International Ops: WGS-84 errors create problems

 - April 30, 2011, 4:20 AM

Imagine the fun if every pilot’s understanding of where London Stansted Airport actually sits on the earth’s surface were a little different. Some might think it was in London proper, others in Essex, and a few more might be willing just to take their chances. When a passenger asked to be flown there, no one could really guarantee everyone would end up in the same place. And the hazards of breaking out of the clouds and finding something other than the airport ahead are not pleasant to contemplate. That’s essentially the problem with WGS-84 errors, and they’re still all too common around the world. The WGS-84 title relates to the World Geodetic Survey, which was last conducted in 1984 but is still used as a major world aeronautical reference standard.

Air Training International president Dave Stohr says there “are actually some 500 different reference systems in the world although only a few are used to identify aviation fixes. GPS, for example, uses WGS-84 for reference. If you’re flying in a country that does not use WGS-84, you might break out of the cloud as much as half a mile off.” So much for GPS. maintains the list of compliant countries. “If you are flying in a non-WGS-84 country, we recommend you not use GPS and navigate using raw data,” Stohr said. WGS-84 compliance in Russia and China for example, is impossible to determine, according to Jeppesen, which means crews can assume only that they do not comply. Countries with similarly vague responses to the WGS-84 compliance question include the Democratic Republic of Congo, the Dutch Antilles and Greece.

“Despite ICAO, WGS-84 compliance is voluntary, not required,” Stohr reminds pilots. “ICAO asked that all signatories be WGS-84 by 1998, but here we are in 2011 and a substantial number of countries still do not comply.”