Citation I (C500)
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 6000; Flight Crew Type 50
Situational Awareness
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural FAR
General None Reported / Taken
Airspace Structure; Human Factors; Aircraft
Upon departure off Runway 32 at FRG a climb to 2900 feet MSL was conducted for our flight northbound. Upon landing we were advised to call New York TRACON. TRACON advised that they showed us cruising at 3100 feet MSL which would have put our aircraft inside the Class B airspace. At no time did the aircraft climb above 2900 indicated altitude. Altimeters were set and cross checked both before departure from FRG and before arrival at [our destination] with the respective local barometric pressures. On the subsequent flight we asked TRACON for a mode C check while in cruise at 10;500 feet which agreed with our indicated Altitude.
Citation pilot departing from FRG northbound at 2900 feet to avoid the New York Class B airspace is informed after landing that his mode C transponder indicated he was at 3100 feet and inside the Bravo.