Narrative:

We flew uneventfully from [our departure airport]. It had been raining at [our departure airport] while the airplane was parked outside overnight. Also; the initial climb was flown in light rain and we used the weather radar to avoid weather returns. Tops were around 30;000 ft and we cruised in clear skies at 40;000 ft. Upon post-flight inspection I noticed an area of frost (5 inches x 4 inches forming under the fuselage. The area was located on the bottom of the tail section; beginning roughly 24 inches after the 'tail stand' placard (just aft of the rear-most inspection panel). There was a definite temperature difference to the touch between the affected area and the surrounding areas of the aircraft skin. After landing the airplane was dry; except for that area. I suspected a block of ice had formed inside the tailcone and it was slowly melting. The temperature on the ground at the destination airport was 15C. No abnormalities were noted on the flight controls (main flight controls and trim worked normally throughout the flight). I am not sure if ice forming in that area has the potential to affect the flight controls cables; but I would recommend cessna to eventually add an additional drain hole or mast.

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Original NASA ASRS Text

Title: During post flight inspection a CE-560XLS Captain discovered an area of frost on the bottom of the tail cone which lead him to believe that ice had formed inside of the tailcone during flight after the aircraft was exposed to rain the previous night.

Narrative: We flew uneventfully from [our departure airport]. It had been raining at [our departure airport] while the airplane was parked outside overnight. Also; the initial climb was flown in light rain and we used the weather radar to avoid weather returns. Tops were around 30;000 FT and we cruised in clear skies at 40;000 FT. Upon post-flight inspection I noticed an area of frost (5 inches x 4 inches forming under the fuselage. The area was located on the bottom of the tail section; beginning roughly 24 inches after the 'tail stand' placard (just aft of the rear-most inspection panel). There was a definite temperature difference to the touch between the affected area and the surrounding areas of the aircraft skin. After landing the airplane was dry; except for that area. I suspected a block of ice had formed inside the tailcone and it was slowly melting. The temperature on the ground at the destination airport was 15C. No abnormalities were noted on the flight controls (main flight controls and trim worked normally throughout the flight). I am not sure if ice forming in that area has the potential to affect the flight controls cables; but I would recommend Cessna to eventually add an additional drain hole or mast.

Data retrieved from NASA's ASRS site as of July 2013 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.