The Auto-GCAS’s capabilities can best be appreciated firsthand.

During a 1-hr. 20-min. flight on the Air Force Research Laboratory/NASA F-16 testbed, this Aviation Week editor observed a variety of scenarios, many flown at extremely low altitudes and high speed, designed to show how the automatic ground collision avoidance system (Auto-GCAS) will prevent mishaps while allowing the full range of tactical flying without triggering nuisance fly-ups.

Project test pilot Kevin “Budman” Prosser began the flight with a full-after­burner takeoff from Edwards AFB’s Runway 22R, followed by a vertical climb to 15,000 ft. While providing a spectacular start, the spirited departure also demonstrated the system’s ability to transition seamlessly from standby to active mode during an aggressive takeoff and climb. The system activates when the gear is raised, altitude exceeds 400 ft. and calibrated airspeed (KCAS)exceeds 200 kt. A smooth transition to active is good, because “with an afterburner takeoff you are raising the gear within the noise of the digital terrain elevation database system, and you don’t want to trigger a fly-up at takeoff,” explains Prosser.

The existing PGCAS (predictive ground collision avoidance system) warning device was then set to trigger at 50-ft. AGL. “We can’t set it any lower, but that’s what it needs to be at to provide the least amount of nuisance alerts and the least amount of warning time. We’re trying to project what the operational guy is experiencing, and by about the third “pull-up” warning he’s started to ignore PGCAS. We found it is only valuable in a nuisance-free environment,” he says.

Before the demonstration could start, the basic operation of the system was validated, including the ability to turn it off. Flying straight and level at 320 KCAS and 9,000 ft. MSL, Prosser pushed the F-16 into a 15-deg. dive and 90-deg. bank before manually engaging the system using the gun-trigger. The pilot-activated recovery system (PARS), triggered by a panel-mounted switch in the production-standard Auto-GCAS, will enable pilots to recover in the event of disorientation.

In response, the aircraft immediately entered an automatic fly-up recovery by rolling wings-level and initiating the standard 5g+ pull-up. Prosser then canceled the maneuver by toggling a paddle switch on the sidestick controller. He reestablished the setup conditions and again placed the F-16 in a dive with bank angle so that I, from the backseat position, could first activate PARS and then cancel it.

From a test perspective, it is an important safety step to check the ability of the backseat position to terminate the system; but it is also intended as a key element of the baseline production configuration in both the single- and two-seat fighter. “As part of the ‘do no harm’ doctrine, we have to make sure that if the system screws up, the pilot can turn it off,” says Prosser. “There was a lot of heated debate over how much control the pilot should have,” he adds.

With Auto-GCAS healthy, we proceeded to the first specific system demonstration. Setting up at 16,000 ft. MSL and 460 KTAS (knots true airspeed), Prosser rolled the aircraft inverted and let the nose fall through at 1g into a 15-deg. dive. With the stick released at this point, the aircraft remained at 1g automatically. The idea is to replicate typical conditions after a pilot has experienced g-loc (g-induced loss of consciousness), or disorientation, and is unaware of the aircraft’s downward trajectory.

Prosser then engaged PARS to initiate the fly-up, which immediately rolled us wings level and headed us back uphill with a 5g+ pull-up. “Here we’re looking at the autopilot. Is it ‘over g-ing’ the aircraft, or maybe rolling it too slow? The whole time, the trajectory prediction algorithm is predicting what the recovery will look like, and we’re comparing our actual recovery profile to what that prediction was like,” he says.

The team has spent substantial time perfecting the recovery characteristics. “There are a lot of variables at play—initial bank angle, atmospherics, stores configuration and so on. The F-22 and F-35 will be relatively easy by comparison, but the F-16 has a vast variety of stores loadings.”