Tcas

[FoxRomeo]

Hi folks,

I'm a tower ATCO in continental Europe.
After a series of incidents we've had a refresher concerning TCAS and its performance.

The main message was: with the XPDR onboard a VFR aircraft (light types in most cases) set on ALT - however no TCAS - a RA is created in the airliners cockpit. To my knowledge both aircraft have to be TCAS equipped to generate RAs.

If one of the technologically experienced could shed light on that matter, please ...

Thanks in advance, FR

[moscho999]

Hi,

there is a difference between coordinated (both a/c are TCAS equipped) and not -coordinated RA's.

That means if the VFR traffic has ALT enabled the other TCAS-equipped a/c gets an RA only - if however, both are TCAS equipped (I am speaking about actual version) the systems "talk" and coordinate their RAs.

Hope the info helped...

[alexban]

as 999 said,the airliner will get a RA,even if the other plane won't have any RA indication.We had such a case with a military plane equiped with TA only xpdr,the airliner got a climb RA at high altitude due to a smart fighter pilot making some target practive.
Brgds alex

[speed freek]

I don't know if anyone else has experienced this but going head to head with a C-5 (and I'm in a Warrior) and they didn't have me on TCAS. I did check my XPNDR, which was on Mode C and transmitting properly. Another time, when my Father was going into Malta, there was a Seneca (or equivalent) ahead of them on the approach, and they didn't have that seneca on TCAS either. Any ideas?

Cheers.

[Ojuka]

Interesting point Speed Freek. Whilst flying a jet with TCAS two or three years ago, we passed a Cherokee no more than 2 nm away at the same height who was definitely squawking mode C and nothing appeared on our display. (I verified this with the Cherokee's pilot on the phone since he was known to me).

However, other light stuff has appeared on TCAS displays I've used with or without mode C read outs.

Strange?

[ICT_SLB]

TCAS should not generate any RAs when the carrier aircraft is below 900 ft agl only TRAFFIC advisories. Our flight test department specifically does not do TCAS ramp tests because it could generate false alerts.

There are several freighters that are routinely parked alongside the main runway here and they have generated alerts - probably because the baro pressure has changed since they shut down and their Transponders are still live.

BTW for certification tests, a ground-based transponder with a variable altitude input (known as a parrot) is set to (say) 1200 feet agl. The aircraft under test is then flown at above and below that altitude and the crew ensure that the correct RAs are displayed & announced.

[FoxRomeo]

Thanks for your help, guys.

You never cease to learn, FR