Xpndr only Vs. TaRa on the ground
My company is implementing the new procedure that before taxi we are to set the transponder on (altitude encoding, Ta only) but at line-up to put it in TaRa mode.
Is there any difference really when operating on ground wheather the xpndr is in Ta or TaRa modes? Just wondering... |
From B738 FCOM:
RAs are inhibited below approximately 1,000 feet radio altitude. Below 1,000 feet when the TA/RA mode is selected on the transponder panel, TA only mode is enabled automatically and the TCAS message TA ONLY displays on the ND. |
Our SOPS have the transponder set to XPNDR only as it interferes with ground surveillance radar at bigger airfields.
|
We also have this SOP. I don't know much about how it works but our tech pilot tells me it is an ICAO recommendation because TCAS units, of airborne aircraft, have been known to miss an RA because they were interogating too many ground returns at the time.
Perhaps a more sensible compromise might have been to only switch on the TCAS when you are number 1 at the holding point. |
I have heard similar explanations, but if there is an aircraft on final, and I'm at holding point, I don't know if there is any difference for the other one wheather I'm sqwaking TA only or TARA. He is only working his own settings and my altitude is showing anyway.
What puzzles me is really that I can't see any difference for me what I sqwak on ground (because RA is inhibited), nor the other airborne traffic (because they are working their own settings and can't see if I'm sqwaking TA or TARA). :confused: |
There is no difference for the one on finals, because he is TA only. The difference is that your transponder will only be dishing out Callsign, squawk and level. At worst, this will only generate a TA (right up to the point of impact). The important thing is that you are not part of any RA contract for those aircraft in your line of sight. When you are TA only, you will always be taken into account for another aircraft to calculate an RA to avoid you or any others.
PM |
I agree with most that either way it's no problem for the aircraft, any ATC people out there with an opinion, I remember a few years ago how the ID tags go into a track drop or something and clog up the display.:confused:
|
See the latest EUROCONTROL ACAS Bulletin
http://www.eurocontrol.int/msa/galle...n_9_Jul-07.pdf which says the following: Should TCAS be operated on the ground? The Advanced Surface Movement Guidance and Control System (A-SMGCS) is to be introduced at a number of European airports. To enable A-SMGCS detection, aircraft must be operating their Mode S transponders, at least from the pushback and until reaching the stand on arrival. TCAS also relies on Mode S technology and for this reason TCAS and Mode S control panels are usually combined in a single unit on the flight deck. Experience shows that TCAS is sometimes turned ‘on’ and turned ‘off’ at the same time as the Mode S transponder. Except for turning TCAS on for a short period of time before crossing an active runway to double-check for the presence of any aircraft on approach, this should not be done for the following reasons:
At the gate: Transponder OFF/STBY, TCAS OFF Pushback request: Transponder ON, TCAS OFF Approaching holding position: Transponder ON, TCAS ON Vacating runway: Transponder ON, TCAS OFF Fully parked at the gate: Transponder OFF/STBY, TCAS OFF |
in the A320 FCOM 3 (s.o.p) before takeoff : it says:
TCAS mode selector......................Select TA or TA/RA. then it says : the FAA recommends selecting TA in the following cases: 1-a known near by traffic that is in visual contact. 2-at particular airports and during particular procedures, identified by an operator as having a significant potential for unwanted or inappropriate RA (closely spaced runways,converging runways...) Good Luck |
Kuwait that's great except this thread is about ground ops. :ok:
|
Several airports in various countries have implemented the requirement to squawk Transponder Only on the ground, either from receipt of a code from Clearance Delivery, or from pushback. These procedures are in accordance with ICAO and IFALPA recommendations that TA and RA be deselected until taking the runway for T/O (including Lineup and Wait) and after clearing the runway after landing.
|
Dream Land
yes you are correct....but what i wanted to say is ...this is the only place that the TCAS selection is mentioned..nothing mention in the taxi section . thanks |
I have been told that aircraft with TA or TA/RA on the ground will affect the ground surveillance radar sweep.
|
The general reasoning behind the recommendation is that every TCAS unit has to talk to every other TCAS unit in range, whether or not you see them on your traffic display. At busy airports or under busy airspace, the rate at which TCAS units can update their situation is reduced by having many other units to interrogate.
You don't need TCAS on the ground, so turn off TCAS (but leave on the relevant mode C/S squawk for Advanced Surface Movement Radar) until ready to get airborne, or to check the traffic on finals when at the hold. It's nothing to do with frequency interference or unwanted RAs, more to do with trying to keep the airbrne units working as efficiently as possible. At quiet airports it's probably not such a problem, of course, but consistency of SOP is quite important so perhaps the recommendation is about encouraging 'good habits' for when you do visit somewhere busier. |
Brilliantly put Gary!
|
All times are GMT. The time now is 09:53. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.