ELT or UEB

[notlang]

all people know DFDR includes ELT with 3 emergency freq built-in. When a/c in crash with a force of 5g for instant, the switch is gonna be active and make ELT works. The matter am in stuck is even when DFDR is under sea, how to allocate its location?
Some guys answered there is a UEB installed inside DFDR and active by water will help people finds exactly DFDR's location. OEB then transmits an ultrasonic freq
But I think with 3 above emergency freq, finding activities can be established without OEB to find exactly the place where DFDR is.
Whoever did research this plz help me.
thks

[MD11Engineer]

In 15 years of work on large commercial transport aircraft I´ve never seen an ELT installed in either the DFDR or the CVR. They certainly have no antenna attached to them either. Obviously a large aircraft wreck on land has a certain chance to be found by using optical means (Mark 1 eyeballs). For crashes into the sea both recorders have an underwater locator beacon attached to them, which will emit "ping" signals when immersed in water.

Jan

[flighttest-engineer]

I will try to clarify the subject:

DFDR's, FDR's CVR's must have an underwater locator beacon installed to locate the recorders in case of drowning in water.
This ULB will automatically transmit a sonar signal at 37,5 KHz for a time duration of approx 30 days if the ULB willbe submerged in water.
If there is has been a crash on land, no automatically triggered locating device is coupled to the DFDR, FDR, CVR.

Deployable recorders (Voice- and Flight Data Recorders) are mostly used on military aircraft and helicopters.
This type of recorders must have ELT's (Emergency Locator Transmitter) integrated into their deployable part, which also contains the memory unit of the recorders.
Upon deployment the ELT's will also betriggered to transmit on the emergency frequencies 121.5 MHz, 243 MHz and 406 MHz. On the satellite emergency frequency (COSPAS-SARSAT) the LAT/LONG-information at the time of deployment will also be transmitted together with the specific aircraft data.
Deployment can be triggered manually or automatically, depending on the used system.

short conclusion:
fixed installed recorders have an Underwater Locator Beacon (ULB) but no ELT installed
deployable recorders have ELT's installed and are floatable.