VHF Aviation frequency specification

[dgoodson]

Curious about this...

As an example (and there are many more...) Jacksonville Center uses frequency 128.075 MHz, When the controller asks an aircraft to switch to this frequency, he will say "Contact Jacksonville one two eight oh seven" and the aircraft will acknowledge "1-2-8-0-7".

Are the radios actually set to 128.070 or 128.075?
I'm wondering if the modern aviation radios are pre-programmed for 128.075 and the 128.07 callout is just historical lingo.
If the radio is actually tuned to 128.070 would it affect performance if a modern receiver were tuned to 128.070 versus 128.075, particularly for weak/distant transmitters?

TIA

 

[mancow]

They are running 25 kHz steps so they truncate the last 5 for brevity.

 

[Whiskey3JMC]

I've heard planes leave out the leading "1" at times as in tower advising the plane to switch to "124.62" the plane will read back "Twenty Four Sixty Two" or "Eighteen Five" for 118.5

 

[737mech]

Most modern airlines use a radio tuning module that only has a five digit display. That is why pilot read back is like that.

 

[nd5y]

Most modern airlines use a radio tuning module that only has a five digit display. That is why pilot read back is like that.

What happens when they fly to Europe and have to use 8.33 kHz channels with 6 digits?

 

[gary123]

They expand the digit information to xx.xxxx.

 

[kc2asb]

Most modern airlines use a radio tuning module that only has a five digit display. That is why pilot read back is like that.

And for brevity's sake as mentioned above. The tower frequency for my local airport is 118.3, which most pilots read back as "eighteen three".

 

[Whiskey3JMC]

Lastly contact Ground point niner (121.9)

 

[andy51edge]

The FAA has standardized to only stating the first two digits after the decimal even though the radio will correctly add that third radio in the background. In the US, all ATC services use 25 kHz spacing. For US controllers, this instruction is found in FAA Order 7110.65 (called the point sixty-five). The letters suffix after the digits is the revision number.

7110.65BB 2-4-17 NUMBERS USAGE k. Frequencies

Frequencies.

1. The separate digits of the frequency, inserting the word “point” where the decimal point occurs.
2. Omit digits after the second digit to the right of the decimal point.
3. When the frequency is in the L/MF band, include the word “kiloHertz.”

EXAMPLE-

Frequency	Statement
126.55 MHz	“One two six point five five.”
369.0 MHz	“Three six niner point zero.”
121.5 MHz	“One two one point five.”
135.275 MHz	“One three five point two seven.”
302 kHz	“Three zero two kiloHertz.”

1. USAF/USN. Local channelization numbers may be used in lieu of frequencies for locally based aircraft when local procedures are established to ensure that local aircraft and ATC facilities use the same channelization.

EXAMPLE-

Frequency	Statement
275.8 MHz	“Local channel one six.”

The text above in bold blue is highlighted by me for emphasis.

Omitting the ground frequency or truncating it to "Contact Ground Point Seven." is found in 7110.65BB RADIO COMMUNICATIONS

Frequency to use except the following may be omitted:

1. FSS frequency.
2. Departure frequency if previously given or published on a SID chart for the procedure issued.
3. TERMINAL:
4. Ground or local control frequency if in your opinion the pilot knows which frequency is in use.
5. The numbers preceding the decimal point if the ground control frequency is in the 121 MHz bandwidth.

EXAMPLE-
“Contact Tower.”
“Contact Ground.”
“Contact Ground Point Seven.”
“Contact Ground, One Two Zero Point Eight.”
“Contact Huntington Radio.”
“Contact Departure.”
“Contact Los Angeles Center, One Two Three Point Four.”

In Europe, they use 8.333 kHz spacing. Radios equipped with 8.333 kHz will display three digits to the right of the decimal. For example, over there they will say "contact Heathrow Tower on One one eight decimal five zero five". Further reading on 8.333 kHz can be found athttps://skybrary.aero/sites/default/files/bookshelf/34196.pdf. Think of 8.333 communications as referring to channels and not frequencies. "Channel" 118.015 is what will be displayed and spoken even though it is actually frequency 118.0167 MHz.