Where the Runway Meets
the Mountains
As if landing an
airplane wasn't demanding enough, the airport at Juneau, Alaska has an extra challenge.
It's surrounded by glacier-covered mountains. And if you miss your first approach there's
no way out except the way you came in since there's a 3,000-foot peak just beyond the end
of the runway. But when Nova Stars, working with the FAA, set up a test of a Differential
GPS navigation system, it helped the pilots tame the mountains and land safely.
The mountains have hindered the use of traditional ILS (Instrument Landing Systems)
since they obstruct radio signals. But the DGPS installed at the airport and on five
specially equipped aircraft now allows pilots make their approach with bulls-eye accuracy.
Layton Bennett, owner of L.A.B. Flying Service, which has a DGPS receiver installed in one
of his aircraft, reports "Our pilots say it's more accurate than anything they've
ever flown."
DGPS corrects the signal degradation that is common with standard GPS, and provides 2
to 3-meter lateral accuracy and 3 to 5-meter vertical accuracy at the airport. The Juneau
test also proves the reliability of the GPS signal at high altitudes, which is not the
prime focal area of the GPS signal footprint. Even better, the precise position
information provides controllers in the tower with a real-time pictures of the landing
aircraft. A two-way data link sends the plane's location back to the tower where it's
displayed on a computer monitor.
The ultimate goal of the Nova Stars/FAA project is to prove the reliability, accuracy
and safety of DGPS and certify it for Class 1 commercial landings. So far, the operation
of the system has been flawless and the results very encouraging. This is one test that
GPS passed with "flying" colors.
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