Narrative:

Aircraft was a tail swap for this flight; ZZZ1-ZZZ. A line check was in progress; and as captain; I was the PF. During climb out of this CAT ii airplane; the airspeed wandered a bit; exceeding 250 KTS momentarily. I disengaged profile mode; but had to also disconnect the #1 autoplt. There was immediate need for a .4 degree nose down trim to be added. I reengaged the #1 autoplt; but passing 10000 ft; the nose was very slow to pitch down; and the increase in airspeed was noticeably slow. Upon another autoplt disconnect; additional nose down trim was needed; accomplished; and this time #2 autoplt was engaged in non-profile mode. The flight continued satisfactorily. Upon #2 autoplt disconnect; during the last stages of an IFR approach; nose down trim was again needed. There were no in-flight warnings nor indications of any malfunction other than a mis-trim upon autoplt disconnect. I verbally debriefed the mechanic upon block in. I thought that there might have been a history beyond the 7 days that I had checked. He indicated that he would research this and as the airplane was to stay in ZZZ for our crew rest period; and we would be flying it back to ZZZ1. I thanked him and stated that his review and report back to me would allow me to more cogently write up the problem; if any; for arrival in ZZZ1. His report in the logbook shows that about 75 gallons of water were drained from the trimmable horizontal stabilizer compartment. Aside from the freezing hazard and corrosive effects that any water poses; the weight of the water far aft; at 6 pounds per gallon; was probably a factor in this abnormality. I have emailed him; both of my crew members; and also thanked the mechanic's boss. NASA will be notified as this is a flight control abnormality caused by the accumulation of a significant (14 inches deep) amount of water in an aft fuselage compartment.callback conversation with reporter revealed the following information: reporter stated that he had conducted an in-depth investigation of this problem. He has discovered that early model aircraft; including A310's; have a 10 MM drain hole prone to clogging while later model aircraft have a 16.5 MM hole less prone to plugging; and the potential problem applies to all models of A300 and A310. The reporter indicated the accumulation of water and de-icing fluids suggest that the non-water tight fairings are certainly not seals. Migration of water and other fluids; either environmental or during and after a de-icing event; is not prevented by the horizontal stabilizer fairings. The reporter indicated the trimmable horizontal stabilizer system has elevator force feel sensors; and an airspeed unit; to null or zero the elevator force during flight. Reportedly; this should still have allowed for proper trim; even though the weight of the water mix was unaccounted for in the weight and balance. The reporter added extra nose down trim to compensate. The reporter has sought information from various mechanics and other flight personnel about the accumulation of water in this area; roughly the size of the cockpit; and learned that it is common; just not to this extent. This area of concern is aft of the pressure bulkhead and therefore neither heated nor pressurized. It is susceptible to ice and if water gets in around the seals with the drain hole plugged; then a great amount of water can be trapped and frozen. In this case; the 14 inches of water allowed the water level to be less than 18 inches beneath an electronics rack. Reporter also determined that at a 20 degree nose up attitude on takeoff and during turbulence the water would splash the trimmable horizontal stabilizer jack screw. This area is only inspected on 'D' checks but reporter believes the air carrier is moving the inspection to a 'B' check which will cause recurring checks at only about 400 hours. The reporter has viewed an aircraft that had been on his air carrier's ramp for 22 hours. There was an accumulation of water; about 2 gallons; that was frozen. This was along the production join line; and was about 3 inches by 3 inches by 3 inches (triangular) and covered about 5 linear ft.

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Original NASA ASRS Text

Title: AN A310 CAPT NOTED LONGITUDINAL TRIM ABNORMALITIES IN FLT. THE REPORTER STATED THAT AFTER THE FLT; A MAINT TECH FOUND 14 INCHES OF WATER ACCUMULATED AFT OF THE REAR PRESSURE BULKHEAD; AND DRAINED 75 GALLONS OF WATER FROM THAT AREA.

Narrative: ACFT WAS A TAIL SWAP FOR THIS FLT; ZZZ1-ZZZ. A LINE CHK WAS IN PROGRESS; AND AS CAPT; I WAS THE PF. DURING CLBOUT OF THIS CAT II AIRPLANE; THE AIRSPD WANDERED A BIT; EXCEEDING 250 KTS MOMENTARILY. I DISENGAGED PROFILE MODE; BUT HAD TO ALSO DISCONNECT THE #1 AUTOPLT. THERE WAS IMMEDIATE NEED FOR A .4 DEG NOSE DOWN TRIM TO BE ADDED. I REENGAGED THE #1 AUTOPLT; BUT PASSING 10000 FT; THE NOSE WAS VERY SLOW TO PITCH DOWN; AND THE INCREASE IN AIRSPD WAS NOTICEABLY SLOW. UPON ANOTHER AUTOPLT DISCONNECT; ADDITIONAL NOSE DOWN TRIM WAS NEEDED; ACCOMPLISHED; AND THIS TIME #2 AUTOPLT WAS ENGAGED IN NON-PROFILE MODE. THE FLT CONTINUED SATISFACTORILY. UPON #2 AUTOPLT DISCONNECT; DURING THE LAST STAGES OF AN IFR APCH; NOSE DOWN TRIM WAS AGAIN NEEDED. THERE WERE NO INFLT WARNINGS NOR INDICATIONS OF ANY MALFUNCTION OTHER THAN A MIS-TRIM UPON AUTOPLT DISCONNECT. I VERBALLY DEBRIEFED THE MECHANIC UPON BLOCK IN. I THOUGHT THAT THERE MIGHT HAVE BEEN A HISTORY BEYOND THE 7 DAYS THAT I HAD CHKED. HE INDICATED THAT HE WOULD RESEARCH THIS AND AS THE AIRPLANE WAS TO STAY IN ZZZ FOR OUR CREW REST PERIOD; AND WE WOULD BE FLYING IT BACK TO ZZZ1. I THANKED HIM AND STATED THAT HIS REVIEW AND RPT BACK TO ME WOULD ALLOW ME TO MORE COGENTLY WRITE UP THE PROB; IF ANY; FOR ARR IN ZZZ1. HIS RPT IN THE LOGBOOK SHOWS THAT ABOUT 75 GALLONS OF WATER WERE DRAINED FROM THE TRIMMABLE HORIZONTAL STAB COMPARTMENT. ASIDE FROM THE FREEZING HAZARD AND CORROSIVE EFFECTS THAT ANY WATER POSES; THE WT OF THE WATER FAR AFT; AT 6 LBS PER GALLON; WAS PROBABLY A FACTOR IN THIS ABNORMALITY. I HAVE EMAILED HIM; BOTH OF MY CREW MEMBERS; AND ALSO THANKED THE MECHANIC'S BOSS. NASA WILL BE NOTIFIED AS THIS IS A FLT CTL ABNORMALITY CAUSED BY THE ACCUMULATION OF A SIGNIFICANT (14 INCHES DEEP) AMOUNT OF WATER IN AN AFT FUSELAGE COMPARTMENT.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAD CONDUCTED AN IN-DEPTH INVESTIGATION OF THIS PROBLEM. HE HAS DISCOVERED THAT EARLY MODEL ACFT; INCLUDING A310'S; HAVE A 10 MM DRAIN HOLE PRONE TO CLOGGING WHILE LATER MODEL ACFT HAVE A 16.5 MM HOLE LESS PRONE TO PLUGGING; AND THE POTENTIAL PROBLEM APPLIES TO ALL MODELS OF A300 AND A310. THE RPTR INDICATED THE ACCUMULATION OF WATER AND DE-ICING FLUIDS SUGGEST THAT THE NON-WATER TIGHT FAIRINGS ARE CERTAINLY NOT SEALS. MIGRATION OF WATER AND OTHER FLUIDS; EITHER ENVIRONMENTAL OR DURING AND AFTER A DE-ICING EVENT; IS NOT PREVENTED BY THE HORIZONTAL STAB FAIRINGS. THE RPTR INDICATED THE TRIMMABLE HORIZONTAL STAB SYSTEM HAS ELEVATOR FORCE FEEL SENSORS; AND AN AIRSPD UNIT; TO NULL OR ZERO THE ELEVATOR FORCE DURING FLT. REPORTEDLY; THIS SHOULD STILL HAVE ALLOWED FOR PROPER TRIM; EVEN THOUGH THE WT OF THE WATER MIX WAS UNACCOUNTED FOR IN THE WT AND BALANCE. THE RPTR ADDED EXTRA NOSE DOWN TRIM TO COMPENSATE. THE RPTR HAS SOUGHT INFO FROM VARIOUS MECHANICS AND OTHER FLT PERSONNEL ABOUT THE ACCUMULATION OF WATER IN THIS AREA; ROUGHLY THE SIZE OF THE COCKPIT; AND LEARNED THAT IT IS COMMON; JUST NOT TO THIS EXTENT. THIS AREA OF CONCERN IS AFT OF THE PRESSURE BULKHEAD AND THEREFORE NEITHER HEATED NOR PRESSURIZED. IT IS SUSCEPTIBLE TO ICE AND IF WATER GETS IN AROUND THE SEALS WITH THE DRAIN HOLE PLUGGED; THEN A GREAT AMOUNT OF WATER CAN BE TRAPPED AND FROZEN. IN THIS CASE; THE 14 INCHES OF WATER ALLOWED THE WATER LEVEL TO BE LESS THAN 18 INCHES BENEATH AN ELECTRONICS RACK. RPTR ALSO DETERMINED THAT AT A 20 DEG NOSE UP ATTITUDE ON TKOF AND DURING TURB THE WATER WOULD SPLASH THE TRIMMABLE HORIZONTAL STAB JACK SCREW. THIS AREA IS ONLY INSPECTED ON 'D' CHKS BUT RPTR BELIEVES THE ACR IS MOVING THE INSPECTION TO A 'B' CHK WHICH WILL CAUSE RECURRING CHKS AT ONLY ABOUT 400 HOURS. THE RPTR HAS VIEWED AN ACFT THAT HAD BEEN ON HIS ACR'S RAMP FOR 22 HOURS. THERE WAS AN ACCUMULATION OF WATER; ABOUT 2 GALLONS; THAT WAS FROZEN. THIS WAS ALONG THE PRODUCTION JOIN LINE; AND WAS ABOUT 3 INCHES BY 3 INCHES BY 3 INCHES (TRIANGULAR) AND COVERED ABOUT 5 LINEAR FT.

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.