Ok, the helicopter & the United flight.
You’re hearing that the United jet got an “R.A.” on final approach. This is a “Resolution Advisory” from the “Traffic alert & Collision Avoidance System” (TCAS).
TCAS is a small unit in the jet or helicopter that talks to other TCAS units in other flying machines. Sometimes little airplanes don’t have a TCAS, so the TCAS in that case just listens to that airplane’s transponder.
When TCAS determines that the airplanes will get close, it issues a “Traffic Advisory” (TA). It announces “TRAFFIC, TRAFFIC” over the speaker & colors the visual depiction of the traffic on your screen so you can see who it’s concerned about, what altitude they are at & whether they are climbing or descending. With that information, you know specifically where to look outside to visually acquire the offender.
It’s not too unusual to get a TA. You don’t have to do anything about it & usually the offender levels off a thousand feet above or below you…TCAS doesn’t know that’s the plan though, and it didn’t like the rate of closure, so it spoke up.
Now, if things start getting even closer & TCAS thinks there will be a collision, it issues a Resolution Advisory (RA). TCAS has been planning for this possibility the whole time & coordinating with the other TCAS…they are chatting to each other specifically, even as both continue to talk to all the other little TCAS boxes in the area, too. TCAS can only tell you to climb or descend (it can’t tell you to turn), so they work together to figure out who will climb & who will descend to create separation the fastest…they will *not* issue the same instructions, like having both jets descend.
Even if the other airplane doesn’t have a TCAS, TCAS can perform basically the same thing by listening to that airplane’s transponder…it’s just that the other little airplane without TCAS is probably still clueless that a potential collision is looming.
Anyway, TCAS comes over the speaker & says “CLIMB, CLIMB” (or descend). It puts a target on your attitude indicator to raise the nose to. If it doesn’t like how you’re doing it, it says “INCREASE VERTICAL SPEED”. It will do this until it announces “CLEAR OF CONFLICT”, at which point you return to your ATC cleared altitude.
You *must* obey TCAS. It overrides ATC instructions. There might be a circumstance where you wouldn’t obey it, but it better be bulletproof because you are going to have to explain yourself. Not obeying TCAS has caused at least one major accident.
As soon as TCAS issues an RA, you tell ATC “Responding to TCAS RA” & they know you are busting their clearance. They’ll focus on making sure you don’t become a problem for someone else in the area. Eventually, the whole thing gets written up in reports & the incident is investigated for a loss of separation.
In the DC crash, the TCAS never said a word, and that’s by design. Below a certain altitude, it inhibits itself, as it assumes you are landing…I think it’s around 1,200’, but don’t quote me on that. As you approach to land, there are a bunch of jets on the ground with their transponders turned on…TCAS can’t filter out who is doing what, and if it worked like it did when you were in the air, you’d never be able to land.
So, that’s basically what happened here. Hope it helps!
Another news piece on the US Army Black Hawk crossed the path of a United Airlines flight headed towards John Wayne Airport in Orange County on Tuesday evening. (full story in the comments)