ACFT MAINT DISCREPANCY EVENTUALLY CREATES AN UNSCHEDULED LNDG; ACFT DAMAGED.

Narrative

ON EVENING OF SEP/XX/93 AN MLG ARRIVED DEN WITH PIREP OF A LOUD NOISE AND MOMENTARY VIBRATION DURING FLT. AFTER LNDG; PLT ALSO RPTED EVIDENCE OF BLUE WATER LEAK AND ICE AT FORWARD LAVATORY SVC PANEL. L ENG WAS EXAMINED FOR DAMAGE. VERY MINOR FAN BLADE NICKS (NOT CONSISTENT WITH ICE INGESTION) WERE NOTED AND REPAIRED; FORWARD LAVATORY WAS LEAK CHKED IN ACCORDANCE WITH MAINT MANUAL. NO LEAKS WERE NOTED. ON NEXT REVENUE FLT; THE L ENG INGESTED ICE; PRESUMABLY FROM FORWARD LAVATORY SVC PANEL LEAK; AND SUSTAINED MASSIVE DAMAGE. FLT WAS DIVERTED TO DES MOINES WHERE ENG WAS REPLACED AND LAVATORY LEAK REPAIRED. SINCE NO LAVATORY LEAKAGE WAS NOTED DURING NORMAL LEAK CHK; I BELIEVE THAT LAVATORY TANK VALVE FAILED DURING FLT AT DIFFERENTIAL PRESSURE ABOVE 4 PSI. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT; AN MLG; WAS CHKED IN ACCORDANCE WITH THE MAINT MANUAL AT THE REQUIRED 4 PSI FOR LEAKS WITHIN THE LAVATORY SYS. A FOLLOW-UP ON THE ACFT MAINT HISTORY A FEW DAYS LATER REVEALED THAT THE ACFT WAS SUFFERING FROM THE SAME PROB. AT THE ACR MAINT BASE THE CHK VALVE IN THE FILL LINE WAS REPLACED; WHICH CORRECTED THE PROB. APPARENTLY THE LIQUID FROM THE LAVATORY WAS SIPHONING BACK UP THROUGH THE FAULTY CHK VALVE IN THE FILL LINE; THEREBY EXHIBITING THE SAME SYMPTOMS AS A PRIMARY LEAK. SUPPLEMENTAL INFO FROM ACN 252040: FORWARD LAVATORY WAS DRAINED; SVCED AND LEAK CHKED IN ACCORDANCE WITH MAINT MANUAL. NO LEAKS WERE NOTED AT 4 LBS PSI.