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The F-16 GCAS is a modified block 25 F-16D to perform flight tests of an automatic ground collision-avoidance system. This system has demonstrated that the use of advanced computing technology can significantly reduce the number of accidents attributed to controlled flight into terrain (CFIT). The U.S. Air Force has lost 4-5 aircraft per year to CFIT since the early 1990s, and the Swedish air force has a CFIT rate about twice that. However, the GCAS system now being developed could reverse those trends.
A USAF, Lockheed Martin, NASA and Swedish air force Advanced Fighter Technology Integration (AFTI) team completed flight tests of an automatic ground collision-avoidance system or Auto-GCAS on an upgraded USAF Block 25 F-16D in the fall of 1998. In 29 flights, the team conducted more than 350 test maneuvers - such as diving at the ground and the side of mountains - to fulfill two key objectives of the program:
* Demonstrate that an Auto-GCAS could significantly reduce critical fighter-aircraft mishaps resulting from pilot spatial disorientation, loss of situational awareness, G-induced loss of consciousness (G-LOC) and gear-up landings.
* Identify any areas where an Auto-GCAS might impede a pilot's performance of standard tactical missions.
During a dramatic 1-hr. demonstration flight for this it became clear that these objectives essentially have been satisfied. The system is not mature enough to install in production fighters yet, but it's about 95% ready.
There is no funded program in place now, but the Air Force will probably field some type of Auto-GCAS on the F-16, F-22 and Joint Strike Fighter. Air Combat Command is developing a formal requirement, and there appears to be enough top-level interest in curtailing perennial CFIT accidents that the AFTI team's research won't be relegated to a dusty shelf, a senior USAF officer said.
The Swedish air force, which routinely flies missions down to 100 ft. above mountainous terrain, could be the first to install a production Auto-GCAS on their JAS 39 Gripens. Sweden's Forsvarets Materielverk (FMV) and Saab participated in Auto-GCAS development and flight tests, and cofunded the program with the U.S. Air Force Research Laboratory under a collaborative agreement. Four Swedish air force pilots have flown Auto-GCAS demonstration profiles at Edwards AFB, and their assessment of the system's viability was very positive.
I found the system to be a sophisticated and complex--but quite robust and effective-- last-ditch method to save an "unaware" or unconscious pilot's life. LMTAS and Saab engineers blended GPS/inertial navigation inputs, a digital terrain database, a radar altimeter, and the AFTI F-16s autopilot with an Aircraft Response Model (ARM) to create a full-envelope, automatic ground collision avoidance system. The block 50 F-16 Terrain-Referenced Navigation System provides a "position" input to help a new algorithm decide what nearby terrain could present a hazard to the aircraft. Based on the fighter's maneuvering attitude at any given moment, a specific area of the terrain database is "scanned," and elevation information is compressed into a 2D model.
The ARM is a sophisticated simulation of the F-16, running at a real-time rate. "It's a fairly complicated algorithm that tracks fuel-burn, takes information from the stores management system [about weapons weight and drag], and even accounts for system processing delays," said Mark A. Skoog, USAF's AFTI F-16 test director. "Using the aircraft's current state, the ARM computes a full six-degree-of-freedom simulation during a roll to wings-level. At wings-level, [ARM switches] to a 2D-type recovery--a second-order modeling of the jet's pitch response. It calculates how much [kinetic] energy it can trade for altitude until the jet reaches a desired zoom-climb speed, then holds that speed."
Ultimately, the computer determines how much time is available before the aircraft will break through a pilot-selected minimum descent altitude (MDA), then triggers an autopilot- commanded protective maneuver. Typically, two chevrons (>
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