Pilots Learning GPS Find It's Not So Easy as ABC  


Pilots Learning GPS Find It's Not So Easy as ABC

by Mike Lenz

The pilot was very impressed with the handheld GPS gift from his spouse. "I have saved a lot of fuel and time on every leg where ATC was able to assign a direct routing. Until I used this GPS, several miles either side of centerline was on course. Now, if I'm more than 100 feet from centerline, I make a correction. After being cleared direct, I haven't had a single ATC call for course correction."

This quote probably conjures up thoughts of a general aviation pilot in a Cessna or Mooney happily navigating using GPS technology. In fact, the author is an MD-80 captain! The pilot's company suggested that he not use the handheld GPS in flight since there was a prohibition against passenger use of such devices because of possible interference. The point is the sophistication and accuracy that pilots can now hold in the palm of their hand now rivals the navigation and flight management systems in some of the world's most sophisticated airliners.

This accuracy and sophistication comes at a cost, however, as was pointed out by a controller who saw three incidents in two weeks when pilots landed at the wrong airport. "With the advent of GPS few pilots look out the window anymore. Pilotage is a lost art. We usually see the boneheads coming and scramble to move everyone out of their way!" The aircraft involved included two business jets and a top-of-the-line single engine aircraft. Pilots of these types of planes are rarely characterized as "boneheads," but in these cases something apparently caused them to make potentially serious mistakes.

 If we look at some of the operational differences between GPS and conventional VOR navigation, two key differences come to light. One is that pilots are now programming an automated system instead of simply tuning a frequency and following a course radial. The other is that the GPS signal is almost always available and will happily take you wherever it is programmed or "misprogrammed!" The phenomenal accuracy pilots are used to seeing with GPS leads them to think, "This thing must be right."

One pilot in a Cessna 152 launched from Allegheny County Airport near Pittsburgh on a training flight to learn to use the GPS. When it was time to return, the pilot selected the destination airport input from the GPS menu option of "nearest airport" and accidentally selected the Greater Pittsburgh Airport (PIT) from the list of airports. The pilot said the contributing factors were a mental fixation on tracking the GPS course line, plus the involvement with programming it and looking for traffic. "It was such a clear day that I thought the airport I saw at eight miles away was Allegheny County. I had the mental fixation that it was the right one." But at three miles from PIT, the pilot realized the error.

 The amazing accuracy of GPS may lead VFR pilots erroneously into a position formerly reserved for instrument-rated pilots who can execute an instrument approach and land in minimum visibility out of a low overcast. There have been reports by VFR pilots who were right over their destination airport at night trying to land using GPS when the airport lighting had unexpectedly failed. They knew they were right over the airport and could faintly make out some features, but fortunately they diverted to another field instead of trying to descend "just a little lower" to get a better look. GPS is accurate, but it generally doesn't display obstacles.

The reliability of the GPS satellite signal is also being taken for granted. Like anything mechanical or electrical, a GPS satellite can fail. Pilots need to have a backup plan. This was best summarized by another airline pilot who used his newly purchased handheld GPS to navigate around some weather when returning home in his Cessna 180. He was so impressed with how accurate and reliable GPS is that he commented that it might lead people into situations where they should not be. He feels all flight instructors should indicate this factor in big red letters to all of their students by telling them to "Don't rely solely on the magic!"

Recognizing some of these GPS operational pitfalls will help pilots see the importance of becoming thoroughly familiar with their GPS before using it in flight. Then it's a good idea to have a flight instructor with you, or at least a safety pilot, for the first few flights. Learning from some of the above tight spots pilots have gotten into using GPS will help others utilize the fantastic benefits that GPS offers pilots while avoiding some of the GPS pitfalls.
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