Murphy's Law: Going The Distance In Montana


December 5, 2018: In October 2018 the U.S. Air Force turned off GPS (satellite-based navigation) over a portion of Montana where the recently expanded Powder River training area allowed warplanes to use airspace up to 16,000 meters (51,000 feet). Ten heavy bombers (B-52, B-1B and B-2) flew in while the GPS was off and tested their skills at navigating without GPS. That means going old school via maps, manual calculations dead reckoning, maps, radar and visual clues on the ground. The last item gets pretty tricky from 15,000 meters up and is especially difficult when clouds are present.

While most warplanes still have the pre-GPS INS (inertial navigation system) equipment long-range flights require the unjammable INS to be updated periodically to adjust for the inherent “drift” in any INS system. This can be done by returning to World War II methods of navigating over water in long-distance aircraft. That would mean using a sextant to get current (approximate by GPS standards) position. That does not help large aircraft using INS as a backup but INS is adequate for giving an aircraft time (an hour or more) to make an emergency landing. Long range bombers do not have that option because INS becomes less accurate the longer you use it. That’s because the gyroscopes and accelerometers used have a tiny inaccuracy (drift) built in which grows over time since the last accurate update.

INS has become smaller, cheaper and more accurate since GPS was introduced in the 1990s and for shorter range aircraft (fighters and fighter-bombers) INS is an adequate substitute for GPS. But for heavy bombers, which sometimes have to fly halfway around the world, the INS drift can get pretty large and at that point, you have to go old school (pre-GPS). Actually, before GPS there were satellite-based navigation systems for updating INS systems but these were superseded by the faster, cheaper and more accurate GPS. Realistic training for a wartime GPS outage is difficult for long-range bombers because they can’t just turn off the GPS and practice. Commercial aircraft are everywhere these days and at all altitudes. Thus the need for a large bit of airspace that can exclude commercial aviation for a while. During such an exercise the air force is monitoring the airspace with ground radar to make sure no aircraft wander in unannounced while the GPS is disabled up there. This “no GPS” training has to be done periodically to validate the training heavy bomber crews are given.

Meanwhile, the navy and ground forces have also been reviving and practicing pre-GPS navigation. Since introduced in the early 1990s GPS has revolutionized movement in unfamiliar areas and nowhere was this more apparent than in the military, where so many personnel on the ground, flying aircraft and steering ships operate in unfamiliar surroundings. Yet after a decade old forms of navigation (using compass, sextant and maps) began to fade away in the military. But after a few years a growing number of commanders and their subordinates realized that that satellites could fail or be jammed and the only alternative would be to fall back on the old ways. Training was revised. Ground troops were reintroduced to pre-GPS training in which troops were taught how to move cross country using a compass and map or simply told to reach a barely visible distant land feature by using landmarks they could see. Naval academies reintroduced celestial navigation and the use of the sextant. Pilots, especially those flying helicopters, were taught the old “visual orienteering” methods.

It was found that without GPS the younger troops, sailors and pilots could still do it old school and seemed to relish the challenge. In one U.S. Navy exercise officers and sailors aboard a destroyer successfully used pre-GPS methods to guide their ship across 2,500 kilometers of open water (from Japan to Guam) and arrive within seven kilometers of where GPS would have taken them. That was close enough to Guam (which is 59 kilometers long) to visually navigate to the naval base and dock. Similarly, there was a recent incident in Central Asia (that was caught on a cell phone video and widely distributed) showing a Kazakh Mi-8 helicopter landing on a highway and asking people in the next vehicle to show up where they were on a map. A truck driver pointed to where the city was they were looking for and the helicopter went on its way. The Mi-8 crew were on a training exercise to see if they could navigate without GPS and back in the old days that sometimes involved landing and asking for directions.

On the ground troops are being reintroduced to the compass, paper maps and orienteering. Most managed to figure it out how it worked before GPS when the joke was that the most dangerous man on the battlefield was a second lieutenant with a map.




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