TCAS and slow moving/stationary targets?

[Papa3]

Hi,

Quick google search on "TCAS filter slow" and similar didn't get me
what I wanted, so here goes... Do TCAS systems filter out targets
which have slow/no ground speed?

Reason for asking... I got into wave yesterday, and while climbing
through 11,000 MSL NW of Allentown PA had an American Airlines CRJ
pass nearby. I would guesstimate that he was about 500 above and a
half mile horizontal. It wasn't really close - I had him in sight
for over a minute and was edging away laterally to gain separation.
But, it was a little closer than the published TA/RA numbers I've seen
in manuals. I was essentially stationary for 20 minutes.

By comparison, later in the flight I watch an A300 make a sweeping
turn around me at 9,000 as I crossed a well-published STAR. I also
checked in with Allentown approach, and they painted me just fine on
their ground radar.

Curious...

P3

[T[_2_]]

On Apr 4, 4:47*pm, Papa3 > wrote:
> Hi,
>
> Quick google search on "TCAS filter slow" and similar didn't get me
> what I wanted, so here goes... *Do TCAS systems filter out targets
> which have slow/no ground speed?
>
> Reason for asking... *I got into wave yesterday, and while climbing
> through 11,000 MSL NW of Allentown PA had an American Airlines CRJ
> pass nearby. * I would guesstimate that he was about 500 above and a
> half mile horizontal. * It wasn't really close - I had him in sight
> for over a minute and was edging away laterally to gain separation.
> But, it was a little closer than the published TA/RA numbers I've seen
> in manuals. * * I was essentially stationary for 20 minutes.
>
> By comparison, later in the flight I watch an A300 make a sweeping
> turn around me at 9,000 as I crossed a well-published STAR. * I also
> checked in with Allentown approach, and they painted me just fine on
> their ground radar.
>
> Curious...
>
> P3

Approach painted you well? As in they could see your transponder
return?
TCAS needs you to have a transponder for it to work.
If approach could only see your skin paint raw radar return, TCAS
would not work, and if you had near zero GS in wave, then the approach
radar would have filtered you out during that time frame.

T

[Darryl Ramm]

On Apr 4, 4:47*pm, Papa3 > wrote:
> Hi,
>
> Quick google search on "TCAS filter slow" and similar didn't get me
> what I wanted, so here goes... *Do TCAS systems filter out targets
> which have slow/no ground speed?
>
> Reason for asking... *I got into wave yesterday, and while climbing
> through 11,000 MSL NW of Allentown PA had an American Airlines CRJ
> pass nearby. * I would guesstimate that he was about 500 above and a
> half mile horizontal. * It wasn't really close - I had him in sight
> for over a minute and was edging away laterally to gain separation.
> But, it was a little closer than the published TA/RA numbers I've seen
> in manuals. * * I was essentially stationary for 20 minutes.
>
> By comparison, later in the flight I watch an A300 make a sweeping
> turn around me at 9,000 as I crossed a well-published STAR. * I also
> checked in with Allentown approach, and they painted me just fine on
> their ground radar.
>
> Curious...
>
> P3

No TCAS I or II do not velocity filter on ground speed. This would be
bad as its foreseeable light aircraft might well have near zero ground
speed. And one reason TCAS got mandated is because light aircraft have
taken down airliners.

This is an old wives tale that I've heard before. The relative speed
(not ground speed) between the threat aircraft and TCAS equipped
aircraft is used to calculate time to collision/proximity parameters
that drive the systems overall TA and RA behavior.

At least one reason this old-wives tale exists seems to be a belief
that aircraft on the ground do not trigger a TA/RA from nearby
airborne aircraft and this must be because there us ground speed
filtering. That's just wrong.

TCAS II (the CRJ will have TCAS II) will have very good altitude data
on you and slightly fuzzy direction data. But its still using that to
projected paths to calculate collision risks if he is not actually
pointed your way with a chance of a collision it should have very low
chance of generating an RA. If your transponder was on and working and
squawking an accurate altitude they may have seen you on their panel
(and hopefully got you visual) or even have had a TA and not needed to
take any action.

Darryl

[JS]

Darryl, are you calling Erik an old wife?
Jim

:-) :-) :-) not three trailers, but I still own the little one

[Papa3]

On Apr 4, 9:02*pm, T > wrote:
> On Apr 4, 4:47*pm, Papa3 > wrote:
>
>
>
>
>
> > Hi,
>
> > Quick google search on "TCAS filter slow" and similar didn't get me
> > what I wanted, so here goes... *Do TCAS systems filter out targets
> > which have slow/no ground speed?
>
> > Reason for asking... *I got into wave yesterday, and while climbing
> > through 11,000 MSL NW of Allentown PA had an American Airlines CRJ
> > pass nearby. * I would guesstimate that he was about 500 above and a
> > half mile horizontal. * It wasn't really close - I had him in sight
> > for over a minute and was edging away laterally to gain separation.
> > But, it was a little closer than the published TA/RA numbers I've seen
> > in manuals. * * I was essentially stationary for 20 minutes.
>
> > By comparison, later in the flight I watch an A300 make a sweeping
> > turn around me at 9,000 as I crossed a well-published STAR. * I also
> > checked in with Allentown approach, and they painted me just fine on
> > their ground radar.
>
> > Curious...
>
> > P3
>
> Approach painted you well? As in they could see your transponder
> return?
> TCAS needs you to have a transponder for it to work.
> If approach could only see your skin paint raw radar return, TCAS
> would not work, and if you had near zero GS in wave, then the approach
> radar would have filtered you out during that time frame.
>
> T- Hide quoted text -
>
> - Show quoted text -

Transponder squawking 1201. Earlier in the flight checked in with
Allentown who were able to verify my location after asking me to
ident. This was when I was buzzing along quite nicely at about 100
kts.

Per Darryl's subsequent post, it's very possible that the geometry
worked out and there was no need for maneuvering. It wasn't
uncomfortably close in the sense I wasn't concerned that paths were
converging.

P3

[Darryl Ramm]

On Apr 4, 10:02*pm, Papa3 > wrote:
> On Apr 4, 9:02*pm, T > wrote:
>
>
>
>
>
>
>
>
>
> > On Apr 4, 4:47*pm, Papa3 > wrote:
>
> > > Hi,
>
> > > Quick google search on "TCAS filter slow" and similar didn't get me
> > > what I wanted, so here goes... *Do TCAS systems filter out targets
> > > which have slow/no ground speed?
>
> > > Reason for asking... *I got into wave yesterday, and while climbing
> > > through 11,000 MSL NW of Allentown PA had an American Airlines CRJ
> > > pass nearby. * I would guesstimate that he was about 500 above and a
> > > half mile horizontal. * It wasn't really close - I had him in sight
> > > for over a minute and was edging away laterally to gain separation.
> > > But, it was a little closer than the published TA/RA numbers I've seen
> > > in manuals. * * I was essentially stationary for 20 minutes.
>
> > > By comparison, later in the flight I watch an A300 make a sweeping
> > > turn around me at 9,000 as I crossed a well-published STAR. * I also
> > > checked in with Allentown approach, and they painted me just fine on
> > > their ground radar.
>
> > > Curious...
>
> > > P3
>
> > Approach painted you well? As in they could see your transponder
> > return?
> > TCAS needs you to have a transponder for it to work.
> > If approach could only see your skin paint raw radar return, TCAS
> > would not work, and if you had near zero GS in wave, then the approach
> > radar would have filtered you out during that time frame.
>
> > T- Hide quoted text -
>
> > - Show quoted text -
>
> Transponder squawking 1201. * Earlier in the flight checked in with
> Allentown who were able to verify my location after asking me to
> ident. * This was when I was buzzing along quite nicely at about 100
> kts.
>
> Per Darryl's subsequent post, it's very possible that the geometry
> worked out and there was no need for maneuvering. * It wasn't
> uncomfortably close in the sense I wasn't concerned that paths were
> converging.
>
> P3

Any maneuvering could always be at ATCs request. However if things go
bad and it gets to an RA (resolution advisory) - the RA are only climb
or descent (or vary rate) instructions so you expect to see things
happen vertically but of course it can be hard to see/tell what is
going on. It is nice if you can monitor the ATC frequency(s) in use so
you can hear ATC directing traffic around you.

Thank you to Erik for using a transponder near traffic areas like
this. And working to understand what might be going on.

Darryl

[Darryl Ramm]

On Apr 4, 9:17*pm, JS > wrote:
> Darryl, are you calling Erik an old wife?
> Jim
>
> :-) *:-) *:-) not three trailers, but I still own the little one

Jim

Jeez I've lost track of how many trailers and gliders you own and on
what continents. "the little one" does not help, you had an ASH-25 --
most other gliders are "little"...

Darryl

[Grider Pirate]

On Apr 4, 11:35*pm, Darryl Ramm > wrote:
> On Apr 4, 9:17*pm, JS > wrote:
>
> > Darryl, are you calling Erik an old wife?
> > Jim
>
> > :-) *:-) *:-) not three trailers, but I still own the little one
>
> Jim
>
> Jeez I've lost track of how many trailers and gliders you own and on
> what continents. "the little one" does not help, you had an ASH-25 --
> most other gliders are "little"...
>
> Darryl

I he means his '27.

[Darryl Ramm]

On Apr 5, 9:17*am, Grider Pirate > wrote:
> On Apr 4, 11:35*pm, Darryl Ramm > wrote:
>
> > On Apr 4, 9:17*pm, JS > wrote:
>
> > > Darryl, are you calling Erik an old wife?
> > > Jim
>
> > > :-) *:-) *:-) not three trailers, but I still own the little one
>
> > Jim
>
> > Jeez I've lost track of how many trailers and gliders you own and on
> > what continents. "the little one" does not help, you had an ASH-25 --
> > most other gliders are "little"...
>
> > Darryl
>
> I he means his '27.

Ah and I just happen to be visiting Williams Soaring today and saw
Jim's '27 in the paint shop. Fancy new Nixon air exhaust and solar
panel and new fuselage paint job being applied. Very pretty.

Darryl