Safety Spotlight

Personal digital assistants (PDAs) with GPS capability have become a staple in many flight bags. Although it is tempting for pilots to use these as their primary navigation source under instrument flight rules, it is not legal, nor the safest way to fly. Case in point: An instrument-rated private pilot flying a Cessna 172 was killed on October 15, 2002, when he attempted a GPS approach to Mount Sterling-Montgomery County Airport in Mount Sterling, Kentucky.

The evening before the accident, the accident pilot completed a checkout in the same Cessna 172. According to the checkout instructor, the pilot was "very competent," completing multiple IFR tasks successfully during the checkout. During the checkout, the pilot started to use a PDA with a GPS antenna but turned it off at the instructor's request. The Cessna 172 they were flying was certified for IFR flight, but it did not have a GPS receiver installed.

On the day of the accident, as the pilot approached Mount Sterling, he requested the GPS approach to Runway 21--despite the lack of an approved, IFR-certified GPS receiver. The approach was approved, and he was advised of the local altimeter setting but did not acknowledge the transmission. The GPS approach to Runway 21 at Mount Sterling consists of four fixes: FELPO, the intermediate approach fix; ISFUR, the final approach fix; an unnamed step-down fix located 2.3 nautical miles from the missed approach point; and Runway 21, the missed approach point.

Radar data indicated that the airplane passed abeam FELPO one nautical mile right of course at an altitude of 2,700 feet. Abeam ISFUR (the final approach fix) the airplane was one-half mile right of course at 2,300 feet. The charted minimum altitude between FELPO and ISFUR was 2,600 feet msl (1,800 feet agl). The airplane struck a tower to the left of the approach course centerline, at an elevation of 1,350 feet.

Weather at the time of the accident included an overcast ceiling at 500 feet agl, three statute miles visibility, temperature 58 degrees, and dew point 54 degrees. The pilot had more than 478 hours of total time, including 106 hours of instrument experience.

The NTSB determined the cause of this accident to be the pilot's failure to follow the published instrument approach procedure, which resulted in an early descent into an antenna tower.

The maker of the software on the PDA had posted a warning on its Web site stating, "The system is not tested or approved by the FAA or any governmental agency and should not be used as a primary flight instrument."

Handheld GPS units are a wonderful resource in the cockpit. A moving map display can significantly improve a pilot's situational awareness. However, none of the handheld units on the market is legal for primary navigation under IFR. If you own a handheld GPS, it is imperative that you use it according to the manufacturer's recommendations.

For more information about GPS in general, download the AOPA Air Safety Foundation's GPS Safety Advisor. Also, look for ASF's newest online course, GPS for VFR Operations, which will be added this spring to the ASF Online Safety Center.

Kristen Hummel manages the GA accident database for the AOPA Air Safety Foundation. She holds a commercial pilot certificate with multiengine and instrument ratings.