Ten days after replacing a Digital Flight Data Recorder (DFDR) on a B717 aircraft while on a field trip; a Mechanic was informed the DFDR they installed did not have the Underwater Locator Beacon (ULB) attached to the DFDR unit.

Narrative

Myself and Technician Y and Technical Support Technician Z were sent on a field service trip to ZZZ1 for a pressurization and ultimately an electrical problem on a B717 aircraft. Because of the number of faults that occurred; we were told by Maintenance Control to replace the Digital Flight Data Recorder (DFDR); so our Technical Support department could review the data back in ZZZ. I assisted Technician Y in the replacement using the B717 Maintenance Manual. We then went to the cockpit and performed a successful Return to Service (RTS) of the unit. We then found out later that the Underwater Locator Beacon (ULB) was not swapped to the new DFDR. I was personally informed of this event after returning to work ten-days later from an unrelated week long training class; by Technical Support Manager X; who found the discrepancy while doing a routine computer audit on maintenance work. The current and approved B717 Maintenance Manual 31-31-01 was followed in the Remove/Replace (R/R) of the DFDR and nowhere did it indicate the possibility of the ULB being missing and there was no reference to the installation of the ULB in that section which is covered in B717 Aircraft Maintenance Manual (AMM) 31-31-12. The airline I worked at before coming here; their vendor always had the ULB installed and was therefore serviceable and ready to install. The B717 aircraft was tracked down to ZZZ2 and Maintenance was asked to remove the panel and check for the presence of the ULB. After discovering the absence of the ULB; one was installed. The B717 Maintenance Manual (M/M) 31-31-01 needs to be revised to indicate checking for the presence of the underwater beacon and a reference made to the installation of the ULB in the B717 AMM 31-31-12. In addition; a warning tag should be installed on the attach mount for the ULB to draw attention to it's absence; if the vendor in use at the time didn't install one.