Tower Ranger

Recently where I work we have had a bit of survey work being carried out by light a/c at 2000ft within about three miles of the final app. track abeam an eight mile final vfr in vmc. SO far no problem. So as per the norm the a/c are on 7000 , still no problem you might think. Despite giving traffic info on this identified VFR traffic a couple of inbounds have refused to descend to close the localiser bcause of RA`s on tcas .
So far the best solution I`ve come up with is to get the VFR to sqwalk standyby untill the inbound is passed but that is not really any sort of answer. What is the pilots opinion , surely this must happen every day all over the country?

RadarContact

If the altitudes were as described it would be very unlikely that the TCAS generated RA's.
Traffic Advisory (TA) would, however, be generated as described above if the target would not have mode C active.

I often fly to airports whith controlled VFR traffic close to the final track. Unless this traffic is in sight and confirmed by tower the approach will not be continued...

Tower Ranger

BIK


Maybe I`ve misunderstood part of your post , surely if the VFR traffic is showing mode C this will not affect the TA in this cicumstance. Basically the a/c will be on closing hdg to establish the loc leaving 3A for 1.5A so surely the TCAS will identify the 2A tfc as a definite conflict.
I totally agree the pilot is " better safe than sorry " and I guess my point is there is no reason this identified VFR traffic receiving a FIS can not be within three miles of the final app track. The airspace is class D and so traffic info both ways but if ATC are now expected to provide std separation on VFR its gonna be a long day at work for us all.
If your in a left hand turn to intercept the chance of seeing vfr traffic below you and on your rhs aren`t too high and I`m not expecting you too cos its just Traffic info.

HEATHROW DIRECTOR

Radarcontact wrote: "I often fly to airports with controlled VFR traffic close to the final track. Unless this traffic is in sight and confirmed by tower the approach will not be continued..."

A very interesting comment. ... Is it you or your ops manual which decides or maybe it's because of the type of airspace? I ask because at Heathrow this situation occurs hundreds of times daily with non-modeC SVFR helicopters and other traffic constantly under our final approaches. Information on this traffic is a) rarely known to Heathrow Tower and b) never passed as traffic information by the radar controllers unless queried. On many transmissions from a/c we hear "Traffic, traffic" in the background but only a tiny minority of pilots query the reason.

ETOPS

BIK_116.8

The problem is that that many light aircraft transponders are mode "A" only. In order to report altitude they would need to either upgrade the altimeter and/or the actual transponder at some considerable cost. Many owners would not do that unless it was a legal requirement.
As for conflicts at low level this is how I cope.......

In UK controlled airspace it is very unusual to get such a situation apart from the helicopters in and out of Battersea - thus I accept that TA's will sometimes occur with little actual risk. If the traffic is mode "C" equipped and notified as as conflict (India 99 etc) then I am allowed to switch my TCAS to TA only thus avoid an RA. It would do this automatically at very low level anyway.

In the USA it is becoming standard practice on parallel approaches to switch to TA only as seperation standards are very tight and in good weather most crews elect for a visual approach hence work under "see and avoid" principles.

If I receive an RA and cannot instantly visually aquire the traffic I will react as per SOP's even if that requires a go-around......

RadarContact

HEATHROW DIRECTOR:

If TCAS issues a TA regarding a target close to the approach track, my first action would be to look for it and ask tower for confirmation. If the tower (or APP) has no contact with the traffic and it was only mode A equipped I would think twice before leaving my altitude. At the place I meant, usually the VFR aircraft are mode C equipped, which makes identification a lot easier as well as evaluating the threat potential.

Simply continuing without seeing the target blindly trusting that nobody would dare to fly through the final track is not my idea of safety.

Tower Ranger

Radar Contact

So relying on ATC to provide a safe , orderly and expeditious service is out of the question unless you see the traffic. I wonder how we ever managed without TCAS .

411A

Some pilots would appear to go "ape sh@t" with a TCAS advisory.

Face it guys, it LIES sometimes. Using common sense would seem to me to be a better alternative. TCAS normally works very well, but is not the nirvana of aviation.

Fokker-Jock

I personally would react as follows;
any RA will be carried out in full nomatter what.
A non mode C equipped A/C would never generate a RA but a TA and the target is identified by the VDU as a non mode-c target. I would then ask for ATC confirmation and if non is given or can be given, then I would reason that the non-C a/c is below radar coverage and therefore no threat to me at my cruising level. However, in IMC low-level one could reason that the non mode-c A/C is VMC and therefore also no threat. And if low-level VMC I would keep constant lookout. There is no reason to change course nor altitude because of a TA on a non mode-c target as the altitude change may lead to disaster just as much as maintaining altitude. Course change can be considered, but using the VDU for guidance is totally useless as the directional error on these are as much as +- 60 degrees in some atmospherical conditions. If ATC has radar contact with you and not the a/c that caused the TA then your altitudes are very likely not similar, and should be no threat.

To this extent, I feel safety is well preserved and would not have any problems continuing VMC or IMC..