On Jan 14th 2019, at 9.10 Indonesia time, the CVR of the crashed Lion Air JT-610 has been found. Another vital device was found earlier.
There are three modern airplanes crashed in to water in Indonesia:
Adam Air, registration PK-KKW, Boeing 737-400, flight KI514, on 1-January-2007, crashed into Majene Sea due to the failure with the Internal Reference System (IRS), rested in 2,000m below the sea surface.
Air Asia, registration PK-AXC, Airbus A320-216, flight QZ8501, crashed on 28-December-2015, into Karimunjawa Sea, due to the failure with the rudder-travel-limiter.
Lion Air, registration PK-LQP, Boeing 737 Max-8, flight JT-610, crashed on 28-November-2018, into Java Sea. The crash cause is still under investigation.
Those three crash locations were found not by the electronic instrument system, but by fishermen.
Then my question is: why did the modern airplane has not been located via its ELT?