Channels and Frequencies

[exfiller]

I would be grateful for any help understanding the division of the R/T spectrum into chanels/8.33 subdivisions:
With increasing congestion in the aviation VHF band I understand that the 25 kilohertz spaced spectrum of 'Frequencies' has been further subdivided into 8.33 kHz subdivisions referred to as 'Channels'. Starting at the bottom of the Aviation R/T spectrum the steps run:

'Frequencies' 'Channels'
118.000
..................118.005 118.010 118.015
118.025
..................118.030 118.035 118.040
118.050
and so on.

Two questions arise:
1. The frequency assigned to each 'Channel' does not seem to be at a numerical spacing of 8.33 kHz, so am I right in thinking that the frequency quoted is merely a channel designation rather than the actual numerical value of the frequency used for that 'Channel'?

2. 'Frequencies' are spaced at 25 kHz, and 3 x 8.33 = 25, which seems to imply that there should be room for 2 'Channels' between each 'Frequency', so why do there seem to be 3 'Channels' (see table above) between each 'Frequency'?

Thanks in advance

Exfiller

[chevvron]

The use of the word 'channel' has ceased in some countries/will cease in UK in May 06

[Oktas8]

Exfiller, I'm not the expert at this, and others on this forum are. But, since no-one else is answering, I'll try to help out.

Q1 - yes.
Q2 - there is room for only two channels between frequencies.

Further explanation - due to rounding errors, channels appear to be unevenly spaced on decimal radios. This table corrects the error in your assumptions:

Actual freq: --- Channel:
118.000-- --- 118.000
118.00833 --- 118.010
118.01667 --- 118.015
118.025-- --- 118.025
118.03333 --- 118.035
... and so on.

As you can see, channel 118.005 does not exist (if you dialled it into your flash new radio, the radio would remain tuned to freq 118.000).
Similarly 118.020 does not exist - if you tuned it in, you'd get frequency 118.01667 which is 118.015 in channelspeak.

Happynewyear,
O8

[exfiller]

Thanks to O8 for the info which helped a lot - and to chevvron thanks for the heads up which I have followed up by getting the relevant ATSIN from the CAA.

All the best
Exfiller

[selfin]

Eurocontrol has a good piece of info here (http://www.eurocontrol.int/eatm/public/standard_page/833.html) and specifically here (http://www.eurocontrol.int/vhf833/public/subsite_homepage/homepage.html) on this subject.

[Gryphon]

You have 2 more freq, but for those airspaces with 25khz. separation, you have to be able of tuning the "old" freq. So:
118.000 ch ---------- 118.000 freq (25khz spacing)
118.005 ch ---------- 118.000 freq (8.33 khz spacing)

[chevvron]

But in future (in the UK) ALL 6 digits will have to be spoken.

[PPRuNe Radar]

All 6 digits have been the ICAO standard since November.

Someone in the CAA though that UK people would need an extra 6 months to train to say an extra digit ... how stupid does that make us look to the world ?? :)

[chevvron]

Steady on, I was on the working group that decided it.
We decided that as we had to hit not just professionals, but everyone including A/G radio operators, FISO's, SPL's etc, there had to be a period of 'education'. According to the Eurocontrol rep, several other european states were of the same opinion.

[PPRuNe Radar]

The State Letter from ICAO notifying the standard was issued on 24 March 2005 giving 7 months notice .. and yet it takes over 1 year 2 months to implement in the UK ?? ;) When was the working group set up ?

I'm impressed that we have embraced the slow turning European beaurocracy so well :ok:

PS the principles have been agreed since 2003 by the European Air Navigation Planning Group (of which the UK is a member), so it could hardly come as a surprise that the change would happen after due ICAO process was followed.

[PPRuNe Radar]

After some more details being received, I'd like to make clear there is no criticism of the UK Working Group implied. Given the fast ball they were passed, a delay was a proper decision.

Perhaps the UK CAA should have mentioned in their Air Traffic Sevice Information Notice 78 just why the UK hadn't met the introduction date. But then no one regulates the performance of a regulator do they ?? ;)

[Mr R Sole]

I recently had a Eurocontrol leaflet sent by my company about the change in frequency phraseology but was puzzled since I only heard one ATCO in the UK refer to a frequency in 6 figures and after reading this thread I see that it is not UK procedure yet?

Can anyone confirm when the new phraseology is to be implemented within the UK? A link to a ATSIN or something similar would be very useful!

[PPRuNe Radar]

ATSIN is on this link in PDF.

01 May 2006 is UK implementation date.

http://www.caa.co.uk/docs/33/ATS078.PDF

[notdavegorman]

Two thoughts:-

1, Why would controllers possibly need additional training to say an extra number? Surely a simple notice to that affect would suffice? If pilots had to be officially re-trained every time a minor change of procedure took place, we'd be in a state of perpetual re-training.

2, Why is the change necessary? I know ICAO said so, but why did they come to that conclusion? The French have already started passing all digits and I have to say it sounds awkward and is in my view amounts to unnecessary verbiage. Talking of things French, if ICAO have to make pronouncements on R/T, perhaps they might start with issues that actually have serious safety implications, like the use of the French language instructions to French aircraft, thereby seriously reducing the situational awareness all other pilots who don't understand the language. Witness the thread regarding a CDG runway incursion.

[chevvron]

1 If you read my earlier replies you'll see it's not just controllers, but ALL pilots with ALL types of licence plus ALL ATS staff from A/G operators upwards.

2 There is some evidence that you pilots are forgetting to switch your radios to 25 khz spacing when changing from an 8.33khz frequency, hence you are not selecting the final '5' in the frequency. This MAY (and I only said may) result in loss of RTF contact and (possibly) scrambling of fighters to intercept you!

[notdavegorman]

1, I was under the impression that 8.33 kHz spacing was only in use over FL195, therefore it's only really controllers and professional pilots who use it. Maybe I'm out of date? Either way, I can't imagine pilots getting any additional training.

2, I suppose if that's what quantitative studies say, than that's the way it must be. Sounds rather odd to my ear though, and not necessarily any more clearer - less concise and they way the French pronounce "425", it sounds more like "forty-five".

[chevvron]

8.33 freq's are presently in use above FL195, but this will soon reduce to FL95.
Under the ICAO rules, if a country has only one 8.33 freq (and the UK presently has one becoming three in March) it is declared an 8.33 khz environment and has to comply with the '6 digit spoken' rule.
I understand that the USA does not use ANY 8.33 khz freq's and is thereby exempt!
By the way, if you are using a 100khz frequency such as 118.6, there will be no change.

[LGB]

Have a six digit frequency change, at the same time you get a speed restriction and a radar heading (and you shouldn't in the first place, really), then by the time you read all back, you have forgot your own callsign ...

Why not have ICAO drop the first digit? Although we all know it is "1", it is one more digit to say, wouldn't it be easier if all frequencies were said without the leading one.

[chevvron]

Can't drop the first digit 'just in case' a UHF frequency is in use.
All controllers should be aware of the 'not more than 7' rule.

[SMOC]

I'm with you LGB, drop the "1", must admit I tried it the other day seems much easier, also how many of us have UHF?

[LGB]

Too late, and unrealistic, but since it doesn't really matter what the frequencies are, they could all have had a sequential number instead of the actual frequency.

With four digits there are 10000 combinations, far more than there are frequencies even at 8.33 (2280, less the ones unused around 121.5). If it had been easy with a letter, it could even have been 2 numbers and one letter, like "change to Kilo 2 9". But then a dial with 25 letters makes it too complicated.

But with 4 digits 0 to 9, we could have saved two digits, but unrealistic, because think of all the work and hazzle, changing all these aircraft radios!

[chevvron]

Yes some pilots, mostly from the USA, do drop it. I (as a controller using only VHF) am not going to complain, but the official line is NO, because of the fact IF you were working a military unit, and they were also using UHF frequencies which begin with 2 or 3, then it 'could' cause confusion.