Narrative:

The problem arose due to the continuation of flight into deteriorating WX conditions while returning from an air show. The departure of our two-ship formation was delayed approximately one hour due to taxiway closures and that pressed us for enough daylight; and also the prospect of a deepening marine layer at our home airport. The latest WX was 4100 ft broken with visibilities of 10-15 miles. Our plan was to follow the highway through the mountains and take a look at the conditions on the descent to see if the ceiling would allow a safe margin to get under the cloud layer as the mountain slope reached the valley. Flight conditions east of the mountain summit were excellent with unlimited ceilings and visibility. From the summit west the situation deteriorated to scattered to broken with 5-10 mile visibilities. About 35 miles east of ZZZ; we heard another formation on our formation frequency and it was apparent that they; too; were attempting the same approach we were. I called and asked where they were and their type. They replied that they were two single engine trainers about 5-10 miles behind us. I didn't like this much because they would be following the same route; descending to about our altitude and would have a very rapid overtake speed on us. We continued our descent to a point approximately 25 miles from ZZZ keeping an eye on the lowering WX conditions and another eye to the rear watching for the following jets. Not at all a comfortable situation in mountainous conditions. Our flight actually went further west and a lot lower than was comfortable; but with the jets closing and still unseen it was time to do the standard 180 degree turn. We probably pressed the limits of 500 ft above the unpopulated terrain at this turn around point to return to the east where the WX continued to be excellent. Prior to making the turn I called the trainers and told them that it was impossible to get under the clouds to continue to the airport and that we were turning around and that they should do the same. They acknowledged; did their 180 degree turn and then headed to ZZZ1 airport. We never did see them even though they were probably a lot closer than we would have liked; especially with their overtake speed. We too; headed to ZZZ1 where there was supposed to be a generally clear area over the airport. The trainers found it and got under the clouds and proceeded on to ZZZ. We were not so fortunate. The hole closed and we couldn't get to ZZZ1 airport so we diverted back to ZZZ2 for the ron. Upon shutdown at ZZZ2; I discovered that I had not reset my transponder from an assigned code provided by approach the day before when we arrived at the air show; to the required VFR 1200. Oops! That probably did not endear me and my aircraft to approach; and eventually center on our return flight. Usually the procedure is for the number two aircraft in the formation to place his transponder on standby; but I knew that we would be flying a rather loose formation so I decided to turn it on. Big mistake! When one rarely uses anything but 1200 I guess it is all too easy to overlook resetting the transponder. My new revised checklist for my aircraft will state 'transponder; on or standby; check code.' so we now know that the problem arose from continued flight into worsening WX conditions. We were somewhat distracted in our decision to do the 180 by the fact that a couple of jets were breathing down our necks. This was probably the major cause for flying a lot lower than we wanted to be before turning around to the excellent WX conditions to the east. The desire to get home; often referred to as 'get homeitis' I'm sure played a part; the WX forecast for the following day was not the brightest. The transponder code error was an oversight that would/should not have happened with a proper checklist or just paying more attention. Apparently the urge to get out before WX conditions deteriorated and nightfall at our home base created way too much complacency on my part. We should have stayed over and departed in the morning; that would have precluded the low altitude flight over the interstate while making the 180 degree turn to climb into morefavorable WX conditions. Callback conversation with reporter revealed the following information: the pilots have heard nothing from the FAA about the incorrect transponder code or the VMC flight to their diversion airport.

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Original NASA ASRS Text

Title: A FLT OF 2 ACFT APCHING ZZZ VFR DIVERTED BECAUSE OF LOW CEILINGS. ONE ACFT WAS SQUAWKING A PREVIOUSLY ASSIGNED ATC CODE THE ENTIRE FLT.

Narrative: THE PROB AROSE DUE TO THE CONTINUATION OF FLT INTO DETERIORATING WX CONDITIONS WHILE RETURNING FROM AN AIR SHOW. THE DEP OF OUR TWO-SHIP FORMATION WAS DELAYED APPROX ONE HOUR DUE TO TXWY CLOSURES AND THAT PRESSED US FOR ENOUGH DAYLIGHT; AND ALSO THE PROSPECT OF A DEEPENING MARINE LAYER AT OUR HOME ARPT. THE LATEST WX WAS 4100 FT BROKEN WITH VISIBILITIES OF 10-15 MILES. OUR PLAN WAS TO FOLLOW THE HWY THROUGH THE MOUNTAINS AND TAKE A LOOK AT THE CONDITIONS ON THE DSCNT TO SEE IF THE CEILING WOULD ALLOW A SAFE MARGIN TO GET UNDER THE CLOUD LAYER AS THE MOUNTAIN SLOPE REACHED THE VALLEY. FLT CONDITIONS E OF THE MOUNTAIN SUMMIT WERE EXCELLENT WITH UNLIMITED CEILINGS AND VISIBILITY. FROM THE SUMMIT W THE SIT DETERIORATED TO SCATTERED TO BROKEN WITH 5-10 MILE VISIBILITIES. ABOUT 35 MILES E OF ZZZ; WE HEARD ANOTHER FORMATION ON OUR FORMATION FREQ AND IT WAS APPARENT THAT THEY; TOO; WERE ATTEMPTING THE SAME APCH WE WERE. I CALLED AND ASKED WHERE THEY WERE AND THEIR TYPE. THEY REPLIED THAT THEY WERE TWO SINGLE ENG TRAINERS ABOUT 5-10 MILES BEHIND US. I DIDN'T LIKE THIS MUCH BECAUSE THEY WOULD BE FOLLOWING THE SAME RTE; DSNDING TO ABOUT OUR ALT AND WOULD HAVE A VERY RAPID OVERTAKE SPEED ON US. WE CONTINUED OUR DSCNT TO A POINT APPROX 25 MILES FROM ZZZ KEEPING AN EYE ON THE LOWERING WX CONDITIONS AND ANOTHER EYE TO THE REAR WATCHING FOR THE FOLLOWING JETS. NOT AT ALL A COMFORTABLE SIT IN MOUNTAINOUS CONDITIONS. OUR FLT ACTUALLY WENT FURTHER W AND A LOT LOWER THAN WAS COMFORTABLE; BUT WITH THE JETS CLOSING AND STILL UNSEEN IT WAS TIME TO DO THE STANDARD 180 DEG TURN. WE PROBABLY PRESSED THE LIMITS OF 500 FT ABOVE THE UNPOPULATED TERRAIN AT THIS TURN AROUND POINT TO RETURN TO THE E WHERE THE WX CONTINUED TO BE EXCELLENT. PRIOR TO MAKING THE TURN I CALLED THE TRAINERS AND TOLD THEM THAT IT WAS IMPOSSIBLE TO GET UNDER THE CLOUDS TO CONTINUE TO THE ARPT AND THAT WE WERE TURNING AROUND AND THAT THEY SHOULD DO THE SAME. THEY ACKNOWLEDGED; DID THEIR 180 DEG TURN AND THEN HEADED TO ZZZ1 ARPT. WE NEVER DID SEE THEM EVEN THOUGH THEY WERE PROBABLY A LOT CLOSER THAN WE WOULD HAVE LIKED; ESPECIALLY WITH THEIR OVERTAKE SPD. WE TOO; HEADED TO ZZZ1 WHERE THERE WAS SUPPOSED TO BE A GENERALLY CLEAR AREA OVER THE ARPT. THE TRAINERS FOUND IT AND GOT UNDER THE CLOUDS AND PROCEEDED ON TO ZZZ. WE WERE NOT SO FORTUNATE. THE HOLE CLOSED AND WE COULDN'T GET TO ZZZ1 ARPT SO WE DIVERTED BACK TO ZZZ2 FOR THE RON. UPON SHUTDOWN AT ZZZ2; I DISCOVERED THAT I HAD NOT RESET MY XPONDER FROM AN ASSIGNED CODE PROVIDED BY APCH THE DAY BEFORE WHEN WE ARRIVED AT THE AIR SHOW; TO THE REQUIRED VFR 1200. OOPS! THAT PROBABLY DID NOT ENDEAR ME AND MY ACFT TO APCH; AND EVENTUALLY CTR ON OUR RETURN FLT. USUALLY THE PROC IS FOR THE NUMBER TWO ACFT IN THE FORMATION TO PLACE HIS XPONDER ON STANDBY; BUT I KNEW THAT WE WOULD BE FLYING A RATHER LOOSE FORMATION SO I DECIDED TO TURN IT ON. BIG MISTAKE! WHEN ONE RARELY USES ANYTHING BUT 1200 I GUESS IT IS ALL TOO EASY TO OVERLOOK RESETTING THE XPONDER. MY NEW REVISED CHKLIST FOR MY ACFT WILL STATE 'XPONDER; ON OR STANDBY; CHECK CODE.' SO WE NOW KNOW THAT THE PROB AROSE FROM CONTINUED FLT INTO WORSENING WX CONDITIONS. WE WERE SOMEWHAT DISTRACTED IN OUR DECISION TO DO THE 180 BY THE FACT THAT A COUPLE OF JETS WERE BREATHING DOWN OUR NECKS. THIS WAS PROBABLY THE MAJOR CAUSE FOR FLYING A LOT LOWER THAN WE WANTED TO BE BEFORE TURNING AROUND TO THE EXCELLENT WX CONDITIONS TO THE E. THE DESIRE TO GET HOME; OFTEN REFERRED TO AS 'GET HOMEITIS' I'M SURE PLAYED A PART; THE WX FORECAST FOR THE FOLLOWING DAY WAS NOT THE BRIGHTEST. THE XPONDER CODE ERROR WAS AN OVERSIGHT THAT WOULD/SHOULD NOT HAVE HAPPENED WITH A PROPER CHKLIST OR JUST PAYING MORE ATTENTION. APPARENTLY THE URGE TO GET OUT BEFORE WX CONDITIONS DETERIORATED AND NIGHTFALL AT OUR HOME BASE CREATED WAY TOO MUCH COMPLACENCY ON MY PART. WE SHOULD HAVE STAYED OVER AND DEPARTED IN THE MORNING; THAT WOULD HAVE PRECLUDED THE LOW ALT FLT OVER THE INTERSTATE WHILE MAKING THE 180 DEG TURN TO CLB INTO MOREFAVORABLE WX CONDITIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE PLTS HAVE HEARD NOTHING FROM THE FAA ABOUT THE INCORRECT XPONDER CODE OR THE VMC FLT TO THEIR DIVERSION ARPT.

Data retrieved from NASA's ASRS site as of January 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.