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Tcas False Alerts Or No Action Needed Alerts?  
User currently offlineJulianUK From United Kingdom, joined Apr 2006, 105 posts, RR: 0
Posted (8 years 4 months 18 hours ago) and read 3350 times:

It is an interesting time to debate how many times TCAS indicates a resolution necessary and none was done or needed - is this a rare occurenence or a regular one? It comes on the back of Airbus thinking about allowing the autopilot to resolve the situation so first I would be interested in learning how many times TCAS is yelling at you but you don't do anything, and if so what would the circumstances be when this happens? Any examples would be great.

28 replies: All unread, showing first 25:
 
User currently offlineA3204eva From United Kingdom, joined Feb 2004, 1060 posts, RR: 5
Reply 1, posted (8 years 4 months 17 hours ago) and read 3335 times:

Well TCAS will advise of an action when another a/c gets in close proximity to your a/c so if you're not visual with the traffic in question then it is a very good idea to follow the TCAS instruction. However, there are times when you do not need to follow TCAS, such as when on final and you are visual with the traffic and you can see that it isn't a threat.

At airports where CCT traffic are instructed to squawk mode C, the a/c's TCAS can go off quite regularly (which why a lot of airports actually instruct CCT traffic to squawk STBY)



"They have lady pilots......... they're not that good, but they have 'em"
User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 2, posted (8 years 4 months 16 hours ago) and read 3331 times:

In an earlier discussion, I described an incident where two planes where flying in the same direction, one a thousand feet above the over. The autopilot on the lower plane disconnected and the plane shot up several thousand feet before the pilots got control back. The TCAS on the upper plane was telling the pilots to climb, bad advice since the other plane was climbing too, but it all happened so fast the pilots didn't have time to react, so they did nothing which turned out be the best response.

User currently onlinePihero From France, joined Jan 2005, 4462 posts, RR: 76
Reply 3, posted (8 years 4 months 12 hours ago) and read 3297 times:
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The TCAS has still a few - identified - drawbacks to be addressed by the av community :
- One is the presentation that is not obvious to some aircrews : the number of pilot actions at the opposite of a resolution is worrying.
-Two is the understanding of "Monitor vertical speed" which in general provokes an increase of the said vertical speed instead of a reduction, as the now philosophy calls.
-Three is the system ignorance of a level-off altitude : this condition happens generally wnen two aircraft in a terminal area, the one climbing being cleared to an altitude 1000 ft below the clearance altitude of the descending one.If their inside each other's trigger volume, you have an unnecessary RA. On the other hand, I prefer that solution, supposing an altitude involuntary bust is always possible. Generally, reducing the vertical speed approaching the level-off altitude allows mw to see better.
-Four is the influence of a fast military jet maneuvering in the vicinity.Quite annoying, but again, the pilot has a better SA.

All in all, I find the device very useful and a great boon to air safety. Proper and strict SOPs should deal with any hesitation.



Contrail designer
User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4491 posts, RR: 21
Reply 4, posted (8 years 4 months 9 hours ago) and read 3276 times:

Quoting Bobster2 (Reply 2):
In an earlier discussion, I described an incident where two planes where flying in the same direction, one a thousand feet above the over. The autopilot on the lower plane disconnected and the plane shot up several thousand feet before the pilots got control back. The TCAS on the upper plane was telling the pilots to climb, bad advice since the other plane was climbing too, but it all happened so fast the pilots didn't have time to react, so they did nothing which turned out be the best response.

Without knowing any more of the story, it almost seems like this was a good idea to follow the RA and climb, especially if (and it sounds like it would be) the lower aircraft was also equipped with TCAS.

Putting the higher airplane in a climb would slow the convergence rate of the two airplanes. It would also allow for more reactionary time for both crews to take appropriate evasive actions (i.e. initiating a turn) which AFAIK isn't commanded by a TCAS.

If the bottom airplane was also equipped with TCAS, even better--the systems in the respective airplanes would be coordinating with each other.



I got my head checked--by a jumbo jet
User currently offlineRendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Reply 5, posted (8 years 4 months 6 hours ago) and read 3245 times:

Well if the above aircraft was told to descend, what do you think would be the outcome?

User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4491 posts, RR: 21
Reply 6, posted (8 years 4 months 6 hours ago) and read 3244 times:

Quoting Rendezvous (Reply 5):
Well if the above aircraft was told to descend, what do you think would be the outcome?

Boom?

I don't understand Reply 2 either. I'd sure like to see that previous discussion.

[Edited 2006-05-28 07:20:14]


I got my head checked--by a jumbo jet
User currently offline777WT From United States of America, joined Jan 2005, 877 posts, RR: 1
Reply 7, posted (8 years 4 months 5 hours ago) and read 3231 times:

Speaking of TCAS.

There's an accident which occured where a DHL aircraft and a russian jet that was carrying school children back from a trip.

The russian jet was starting to dive, the TCAS in the DHL was telling them to climb.
But Switerzland ATC told the DHL to go against the TCAS and to dive, was told twice...

The end result? Russian jet was still diving, DHL dived and collied head on with the russian jet.

A while later, one father of the killed school children built a shrine near where the person working the ATC on that day and went out then killed him while he was leaving work to go home.

If the DHL followed the TCAS and disregard the ATC commands, this wouldn't have happened.


User currently offlineSabenaboy From Belgium, joined Feb 2001, 187 posts, RR: 2
Reply 8, posted (8 years 4 months 5 hours ago) and read 3229 times:

777WT,
You've got it wrong. It's the russian plane that disregarded his TCAS command by following ATC instructions.

http://en.wikipedia.org/wiki/Bashkirian_Airlines_Flight_2937

When you get a TCAS command (RA), You follow it promptly and correctly. PERIOD.

Regards,
Sabenaboy


User currently offlineZeke From Hong Kong, joined Dec 2006, 9109 posts, RR: 75
Reply 9, posted (8 years 4 months 3 hours ago) and read 3217 times:

Quoting Bobster2 (Reply 2):
The TCAS on the upper plane was telling the pilots to climb, bad advice since the other plane was climbing too, but it all happened so fast the pilots didn't have time to react, so they did nothing which turned out be the best response.

Incorrect the ONLY response is to follow the RA, even if at the max certified altitude and it says climb, you climb.

The only concern I have with TCAS is with eastern block equipment and airspace where some of the equipment does not transmit the altitude in ft, its in meters. I know over a reporting point in Yangon FIR the only way a TU154 and a 744 avoided a collision was by listing to a position report, the situational awareness that the 744 crew avoided a collision. The 744 was at 36000 ft, the TU154 at 11000m, the 744 TCAS did not go off at it was comparing 11000 ft to 36000 ft, TCAS does not transmit units of measure being used.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlineWing From Turkey, joined Oct 2000, 1571 posts, RR: 24
Reply 10, posted (8 years 4 months 1 hour ago) and read 3208 times:

A TCAS RA and a GPWS in IMC conditions are two scenerios that you react first and think about it later.

Quoting JulianUK (Thread starter):
how many times TCAS indicates a resolution necessary and none was done or needed

I think you are thinking of a TA(Traffic Advisory).TCAS does not generate non necessary RA's or pilots doesnt think about the RA's as unnecessary,neither think about it.Because time is very limited in a RA situation.

I experienced a real situation of a RA and the biggest thing I remember was how slow was my airplanes escape rate ,against the speed of intruding airplane's picture getting bigger in my window.

In a traffic advisory however you have more time to locate the target visually and be prepared.And there are some cases that the entire TA is wrong.For example A traffic is climbing to FL 28O,and you are descending to FL 290 toward the same waypoint. TCAS doesnt know what is the altitude written on your FCU ALT window and you continue descent with a rate more than 1000 fpm.It will trigger you a TA even though you know that you willl be levelled with a 1000 feet seperation between each other.So there is no action necessary other than reducing the VS to less than 1000 fpm.I think this is what you are referring to.

Quoting Bobster2 (Reply 2):
In an earlier discussion, I described an incident where two planes where flying in the same direction, one a thousand feet above the over. The autopilot on the lower plane disconnected and the plane shot up several thousand feet before the pilots got control back. The TCAS on the upper plane was telling the pilots to climb, bad advice since the other plane was climbing too, but it all happened so fast the pilots didn't have time to react, so they did nothing which turned out be the best response.

TCAS of two airplanes talk to each other and it generates the plane in lower condition a Descent and the plane in the higher condition a Climb.The idea is to seperate airplanes from each other.
In the scenerio you described the lower airplane should have issued a Descent advisory.TCAS doesn't know if the pilots can follow the commands or not but it tels you what to do.Same for the upper airplane they should have climbed,that was the RA given.And I know it happens very fast but there is always time to react.And thats not a violent reaction either.

As a result if that encounter really happened many mistakes added up and coincidently made a correct result(which is the accident not happened) but many times this is not how it ends.



Widen your world
User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 3 months 4 weeks 1 day 20 hours ago) and read 3173 times:

Quoting JBirdAV8r (Reply 6):
don't understand Reply 2 either. I'd sure like to see that previous discussion

Here's the official incident report:
http://www.aaib.gov.uk/cms_resources/dft_avsafety_pdf_501275.pdf

The main point is that the A340, at the lower altitude, suddenly shot up at 6000 ft/sec and the pilots never heard or saw a TCAS warning because they had higher priority issues to deal with. The A330 pilots were trailing the A340 and saw most of what happened. But they did not have time to respond to TCAS. And the TCAS had no way of knowing where the A340 was going, so TCAS ended up giving contradictory instructions to the A330, first climb, then descend.


User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4491 posts, RR: 21
Reply 12, posted (8 years 3 months 4 weeks 1 day 16 hours ago) and read 3163 times:

Quoting Bobster2 (Reply 11):

The main point is that the A340, at the lower altitude, suddenly shot up at 6000 ft/sec and the pilots never heard or saw a TCAS warning because they had higher priority issues to deal with. The A330 pilots were trailing the A340 and saw most of what happened. But they did not have time to respond to TCAS. And the TCAS had no way of knowing where the A340 was going, so TCAS ended up giving contradictory instructions to the A330, first climb, then descend.

Appears there's always more than originally meets the eye  Wink Thanks!



I got my head checked--by a jumbo jet
User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 13, posted (8 years 3 months 4 weeks 1 day 15 hours ago) and read 3155 times:

Quoting Bobster2 (Reply 11):
shot up at 6000 ft/sec

A vertical speed of 4000 mi/hr? Better change that ft/sec to ft/min.  ashamed 


User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 14, posted (8 years 3 months 4 weeks 1 day 15 hours ago) and read 3153 times:

Quoting A3204eva (Reply 1):
there are times when you do not need to follow TCAS, such as when on final and you are visual with the traffic and you can see that it isn't a threat.

RA is inhibited below 1000'agl so you shouldn't get anything but a possible TA anytime on final.


User currently offlineRendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Reply 15, posted (8 years 3 months 4 weeks 1 day 14 hours ago) and read 3149 times:

Yeah, at low altitudes, the displace changes from "traffic" to "TA only" (on Boeing 747-400).

But like has been said, you follow the RA unless you can visually see the other aircraft. If you can't see it, why would you want to second guess or ignore the equipment that is made to help you avoid collisions?


User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 16, posted (8 years 3 months 4 weeks 1 day 12 hours ago) and read 3135 times:

Quoting Rendezvous (Reply 15):
you follow the RA unless you can visually see the other aircraft

That's correct. For us following an RA is MANDATORY unless terrain or wx is an obstacle, for unusual stall or configuration considerations(eg. eng. out), or pilot knows of other non-TCAS a/c that must be avoided.


User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 17, posted (8 years 3 months 4 weeks 1 day 11 hours ago) and read 3129 times:

It appears there are some dangerous misconceptions about TCAS in this discussion.

What is really frightening is that some people think it acceptable to ignore a TCAS RA because they are visual with the traffic. You have no way of being certain that the aircraft you are looking at is the aircraft causing the warning.

Are you certain that you will always correctly identify the threat aircraft and that you will always correctly identify its flight path and how close to you it may come?

Are you willing to bet your life on that?

Ignore a RA because you correctly visually identified the traffic causing the warning and correctly decided it posed no danger and you'll still be around to tell us all just how safe your actions were.

Ignore a RA because you have visually identified the wrong traffic and missed the one actually causing the threat, and you may well not be around to admit you were wrong.

To sum up:

TCAS RA in IMC.................................................Follow the RA, tell ATC.
TCAS RA in VMC................................................Follow the RA, tell ATC.
TCAS RA in VMC, traffic in sight...........................Follow the RA, tell ATC.
TCAS RA in VMC, traffic in sight, not a danger.......Follow the RA, tell ATC.
TCAS RA, contrary to what you think best.............Follow the RA, tell ATC.
TCAS RA, contrary to ATC instructions.................Follow the RA, tell ATC.

The only time a TCAS RA should not be followed is when to do so would immediately and obviously endanger the aircraft. That's going to be a judgment call for the Captain on the day.

A TCAS RA is a serious warning, which may require immediate action. You could potentially be as little as twenty seconds or so away from a mid-air collision.

The system is not infallible, but it has already saved aircraft. It is a real benefit, especially in those remote, or poorly controlled, parts of the world.

Please, let's not start second-guessing a last ditch warning system.

Regards

Bellerophon


User currently offlineNW747-400 From United States of America, joined Jun 1999, 502 posts, RR: 0
Reply 18, posted (8 years 3 months 4 weeks 1 day 9 hours ago) and read 3116 times:

Although it had its teething problems, TCAS has been a valuable tool and has prevented midair collisions. There are 4 typical levels of TCAS advisories, the following are specific to a CRJ:

Level 1: "other traffic" - aircraft within 40nm of the aircraft and within +/-2700 feet, depending on what setting the crew is using

Level 2: "proximate traffic" - aircraft within 6 nm and 1200'

Level 3: "traffic advisory or TA" - aircraft within 40 seconds of possible collision. A TA will not generate a conflict resolution for the pilot to follow on the CRJ; however, it will in other aircraft...the B744 offers a resolution for a TA i believe. Following a TA from the TCAS can result in the pilot being violated by ATC because it is not considered an emergency situation

Level 4: "resolution advisory or RA" - aircraft within 25 seconds of a collision. A warning is issued to the pilots and a vertical escape path is defined on the VSI. Pilots must maneuver the airplane to stay within the green arc on the VSI. If in RA is issued by the TCAS, the resolution maneuver takes priority over any ATC instruction. An Aeroflot aircraft actually collided with a DHL aircraft because the Aeroflot pilots followed ATC instruction rather than the RA issued by the TCAS.

So in response to your question, the TA is a "no action needed" alert unless the captain feels otherwise. I've never had a false RA, but if you are going to disregard one you better be well aware of the situation because a collision is usually imminent.


User currently offlineRendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Reply 19, posted (8 years 3 months 4 weeks 1 day 2 hours ago) and read 3094 times:

Bellerophon, yeah after thinking about it I completely agree with you.

User currently offlineDc-10tech From United States of America, joined Jun 2001, 298 posts, RR: 2
Reply 20, posted (8 years 3 months 4 weeks 1 day 2 hours ago) and read 3089 times:

Quoting CosmicCruiser (Reply 14):
RA is inhibited below 1000'agl so you shouldn't get anything but a possible TA anytime on final.

Flap position is also monitored by the TCAS computer so that it does not give an RA instruciton that the aircraft is not configured to perform.

[Edited 2006-05-29 11:25:35]


Forums.AMTCentral.com
User currently offlineDC-10Tech From United States of America, joined Jun 2001, 298 posts, RR: 2
Reply 21, posted (8 years 3 months 4 weeks 1 day 2 hours ago) and read 3083 times:

Quoting NW747-400 (Reply 18):
Level 3: "traffic advisory or TA" - aircraft within 40 seconds of possible collision. A TA will not generate a conflict resolution for the pilot to follow on the CRJ; however, it will in other aircraft...the B744 offers a resolution for a TA i believe. Following a TA from the TCAS can result in the pilot being violated by ATC because it is not considered an emergency situation

I'm not aware of this feature in TCAS. TA's are advisory in nature only, there is no conflict resolution generated from a TA. A target within the threshold will generate the TA 'traffic, traffic' alert, if an impending collision is detected, then a Resolution Advisory will be generated.



Forums.AMTCentral.com
User currently offlineNW747-400 From United States of America, joined Jun 1999, 502 posts, RR: 0
Reply 22, posted (8 years 3 months 4 weeks 1 day ago) and read 3078 times:

I also forgot to mention: an RA can give commands that an aircraft is not capable of performing. That is one fault of the system.

User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 23, posted (8 years 3 months 4 weeks 22 hours ago) and read 3067 times:

TCAS says Climb/Descent......Just Follow the Instructions.
True Warning or False is not Important.
regds
MEL



Think of the brighter side!
User currently offlineDC-10Tech From United States of America, joined Jun 2001, 298 posts, RR: 2
Reply 24, posted (8 years 3 months 4 weeks 6 hours ago) and read 3035 times:

Quoting NW747-400 (Reply 22):
I also forgot to mention: an RA can give commands that an aircraft is not capable of performing. That is one fault of the system.

By regulation, it is not supposed to. This is why rad alt and flap position are fed to the TCAS computer and why alerts are inhibited below (appoximately) 1000ft AGL.



Forums.AMTCentral.com
25 FlyMatt2Bermud : While on downwind visual approach we had two RA's flying into Naples, Florida one sunny afternoon created by small aircraft in our vicinity. These occ
26 Post contains images Skyman : I agree with you on all points. Thanks for linking the Ueberlingen story so I don't have to write it down again. I'm a bit surprised that the story d
27 HAWK21M : What Type Aircraft. regds MEL
28 Post contains images FlyMatt2Bermud : We were in the Challenger 604 shown below. The other aircraft were both single engine Cessnas. [
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