Moderators: richierich, ua900, PanAm_DC10, hOMSaR
teachpdx wrote:
How common is TCAS (RA) activation in normal operations?
And why does it seem that the crew chose to embellish the situation to the passengers, making it sound more serious than it was? You’d think that they would try to downplay the situation. How common is it to sensationalize things over the PA?
Starlionblue wrote:They're not uncommon. So common, in fact, that the A350 has auto-TCAS as standard and the A330 as an option. The A350 even has auto-TCAS during an automated emergency descent.
As for how many events a year, I don't really know. I've seen TAs but not an RA yet. One more reason to watch your climb/descent rate if there is traffic around.
Woodreau wrote:The two transponders talk to each other to coordinate the RA. This becomes a problem at airports like DEN where some airlines turn their transponders to TA only. When the two planes get vectors to final, one transponder tells the other transponder it’s not going to move because it’s TA only so the other transponder commands a RA to resolve the conflict because it in TA/RA.
When both transponders are set to TA and not TA/RA then no RAs result.
Woodreau wrote:The two transponders talk to each other to coordinate the RA. This becomes a problem at airports like DEN where some airlines turn their transponders to TA only. When the two planes get vectors to final, one transponder tells the other transponder it’s not going to move because it’s TA only so the other transponder commands a RA to resolve the conflict because it in TA/RA.
When both transponders are set to TA and not TA/RA then no RAs result.
BoeingGuy wrote:The Transponders are on or in standby. It’s the TCAS computers that are in Standby, TA ONLY, or TA/RA.
IAHFLYR wrote:BoeingGuy wrote:The Transponders are on or in standby. It’s the TCAS computers that are in Standby, TA ONLY, or TA/RA.
That cannot be correct as if the transponders in on standby there is no way for ATC to track the airplane other than a raw RADAR return which does not allow for the call sign, ground speed, nor altitude to be depicted on the controllers display.
BoeingGuy wrote:Is is correct. My comment had nothing to do with ATC tracking an airplane. I was describing possible states of the system.
IAHFLYR wrote:BoeingGuy wrote:Is is correct. My comment had nothing to do with ATC tracking an airplane. I was describing possible states of the system.
Okay however, when you put down "the transponders are on or in standby" that is what my comment was based upon.
Stand-by: Power is applied to the TCAS Processor and the Mode S transponder, but TCAS does not issue any interrogations and the transponder will reply to only discrete interrogations. The transponder still transmits squitters.
Transponder (mode): The Mode S transponder is fully operational and will reply to all appropriate ground and TCAS interrogations. TCAS remains in Stand-by
If the Mode S transponder fails, the TCAS Performance Monitor will detect this failure and automatically place TCAS into Standby.