During the safety briefing at the beginning of each flight, the crew tells you that, in the event of a crash landing in water, you should NOT inflate your life vest before exiting the plan. Ethiopian Airlines Flight 961 demonstrated why this is such an important rule.
On November 23, 1996, this Boeing 767 was hijacked on a trip from Addis Ababa to Nairobi. The hijackers were Ethiopians who were seeking Asylum in Australia. Threatening to blow up the plane, the hijackers demanded the plane be rerouted to Australia. However, it didn't have enough fuel and ran out over the Indian Ocean.
Both engines failed and the plane plummeted to the water. One hundred and twenty-five out of the one hundred and seventy-five aboard died. It was the only true widebody airliner water landing with any survivors. More could have lived if they had not inflated their life vests inside the cabin. Many did so and were then trapped by rising water as the plane quickly sank.