TCAS on the Ground
 

Hi
Am i right in thinking that TCAS is not used on the ground, eg to avoid a collision with another aircraft on a runway in bad weather ?

Thanks for any replies

It's inhibited from giving warnings below a certain height to avoid false warnings at low level. In any event it can only avoid collisions by giving climb/descent instructions not turning instructions so it wouldn't be useful on the ground.

Sometimes on take off it might show the one ahead whilst still on the runway but that is a side effect rather than a design feature.

TA only below 1000ft. Whilst on the ground it will display all transponding traffic within the range selected but obviously it won't give any aural alerts.

Many find it useful to turn it on while holding at the number one position to build situational awareness concerning arriving traffic. It is especially useful if you are in position awaiting takeoff clearance, as it will display most squawking traffic on final (behind you).

Aural inhibition on the ground is true..... but have been on short finals and recieved the Traffic Traffic advisory from ac holding.

It's supposed to do that xodus!:ok: You won't be given any RA's below 1000ft, just TA's.

I believe the use of TCAS on the ground is vitally important in Low Visiblity Ops, because it allows the pilot to crosscheck...

1. The approach is clear before lining up
2. The preceding a/c has taken off into the fog.

Cheers, TP

Mandatory at many airfields now
 

To assist in ground traffic management, and to monitor runway incursions.

Not certin which, but if you check the taxi or ground information it will advise you to turn on tpr....

Bumz

TP,

Basing low vis ops on ACAS use is another example of people trying to use it for purposes its not designed for.

Display filtering means it does NOT reliably display all nearby traffic. Also, Display smoothing leads to significant lag, which means azimuth plotting can lag badly, this can be a real problem during turn rates associated with ground operations rather than flight operation. So, if you have a high turn rate, e.g. turning the corner on a taxy way (perhaps just before a holding point) the horizontal picture can be misleading. Specifically, an aircraft on finals can look like downwind traffic for a few seconds.

Basically, ACAS can tell you an aircraft is somewhere, but it can not reliably tell you an area is vacant. In fact, the busier the area, e.g. a holding point with a dozen aircraft, all mode S-ing and ACASing, packed into a tight space, the more likely it is the ACAS will go into interference limiting mode and stop full time tracking all the blips, which leads to them being removed from the traffic display.

Hence, in ground ops, ACAS can be used to avoid danger, but it can not be used to confirm safety. Certainly no panacea.

CPB

Capt Pit Bull

My checklist tells me to put the TCAS to TA/RA only when cleared to line up or take-off, so hopefully we should not have twelve a/c all ACASing away at the holding point ( assuming all operators use the same system). Out of interest, what does your checklist say?

And my Ops Manual requires me to check the TCAS in LVP's before lining up. I accept that the absence of returns does not guarantee empty airspace, but it all helps SA.

Cheers, TP

TP

<nods>

Inspite of the fact that the manufacturers say to do what you do, I happen to know that a certain company I might work for has the procedure to select TA/RA at the beginning of taxying. Therefore at major bases we do sadly have the prospect of a lot of ssr calling going on in a small area.

I agree with your SA point in principle, but in practice the TCAS display has the potential to degrade SA as well as improve it.

Cheers, CPB