Here is a post I posted in another forum of airline/airplane buds -
What's your theory on that engine?
I'm not a fan of hollow anything from fan blades to props in the 50's into 60's. I'm no metallurgist
but I can't help but think these hollow blades on some engines are just flat out not as sound as solid metal
My 2 cents is they had a bird strike on the takeoff roll that went unnoticed and bird hit the blade that is missing
about 3 or 4 inches from the attachment and this is at the base of the hollow point internal inside the blade,.and compromised the blade?
Engine and blade kept running fine till the compromised spot cut loose at 13,000 feet.
My other theory is it was metal fatigue at the bottom of the hollow point inside the blade and if so there are a lot of fans/engines out there that need attention/AD!
I remember reading about the hollow props in the 50's save weight and carry more fuel! TWA used them
on the LHR-LAX Connie flights and they had some props come apart and they would land in the middle of no-where Canada
on three engines needing an engine and prop change!
Hopefully someone will find the blade that cut loose may have some answers! If it was some sort of bird strike I think that evidence will be in the engine core
and some minor burbs on the FDR and the powerplant data from ACARS will show it too!
I like to put on my investigator hat at times!
Adding this now - I think the continued fire after shutdown came from ruptured hydraulic lines in the thrust reverser system.