Small Aircraft
Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 30; Flight Crew Total 2200; Flight Crew Type 170
Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action
Human Factors
Forgot to reset transponder after an IFR flight while flying home VFR. Flew out from under STL Class B with incorrect code. Was not on a flight plan or talking to ATC. Noticed on ADS-B that I was either ghosting or getting very close to an airplane indicating a climb and heading the same direction and within 100 feet. I was climbing. Decided to descend and see if the image changed. It did. Never saw the airplane; but evidently came very close to it. I slightly changed course; as did the other plane; which appeared to stop climbing at 7;000 feet. I continued my climb to 11;500 without further incident. Unfortunately still squawking the code given earlier in the day; eventually changing code to 1200 about 3/4 the way home.
GA pilot reported a NMAC on climbout from STL class B while not communicating with ATC. He did not reset the transponder code to 1200 from a previous flight.