In a little less than another 2 sec., as the now frantic instructor makes a third call for the student pilot to pull up, the Auto-GCAS executes a recovery maneuver at 8,760 ft. and 652 kt.
The student pilot at this point comes around and pulls back on the stick, momentarily increasing Gs beyond the Auto-GCAS standard recovery level of 5 to 9.1.
Since he came around "at this point" and seeing he still had few seconds left to zero, we don't know with 100% certainty that AGCAS was truly pilot's only option.
Auto-GCAS started pulling out at 8,760 feet ASL and bottomed out at a hair under 3,000ft AGL (Judging by the Radar altimeter).
It looks like the pilot start pulling back on the stick at about 6,690ft ASL (Based on the G-Meter going above 5Gs). If the pilot had woken up at that point and immediately pulled back then the AGL clearance drops to about 1,100ft AGL.
Then we have to consider the fact that the plane was already pulling up when the pilot yanked back on the stick. Had the Auto-GCAS not already been pulling the plane up then the pilot would have been lower when he started the recovery.
The "At this point" in the article is not well worded because "At this point" actually looks to be a second or so after Auto-GCAS activated which, when plummeting towards the ground at 650 knots in a 55 degree dive. is basically another 500'ish feet lost
All in all this implies HEAVILY that even if the pilot recovered without Auto-GCAS the margin between survival and lawn-darting would have been a LOT less than 1000ft which is far too close for comfort.
Addendum to my previous comment: As someone else pointed out the GCAS had already rolled him right-side up as well.
Without that he would have taken an extra second or two to reorient himself and take appropriate action.
That delay, plus what I wrote above would make it a certainty in my mind that he would have had an unscheduled plane to ground rendezvous without the Auto-GCAS.
To me it's impressive how fast he still responds after losing consciousness. If you've ever fainted, there's this period where you don't know where you are or even WHO you are, let alone being able to fly a plane.
No, this system only countermands order to fly into ground, not other high G manoeuvres. The 9 G would probably end up snapping wings or in an uncontrolled roll.
F-16s are G-limited to 9G. You can happily pull 9G day in, day out. The actual G loading the plane is certified for would be much, much higher than this (probably at least double).
Look at the rate of descent. He had the plane on its back for a while, losing altitude at around 1000 FPS. May have been above Mach 1. Auto-GCAS took over and snap rolled the plane around to wings-level, then pulled up. This is the most aggressive autopilot on a manned aircraft ever.
Yet it won't take over until it really, really has to. Pilots can fly close to terrain.
It's interesting that the GCAS took over based on data other than the radar altimeter. There's no radar altimeter data when the plane is on its back, because the downward-pointing radar is looking in the wrong direction. Note that the GCAS arrows are moving in before the radar altimeter data reappears.
I would assume that it keeps the last known offset between the radar altimeter and the pressure altimeter. It may have also pulled up based on the pressure altimeter, as obviously the plane won't be flying below sea level regardless. But the latter is less clear. It appears to pull up before the "sea level" altitude gets too low, but the minimal reading may look less severe because the pilot increased the pullout to 9G.
It might also mix in data from GPS and topo maps. It's also possible they have some internal dead reckoning system to perform holdover while the craft is doing aggressive maneuvers. There are a lot of ways to skin that cat.
The student pilot at this point comes around and pulls back on the stick, momentarily increasing Gs beyond the Auto-GCAS standard recovery level of 5 to 9.1.
Since he came around "at this point" and seeing he still had few seconds left to zero, we don't know with 100% certainty that AGCAS was truly pilot's only option.