Oops I left the tcas on....

[hawk37]

So...pilot A leaves the tcas on after landing, and his aircraft has no weight on wheel switch to prevent it's functioning. transponder is functioning.
Does this present any unusual situations to other flights?

Might an aircraft in flight get a TA, for example?

[halfofrho]

Theres plenty of information on google about using TCAS enabled transponders on the ground. One that caught my eye was this. (http://www.eurocontrol.int/sites/default/files/content/documents/nm/safety/ACAS/safety-additional-information-tcas-ras-generated-due-to-transponder-testing-on-the-ground-20080703.pdf)

[NSEU]

Don't know how reliable they are, but reading through some old engineering notes....

There will be no display of aircraft on the ground if your own aircraft descends below 1700' Rad Alt Height. "Ground aeroplanes" are those considered to be within +/-380 feet of ground level for Mode C aircraft or those with the vertical status set to "Ground" for Mode S.

I don't know why, though, if you're sitting at the gate and watching the TCAS, you see targets flying all the way to the ground (0' relative altitude).

[FlightPathOBN]

That was before they began using transponders on ground equipment.

[Capn Bloggs]

That linked document is 2007, so would also be questionable. In Australia, we leave our Mode S transponders on until we park:

b. On receipt of ATC clearance, or requesting the earlier of Push Back or Taxi, select TA/RA/XPDR/ON AUTO as applicable.
Note 1: If AUTO mode is not available Select ON (e.g. XPDR) and assigned Mode A code.
Note 2: Australia does not require TA/RA to be deselected while aircraft is on ground.
c. When parked and shutting down engines, select STANDBY.

Mode C transponders must be Standby until commencing takeoff roll and immediately after landing.

I've never had a TCAS RA caused by another aircraft on the ground.

[ahramin]

That document relates to maintenance testing transponders and is still valid. The transponder is told it is at various altitudes and the tech checks to see if the reported altitude matches. If proper procedures are not followed this can generate TAs and RAs but this is expected behaviour.

Leaving your transponder on on the ground can be a nuisance for ATC but it will not generate TAs and RAs to current TCAS/ACAS systems. Older systems did not filter out ground traffic and will indeed generate advisories but the solution is to upgrade the software in the system.

If your transponder does not have an auto function, don't turn it on until entering the runway for takeoff, and turn it off as soon as you exit the runway. Mode S with auto can be left in auto from startup to shutdown.

[atpcliff]

We are required to turn our Mode C on when crossing runways and before we move on to a runway after we are cleared to lineup and wait, or cleared for takeoff. We do this to check the TCAS for traffic before we physically go onto the runway.

I do not remember seeing any ground targets on TCAS as we are landing.

[FlightPathOBN]

The TCAS system understands when an aircraft is on the ground. It is prudent to go to standby because the more data transmitted from one aircraft in accordance with the system design, the lesser the number of aircraft that can participate in the system, due to the fixed and limited channel data bandwidth

The TCAS system builds a three dimensional map of aircraft in the airspace, incorporating their range (garnered from the interrogation and response round trip time), altitude (as reported by the interrogated aircraft), and bearing (by the directional antenna from the response). Then, by extrapolating current range and altitude difference to anticipated future values, it determines if a potential collision threat exists.

The next step beyond identifying potential collisions is automatically negotiating a mutual avoidance maneuver (currently, maneuvers are restricted to changes in altitude and modification of climb/sink rates) between the two (or more) conflicting aircraft.

A protected volume of airspace surrounds each TCAS equipped aircraft. The size of the protected volume depends on the altitude, speed, and heading of the aircraft involved in the encounter.

[Intruder]

Mode C is altitude reporting. AFAIK, Mode C should be activated whenever the transponder is turned ON. I know of no standard procedures where the "altitude off" setting is used, other than in direct response to a specific ATC request.

Our procedures also state that Mode S/TCAS be selected when the Before Takeoff Checklist is accomplished. That is usually done when approaching the TO end of the runway. Since AFAIK all commercial aircraft DO have RA inhibited on the ground, the OP's question is moot unless there is a system failure. I don't know if the bandwidth limitations mentioned by FlightPathOBN are related to TA or RA, but seeing a target near or on the runway when on final approach may make visual confirmation of a runway intrusion that much easier...

[FlightPathOBN]

Yes, some airports now have a ground system, (hence post #4) so there are different requirements..

In regards to altitude, for TCAS II, (which all should be using)...

INCREASE DESCENT (Resolution Advisories) RAs are inhibited below 1,450 feet radio altitude while descending and 1,650 feet while climbing.
DESCEND RAs are inhibited below 1,000 feet radio altitude when descending, and below 1,200 feet radio altitude when climbing.
All RAs are inhibited below 900 feet radio altitude when descending, and below 1,100 feet radio altitude when climbing.
TCAS voice alerts are inhibited below 500 feet radio altitude.

EGPWS (Enhanced Ground Proximity Warning System), wind-shear and stall warnings will take precedence over TCAS II RAs. TCAS II will automatically switch to the TA-only mode of operation once one of the above mentioned warnings has been generated. It will remain in TA-only mode for 10 seconds after the GPWS/TAWS or wind shear warning is removed.

[nick14]

It's company policy that our transponders are left in alt off until parked.

We have a system of inhibits and afaik the system doesn't generate anything other than the visual indication of a TA below 500' so no problem at all really.

[hawk37]

OCK465
any idea why mode C is to be operated on the ground in DFW? Might that be that aircraft in flight can then inhibit display of such aircraft as NSEU says?

NSEU, you say "There will be no display of aircraft on the ground if your own aircraft descends below 1700' Rad Alt Height. "Ground aeroplanes" are those considered to be within +/-380 feet of ground level for Mode C aircraft..."
Do you think this is determined by comparing the target's mode C altitude to your mode C and your rad alt? If so, then perhaps I would not get a climb climb climb if I was above an aircraft taking off, when it is still below 380 feet above the airport?

thanks,

Hawk

[FlightPathOBN]

Post #11 gives the explanation from the manufacturer on the TCAS II system

regarding Resolution Advisories and the respective altitudes....:ugh:

[OK465]

All RAs are inhibited below 900 feet radio altitude when descending, and below 1,100 feet radio altitude when climbing.

What if you're at 1000 feet level? :}

[FlightPathOBN]

Really OK...really?

as the song goes "just think about it"

BTW... Remember the old days when Obama's biggest embarrassment was Joe Biden?

[Capn Bloggs]

Don't worry, OK465. Some of us see your sense of humour! :ok:

[jfkjohan]

OK465, RA is AGL/AAL.

oh wait, you knew that.


Ahh, i get the joke now!


Proceed :)