Narrative:

We were flying a G1000 equipped da-40XL single-engine airplane. On the way to ZZZ; I was the PF; under an approved view-limiting device; and mr.X was my safety pilot. We filed and flew on an IFR flight plan uneventfully to ZZZ. When we had the field in view; approach cleared us for a visual approach and we cancelled IFR with them while still in the air. The controller told us to squawk VFR; at which time I hit the VFR soft button on the G1000 transponder screen and noted 1200. We followed through to an uneventful landing at ZZZ. On the ground at ZZZ; mr. X and I shut down the airplane and switched seats for our return trip. For the return trip; mr. X would be the PF and I would be his safety pilot; or acting PIC. Due to time constraints; we elected to depart VFR since the WX at ZZZ and enroute would be amenable to such. We then performed a standard run up; including checking the transponder. Out of habit; we again pressed the VFR softkey on the G1000; but neglected to note the code in the transponder window. Unfortunately; this is the crux of the problem; because the G1000 exhibits some rather aberrant behavior in this circumstance. It seems that when you hit the VFR softkey a second time on the G1000; regardless of whether you have shut down or not; it will reassign to the transponder the previous code and not 1200. In our case; it reassigned abcd if memory serves. This is; in my opinion; as both a software engineer and a private pilot; very undesirable behavior. First; it violates the function of nearly every other transponder in existence in that the VFR button should always enter 1200. Second; it assigns the previous code even after a shutdown; for which I can think of no reasonable use other than to cause us and other G1000 pilots the exact problem we experienced this day. We departed with this previously assigned transponder code; and flew under the class bravo shelf until clear of it before climbing to our cruise altitude of 5500 ft MSL. It was not until we were just over ZZZ1 that mr. X noticed the code was incorrect. As acting PIC; I decided to call center and alert them to the fact that we had an erroneous transponder entry and that we were at that time switching it to 1200. Center acknowledged the error and said they were made aware of it upon our departure. The controller told us to squawk VFR (1200) at that time which we did. Conclusion and recommendation: as acting PIC it was my responsibility to check the transponder code; and I failed to do so in a timely manner. A significant contributing factor is the odd behavior of the G1000 VFR softkey; which contradicts the behavior of every other transponder with which I have experience. It is my recommendation; to promote safety and uniformity of function; that the certification process for transponders be amended in a manner that requires the VFR button to always enter 1200 in a transponder. Doing so will relieve confusion on the part of both pilots and controllers; and could potentially save a traffic conflict in the event ATC expects an aircraft transmitting a particular code to be on a particular type of flight plan.

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Original NASA ASRS Text

Title: DA-40XL PRIVATE PLT HAS CONCERNS WITH THE G1000 VFR SOFTKEY FUNCTION. PRESSING THE BUTTON TWICE RESTORES THE PREVIOUS IDENTIFICATION CODE.

Narrative: WE WERE FLYING A G1000 EQUIPPED DA-40XL SINGLE-ENGINE AIRPLANE. ON THE WAY TO ZZZ; I WAS THE PF; UNDER AN APPROVED VIEW-LIMITING DEVICE; AND MR.X WAS MY SAFETY PLT. WE FILED AND FLEW ON AN IFR FLT PLAN UNEVENTFULLY TO ZZZ. WHEN WE HAD THE FIELD IN VIEW; APCH CLEARED US FOR A VISUAL APCH AND WE CANCELLED IFR WITH THEM WHILE STILL IN THE AIR. THE CTLR TOLD US TO SQUAWK VFR; AT WHICH TIME I HIT THE VFR SOFT BUTTON ON THE G1000 TRANSPONDER SCREEN AND NOTED 1200. WE FOLLOWED THROUGH TO AN UNEVENTFUL LNDG AT ZZZ. ON THE GND AT ZZZ; MR. X AND I SHUT DOWN THE AIRPLANE AND SWITCHED SEATS FOR OUR RETURN TRIP. FOR THE RETURN TRIP; MR. X WOULD BE THE PF AND I WOULD BE HIS SAFETY PILOT; OR ACTING PIC. DUE TO TIME CONSTRAINTS; WE ELECTED TO DEPART VFR SINCE THE WX AT ZZZ AND ENROUTE WOULD BE AMENABLE TO SUCH. WE THEN PERFORMED A STANDARD RUN UP; INCLUDING CHECKING THE TRANSPONDER. OUT OF HABIT; WE AGAIN PRESSED THE VFR SOFTKEY ON THE G1000; BUT NEGLECTED TO NOTE THE CODE IN THE TRANSPONDER WINDOW. UNFORTUNATELY; THIS IS THE CRUX OF THE PROBLEM; BECAUSE THE G1000 EXHIBITS SOME RATHER ABERRANT BEHAVIOR IN THIS CIRCUMSTANCE. IT SEEMS THAT WHEN YOU HIT THE VFR SOFTKEY A SECOND TIME ON THE G1000; REGARDLESS OF WHETHER YOU HAVE SHUT DOWN OR NOT; IT WILL REASSIGN TO THE TRANSPONDER THE PREVIOUS CODE AND NOT 1200. IN OUR CASE; IT REASSIGNED ABCD IF MEMORY SERVES. THIS IS; IN MY OPINION; AS BOTH A SOFTWARE ENGINEER AND A PRIVATE PLT; VERY UNDESIRABLE BEHAVIOR. FIRST; IT VIOLATES THE FUNCTION OF NEARLY EVERY OTHER TRANSPONDER IN EXISTENCE IN THAT THE VFR BUTTON SHOULD ALWAYS ENTER 1200. SECOND; IT ASSIGNS THE PREVIOUS CODE EVEN AFTER A SHUTDOWN; FOR WHICH I CAN THINK OF NO REASONABLE USE OTHER THAN TO CAUSE US AND OTHER G1000 PLTS THE EXACT PROBLEM WE EXPERIENCED THIS DAY. WE DEPARTED WITH THIS PREVIOUSLY ASSIGNED TRANSPONDER CODE; AND FLEW UNDER THE CLASS BRAVO SHELF UNTIL CLEAR OF IT BEFORE CLBING TO OUR CRUISE ALTITUDE OF 5500 FT MSL. IT WAS NOT UNTIL WE WERE JUST OVER ZZZ1 THAT MR. X NOTICED THE CODE WAS INCORRECT. AS ACTING PIC; I DECIDED TO CALL CENTER AND ALERT THEM TO THE FACT THAT WE HAD AN ERRONEOUS TRANSPONDER ENTRY AND THAT WE WERE AT THAT TIME SWITCHING IT TO 1200. CENTER ACKNOWLEDGED THE ERROR AND SAID THEY WERE MADE AWARE OF IT UPON OUR DEP. THE CTLR TOLD US TO SQUAWK VFR (1200) AT THAT TIME WHICH WE DID. CONCLUSION AND RECOMMENDATION: AS ACTING PIC IT WAS MY RESPONSIBILITY TO CHECK THE TRANSPONDER CODE; AND I FAILED TO DO SO IN A TIMELY MANNER. A SIGNIFICANT CONTRIBUTING FACTOR IS THE ODD BEHAVIOR OF THE G1000 VFR SOFTKEY; WHICH CONTRADICTS THE BEHAVIOR OF EVERY OTHER TRANSPONDER WITH WHICH I HAVE EXPERIENCE. IT IS MY RECOMMENDATION; TO PROMOTE SAFETY AND UNIFORMITY OF FUNCTION; THAT THE CERTIFICATION PROCESS FOR TRANSPONDERS BE AMENDED IN A MANNER THAT REQUIRES THE VFR BUTTON TO ALWAYS ENTER 1200 IN A TRANSPONDER. DOING SO WILL RELIEVE CONFUSION ON THE PART OF BOTH PLTS AND CTLRS; AND COULD POTENTIALLY SAVE A TFC CONFLICT IN THE EVENT ATC EXPECTS AN ACFT TRANSMITTING A PARTICULAR CODE TO BE ON A PARTICULAR TYPE OF FLT PLAN.

Data retrieved from NASA's ASRS site as of May 2009 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.