Capt Happy goes to Southwest

[MikeD]

I was an ATC'er before RA. I've had air carriers get an RA from my aircraft and climb more than once, I don't really get it.

• I'm at 4,500 10 miles off shore heading for Catalina. Straight and level, altitude hold engaged. Busy airspace.
• SWA is at 5,000' off the Santa Catalina VOR on an extended radar downwind for John Wayne.
• ATC has called traffic to both of us, I've reported SWA in sight.
• On ADS-B I see SWA is climbing, later reports to ATC he got a RA and had to climb.

Here's what I don't get.

• Vertical separation of 500' between a VFR and an IFR aircraft is considered adequate.
• An aircraft that leaves an assigned altitude without a clearance used to be a violation.
• Who assumes fault if the RA caused a separation error with a 3rd aircraft? Say traffic at 6,000' heading for LGB?

What’s weird is that 500’ separation of two level flying aircraft, would cause an RA. Unless it sensed you climbing or he was descending at that moment, does 500’ hard separation of two level-altitude aircraft normally cause an RA? A TA I could see. But an RA?

 

[bp]

in my experience 500' separation only works if there's zero closure and you'll likely still get a TA from a GA aircraft because 95% of them are reporting not quite accurate altitudes on the mode c, so that 500 looks like 3 or 400 to the TCAS

 

[fholbert]

What’s weird is that 500’ separation of two level flying aircraft, would cause an RA. Unless it sensed you climbing or he was descending at that moment, does 500’ hard separation of two level-altitude aircraft normally cause an RA? A TA I could see. But an RA?

Then 500' is acceptable, after that incident I assumed it was 1000' . SWA was leveling at 5,000. That may have caused it. Thanks.

 

[fholbert]

in my experience 500' separation only works if there's zero closure and you'll likely still get a TA from a GA aircraft because 95% of them are reporting not quite accurate altitudes on the mode c, so that 500 looks like 3 or 400 to the TCAS

For altitude it's using my mode c? Not ADS-B?

 

[Minuteman]

500 feet vertical separation is sufficient to trigger an RA. By default, advisories are driven the "tau" envelope that represents a combination of range and rate-of-closure for intruders, with separate criteria for "range" and "vertical" taus, which are combined to make the tau envelope.

The default tau envelope for distance and rate-of-closure would intercept the origin, so with only a basic tau computation, two aircraft flying in close formation would not trigger a TA/RA.

Recognizing that two aircraft slowly converging into each other is still usually a bad thing, lower limits for range and vertical separation were added to trigger an advisory when some minimum distance was crossed. These are DMOD for range and ZTHR for vertical separation.

In the Catalina Island/SNA extended final example, a straight-and-level 500-foot vertical separation would have triggered an RA up to roughly 2 miles (assuming a closure rate of 240 knots) where the range tau envelope is crossed (30 seconds) and ZTHR was driving the minimum vertical separation boundary (600 feet).

https://www.faa.gov/documentlibrary/media/advisory_circular/tcas%20ii%20v7.1%20intro%20booklet.pdf

 

[Wardogg]

I think the refineries are fed by lines coming up from the Patoka terminal in south central IL, which ostensibly come in from the SW.

Landing 31 today. I was peeking around but I didnt see a whole lot around coming in from the SW. Less than I thought there would be. I guess I was thinking more towards Joliet.

 

[nabbyfan]

I was an ATC'er before RA. I've had air carriers get an RA from my aircraft and climb more than once, I don't really get it.

• I'm at 4,500 10 miles off shore heading for Catalina. Straight and level, altitude hold engaged. Busy airspace.
• SWA is at 5,000' off the Santa Catalina VOR on an extended radar downwind for John Wayne.
• ATC has called traffic to both of us, I've reported SWA in sight.
• On ADS-B I see SWA is climbing, later reports to ATC he got a RA and had to climb.

Here's what I don't get.

• Vertical separation of 500' between a VFR and an IFR aircraft is considered adequate.
• An aircraft that leaves an assigned altitude without a clearance used to be a violation.
• Who assumes fault if the RA caused a separation error with a 3rd aircraft? Say traffic at 6,000' heading for LGB?

I’m an Enroute guy not terminal but I never use 500ft between IFR/VFR, it creates an RA every time. All the time on BUR/VNY guys there’s idiots flying northbound directly upstream into descending LAX/BUR traffic. Stop the jets 1500’ above and then let them be a bit high and catch up on the arrival later.

My favorite are the guys who depart CMA or OXR VFR and rocket climb directly into the IRNMN at 17500 and then get pissy when they don’t get an IFR clearance for 40-50 miles. There’s a reason you don’t get to go that way when you depart the airport IFR lol.

 

[Cherokee_Cruiser]

I was an ATC'er before RA. I've had air carriers get an RA from my aircraft and climb more than once, I don't really get it.

• I'm at 4,500 10 miles off shore heading for Catalina. Straight and level, altitude hold engaged. Busy airspace.
• SWA is at 5,000' off the Santa Catalina VOR on an extended radar downwind for John Wayne.
• ATC has called traffic to both of us, I've reported SWA in sight.
• On ADS-B I see SWA is climbing, later reports to ATC he got a RA and had to climb.

Here's what I don't get.

• Vertical separation of 500' between a VFR and an IFR aircraft is considered adequate.
• An aircraft that leaves an assigned altitude without a clearance used to be a violation.
• Who assumes fault if the RA caused a separation error with a 3rd aircraft? Say traffic at 6,000' heading for LGB?

That’s just TCAS.

Holding near EWR once at an IFR altitude (I think 8,000) and a VFR guy was coming at 7,500. Completely legal. But TCAS won’t like 500 ft. We get a RA but IIRC and again IIRC, it was a monitor vertical speed kinda thing, where the red shows below you, and AT or above is green. But pilots will still report the RA because technically it is a resolution.

This is why I don’t like VFR traffic that close to me. Even when legal, TCAS will go off.

As for your last question, TCAS “talks” to other TCAS on other jets. You can have multiple RAs in multiple jets for the same situation.

 

[Cherokee_Cruiser]

What’s weird is that 500’ separation of two level flying aircraft, would cause an RA. Unless it sensed you climbing or he was descending at that moment, does 500’ hard separation of two level-altitude aircraft normally cause an RA? A TA I could see. But an RA?

It’s a RA. TA would’ve the yellow dot only. But RA is the whole red square box and a resolution displayed. Of course on the 737 it’s a PFD thing. On the MAX, I remember in the sim the instructor was so excited to show the RA on the VS tape and how awesome that was. Inside I was thinking ok great, it’s like an Airbus now. Big deal.

 

[Kingairer]

I’d be ticked too. Don’t put a Cessna at the same altitude and same space as me on a final approach with only a “insight”.

 

[MikeD]

It’s a RA. TA would’ve the yellow dot only. But RA is the whole red square box and a resolution displayed. Of course on the 737 it’s a PFD thing. On the MAX, I remember in the sim the instructor was so excited to show the RA on the VS tape and how awesome that was. Inside I was thinking ok great, it’s like an Airbus now. Big deal.

The Classic, same. The Jurassic……what’s TCAS?

 

[Minuteman]

As for your last question, TCAS “talks” to other TCAS on other jets. You can have multiple RAs in multiple jets for the same situation.

Small expansion on that: what you're describing is "TCAS II" which has "coordinated resolutions." All kinds of TCAS (TCAS I or PCAS) know the bearing and range of intruder aircraft (and altitude assuming they're mode C or S), but those systems offer only traffic advisories if anything. AFAIK, even modern ADS-B transponders on GA aircraft (where TCAS is a built-in ancillary function instead of being a separate box) are TA-only.

On a coordinated resolution (where both aircraft have TCAS II), the two-or-more aircraft will use the Mode S broadcast to communicate what their resolution guidance is, or choose a guidance based on what they hear, to maximize the closest approach distance. E.g., TCAS II should prevent a scenario where two aircraft moving towards each other both issue the same resolution guidance and end up still moving towards each other. It can get interesting when the computers decide the best course of action to the climb/descend through the past of the intruder aircraft, just do it faster.

The Classic, same. The Jurassic……what’s TCAS?

Wow, I would have guessed that TCAS II was required for RVSM. But it isn't; only that if an aircraft does have TCAS II in RVSM, it has to be v7 (which I think is just a software update for almost all vendors.

 

[Fixtur]

Couple years ago coming back from Mexico landing CRQ in the beechjunk. We're abeam Miramar at 5000 when a busy and distracted controller gives us a couple of Marine helos he's not talking to to look out. No joy (they're painted in low vis colors for chrissakes). Sure enough, we get the RA about 30 seconds later, to which I duly respond per the training, even though I saw what I thought was the offending helicopter just as I initiated the climb. He was close, but I kind of wondered why I needed to climb 1800ft/min to avoid.

A few minutes later after all the excitement the captain tells me I saw the the farther helicopter, and the pilot of the one I just missed had blue eyes and crooked teeth.

This is why we respond to RAs as given.

 

[GolfChuck]

Then 500' is acceptable, after that incident I assumed it was 1000' . SWA was leveling at 5,000. That may have caused it. Thanks.

This implies the SWA was in the descent. The TCAS doesn't know the plan is to level off at 5000. Even if it is programed into the FMS, the TCAS assumes the current trajectory of the aircraft. At least that is how all the training I have ever gotten on it goes. I've seen departures out of AGC cause RAs with arrivals to 32 at PIT because that Lear Pilot decided to do a maximum performance climb to 3000 with the arrival traffic level at 4000.