Ground based TCAS trials

[Dan Dare]

Does anyone know if ground based TCAS trials at all levels affect aircraft flying overhead? Have you experienced spurious TA/RA flying over an airfield?

Most days we have trials at any level up to FL400 and I've often wondered what the overflights must think.

[mpenage]

Where possible ATC Transponders and TCAS systems are tested inside a Hangar to take advantage of its shielding properties. UK CAA notice number 68 states all the other considerations that are required when ground testing.

[near enuf is good enuf]

"shielding properties"
I'm afraid it doesn't work, as I've found out to my embarassment.

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[Kiwiconehead]

I suppose that it could show up as a target on an overflying a/c's TCAS.

Down here in Oz I usually give approach a call and get a discrete code that they can then squelch it so that they don't have a target floating up and down directly over the field. I found out that the Oz ATC sys won't ignore a test range of codes (0000-0400) in some countries.

[mpenage]

Never had a problem myself. Including full functionals after new installations.

[ETOPS]

Dan Dare

The trick here is to make sure altitude reporting is switched on (Mode C ). Thus the target you are generating will be ignored by overflying aircraft as they will read you as being below 160 feet. It should all be in the manual the kit came with. You do still have the manual? Don't you??

[Kiwiconehead]

You gotta have Mode C on anyway for a TCAS test. Also for the test (at least with Collins on Bae146) you pump a/c up to 10,000' then use the ramp test set to simulate 12700',12800', 7300', 7200', and on the nose at 10,000'. This is to test the ABV/BLW target rejection and test TA/RA indications.

This is from memory but think alts are correct. Also A/C is simulated airborne and Radalt is above 2500' so Mode S will think its flying and will respond to ATC interrogations. Inside hanger is usually enough but there is possibility of it showing up on ATC screens and other aircraft TCAS.

[Dan Dare]

I can vouch for the fact that the Mode C reply indicates any level (often FL400) and that the hanger provides no shielding in the tests I've seen. The assigned squawk can be filtered out of the controllers radar display, but not from overflying TCAS equipped aircraft. What measures are undertaken to stop nuisance TA/RA?

[Dan Dare]

Still no answer. Does nobody know?

[redtail]

I get the same results as Kiwiconehead. Our paperwork requires a call to tower to get their blessings before proceeding. So far it has been a non-issue, as I am one of the invisible elves on midnights, so there is no traffic to be concerned or affected with my ghost airplane. If there was a problem, shouldn't tower be able to inform the crews?