Two days ago I wrote about the latest airline “close call.” It happened before dawn this past Saturday, in near zero-visibility conditions, at the Bergstrom Airport in Austin.

—A Boeing 767 flown by FedEx was cleared to land, on a “Cat III” approach that allows an airliner to touch down safely even if the pilots cannot see the runway. Meanwhile a Boeing 737 flown by Southwest was cleared to take off from that same runway, directly in the descending airplane’s path.

—It appears that quick action and situational awareness by the FedEx crew prevented a mass-casualty disaster.

I’m writing today to highlight two online assessments of the incident. The first one greatly clarifies what happened and how things went wrong. The second argues that this should be seen not as an isolated mishap but as a warning sign.

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The aviation site VASAviation has a useful YouTube animation that matches radio transmissions with an approximation of where the two planes were. You can watch it on the embedded version above (used with permission) or at this link.

Here is a viewer’s guide to what you’re seeing and hearing. The three voices you’ll hear are:

Austin Tower, the controller clearing the planes to land and take off.
FedEx 1432 Heavy, the Boeing 767 getting ready to land.
Southwest 708, the Boeing 737 getting ready to take off.

• Time 0:11, FedEx: The FedEx plane makes its inbound call. The crucial information it conveys is that it is on a “Cat III ILS” approach to Runway 18 Left in Austin.
  Cat III is essentially an auto-land procedure. Precise signals from beacons on the runway guide the plane (via its autopilot) all the way down, even through fog so thick that pilots never see the ground.

• Time 0:20, Tower: The Austin controller clears the FedEx plane to land. He gives them “RVR” readings — Runway Visibility Range. They indicate that visibility is very poor.

• Time 0:38, Southwest: Southwest announces that it is holding short of the same runway, and “we’re ready.” In aviation parlance this would mean: We’ve been through all the checklists and procedures, we’re all set to give it the gas and go.

• Time 0:42, Tower: The controller reads the same RVR information to Southwest. This takes until time 0:56.
  Then the controller says there’s a “heavy 767” three miles out for landing, and clears Southwest for takeoff.
  I don’t know exact 767 approach speeds for this stage of flight, but it would cover 3 miles in hardly any time.
  This transmission is sure to be the focus of attention. Why not add the familiar terms “cleared for immediate takeoff” or “cleared for takeoff, no delay”? (I have heard both of these phrases hundreds of times.) Why not tell Southwest “hold for landing traffic”, which I’ve also heard countless times? Why didn’t Southwest itself request a hold? Investigators will ask.

• Time 1:15, FedEx: The FedEx crew asks, “confirming we are cleared to land Runway 18 Left?” Meaning: “You know you’ve just put a plane in front of us, right?”

• Time 1:20, Tower: Con