Is a releasable locator beacon (ELT) required for aircraft carrying passengers over a water area?
Is an ELT required on any type of aircraft carrying passengers over water? 


Generally, commercial transport aircraft are not required to carry an ELT.


  how are aircraft planned to be located after an accident over the ocean?



I believe pilots are expected to use radio to inform controllers of any emergency.
If ATC are unable to contact an aircraft for an extended time, they instigate S&amp;R based on the last known location of the aircraft.
The FDR and CVR are required to include an underwater location beacon (ULB), though this is only short range and has limited duration.
It is expected that, sometime in the future, commercial transport aircraft will be required to have automated systems that report their position frequently (perhaps every 15 minutes)




References:


IATA - Aircraft Tracking Task Force (ATTF)
ATTF FAQ
ICAO Normal Aircraft Tracking Implementation Initiative