In flight flyby; why no TCAS warning?

[dho112 17]

Flight from KMCO to KSEA and I was reading while keeping one eye on the screen, and an aircraft drifted in from the left about a mile distant and above.  I watched as it continued to move directly across my nose always above while I checked TCAS, which was on, normal and monitoring.  The aircraft clearly appeared in the display but was neither flagged with an audio warning nor red warning color.  I was probably doing 20 knots over his speed and catching up very, very slowly...

 

After moving from left to right, it then descended suddenly before making a course change away from me until it disappeared behind.  During the entire maneuver our speeds were nearly identical, and there was no danger of collision as long as everything continued as it did.

 

It seemed extremely close though and I was surprised since TCAS is usually VERY good at warning me, or getting my attention when appropriate.  Is this particular incident a failure or shortcoming of the simulation, or are planes on nearly the same heading and speed allowed to fly this close without TCAS warning?  I would think when you can clearly read the livery on the other plane, it might be too close?

[scandinavian13 5,192]

 

 

During the entire maneuver our speeds were nearly identical, and there was no danger of collision as long as everything continued as it did.

 

Think about your post a little bit more...

 

TCAS: Traffic Collision Avoidance System :wink:

 

No sense in setting off warnings about something unless you need to be warned about it.  It showed you the traffic.  Why set off warnings if it doesn't predict you're going to hit it?

 

Simisms die hard I guess...

[dho112 17]

True true, but I was thinking it was a situation where proximity might have been an issue had one of us altered our trajectories.  The other aircraft actually had made a course change while in my vicinity, and I was thinking what if it had been a course or speed change that might get us closer together in a matter of seconds?  Too soon to react?  Instead of the one he made to veer away from me...

 

TCAS in FSX (PMDG) has often given me a first level annunciation "Traffic!" and when I identified the source either visually or on TCAS radar I've often said to myself "Really?  He's a danger?  That far away?"  and in this particular case I was reading logos on the side of the other plane

 

I suppose it must have something to do with closure speed, or if the courses are reciprocal within a certain window...  This particular incident did sort of unfold in slow motion, and it was interesting to watch, but the whole time I had my hands on the controls just waiting for him to do something odd

[Dave_YVR 1,000]

 

 

I was thinking it was a situation where proximity might have been an issue had one of us altered our trajectories. The other aircraft actually had made a course change while in my vicinity, and I was thinking what if it had been a course or speed change that might get us closer together in a matter of seconds?

 

Again, think about changing your course or the AI's. It still wouldn't have put you into a potential collision situation. If you had started climbing, the TCAS would have alerted you.

 

 Have a read to get a slightly better understanding on how TCAS works and what it actually does. It's good stuff to know.

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

[B747tebs 80]

[dho112 17]

Thanks again for the info guys. I'll have a read about TCAS too, thank you for the link Dave!

 

And thank you for that video Tebin, interesting stuff!  I guess my little flyby was nothing then! LoL!  I'm assuming that was not on a landing approach given the high altitude contrails  So it was just a "howdy!  I'm going your way too!" kind of moment