Narrative:

I was taxiing out for an IFR flight after waiting for rain to pass over and for the airport return to VFR for our departure. As we taxied from parking I took the closest taxiway; which also appeared to be the most direct. When we reached the end of this taxiway and started the 90-degree turn (to the left) the left main went off of the pavement (by inches) and onto the grass. Due to the amount of rain in the immediate past week as well as that day; beneath the grass was soft watery mud. The main wheel sunk in the mud pulling the airplane around (even though we were moving very slowly and I had pushed the nosewheel to the right expecting the main wheel to return to the pavement) allowing the nosewheel to leave the pavement also. Both the left main and the nosewheel sunk in the mud to about mid-axle. The airport operator had a tug/tractor; but was sure it would get stuck if he placed it in front of the airplane to attempt to extract it from the mud (I should point out that the airport was well grassed and no mud was visible; until you stepped on the grass and sank into the mud). We called a specialty service with airbags; a winch; and soft straps to safely extract the airplane from the mud. We contacted our a&P to insure that the procedures we were about to employ were safe and again after washing the mud from the wheels and checking the airplane over to insure that it was safe to fly. In my opinion (and this was also stated by one of the FAA inspectors at the scene); the taxiway turn was not properly radiused. I don't think any airplane the size and geometry of my light twin (mains are 19' wide) can make that 90-degree turn on the narrow taxiway without a main leaving the pavement unless special procedures are taken rather than following the yellow center line. The airplane was not damaged and no one was injured. To prevent a recurrence either properly radius the turns on this older taxiway or put up signage recommending against its usage by anything other than small singles. Human performance considerations: perception was that the older taxiway was safe to use and that the turns from it were properly radiused and you would remain on the pavement if you followed the centerline. This taxiway appeared to offer a more direct route to the runway. After the rain and with the clouds shielding the sun; the older taxiway was black asphalt with a bright yellow centerline. The newer taxiway was a concrete color and visually did not show up as well as the older taxiway. As we found out; the newer taxiway was wider and also had better radiused turns. Finally; the older taxiway is the same color (black asphalt with yellow centerline) as the taxiways at our home base. So there was a subconscious 'preference' for it due to its appearance being more familiar.

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Original NASA ASRS Text

Title: A light twin pilot became stuck in the mud when his left main tire went off the pavement into wet grass and mud at GEZ. The reporter stated he felt the radius of the turn was inadequate and should either be fixed or signage should be installed to warn of the situation.

Narrative: I was taxiing out for an IFR flight after waiting for rain to pass over and for the airport return to VFR for our departure. As we taxied from parking I took the closest taxiway; which also appeared to be the most direct. When we reached the end of this taxiway and started the 90-degree turn (to the left) the left main went off of the pavement (by inches) and onto the grass. Due to the amount of rain in the immediate past week as well as that day; beneath the grass was soft watery mud. The main wheel sunk in the mud pulling the airplane around (even though we were moving very slowly and I had pushed the nosewheel to the right expecting the main wheel to return to the pavement) allowing the nosewheel to leave the pavement also. Both the left main and the nosewheel sunk in the mud to about mid-axle. The airport operator had a tug/tractor; but was sure it would get stuck if he placed it in front of the airplane to attempt to extract it from the mud (I should point out that the airport was well grassed and no mud was visible; until you stepped on the grass and sank into the mud). We called a specialty service with airbags; a winch; and soft straps to safely extract the airplane from the mud. We contacted our A&P to insure that the procedures we were about to employ were safe and again after washing the mud from the wheels and checking the airplane over to insure that it was safe to fly. In my opinion (and this was also stated by one of the FAA inspectors at the scene); the taxiway turn was not properly radiused. I don't think any airplane the size and geometry of my light twin (mains are 19' wide) can make that 90-degree turn on the narrow taxiway without a main leaving the pavement UNLESS special procedures are taken rather than following the yellow center line. The airplane was not damaged and no one was injured. To prevent a recurrence either properly radius the turns on this older taxiway or put up signage recommending against its usage by anything other than small singles. Human Performance Considerations: Perception was that the older taxiway was safe to use and that the turns from it were properly radiused and you would remain on the pavement if you followed the centerline. This taxiway appeared to offer a more direct route to the runway. After the rain and with the clouds shielding the sun; the older taxiway was black asphalt with a bright yellow centerline. The newer taxiway was a concrete color and visually did not show up as well as the older taxiway. As we found out; the newer taxiway was wider and also had better radiused turns. Finally; the older taxiway is the same color (black asphalt with yellow centerline) as the taxiways at our home base. So there was a subconscious 'preference' for it due to its appearance being more familiar.

Data retrieved from NASA's ASRS site as of April 2012 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.