False Tcas/acas Alerts

[Pierre Argh]

Early one morning recently, a twin turbo prop was established on final approach at a UK regional airport. At 7.5nms finals and about to descend on the GS, the pilot broke off the approach saying he had received a TCAS RA.

Although the aircraft was in unregulated airspace, all possible indications are that there were no other aircraft in the vacinity, probably nothing within 20-30nms... there was no other visible SSR, and no primary radar returns showing on two independant systems.

Although this incident is still under investigation, can anyone shed any light on spurious TCAS/ACAS indications, generally? Is this a known phenomena, does it happen often... what might be the cause?

[Lon More]

The Dallas Bump? - or reply received from aircraft on the ground? But both require other a/c. Have had it several times in the past in Upper Airspace with no other traffic around.

[MrBernoulli]

I am aware of recent problems with TCAS in mil aircraft giving spurious RAs. I think a 'wiring/installation problem' was causing the TCAS to give an RA against itself! Yes, I know that sounds ridiculous but that was the reason given.

Would any RAF engineering folk at the secret base in Oxfordshire like to expand/confirm/deny that?

[HEATHROW DIRECTOR]

On a number of occasions at West Drayton I observed the ATC SMF system giving "red" alerts on a single aeroplane. Somehow the system had decided the thing was in conflict with itself! I have also experienced similar situation to that reported by Pierre.

[Scott Voigt]

We've also seen aircraft from time to time who have alerted on themselves. I've seen no explanation for why this would happen though.

regards

Scott

[Pierre Argh]

Thanks Guys... since posting I found the following in an article on TCAS, and problems with the system in its "early stages", on the Aeronautics Learning Laboratory for Science, Technology & Research (Allstar) website

"...These were particularly disturbing because many alerts occurred when aircraft were on final approach, one of the busiest and most critical phases of flight. Version 6.00 was the original software for TCAS II. When using this software, some very interesting problems occurred. False conflict alerts were being triggered by transponders on ships and bridges. Additionally, parallel final approach courses less than 5000 feet apart were causing false alerts. It has even been reported that a pilot’s own aircraft can cause a false alarm. In this situation the pilot found himself trying to outmanoeuvere himself..."

Whether the aircraft in question was fitted with outdated equipment, or the bugs still persist I don't know?

[BOAC]

In this situation the pilot found himself trying to outmanoeuvere himself - ahh! - but did he get away?:D

[DirtyPierre]

Pierre,

We used to get quite a few spurious TA/RAs with TCAS version 6. Since all companies here in Oz now have version 7, the problem seems to have been fixed.

[Pierre Argh]

The more I read the more it sounds like the version 6.00 software could be the problem... seeing as the subject aircraft in my incident is fairly low tech, and from a small airline operating just a handful of aircraft, it is probable they haven't forked out for the latest technology?

Are companies allowed to use different versions in the UK?

[NATCA BNA]

I had a Southwest airlines B737 that was climbing out of 60, that said he had a TCAS alert and asked if there was traffic off his right. The closest traffic off his right was up at FL350, and 7 miles off his left at 90.

TCAS still has problems, but it is better than it use to be.

Mike
NATCA BNA