Water Entry Caused MH-47 Accident
Rotor & Wing Magazine, February 1998, Page 12
Investigation into the 1996 crash of a US Army MH-47E operated by the 160th Special Operations Aviation Regiment at Fort Campbell, KY, found the likely cause to be loss of electrical power due to the presence of water in the helicopters primary (electrical-ed) distribution panels (PDPs). The helicopter was returning from a night-vision goggle navigation flight when it requested IFR clearance to perform an instrument approach. Approach Control directed a 15 degree right turn to the crew; the radar controller noted that the helicopter tightened its turn radius and passed its assigned heading. Controllers then lost contact with the MH-47E, which was found crashed shortly thereafter.
Investigators determined that heavy precipitation, helicopter washing, or extended overwater operations can result in water leaking into the cockpit area and entering the auxiliary power distribution panels. This causes the circuit breaker bus ties to short, resulting in either partial or complete loss to primary and standby flight instruments.
Since the accident, changes have been made to protect PDPs from water intrusion by either channeling water away from pilots doors and windows, or by designing and installing a cover for the PDP and circuit breakers.
Specwar Ed note- Both regular and Special Operations Chinooks have the capicity to pick up small boats by submerging the aft ramp and part of the cargo deck in the water and having them drive in. This manuever is risky and also lets A LOT of water into the aircraft (I've seen it done). This was not listed as a potential cause of the crash, but I believe the 160th aircraft may do it enough for it to count as one.