SRA's question

[Minesapint]

Are there any issues related to the provision of SRA's using primary radar only? :confused:

[Spitoon]

In what sense? An accurate SRA relies on using data which is as unadulterated as possible. Take out plot extraction and other processing and the target is more likely to be where it appears on the display.

This speaking as someone who learned how to do SRAs on a 3cm pencil-beam primary radar with the barest minimum of processing of the picture. SRAs terminated at 1/2 mile from touchdown - and on a good day you could see runway edge lights.

[anotherthing]

short answer - no.

[throw a dyce]

We used a 264 primary only for SRAs many moons ago.It was offset to the east of the field,but because the blip was quite big,the best results meant running the edge of the blip nearest the radar down the centreline.Otherwise they would be lined up on Asda car park.None of your processed radar then.:)

[radarman]

Not sure what 'issues' you mean. The radar head would certainly need to be on the airport. But as far as I know SRA's can only be done using primary. We're certainly only allowed to do them on primary. I think there would be too many accuracy issues trying to use secondary.

[matspart3]

At Gloucester, we don't have any choice....haven't got SSR

[flowman]

Did thousands of 'em on primary, never had an issue.

[Minesapint]

Many thanks for the responses. I should have said that the assumption was using an optimised airport radar.

[Widger]

IIRC an SRA radar needs a higher probability of detection (PD) than one used solely for surveillance. The radar update rate is also critical. That is why at old airfields that had 264 radars, the SRAs were conducted with a different radar...cannot remember the name of it now.
:ok:

[letMfly]

IIRC an SRA radar needs a higher probability of detection (PD) than one used solely for surveillance. The radar update rate is also critical. That is why at old airfields that had 264 radars, the SRAs were conducted with a different radar...cannot remember the name of it now.
:ok:
Not at Aberdeen; as Throw a Dyce said we did SRAs on the 264. Actually it was a 264AH which was modified to give a smaller overhead, but it was still essentially an area radar with half mile wide blips. Some pilots used to whinge that they were 100 yards off the centreline when they broke cloud at two miles, unaware that they were really getting a glorified cloud-break procedure :eek:

[Spitoon]

Ditto letMfly and Throw a Dyce - one place I worked at used a 264 for SRA. Only for two milers for obvious reasons but no problem in using it - at least the blips didn't fade away half way down the approach like they often did on a 430.

[Chilli Monster]

That is why at old airfields that had 264 radars, the SRAs were conducted with a different radar
Filton is STILL operating with a 264H, still doing SRA's with it.

[Evil Lord Ham]

More to the point, are there any issues with using SSR to do SRAs? As radarman says, SRAs can only be done with primary present. But modern SSRs are probably as/more accurate than primary. So any good reason for the rule other than history?

[Red Four]

Yes. SSR only outside CAS not a good idea...

[RADAC]

radarman - I can think of a few NATS off airfield radars that are used for 2nm SRA - Pease Pottage for Gatwick, Debden for Luton/Stansted and Allanshill/Perwinnes for Aberdeen. But as has been mentioned a 2nm SRA is only in reality a cloud break so accuracy isn't outside the normal requirements of radar optimisation.

Interestingly SRA being a primary only function is a slight misdiscription since if the Primary radar is co-located with an SSR in most cases the primary position is set to that of the SSR. - certinly smooths the track!!

[CUNIM]

The old Decca 424 was excellent for half mile SRAs as long as you knew how to use the Wx filters.:ok:

[Evil Lord Ham]

Yes. SSR only outside CAS not a good idea...

But SRAs are not for separation, therefore the issue of other traffic is not relevant (I stand to be corrected of course). Isn't the only issue the accuracy of the data being used to guide the aircraft to the termination point? I am talking specifically about SRAs not general separation services.

[throw a dyce]

Radac,
Allanshill can't be used for 2nm SRA.The primary coverage low level on 34 isn't good enough.The radar is over 20 miles from the airfield.However Perwinnes is fine.:)

[Jayfoe]

The regulations regarding radars used for SRAs are contained in CAP 670. In general;

11.1.1 When used for surveillance radar approach (SRA) purpose (i.e. primary only), the
accuracy shall be better than 1 degree of bearing and 55 Metres, + 5% of target range
(365).


11.5
Rotation Rate
11.5.1 The effect of rotation rate on system performance shall be defined and justified (451).
11.5.2 A primary radar providing the positional data for the following services shall rotate at
the following effective minimum turning rates:
a) General TMA Zone and approach work, a rotation rate of 5 RPM (452).
b) SRA to 2 NM, a rotation rate of 10 RPM (453).
c) SRA to 1 NM, a rotation rate of 15 RPM (454).
d) SRA to 0.5 NM, a rotation rate of 20 RPM (455).

Here is the address of the CAP 670 document on the CAA website;

www.caa.co.uk/docs/33/cap670.pdf (http://www.caa.co.uk/docs/33/cap670.pdf)

Hope this answers your question

[Talkdownman]

The old Decca 424 was excellent for half mile SRAs as long as you knew how to use the Wx filters

Still is.......!! :ok:

[chevvron]

It might be possible with SRG approval to do a 2nm SRA using SSR only providing the SSR head is on or close to the airfield, but anything less than 2nm is definitely not possible due to the requirements for touchdown/centreline markers ie for 1nm you MUST have at least one centreline marker and for 1/2 nm you MUST have touchdown markers bracketing the touchdown point.