TCAS

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TCAS

Postby ARMO » 26 Apr 2007, 21:55

DURING CRUISE FLIGHT LEVEL FL 390, I CROSSED WITH ANOTHER 737 1000 FT ABOVE (VISUALY) WITH NO TCAS ICON INFORMATION. SAME THING HAPPENED 5 MINS LATER WITH ANOTHER TRAFFIC (A -320) 1000 FT BELLOW .
THE TCAS WAS WORK PROPERLY DURING CLIM AND DESCEND, BUT NOT IN CRUISE..... ?????
PERFORMED TCAS CHECK, OK .
ANY WAY, NO TCAS INFORMATIONS (ICONS) AT LEVEL OFF. ?????
ARMO
 
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Postby sjap » 28 Apr 2007, 13:50

Answer from another forum by Wanderer (on this forum : http://www.aircraftmech.com/forum/index.php):


"The pilot did not mention a couple of things.

Where was the above/normal/below setting?

What was the range set at? If it was set at 2.5 or 5, perhaps the other aircraft was "out of range"

Also, does this aircraft have two directional antennas or only one?"

Best regards
sjap
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Postby sander » 28 Apr 2007, 19:05

Hi ARMO, assuming that the TCAS system was nog in above or below setting.

Did u see the relative altitude next to the proximate traffic icon (white diamond)? if not their setting could have been to 'altitude reporting off'.
If u didn't see their TCAS icons at all then it is possible that they didn't have TCAS, TCAS not working or not selected on (unlikely).
If u did see the TCAS icon with the relative altitude displayed this means that TCAS has picked the other aircrat up but didn't see it as a threat. When your aircraft is above 20000 feet, the TCAS system is in a so called level 7 sensitivity mode wich means that the TCAS will only give the appropriete caution (TA, RA, proximate traffic or other traffic depending on the situation).
For example, the RA caution occurs when the calculated approximate time of collision is 35 seconds.

Above 20000 feet when the intruder is within less than 1200 feet relative spacing in a range of 6 nautical miles, the TCAS will see this as approximate traffic. This is indicated by the solid white diamond. (other traffic is the open white diamond, TA is a amber circle and RA is a solid red square).

How did u establish the relative altitude between you aircraft and the intruder, did u read it off at the TCAS symbol, got it from ATC or VHF or did u visually estimate it due to no TCAS icons at level off (not entirely clear if u saw any TCAS icons at all at the time of the incident).

If your TCAS icons dissapeared when u know there is other traffic around I would suspect a system failure and get the ground engineers to look at it. There are pretty good TCAS system testsets available.
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TCAS

Postby ARMO » 30 Apr 2007, 05:11

Dear all,
Sorry for missing some infos. Here there are:
The equip. does not have “expanded” functions as above /bellow (only normal).
The range was set 2,5 , 5, 10… all of then . I had the aircraft (same company) visually in sight right above us 1000 ft (was informed by the controller). Opportunely, same time, I called the guys on the radio and they said that their transp. and TCAS was working ok and they DID NOT catch us on their TCAS as well….
No indication was provided by the TCAS (ANY ICON) for both aircrafts (other pilot said).
Like I said before, after 5 mins same thing happened again with another acft (A-320) 1000 ft bellow visually (and informed by the controller).
Again : THE TCAS WAS WORK PROPERLY DURING CLIM AND DESCEND, BUT NOT IN CRUISE ??????
Thanks.
ARMO
 
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Postby sander » 30 Apr 2007, 18:00

Hi ARMO, assuming that u and the other aircraft had the TFC button in the proper selection, u should have gotten a proximate traffic indication at least.
U had no indications at all? not even a 'other traffic' indication?
Did u see any other aircraft in cruise other than the two that u didn't pick up?

This is starting to sound as if your TCAS system has a failure in it, it would be interesting to know if the other two aircraft had any problems with other aircraft as well or if your aircraft was the only one.
The relative altitude that the TCAS picks up is Air Data altitude and this is the same altitude the controller gets and also the same as u and the other crew sees on their instruments so if that says 1000 feet than that should be the figure that TCAS should be working with and within 6 NM's aircraft within 1200 feet should be indicated by proximate traffic.
Image
Even in altitude reporting off there should be a indication at least but with no altitude information.


How did the technical department solve this issue? Did anything interesting come out of the functional test?
sander
 
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TCAS

Postby ARMO » 02 May 2007, 19:04

Definitely this was exactly what happened.
Again, TCAS and Transponder was working and settings as described before.
Traffics known 1000 ft bellow and above our acft with NO INDICATIONS (as should be) on the displays (NO ICONS). Aircraft 1000 ft above (same company) did NOT receive ANY indication on their displays as well (capt. Reported by VHF).
This issue is being investigating by my company, and probably, as you said, it looks as a TCAS system has a failure…..
Any way, it seems to me very strange and must be clarified.
Sander, you said about “sensitivity” level of transponder. Do you have more info about it?
Thanks.
ARMO
 
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Postby sander » 09 May 2007, 04:25

Sure ARMO.

The TCAS system uses 6 different sensitivity levels (1 through 7).
Below 1000 feet, the TCAS system is in a level 2 sensitivity mode and the system doesn't give RA alerts at all.
Different sensitivity levels are dependant on the altitude of your aircraft.
The intruder closure rate, the intruder range and altitude combined with the sensitivity level of the TCAS is used to calculate a TAU. The area around the aircraft is considered the protected area. The estimated time in wich a intruder aircraft becomes a thread is called TAU. There is a different TAU value for TA as there is for RA because the RA range is smaller.
Image

In sensitivity level 3 for example, the TAU for RA is 15 seconds while at level 7 the TAU for RA is 35 seconds wich makes the RA protected area significantly larger.


Your complaint however does not warrant a RA, a TA could have been expected but a proximate traffic symbol must have definately been present if both aircraft were equipped with TCAS systems.
I am interested to know what has caused this. please keep us in the loop ARMO.
Greets,
Sander
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Postby sander » 09 May 2007, 04:27

Image

picture didn't work.... :o
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