Riddle me this, pilots

Once below a certain agl altitude the TCAS will not give and RA but only
a TA.

Roy Smith wrote:
I asked:

Do TCAS RA's take terrain into account?


Newps wrote:

Yes, the airplane knows how high it is. It will not drive it self into
the ground.


Bob Noel wrote:

TCAS units do not contain terrain databases.


I'm having a hard time making these two responses jive :-)

"Newps" wrote in message news:ihu1b.227105$Ho3.29390@sccrnsc03...
Once below a certain agl altitude the TCAS will not give and RA but only
a TA.

It's needs to be hooked to the radar altimiter in addition to the pressuer alt. from the
encoder/air data computer?

Snowbird wrote:

Newps wrote in message news:dTf1b.167931$cF.58574@rwcrnsc53...

Roy Smith wrote:

Newps wrote:



If the TCAS gives an RA the airliner must take the action
suggested.


Do TCAS RA's take terrain into account?

Yes, the airplane knows how high it is. It will not drive it self into
the ground.


Knowing how high it is, is only part of what's needed -- does it
know where it is, and how high the terrain is nearby?

Doesn't need to know where it is. Only how far above the ground it is
or will be in a few seconds. The TCAS will only tell you to go either
up or down, not right or left.

In article , Roy Smith
wrote:

I asked:
Do TCAS RA's take terrain into account?

Newps wrote:
Yes, the airplane knows how high it is. It will not drive it self into
the ground.

Bob Noel wrote:
TCAS units do not contain terrain databases.

I'm having a hard time making these two responses jive :-)

I haven't had an opportunity to check my TCAS sources. But
I seem to remember the TCAS II unit having some interface
with the Radar Altimeter. Also, I'm pretty sure that a GPWS
(or TAWS) warning/alert/whateveritiscalled takes priority over
an RA.

Note that a radar altimeter isn't normally used above 2500' agl.

does that help?

--
Bob Noel

"Everett M. Greene" wrote in message
...

That's not proof, that's a statement. The other plane was
"saying" it's VMC.


A pilot's report of his flight conditions is taken as fact.

"Newps" wrote in message
news:ihu1b.227105$Ho3.29390@sccrnsc03...

Once below a certain agl altitude the TCAS will not give and RA but only
a TA.


How does the TCAS know the AGL altitude?

I think the logic of what you say is correct but in the heat of things but
is not intuitive to a pilot who has not been taught this and had the
opportunity to think it out on the ground. The instinctive reaction of a
pilot otherwise is to turn left when he is told traffic is on the right,
even though futher analysis under calm conditions leads to an alternate
conclusion as you noted.

--
Richard Kaplan, CFII

www.flyimc.com

"Steven P. McNicoll" writes:
"Everett M. Greene" wrote:

That's not proof, that's a statement. The other plane was
"saying" it's VMC.

A pilot's report of his flight conditions is taken as fact.

Procedurally, you are correct -- if the pilot says he's IMC,
ATC handles him accordingly. However, his statement isn't a
"fact" in the legal sense in that it's uncorraborated and in
the situation being discussed, another pilot is "saying" it's
VMC by his actions. Which of the two "facts" is correct?

"Everett M. Greene" wrote in message
...

Procedurally, you are correct -- if the pilot says he's IMC,
ATC handles him accordingly. However, his statement isn't a
"fact" in the legal sense in that it's uncorraborated and in
the situation being discussed, another pilot is "saying" it's
VMC by his actions. Which of the two "facts" is correct?


The pilot not communicating with ATC isn't saying anything.

Peter Duniho wrote:

wrote in message ...
It has already saved a few friends of mine, in one case IFR vs. IFR in the
flight levels. Perhaps it is not as safe as it could be, but it's a lot
safer
than not having it at all.

Again, you are mistaking a technology that helps increase overall safety
statistics with one that can be counted on in every situation to improve
safety.

There's a difference.

Yes, the former is achievable; the latter is not.