Helicopter
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 40; Flight Crew Total 4600; Flight Crew Type 500
Human-Machine Interface; Confusion; Communication Breakdown; Troubleshooting
Aircraft Equipment Problem Less Severe; Airspace Violation All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Security
Air Traffic Control Issued Advisory / Alert; Aircraft Automation Overrode Flight Crew; General Police / Security Involved
Aircraft; Procedure
Operations inside of the D.C. SFRA had been conducted for approximately 2 hours with no problems; and Ops were complete. I was enroute to my base to refuel; park and standby. Approximately 4 miles West of landing I was contacted by Potomac Approach on 119.700 and asked for my location. I responded. Potomac then asked me to Ident. As I reached to press the Ident button; I observed my assigned Mode 3/A Squawk code no longer appeared in the Bendix/King KT-70 TSO transponder's display window - instead it showed 1200. I cycled the transponder's power knob to OFF then back to ALT - however 1200 continued to be displayed. At some point during the flight the transponder had dumped the Mode 3/A code and switched; uncommanded; to 1200. At no point did I press the 'VFR' button on the transponder. At no point did I touch the knobs to manually set a new transponder code.Prior to landing the Approach Controller gave me a phone number to call after landing. After landing and shutdown; I called the number. They asked several questions about my personal information (Name; address; FAA Certificate number; etc). They asked if any part of ATC had instructed me to squawk 1200 - I answered No. They also asked if I had purposely or accidentally set my Mode 3/A code to 1200 - I answered No. I then explained that the transponder had switched to 1200 uncommanded; with no input or interaction from myself. They informed me that I would likely receive a follow-up phone call from someone on the matter.
The KT-70 transponder of an aircraft operating in the D.C. SFRA transitioned from the PCT assign code to 1200 uncommanded. ATC questioned the pilot who was told to call after landing.