Narrative:

We had an unscheduled airplane change (second change of the day). As I went around the tail of the plane during my preflight inspection; I noticed water draining out of a drain hole on the aft bottom end of the plane. (I did check to make sure it was water and not gas.) at first; I thought little of it; figuring it was just sink drain water or something. As I continued my preflight; however; I realized that the sink drain was a different outlet; and that the water was still draining; a very steady stream from a 3/8' identification drain tube just aft of the pressure bulkhead; and that enough had drained out to make a sizable puddle on the ground. At that point; I decided we needed to have it looked at; so I (with captain's concurrence) called maintenance. It turns out there was a large area of ice and snow frozen inside the tail; on the floor of the tail cone fairing (around 3' thick by 2 ft. By 2 ft. According to maintenance). Since the weather was finally above freezing for the first time in months; and with the assistance of heat from the APU; the ice was melting and draining out of the drain hole. Neither the captain nor I were comfortable flying with that (even though it had apparently been flying for at least several days to weeks in that condition); so we asked maintenance to correct it. They creatively used the jetway air (with an extension hose) to run heated air into the area (the APU heat was not enough to melt it very quickly) and after about 45 minutes they had melted the remaining ice and snow (it was in an inaccessible location so they couldn't just break it up and pull it out). Anyway; all's well that ends well; and we got safely to our destination last night after a very long day (originally scheduled for 7:34 block and 12:51 duty). I wonder (1) how did that much water/ice/snow get trapped there; and (2) why wasn't it found earlier? Water or snow entered the tail of the plane and was trapped (possibly due to a blocked drain tube). At some later time; the water melted (and possibly the drain became unclogged) and drained from the back of the airplane.

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Original NASA ASRS Text

Title: A B737-300 accumulated ice inside the tail cone aft of the pressure bulkhead and forward of the APU. The water's entry point is unknown but the aircraft was parked for 2 days at a location with heavy snow accumulations.

Narrative: We had an unscheduled airplane change (second change of the day). As I went around the tail of the plane during my preflight inspection; I noticed water draining out of a drain hole on the aft bottom end of the plane. (I did check to make sure it was water and not gas.) At first; I thought little of it; figuring it was just sink drain water or something. As I continued my preflight; however; I realized that the sink drain was a different outlet; and that the water was still draining; a very steady stream from a 3/8' ID drain tube just AFT of the pressure bulkhead; and that enough had drained out to make a sizable puddle on the ground. At that point; I decided we needed to have it looked at; so I (with Captain's concurrence) called Maintenance. It turns out there was a large area of ice and snow frozen inside the tail; on the floor of the tail cone fairing (around 3' thick by 2 ft. by 2 ft. according to Maintenance). Since the weather was finally above freezing for the first time in months; and with the assistance of heat from the APU; the ice was melting and draining out of the drain hole. Neither the Captain nor I were comfortable flying with that (even though it had apparently been flying for at least several days to weeks in that condition); so we asked Maintenance to correct it. They creatively used the Jetway air (with an extension hose) to run heated air into the area (the APU heat was not enough to melt it very quickly) and after about 45 minutes they had melted the remaining ice and snow (it was in an inaccessible location so they couldn't just break it up and pull it out). Anyway; all's well that ends well; and we got safely to our destination last night after a very long day (originally scheduled for 7:34 block and 12:51 duty). I wonder (1) how did that much water/ice/snow get trapped there; and (2) why wasn't it found earlier? Water or snow entered the tail of the plane and was trapped (possibly due to a blocked drain tube). At some later time; the water melted (and possibly the drain became unclogged) and drained from the back of the airplane.

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.