GPS Cleans Up After a Thunderbolt

April 2, 1997: Within 90 minutes of take-off, the attack jet had vanished. Hours later, radar spotted it flying over the Colorado Rockies—nearly 800 miles off course from its start at Davis-Monthan AFB near Tucson, Arizona. Was the pilot—Air Force Captain Craig David Button—incapacitated with the aircraft on autopilot, or were his actions methodical? Initial theories included those as far fetched as a Hollywood movie script.

April 20, 1997: Mysteries still surrounded the event, but debris from the aircraft was finally found. The impact point was 13,168 feet above sea level on Gold Dust Peak, 10 miles south of Edwards, Colorado, west of Vail. Searches conducted by Air Force flight crews as well as pararescue teams on the ground located the wreckage, which covered an area of approximately four acres. An investigation would follow, but the more immediate question was how to deal with tons of debris and ordnance strewn across some of the most pristine and popular hiking areas in the world.


The Air Force Turns to GPS
In July of 1997, a Request for Proposal (RFP) was issued by the Air Force that would recruit the assistance of several civilian contractors in the effort to clear the area of unexploded ordnance (UXO) and other debris, as well as to remediate possible contamination by an assortment of fuel, oil and hydraulic fluids that were estimated to be on board the aircraft when it crashed into the mountaintop. Air Force officials were concerned that not only did the unstable UXO present a dangerous accidental detonation hazard to hikers and others in the area, but also fuel and other fluids could seep into the porous tundra and result in the pollution of lakes and streams below the crash site. Security personnel were posted around the area to prevent curious intruders from accidentally detonating the UXO until a remediation contractor could be selected and a plan developed. Within days of returning the RFP, Tetra Tech EM Inc., of Denver, Colorado was chosen as the successful contractor in the remediation of the site. Subcontractors included CMS Inc., of Tampa, Florida for UXO identification and remediation, GeoSeis of Ft. Collins, Colorado for helicopter services, Blackhawk Engineering of Golden, Colorado for ground-penetrating radar (GPR) services, and Innovative Access of Evergreen, Colorado for mountaineering services.

One reason for Tetra Tech EM Inc's selection as the primary contractor on this project was their previous application of Global Positioning System (GPS) and Geographic Information System (GIS) technology in remediation projects. Furthermore, their experience using Trimble's GPS Pathfinder Pro XR mapping system, TDC1 (tm) data logger, and Criterion's laser rangefinder led them to believe that these tools were well suited for the unusual nature of this project. The equipment to be used had to be lightweight, easy to operate, and flexible enough in its operation to adapt to any situation encountered on the mountaintop.

Ordnance Training
Remediation crews were prepared for the task ahead with a two-day training given by Air Force bomb disposal crews and UXO experts from CMS, Inc. This course addressed safety concerns of crew members, as well as what was needed to occur in order to accomplish the job quickly and, most important, safely.

Air Force ordnance officials listed three types of weapons being carried by the aircraft when it left Davis-Monthan: four 500-lb. Mk 82 bombs, more than 500 30-millimeter cannon rounds (the so-called "30 Mike-Mikes"), as well as dozens of flares and other pyrotechnics. Furthermore, Air Force investigators had determined many factors pertaining to the crash itself, such as the angle of impact, whether the engines were running or not at the time of the crash, that the pilot had not ejected, and other issues. This provided background information that allowed us to focus search efforts in areas of highest probability.

Concerns and Preparations
The unusual nature of this project necessitated extreme precautions to prevent mishaps during the remediation and recovery process. Not only were remediation crew members concerned with accidental detonation by coming into personal contact with unstable UXO, but also with the nature of the sophisticated weaponry, which raised a number of extenuating concerns. First, radio signals are frequently part of the detonation mechanism in many types of ordnance. Accidental detonation of unstable UXO by 2-way radios was a dangerous possibility. Second, the behavior of today's weapons makes finding them under these unusual circumstances difficult and very dangerous. For example, bombs don't always detonate upon impact with their target. Depending upon the shape and construction of the ordnance, trajectory, and soil composition, it is possible for a bomb to strike the ground and "skip" along its surface or even penetrate the ground and "porpoise" back out, only to be found down-range from the initial point of impact. Third, the possibility of electrical storms causing accidental detonation of UXO concerned the crew members.

Logistics dictated that no more than 16 team members be on the mountain site at any one time, although more than 100 contractor and Air Force personnel served mission support capacities throughout the project. The relatively small number of crew members on the site at any one time helped prevent mishaps, and allowed for quick transport by helicopter to the base of operations in the event of bad weather.

Another concern of the remediation team was complacency. After the first few days on the site with no live weapons found, it became easy to discount the danger. Redundancy of tasks and physical exhaustion could have bred complacency. They were forced to keep reminding themselves what they were dealing with in order to prevent an accident. They all realized that they could find something deadly at any moment—and in the worst possible way. Fortunately, the professionalism and cooperation exhibited by all of the crew members working together, especially those responsible for removing UXO, helped reassure everyone that their mission could be accomplished safely and effectively.

On the Face
July 19, 1997: The mission began. The Air Force UXO team conducted a visual survey below the snow level to clear the area of possible live munitions that could present dangers to the remediation crew. All crew members and their equipment were airlifted daily by helicopter from the base of operations at Eagle County Airport, in Gypsum, Colorado., to the crash site. Once they arrived on the scene, it was easy to see why the Air Force had taken what seemed like so long to discover the crash site. Button had flown his aircraft into the sheer face of a cliff, with fresh snow falling shortly thereafter. The debris field was in a small, but permanent snowfield at the top of Gold Dust Peak. Even the best pilots would have had trouble seeing the site from the air, especially considering the large area they were searching, but to those on the ground, the point of impact was very evident: there was crushed rock with numerous pieces of small debris embedded in the rock. A large amount of debris also fell to the foot of the cliff. The resulting impact scattered debris over 39 acres in every direction of the impact point.

Slow…but Safe Going
As if the working conditions weren't dangerous enough involving only the UXO, crew members had to factor in the numerous hazards involved in working on the sheer face of a cliff, especially among those who had never been rock climbing before. Fortunately, the mountaineering crew from Innovative Access prepared fixed lines to secure crew members, as well as equipment, securely to the face of the cliff, allowing all of them to work safely.

Safety was also a concern in dealing with inclement weather. For this reason, the GPS laser rangefinder crew was perched on a natural ridge located west of the debris field. From this vantage point, they were also in a good position to observe climbers on the cliff's face that might present falling rock dangers to other climbers and to observe the often-rapid advancing weather systems on the mountain.

Technology Combinations
Their remediation plan called for them to first lay out a 50' x 150' linear grid of the impact point and the surrounding snowfield with the GPS. This was accomplished by marking each search column at the bottom and top. Then, with the Ground-Penetrating Radar (GPR) or the magnetometer mounted to a sled, the site was traversed. As the GPR or magnetometer signaled a "hit," those points were noted with the GPS. The Blackhawk crew took their own characterization data from each "hit" in order to determine whether they were dealing with UXO, harmless debris, or ferrous rock.

This analysis can be tricky. For example, if a writing pen were to be dropped point-first into a sand box, then seen from overhead, the image projected would be a point instead of a pen's length. This is the same problem they faced with ordnance forced into the mountaintop and viewed with the GPR. The GPR characterization had to be carefully analyzed to gain the full benefit, as well as to prevent an accident.

All of this was made much more difficult when they were working on the actual cliff face. This situation was solved by marking out three-foot swaths across the face of the cliff, then raising or lowering the sled at an even rate over each swath. Again, hits were noted and marked for later analysis. The precise positioning given by the GPS also allowed them to know exactly where we left off when work started the next day of operations.

After the fieldwork for the day had been completed, GPS data was transferred from the TDC1 data logger to a desktop PC back at the command post, using Trimble's GPS Pathfinder Office software. The GPS data was then differentially corrected to improve accuracy using data from the base station maintained by CompassCom Inc. in Englewood, Colorado, approximately 250 miles away. The distance to the baseline was further than ideal, both in horizontal and vertical distance. However, due to the time-critical response and the nature of the project, alternatives could not be arranged in a timely manner. The GPS data was then exported into ESRI shape files and coverages for insertion into ArcView and ARC/INFO GIS software in order to map the areas under investigation.

The unique mission presented its own difficulties. The survey covered more area in the vertical dimension than in the horizontal, making the debris location maps more complicated than usual. This was kept in mind when mapping out the data and presenting it in a 2-dimensional format.
Blackhawk Geometrics had their own analysis problems to deal with—taking hundreds, perhaps thousands of signals gathered by the GPR and deciding whether they were ordnance, harmless debris, or simply ferrous metals embedded in the rock. This analysis was also made easier by the accuracy of positional data provided by the GPS, since the accuracy of Blackhawk's analysis could be tracked relative to another search column's readings.

Back on the Mountainside
Each day, as new debris was found, logged and removed, the specially adapted, high altitude Lama helicopter would remove crates filled with from 80 to 1,000 lbs. of wreckage to nearby Eagle Airport, where it was weighed and cataloged. This process allowed them to estimate how much of the wreckage they were finding and removing from the mountaintop. Debris ranging from the size of a dime to several feet long was removed. In all, more than 21,500 pounds of the 26,000-pound plane was removed from the rock crevices and snow fields of Gold Dust Peak.

At their base of operations in Eagle, technology capabilities allowed crews to show Air Force officials work completed as it progressed. Further, they were able to assure officials with a high degree of confidence that areas had been cleared of UXO dangers and toxic substances.
In the end, the team concluded in a report to the Air Force that all ordnance carried by the aircraft was either exploded on impact or disintegrated in the resulting explosion. No live ordnance was found in their efforts.

In the Valley
Of equal importance to Air Force officials was the prevention of potential environmental damage due to seepage of fuel, oil and hydraulic fluid into the porous tundra, which would in turn find its way into the lakes and streams below the crash site. It is estimated that the aircraft was carrying 25 gallons of fuel, 14 pints of oil, and 25 gallons of hydraulic fluid when it crashed.
Remediation team members used the GPS Pathfinder Pro XR to locate soil samples taken from the crash site to the lake below, allowing topography to be the guide. In the event that the explosion caused some of the liquids to blow over the ridge from the crash site, samples were also taken from that area.

Five soil samples were taken at the impact site for analysis. More than 100 water samples were taken from streams and lakes in the area.

In the end it was determined that virtually all fuels and fluids were either burned in the crash or evaporated shortly thereafter, since no measurable amount of the 35 chemical elements used in these liquids were found in the samples.

One year after the remediation effort, Tetra Tech crews returned to the crash site for a second time, verifying the original conclusions through an extensive foot search and telescopic visual survey. Again, no live UXO were found, and no evidence of environmental degradation from fuels or fluids from the crashed A-10 was observed in the area.

A Look Back
In retrospect, their work might seem rather anti-climactic. The larger mountainside dwarfed the search area, with its relatively small snowfield, but considering the amount of work that needed to be done in such a small area and in such extreme conditions of elevation, terrain, and weather, the contributions of GPS and GIS technology were immeasurable.


John Humphrey works for Tetra Tech EM, Inc., in Denver, Colorado, and has worked for a variety of environmental and civil engineering firms over the last 15 years. He is currently involved in site characterization mapping and GPS work in the Bering Sea.

Fraser Roberts has been using GIS in the environmental field for nine years. At the time of the A-10 incident he worked for Tetra Tech. He is currently a Senior GIS Analyst for MFG inc., in Boulder, Colorado.

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