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The Class C airspace at that location starts at 2,100 feet. The Cessna was at 1,300 feet. The airliner was at 1,700 feet. The Cessna did not have to be coordinating with ATC because they were NOT in controlled airspace that requires radio communication with ATC, but it is optional and recommended.

The real question here is, why does Austin Approach Control have airliners driving around lower than the ceiling of the Class C protected airspace, where EVERY pilot knows that there are little putt-putt planes pottering about down there?

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That's essentially the approach for the landing to the airport. I'd assume the AA flight was on its way in for landing.

It definitely strikes me as a place that wouldn't be a great idea to fly your plane past if you're not planning to be on comms with ATC.

Seems like maybe the airspace used for the approach should be class C?

How does one find a map?

skyvector.com

No, that's essentially underneath the landing path to the airport. Aircraft operate in three dimensions, and the airspace is sized and configured in three dimensions to support all the navigation needs and users in the area.

Did you know that there is a "tunnel" of uncontrolled airspace directly about Los Angeles International, between 3500 feet and 4500 feet, and you can fly through with commercial airliners whizzing about, talking to absolutely no radar services or ATC controllers? Called the LAX SFRA.

https://www.aopa.org/advocacy/advocacy-briefs/air-traffic-se...

Ah, so the actual issue is that the approach path is inexplicably not controlled airspace? That seems like a different version of bad :-/

The Class C airspace is sized to contain the approach paths, including a buffer above and to the sides, as controlled airspace. But underneath the approach path and Class C airspace is generally uncontrolled airspace, untill you are very close, within a few miles, of the airport. (Technically it is called Class E or Class G airpspace depending on the area and altitude) Think of the controlled airspace as shaped like an upside-down wedding cake. Oh look, the FAA has a graphic for that:

https://www.faa.gov/air_traffic/publications/atpubs/aim_html...

Also, don’t forget that Class E airspace is controlled airspace, as IFR aircraft must operate with an ATC clearance. Airliners operate in Class E all the time. 1. ATC must vector them around VFR aircraft, and 2. VFR aircraft must see and avoid.

Yes, I intentionally did not include that fact, as it it is confusing for a layperson, than an airspace is called "controlled" even though it is only controlled for participating IFR aircraft. For the understanding of a layperson, Class E and G airspace do not require radio communication, radar contact, or permission to enter for little Cessna drivers in nice weather. Heck, you do not even need to have a radio installed, or even an electrical system, if you do not want one.

Respectfully, you are incorrect, and if you are a pilot, this is a dangerous misunderstanding. ATC does NOT provide radar separation services between VFR and IFR aircraft in Class E airspace. Reference the AIM, section 3-2-6-(f). Only separation between IFR aircraft is provided, and you may or may not get advisories and vectors for VFR traffic. How could it be otherwise, technically? The VFR aircraft may not even be equipped with a transponder, one is not required if you are more than 30 miles away from one of the 30 major Class-B airports in the country, and it might be made of bamboo and cloth with negligible radar cross section, so ATC may not even be aware of it's existence.

Separation between IFR and VFR aircraft in Class E airspace requires see-and-avoid by both the IFR aircraft and the VFR aircraft, and it is the responsibility of both pilots in command to ensure this happens. That's why we have the visibility and speed limitations that we have in Class E airspace, to provide enough time and distance for see-and-avoid to occur. But it requires at least one person in each flight deck to have their eyes out the window, not face down looking at the fishfinder.

There has grown a culture of complacency at the major airlines when it comes to integrating with parts of national airspace system that are outside of being directed by a controller - witness the recent Southwest debacle where they took off from a closed runway with personnel working because they did not understand, did not know, or ignored the standard dispatch procedures for operating before a control tower opens.

You are absolutely right about separation between VFR and IFR aircraft. I stand corrected.

Looking at the charts, the Cessna brushed right up against the ground-4500 class C space. Not the smartest place to be off-frequency, in what sounded like mixed viz conditions. At the same time yeah, Austin Approach screwed up - "that traffic's through your final", when obviously it wasn't.

But this is also why you have a layered system of safety. Here, there are three layers:

1. Uncontrolled aircraft stay in uncontrolled airspace, airliners generally stay in controlled airspace (speaking generally, I know class E is controlled, but it's not positive control, and I know that the class C doesn't extend up to the class A) (successful)

2. The airliner had TCAS, as required, and the small plane had a working transponder, as required. As long as the airliner followed the RA, they would remain safe (successful)

3. The controller was supposed to provide separation on a workload permitting basis (not fully successful, the goal is more separation than was provided).

The ultimate result though was that the two planes missed each other by a fairly comfortable margin. The great thing is that the system doesn't depend on everyone being perfect to have a safe outcome, and it's been many years since an airliner has hit another plane in the U.S.

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