A C150 pilot invades the class D of pdk while using a hand- held GPS for position awareness. Approac...

Attributes
ACN	402213
Time
Date	199805
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pdk airport : lzu
State Reference	GA
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : pdk
Operator	general aviation : personal
Make Model Name	Cessna 150
Operating Under FAR Part	Part 91
Flight Phase	cruise other cruise other
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 28 flight time total : 820 flight time type : 815
ASRS Report	402213
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	non adherence : far other anomaly other other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : exited penetrated airspace other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I departed lzu airport with the intent of taking aerial photographs of a site located near the edge of pdk's class D airspace. To maintain a proper position outside of the class D airspace, I relied on my hand-held GPS to inform me of my accurate position (down to 1/10 mi on the display). While circling the photographic site, I also monitored pdk's tower frequency so that I could maintain an awareness of any departing or arrival traffic that might become a factor. While snapping photos, an announcement was broadcast by the tower controller requesting the intent of the aircraft east of the airport at my altitude. I responded, and advised the controller that I was taking photos. The controller then advised me that I was within her class D airspace. According to my GPS, I was still outside of the class D, but as I talked with her, I watched the numbers decrease until her statement was true, even though at the time, I was flying away from the class D. After returning to my home airport, I visited the local avionics shop to determine why my GPS had responded as it had. After a conversation with one of the technicians, he explained that there is a delay in the processing of the information represented on a GPS display, and an especially long delay in the processing of information on older hand-held units like the one that I owned. Even though the GPS will display distance down to 1/10 mi, the lag time generated by the signal processing will produce a sizable distance error, which can 'sucker' a pilot with a real-time false position, or in my case, distance from an airport. In retrospect, I should have contacted the tower, even though I planned on remaining outside of the class D airspace. Close to the edge of a line drawn on a map doesn't necessarily guarantee safety, and the more prudent action would have been to 'check in,' and provide the controller with a better understanding of why I was flying in circles.

Original NASA ASRS Text

Title: A C150 PLT INVADES THE CLASS D OF PDK WHILE USING A HAND- HELD GPS FOR POS AWARENESS. APCH CTLR ADVISES HIM ON HIS MONITORING RADIO THAT HE IS IN CLASS D AIRSPACE WITHOUT CLRNC.

Narrative: I DEPARTED LZU ARPT WITH THE INTENT OF TAKING AERIAL PHOTOGRAPHS OF A SITE LOCATED NEAR THE EDGE OF PDK'S CLASS D AIRSPACE. TO MAINTAIN A PROPER POS OUTSIDE OF THE CLASS D AIRSPACE, I RELIED ON MY HAND-HELD GPS TO INFORM ME OF MY ACCURATE POS (DOWN TO 1/10 MI ON THE DISPLAY). WHILE CIRCLING THE PHOTOGRAPHIC SITE, I ALSO MONITORED PDK'S TWR FREQ SO THAT I COULD MAINTAIN AN AWARENESS OF ANY DEPARTING OR ARR TFC THAT MIGHT BECOME A FACTOR. WHILE SNAPPING PHOTOS, AN ANNOUNCEMENT WAS BROADCAST BY THE TWR CTLR REQUESTING THE INTENT OF THE ACFT E OF THE ARPT AT MY ALT. I RESPONDED, AND ADVISED THE CTLR THAT I WAS TAKING PHOTOS. THE CTLR THEN ADVISED ME THAT I WAS WITHIN HER CLASS D AIRSPACE. ACCORDING TO MY GPS, I WAS STILL OUTSIDE OF THE CLASS D, BUT AS I TALKED WITH HER, I WATCHED THE NUMBERS DECREASE UNTIL HER STATEMENT WAS TRUE, EVEN THOUGH AT THE TIME, I WAS FLYING AWAY FROM THE CLASS D. AFTER RETURNING TO MY HOME ARPT, I VISITED THE LCL AVIONICS SHOP TO DETERMINE WHY MY GPS HAD RESPONDED AS IT HAD. AFTER A CONVERSATION WITH ONE OF THE TECHNICIANS, HE EXPLAINED THAT THERE IS A DELAY IN THE PROCESSING OF THE INFO REPRESENTED ON A GPS DISPLAY, AND AN ESPECIALLY LONG DELAY IN THE PROCESSING OF INFO ON OLDER HAND-HELD UNITS LIKE THE ONE THAT I OWNED. EVEN THOUGH THE GPS WILL DISPLAY DISTANCE DOWN TO 1/10 MI, THE LAG TIME GENERATED BY THE SIGNAL PROCESSING WILL PRODUCE A SIZABLE DISTANCE ERROR, WHICH CAN 'SUCKER' A PLT WITH A REAL-TIME FALSE POS, OR IN MY CASE, DISTANCE FROM AN ARPT. IN RETROSPECT, I SHOULD HAVE CONTACTED THE TWR, EVEN THOUGH I PLANNED ON REMAINING OUTSIDE OF THE CLASS D AIRSPACE. CLOSE TO THE EDGE OF A LINE DRAWN ON A MAP DOESN'T NECESSARILY GUARANTEE SAFETY, AND THE MORE PRUDENT ACTION WOULD HAVE BEEN TO 'CHK IN,' AND PROVIDE THE CTLR WITH A BETTER UNDERSTANDING OF WHY I WAS FLYING IN CIRCLES.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

A C150 pilot invades the class D of pdk while using a hand- held GPS for position awareness. Approach controller advises him on his monitoring radio that he is in class D airspace without clearance.