[cameldrv]

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.