C172 pilot, through habit pattern, hit the button that changed the transponder code to VFR, 1200.

Attributes
ACN	576502
Time
Date	200303
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : gai.airport
State Reference	MD
Altitude	msl single value : 3000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : pct.tracon
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Flight Plan	VFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 26 flight time total : 91 flight time type : 90
ASRS Report	576502
Person 2
Affiliation	government : faa
Function	controller : approach
Events
Anomaly	non adherence : clearance non adherence : far non adherence : published procedure other anomaly other
Independent Detector	other flight crewa
Resolutory Action	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Approaching the dc ADIZ from the north, I obtained a transponder code and clearance into the ADIZ. Just prior to entering the ADIZ some 15 to 20 mins later, I asked ATC to confirm my ADIZ clearance. ATC said that clearance had already been given before. ATC also advised that frequency change was approved and that I should maintain my squawk code until on the ground at gaithersburg. I repeated the instructions and changed frequency. By force of habit, I also pushed the VFR button on my transponder and started squawking 1200 in the ADIZ. After announcing my position on the CTAF, I realized my mistake and immediately restored the assigned squawk code. I then returned to the bwi approach frequency and explained my error. The controller reminded me that I was to remain on the squawk code until on the ground. I repeated the instruction and apologized. The controller said, 'no problem.' this error was caused purely by habit. Controllers are constantly telling you 'frequency change approved, squawk VFR.' I was not told to squawk VFR in this case, but I did anyway because that's what I always do, or did before the ADIZ. Also, I did not expect to be told to change frequency when I asked for confirmation of my ADIZ clearance. This caught me slightly off guard. It was clear to me that this controller did not want to be dealing with me so I tried as quickly as I could to repeat his instructions and proceed to the CTAF. That haste on my part also contributed to my mistake. I hope that my quick recognition of this mistake and my correction of it helped to limit the trouble I caused.

Original NASA ASRS Text

Title: C172 PLT, THROUGH HABIT PATTERN, HIT THE BUTTON THAT CHANGED THE XPONDER CODE TO VFR, 1200.

Narrative: APCHING THE DC ADIZ FROM THE N, I OBTAINED A XPONDER CODE AND CLRNC INTO THE ADIZ. JUST PRIOR TO ENTERING THE ADIZ SOME 15 TO 20 MINS LATER, I ASKED ATC TO CONFIRM MY ADIZ CLRNC. ATC SAID THAT CLRNC HAD ALREADY BEEN GIVEN BEFORE. ATC ALSO ADVISED THAT FREQUENCY CHANGE WAS APPROVED AND THAT I SHOULD MAINTAIN MY SQUAWK CODE UNTIL ON THE GND AT GAITHERSBURG. I REPEATED THE INSTRUCTIONS AND CHANGED FREQUENCY. BY FORCE OF HABIT, I ALSO PUSHED THE VFR BUTTON ON MY XPONDER AND STARTED SQUAWKING 1200 IN THE ADIZ. AFTER ANNOUNCING MY POS ON THE CTAF, I REALIZED MY MISTAKE AND IMMEDIATELY RESTORED THE ASSIGNED SQUAWK CODE. I THEN RETURNED TO THE BWI APCH FREQUENCY AND EXPLAINED MY ERROR. THE CTLR REMINDED ME THAT I WAS TO REMAIN ON THE SQUAWK CODE UNTIL ON THE GND. I REPEATED THE INSTRUCTION AND APOLOGIZED. THE CTLR SAID, 'NO PROBLEM.' THIS ERROR WAS CAUSED PURELY BY HABIT. CTLRS ARE CONSTANTLY TELLING YOU 'FREQUENCY CHANGE APPROVED, SQUAWK VFR.' I WAS NOT TOLD TO SQUAWK VFR IN THIS CASE, BUT I DID ANYWAY BECAUSE THAT'S WHAT I ALWAYS DO, OR DID BEFORE THE ADIZ. ALSO, I DID NOT EXPECT TO BE TOLD TO CHANGE FREQUENCY WHEN I ASKED FOR CONFIRMATION OF MY ADIZ CLRNC. THIS CAUGHT ME SLIGHTLY OFF GUARD. IT WAS CLR TO ME THAT THIS CTLR DID NOT WANT TO BE DEALING WITH ME SO I TRIED AS QUICKLY AS I COULD TO REPEAT HIS INSTRUCTIONS AND PROCEED TO THE CTAF. THAT HASTE ON MY PART ALSO CONTRIBUTED TO MY MISTAKE. I HOPE THAT MY QUICK RECOGNITION OF THIS MISTAKE AND MY CORRECTION OF IT HELPED TO LIMIT THE TROUBLE I CAUSED.

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.