What happened
The aircraft was conducting an air taxi and sightseeing flight, serving as an optional tour for passengers traveling to a cruise liner. While returning to the airport after viewing glaciers, the aircraft was flying along an inlet shore characterized by steep mountains descending into the water with only infrequent small beaches.
Approximately 1,200 feet above the water and 1.5 miles from the airport, the engine lost power. The pilot ditched the aircraft about 100 feet from the shore near small cliffs. Upon impact, passengers exited into 39-degree water, but none exited wearing life vests. The pilot threw one life vest out of the aircraft and exited as the plane sank.
One passenger, with assistance from her husband, was able to don the thrown life vest and partially inflated it using the oral inflation tube. A rescue helicopter arrived approximately 10 minutes later. The pilot and the passenger wearing the life vest were rescued, but there were 2 fatalities as two passengers drowned, and another 2 passengers were not found.
The investigation
An examination of the engine revealed that the left magneto impulse coupling had failed, which stopped the rotation of the magneto drive gear. Additionally, several teeth on the intermediate idler gear were damaged, which resulted in the disconnection of the crankshaft from the accessory gear train.
Findings
Investigators noted that the passengers did not recall receiving a briefing regarding the location of life vests or how to use them. While life vests were stored in seat-back pouches, the openings to these pouches were obscured by slip-cover style seat covers.