Generally, without knowing the details of this accident, dual engine failures are typically caused by one of the following:
starvation (e.g. due to iced fuel filters)
water, lots of it.
operating the aircraft outside the flight envelope
In general there's a few reasons for a multiple engine failure:
Running out of fuel: This has happened more than once when the wrong fuel load was put on the airplane, see the Gimli Glider and the Azores Glider, there's also a case where hijackers forced an airplane to run out of fuel and ditch because they wanted to flee to Australia
Fuel Contamination: ...
I will not speculate as to the cause of the mishap to which you are referring (Transair 810), however, I believe I can provide some clarity regarding the route over water. The Honolulu airport is located relatively close to Waikiki, a neighborhood with a lot of hotels and apartments. Many airports have noise abatement procedures in place to minimize the ...
The oil systems on the two engines are separate, for the obvious reason. If there is (uncontaminated) fuel in the tanks, pilots can't starve the engines without deliberately closing the engine start lever (i.e. shutting the motor down themselves) or getting into unusually nose-high attitudes. The latter don't matter when boost pumps are operating- which is ...
No flotation devices:
Remain within 50 NM from "shore".
Unless, takeoff/landing path is over water with a ditching likelihood.
If takeoff/landing path is over water with a ditching likelihood.
Greater than 50 NM from "land suitable for making an emergency landing".
Life-jackets and life rafts: