no radar coverage. They probably have a map of their area and some cool computer tools to help them. The sky is all parcelled out vertically and horizontally into different classes of airspace, some requiring air traffic control and some not. A pilot might first talk to the clearance delivery position, then call ground for taxi clearance. The ground controller instructs the pilot to contact tower at the hold short line. The tower controller passes us on to departure or terminal and then terminal instructs us to switch to Centre. All the way across Alberta, and much of northern Canada we're talking to Edmonton Center, but as I cross Alberta I'm progressively switched between frequencies, so I'm always in range of the antenna that transmits and receives on that frequency.

The controller might say, "ABC, Contact Edmonton Centre on 132.75" and then I say "ABC, 132.75." I tune 132.75 and then call that controller, saying, "ABC, one five thousand." If a pilot neglects to acknowledge a frequency change, and just goes straight to the next frequency, the poor controller that directed her to change has no way of knowing whether she changed or just fell asleep. And of course she has to check in on the new frequency or the new controller doesn't know that the change has been made successfully. Sometimes the controller's wording is "Contact me now on 133.4." That means the one controller is managing multiple frequencies. "Contact me now" means "Switch to my other frequency" Sometimes they just say that, too, or "Switch to my frequency ..." When things aren't too busy, in remote areas or overnight there are fewer controllers, so one person may manage all the frequencies in a vast swath of airspace. Sometimes the controller sets it up so that all the pilots on the various frequencies she is controlling can hear the controller regardless of which frequency she is broadcasting on, and sometimes we can hear the other aircraft on those frequencies too. This makes it easier for us not to call on one frequency when the controller is speaking or listening on another. Sometimes the frequencies aren't paired this way so we do sometimes talk at the some time as the controller is busy on another frequency, and she has to ask us to go again.

I learned to fly IFR during the day in busy airspace where all the frequencies had their own controllers. I would read back my frequency change instructions, change frequencies, and check in with the next controller. And then I went north and honed my skills in remote areas in uncontrolled airspace where there were no Centre controllers to talk to, just pilots talking to one another, reporting when we changed altitude or passed over waypoints. So it took me a really long time to notice something. Here comes the confession.

If a controller says, "Contact me now on 132.75" you don't need to read that back on the original frequency and then switch frequencies and check in." You can just dial in 132.75 quickly and say, "ABC on 132.75." This did not dawn on my for the longest time. I noticed a pilot doing it one day, when the controller had paired the frequencies, so I could hear the pilot given the instruction to switch and simply acknowledge it on the new frequency. I think most people do this most of the time. Do you?

9 comments:

Steven Barnett said...

I think it would depend on how quickly I could tune the new frequency. Having the frequency already in standby would be easiest of course, but if not, some of the older planes I've flown have rather finicky dials that like to skip a digit and take longer to get right.

Colin said...

Like Steven said, it depends on how quick I am to dial in the new frequency. Most of the time I am paying enough attention that I can come up on the new frequency without a delay, but I don't want to leave the controller hanging if it is taking too long, so I will read it back and THEN switch.

airfierce said...

Also, it's good to read back to make sure you heard the frequency correctly (same idea as with the IFR clearance readbacks, I guess, though not as safety-critical).

D.B. said...

No, but I will from now on! Thanks for the tip!

5400AirportRdSouth said...

I just discovered this last week! Oddly enough, it was also flying over northern Alberta... Maybe we heard the same person do it!

Andrew Alexander said...

I acknowledge all frequency changes, even "contact me on ... " instructions. The delay between the instruction being issued and the pilot contacting them on the new frequency may be fairly brief, but in most cases, it will be longer than the time required for a prompt acknowledgment of the instruction. Whatever that additional time is, it leaves the controller sitting there with the question "did N123xy hear the instruction and hear it correctly?" unanswered, not knowing whether to continue listening for your response or to move on to their next piece of business. Add to that the possibility of you mishearing the frequency and dialing the incorrect one, the new frequency suddenly becoming busy just as you tune to it, you being juuuust outside of contact range on the new frequency because the controller was a little optimistic on how far your radios would carry on that RCO, and it may be a while before you are able to check in on the new frequency and the controller can drop the "did they hear the frequency change correctly" question from their mental list of unfinished business they're carrying in their head. The other consideration is that there may have been someone on the original frequency waiting to contact the controller, and they are waiting for you to read back the frequency change, so that they know your exchange with ATC is complete, and they can transmit without stepping on your transmission. I have, on occasion waited a considerable time for another pilot to read-back instructions, wondering if they are going to respond, or they're done talking. A quick read-back of the frequency change doesn't take much time or effort, and it does let the controller know immediately that you have heard and understood, and it lets others on frequency know immediately that you've heard the last instructions and the frequency is not clear for others to use. Yes, it is somewhat redundant, but the same can be said about almost all other aspects of ATC communication. It's redundant, it's designed that way to make it more positive. It is true that most of the time any redundancy could be omitted, but the redundancy isn't built into the system for the times that things are going perfectly, it's there for the times that things aren't going perfectly.

FWIW, the US AIM specifies a readback of frequency changes, but makes no exceptions for frequency changes to the same controller. They do however note that when changing to a frequency with the same controller, the initial callup phraseology (Full call sign, altitude, etc) may be omitted. One could speculate that it is intended that a frequency change to the same controller does not require the normal initial callup phraseology (full call sign, altitude maintaining, etc. ) ay be omitted. One could speculate that the direction to read back frequency assignments does not extend to changes to the same controller, but the text does not support that speculation.

Does the Canadian AIM address this situation?

Andrew Alexander said...

As to your question, "Do You?", I think that you are asking "Do you skip the acknowledgment and just change frequencies?" In which case, obviously I don't, and the majority of the guys I fly with do not, and majority of the other pilots I hear on frequency do not.

dantheman99 said...

As a controller in a busy class D airspace, I issue this instruction on a regular basis, but typically paired with another instruction. "N12345, left traffic RY12L, change to my frequency 119.1". The pilot replies "left traffic RY12L, call you 19.1".

If working ground and clearance combined, May tell an A/C on clearance "N12345, XXX clearance, change to my frequency 121.3". The pilot will typically read back just ".3" or "call you .3"

As many other posters have said, I prefer to know that you got the freq, I have pilots read back the wrong frequency often enough that it would be a factor.

dantheman99 said...

As a controller at a busy Class D tower I will tell you I always like to know that a pilot got the freq change ahead of time, it saves the possibility of you dialing the wrong frequency and not being able to respond to an instruction 30sec -1min later.