@Mutt
Last time they also didn't loose the "whole engine" but a portion of the LPT module ( like the actual event at Cairo) !
Subject CF6-50E2 engine ( 1st event ) is still sitting at JED if u want to have a look
It's a well known problem ( LPT Stg.3 disk failure ) caused by vibrations due to HPT rotor unbalance. Most often happened due to mid chord burning of HPT Stg.1 blades ( known prob ). Since most of the B747 classic operates have a deactivated AVM system, increased N2 vibrations can't be observed during TAKO and Cruise.
FAA has recently surperseded the initial AD Note for repetitive BSI inspection ( 175 CIS ) and issued AD2010-12-10 calling for a repetitive BSI of 75 CIS + additional checks ( e.g. EGT system etc ) + special instruction in case of TREND shifts or reported vibs.
The new AD Note was issued after the NTSB recommendation to FAA office ( other thread ).
It has ( normally ) nothing to do with bad maintenance or so but with problems on some HPT Stg.1 blade part numbers. If these blades are "burning" down ( like matches ), the N2 system can go into unbalance with an intersetion to the N1 system, causing cracking ( HCF / HAF ) at the outer rim of the LPT Stg.3 disk. So actually the problem is not the LPT stg.3 disk itself as highlighted by the FAA but the final "result" of the HPT blade problem.