Originally Posted by WHBM
I still don't see any analysis of the following :
1. How can the engine design have been in service for 15 years before such incidents happened. What caused it to work fine on comparable flights until now ?
A very interesting point, which we have also been discussing on a closed mailing list. Two possibilities spring to mind:
1- There have been some previous incidents, but all happened at altitude, as with the Delta flight, and were thought to have been non-events, except for a driftdown. They may also have been wrongly attributed to core-icing or other factors.
2- With ETOPS extensions, extended flights over arctic regions, even in the Northern winter, have increased in recent years, leading to a much higher number of flights with very cold fuel.
2. What are the specific aspects of the design that cause this to be a problem, which are not present in engines from other manufacturers, or other designs from the same manufacturer ?
This has been discussed quite early after the BA 038 accident.
One of the main design differences is that in the Trent design, the fuel first goes through the low pressure pump (this is not the boost pump or override/jettison pump in the tank, but a mechanically driven engine pump), then through the FOHE, and then through the HP:
LP-Pump -> FOHE -> HP pump
In the GE design, the fuel first goes through the LP and HP pumps, and then through the FOHE:
LP-pump -> HP-pump -> FOHE
The HP pump heats the fuel somewhat, which may be enough to avoid ice accretion.
I'm not certain about the PW design.
Another point may be the structure of the FOHE fuel inlet face, which in the Trent design, as we have seen, has protruding fuel pipe ends, upon which ice may accrete.
Your point 3) has already been answered.
Bernd