TCAS RAs on approach
 

Can anyone tell me if TCAS RAs are suppressed on final approach to land (and if so below what altitudes)?

At various control zones there are a lot of vfr aircraft either transitting through the overhead or engaged in other tasks close to the approach track of inbound aircraft. While in theory only traffic information needs to be passed there are many occasions when a TCAS RA is reported and is followed by the crew.

If TCAS is suppressed what information does the crew receive about the vfr aircraft?....is it a Traffic Alert as opposed to Resolution Advisory?...and what action would/should the crew take? (Providing they are visual with the vfr aircraft and would otherwise be happy to continue to land).

Many thanks

and does the same apply for departures?

TCAS goes to "TA only" below 1000' radio. If you have a TA and have the traffic visual then you can decide what to do by traditional methods. What's more concerning is when you can'r see it...:eek:

A fairly comprehensive technical description "Introduction to TCAS II Version 7.0." is available here:

http://www.arinc.com/tcas/

(Free registration required).

The TCAS document referenced above states RA's are inhited below 1000 plus or minus 100. In practice I believe - RAs are inhibited below 900' on approach and I think below 1100 after climb. RA's become TA's when inhibited.

RA's are also suppressed during Windshear warnings.

Thanks guys,

All useful info...do all companies operate TCAS like that or is it down to crew choice?

The 900'/1100' RA suppression is a technical feature of the system. My company does not select TA only for parallel approaches (CDG, AMS) and I do not recall hearing about a problem. FRA, BRU, SVO the same, albeit those are not parallel approaches de facto. LHR (LED..) to my knowledge do not operate in parallel at all.

<<LHR (LED..) to my knowledge do not operate in parallel at all.>>

Heathrow can, and does, operate parallel approaches but only under certain conditions when both runways are in use for landing. This usually occurs in the early morning when there are lots of arrivals and few departures. Rules are that radar separation must exist between landing aircraft, but not vortex separation on final approach between aircraft on different runways. In good visibility and daylight radar separation between aircraft on separate runways can be dispensed with if the pilots can see each other and can provide their own separation.

All the above with the usual proviso that things may have changed since I retired!!

Correct. Threats are displayed as TA below the inhibit altitude, and during windshear and Ground Prox warning.

Aircraft reporting within 180' of runway height are considered to be on the ground, and not displayed on TCAS.

I was riding jumpseat in a 737-3 into rwy 30 at KLGB one dark December early evening rush hour a dozen years ago when TCAS was still in its youth. When we were at about 1200' on the ILS, the TCAS said, "Monitor Vertical Speed," and the whole upper arc of the RA/TA/VSI went red. There was a hover bird at about our altitude right over the middle of the airport, giving us a red target.

Then again, "Monitor Vertical Speed," and the whole lower arc of the VSI went red too, leaving just a tiny green arc at 0' VS. There was a light aircraft on short final to 25L, the second red target. The captain (not flying) turned around to me, "What do we do now?"

Almost before I chuckled the words out to go ahead and land, the traffic on 25L sank below 200' and we crossed 900', shutting off the warnings.

As for parallel approaches, they are a nuisance when one or more of the aircraft are on base leg, and a collision appears likely to a TCAS. Once both planes are on final, the rate of closure between them goes to near zero, and the TCAS shuts up. The key to TCAS is projected altitude difference and rate of closure.

GB

Got an RA once going into San Francisco, doing parallel approaches, in a 747. The other guy was turning onto final, while we were straight in. We'd forgotten to select TA ONLY.