Conflicting RT frequencies

[modelman]

I was in the overhead yesterday at Sywell at 3000'QNH,talking to them on 122.70 when I clearly heard transmissions for Compton Abbas from a pilot who was in their vicinity.When I got home,I discovered Compton is also 122.70.
Is it normal to pick up RT from that distance (about 94nm)?

MM

[High Wing Drifter]

No it isn't normal, but it isn't infrequent either. Especially within High Pressure systems, particularly so with an inversion. VHF can be ducted beyond its normal range in such circumstances. I've heard Sibson when in the Blackbushe circuit and some French place as Lashenden.

As an aside, I couldn't get a reliable lock on Compton DME yesterday. Even when 40nm and at FL50.

[Contacttower]

Paris can be heard loud and clear at Thruxton on some days!

[BackPacker]

If my calculations are correct, then at 3000 feet (1 km) the horizon is 113 km away. So you should be able to communicate, line of sight, with everything on the ground not more than 113 km away (theoretically). If the other guy was also at 3000 feet, the distance from him to his horizon is another 113 kilometers. So theoretically, if the both of you are at 3000 feet and your signals just skirt over the horizon, 226 kilometers should be line of sight.

So 94 nm sounds possible even without having to resort to explanations along the lines of freak atmospheric conditions.

[robin]

I was flying into Compton Abbas on Friday, and was getting confused by picking up the radio from Sywell.

We have similar problems picking up signals from northern France on occasion.

Incidentally, Bodmin is on the same frequency, but I suppose the high grpup to the SW prevents too much interference.

[High Wing Drifter]

BackPacker,

One would assume that transmitter power is taken account of in 'normal' conditions to assign two airfields with the same frequency.

[Talkdownman]

It is essential only to Tx within the Designated Operational Coverage (DOC) to obviate interference. The relevant DOC is usually stated in the AIP.
The problem with Blackbushe and Sibson was that Sibson traffic was calling outside its DOC because the frequency was being used as a high-level DZ frequency. This has now been resolved, to the great relief of Blackbushe users.

[BackPacker]

I don't think it's transmitter power that's taken into account. What they do instead, is to give each location/frequency combination a sort of "protection area" which essentially means that as long as you transmit from within that protection area, your signals should not cause trouble in the "protection area" of another location that happens to use the same frequency.

I don't know if I've got the terms correct, and I did a google search but could not come up with a proper reference. But there should be a list or something in the ANO, LASORS or on the CAA website that spells out that, for instance, you should only contact an A/G station if you are within 10 or so miles, at 3000 feet or below, while a frequency for Approach or Center can be contacted within 100 miles up to FL suchandsuch, without causing trouble for other facilities using the same frequency. One frequency can therefore be assigned to dozens of A/G facilities without causing problems, or to only one Approach facility.

Anybody who has the correct terminology and the correct table?

(Edited to acknowledge that Talkdownman beat me to it. The correct term is Designated Operational Coverage. Now if only I could find a list of these somewhere.)

[cotterpot]

TDM
The problem with Blackbushe and Sibson was that Sibson traffic was calling outside its DOC because the frequency was being used as a high-level DZ frequency. This has now been resolved, to the great relief of Blackbushe users.
As far as I was aware the drop planes only called when taking off and rejoining. Not sure that was the problem. It was quite common to hear Blackbushe in the Sibson circuit at 1000' on any day so the relief was mutual I expect.

[Dave Gittins]

It's standard practice in the USA to have a common frequency for unicoms (on 122.7) over numbers of fields in radio range of each other.

As long as everybody makes it clear which field that are addressing no harm seems to come.

Appreciate of course that is deliberate and the situation under discussion here isn't.

Perhaps somebody is trying to introduce Unicoms here.

:}

[hobbit1983]

I was landing at Chilbolton last month, using Safetycom, and managed to pick up transmissions from a gliding site nearby. How did I know it was a gliding site....they asked who I was, identified themselves and then asked me to keep the frequency clear!

Can any forumites (I checked with more knowledgable persons back at the club afterwards; the consensus was that Safetycom could be used in this matter, but asking someone to clear the freq was not on) shed any light on what frequencies glider sites normally use, and whether or not safteycom is/should be one of them?

[rusty sparrow]

On the Elstree Information frequency (112.40) around 10am this am - at 2100 in the local area. High pressure and inversion can create a 'radio frequency mirror' that allows transmissions that otherwise would escape into outer space to be bent back towards Earth.

[ProfChrisReed]

The frequencies reserved to gliding are:

129.975 (ground/air)
130.1
130.125
130.4 (especially for gliders cloud flying)

129.9 is shared with parachuting, hang gliding etc. for ground retrieval purposes.

I can't find any mention of Safetycom in the BGA Laws & Rules, but my personal view is that gliding clubs should only use it under the same conditions as other aircraft, i.e. where there is no other allocated frequency.

[High Wing Drifter]

BackPacker,

Thanks for the explanation, something I didn't know (or forgot along the way). I see the issue raised here was hearing the aircraft. But, I was thinking about hearing the ground station too. But now I stop and think about it I can't categorically confirm that as I didn't really think too deeply about it before.

[chrisN]

In addition to the gliding frequencies in general use, which Prof Chris Reed has posted, some gliding clubs have properly registered and allocated specific frequencies. E.g., Lasham uses 131.025 for circuit traffic, again, properly registered and allocated. There may be others too.

(from: www.lasham.org.uk/members/manual/Local%20flying%20rules%20and%20procedures.pdf - :

“ . . . recommended that all pilots in the vicinity listen on Lasham’s frequency (131.025 MHz) in case another pilot is announcing an unusual circuit. ...”


Chris N.

[BEagle]

Within the UK, you should not transmit at:

More than 25nm/4000 ft on Tower frequencies
More than 25nm/10000 ft on Approach frequencies
More than 10nm/3000 ft (ideally 1000 ft) on A/G frequencies.

Safetycom (135.475 MHz) is NOT the same as Unicom. No-one has any right to Safetycom and it is not an alternative to any published station frequency:

Transmissions shall be made on SAFETYCOM only when aircraft are below 2000 ft above aerodrome or location elevation or below 1000 ft above promulgated circuit height (if applicable). Transmissions shall be made only within 10 nm of the aerodrome or location of intended landing.

The frequency shall be used only to transmit information regarding the pilot’s intentions, and there should be no response from the ground, except where the pilot of an aircraft on the ground also needs to transmit his intentions. Exceptionally, where the pilot of an aircraft on the ground has information critical to the safety of an aircraft in a condition of distress or urgency, the frequency may be used to transmit that information.

That gliding site needs to wisen up!

[chrisN]

Which gliding site, and wisen up to what? I don't mind passing on a message if it is sensible and comprehensible, but I would not know what to say to whom on this.

Chris N.

[Spruit]

Which gliding site, and wisen up to what?

See reply #11 if your a tad confused!

Spru!

[Dave Gittins]

I am easily confused and as I almost universally stay in contact with some recognisable ATS (Radar, FIS, A/G or Aerodrome) haven't come across SafetyCom before.

Whilst appreciating BEagle's explanation of the limits that should be applied to it's use ..... exactly what is it's use and who listens out on it ??

Sounds like it has it's own set of "Guard Police" somewhere around Chilbolton (sorry but Post #11 didn't indicate to me where the gliders were either).

DGG

[chrisN]

Spru and Beagle, I would be happy to contact the gliding club in post 11, if that is the one Beagle meant, if I knew who it was and whether the GA pilot was in or outside their legitimate cylinder of using the frequency. The posting says nothing on either point.

My query (not confusion) was also aimed at finding whether that gliding club or the web site I referred to (Lasham) was the point of Beagle's post.
If no one is concerned enough to help, other than make sarcastic remarks, I won't try to assist.

I am grateful for Beagle's info about the cylinder in which these frequencies can be used.

Chris N.

Eddited to add, Hobbit: feel free to send me details by email to
[email protected] if you wish.

[hobbit1983]

I would prefer not to make allegations on a public forum, therefore chrisN; have emailed you.

Dave G - for example, when landing at Chilbolton, I was using Safetycom to transmit my intentions to other aircraft in the area of the strip. i.e. "Chilbolton Traffic, G-ABCD is a white/yellow C42/Cub/Husky, downwind for landing on runway 06"

(I realise that the aircraft descripton may not be required or part of normal procedure). It's my understanding that the frequency is to be used to transmit pilot intentions at airstrips where no discrete frequency is allocated, therefore I presume the main users would be farmstrip flyers. I use it when operating at farmstrips; and it's certainly useful.

BEagle & ProfChrisReed - thankyou for the information.

With regard to the glider frequencies, are there any specific rules regarding communication between powered aircraft in the area of a gliding site?

When under a RIS & in the vicinity of gliding sites, I often recieve reports of "primary contacts only in your area etc" which of course are most likely to be gliders, and it would be useful, not to mention safer, to be able to communicate traffic information/intentions to them.

[gpn01]

Hi Hobbit, whilst wanting to communicate with gliders details of your (and their) whereabouts are laudable, there are a few factors to consider:

129.975 is the main frequency used for A/G communications betweenn gliders and base (within 10nm of the airfield). This one frequency (spread across most gliding Clubs in the UK) suffers badly from overlapping useage. See previous posting about how far a VHR transmission at x thousand feet is and bear in mind that gliders may be talking to base at 5000' - we hear people from all over the UK (and France at times!). So, a powered a/c calling to say that he's near one gliding site, and requesting traffic info, is likely to be heard by many other gliding sites.

The majority of local glidiing activity is non-radio. Therefore you cannot assume that all possible contacts are listening (or broadcasting).

Gliders don't have absolute control over their position and will change heading, height and speed quite rapidly and so only traffic information would be of the "yes, we're flying" nature. Even if a local Club isn't flying, there may be other non-local gliders in the vicinity too.

Can't beat a good lookout and avoid known glider activity where possible.

[hobbit1983]

Ah I see; didn't realise that many gliders were non-radio. No worries; mark 1 eyeball use & a wide berth is certainly what I do normally.

[gpn01]

It's not having to use a radio that many pilots find so appealing. It also means that we can use our ears to listen to things like changes in the airflow (which can be a good indicator that you've located a thermal). Also, the less time we spend dabbling with radios, doing frequency changes, etc. the more time we spend looking out around us.

[chrisN]

Hobbit, got your email but my replies bounced. See your p.m.s

Regards - Chris.

[hobbit1983]

Actually I got both those! Am in the middle of typing a reply - will pm very shortly

[chrisN]

I have investigated the Chilbolton episode mentioned in posting number 11 with Hobbit. We are both fairly satisfied now that there is no point in pursuing it any further. The most likely explanation is that Hobbit’s safetycom transmission was actually heard on a gliding site radio, tuned as it is entitled to be to the gliding ground to ground frequency of 129.9. They heard a non-gliding transmission, and themselves broadcast that it was a gliding frequency, which powered aircraft elsewhere, and not using gliding circuits, should not be using. Both parties were individually correctly on the frequency on which they were transmitting, but the vagaries of radios meant that transmissions from one radio on one frequency were heard by another radio operator on another frequency.



As background, for those who are not aware of it, let me explain my own personal experience, which I know others have experienced too.



Glider radios are much less powerful than GA, airliner, and airport radios, to say nothing of broadcasting stations. All the glider radios I have owned, including portable Icom types, have been of this low power, and had full Radio Communications Agency and CAA approval for their use. In spite of that, I have on occasions received transmissions from airliners flying into Stansted area, transmitting on Stansted Approach Frequency (these days termed Essex Radar), and even music when flying in the vicinity of terrestrial radio broadcast stations.



Hobbit has explained to me, concerning his aircraft radio, that “This particular set was quite old & prone to static/interference. So much so that on occasion instructors have been know to notifiy the ATSU that a particular training flight will be flown non-radio as the transmissions recieved in the circuit were not understandable. It is a club aircraft & the radio is to be replaced during the next check, so I understand. . . . . I agree totally that the radio is not performing to specification - the flying club to which the aircraft belongs to have acknowledged this (at last!), and it is to be replaced very shortly. We have been after this for some time - it has on one occasion caused misunderstandings due to the poor transmission quality. On this particular day, at the club during pre-takeoff checks, transmissions were readable, which is why I elected to use the set at Chilbolton. However, as you say, lower-powered aircraft/glider sets would not (and indeed weren't) as readable as the airfield A/G service.”





I have spoken to the gliding club, which Hobbit thought was most likely to be the one from which he heard a transmission, and they confirmed that their base radio only tunes to the gliding frequencies, by means of a preset selector. Normally it is tuned to 129.9, which is allocated to gliding for ground use only, and is used for transmissions between their launch point and their winch. They have no recollection of anyone from a powered aircraft, talking to them, but of course the person I spoke to may not have been around or may not have heard of anyone making a response off the cuff, some days ago. We are not even absolutely certain of the gliding site, as Hobbit is unable to confirm it definitely, but it does seem to be the most likely one based on proximity to Chilbolton.



Their radio is one that has type approval, and so meets specification requirements, and as I suspected, it is of the typical low power that glider radios and gliding site base radios usually utilise.



Hobbit also mentioned to me that: “ . . . There was no explicit use of the word Safetycom or similar confirmation. . . . after my downwind call I was asked to identify myself. Having done so, I recall being told "please could you keep this frequency clear, this is a glider channel" to which I replied affirmative. . . . . The clincher is of course I cannot recall the callsign! This is due I believe to the poor reception qualites of the aircraft radio (I recall being able to make out what sounded like position reports in the transmission, but not the full transmission) and also due to the fact that some of the transmissions did not appear to have callsigns at all times.”



In my experience of visiting many gliding sites, and through my experience as a former BGA airspace committee chairman, executive committee member, vice-chairman, and currently regional safety officer, I have never come across any gliding club which uses the safetycom frequency. Without exception, any UK gliding site which has a base radio uses either one of the allocated gliding frequencies or a specific one allocated and approved for that site in the same way as any other GA aerodrome can apply for its own frequency.

Chris N.