Citation Excel (C560XL)
Flight Crew Air Transport Pilot (ATP)
Other Internal Airframe Ice Formation
General Maintenance Action
Procedure; Aircraft
The flight was uneventful. After take-off and during the descent; we had to fly through some clouds but did not encounter significant precipitation. The weather radar was on; but it did not detect any returns. Upon post-flight inspection I noticed a fairly large area of frost (12 inches x 6 inches) forming under the fuselage in the tail cone area; beginning roughly 24 inches after the tail stand placard (end of the rear most inspection panel on the belly) and continuing aft for about 6 inches. When I wiped the frost off I noticed a dramatic temperature difference of the skin of the aircraft; between the affected area and the surrounding areas. The airplane was practically dry; except for that area. We suspected a block of ice had formed inside the tail cone and it was slowly melting. Roughly an hour after landing (with temperatures on the ground exceeding 20 degrees C) the skin still felt cold to the touch and it was still collecting moisture. We spoke to the Chief Pilot and Maintenance Control and decided to write up the airplane so as to create a record. We were not able to determine whether the airplane was in compliance with a related Cessna service bulletin but if I remember correctly there were no drain holes under the belly of this XL. The flight controls were not affected at all.
A CE560XL flight crew discovered evidence of frozen water inside the tailcone of their aircraft after a short flight that encountered little or no precipitation. It appeared that a service bulletin concerning the installation of drain holes in that area had not yet been complied with.