Last month, I talked about how the British Airways 777 accident and the Delta 777 incident had been connected by an interim report from the UK. The NTSB has, after review, agreed with these findings and is now requiring “urgent” action. But “urgent” is not as dire as it sounds. It does not require aircraft to be grounded, and it will take at least a year, most likely, before the work is complete.
The NTSB has told Rolls-Royce that it needs to redesign the Fuel Oil Heat Exchanger (where cold fuel passes hot oil and they cool/warm each other to proper temperatures) to prevent ice 
accumulation and subsequent blockage of the the fuel lines. You may remember that the hot oil wasn’t properly warming the cold fuel and ice was forming. This has, so far, only been a problem on the Rolls-Royce Trent 800 engines, though Rolls believes that this could ultimately have a larger impact after further research is done on icing for long flights at very cold temperatures. But that’s another story.
Rolls is working on the fix already and expects to have it ready within a year. Once the redesign is complete, airlines will have no more than six months to implement the fix. So if this is so “urgent,” why aren’t the planes being grounded? Well, procedures have already been put into place to help avoid these types of incidents, but the NTSB doesn’t think that’s a good long term solution. In the NTSB’s words:
While the procedures may reduce the risk of a rollback in one or both engines due to [Fuel Oil Heat Exchanger] ice blockage, they add complexity to flight crew operations, and the level of risk reduction is not well established. And because the recovery procedure requires a descent, the aircraft may be exposed to other risks such as rising terrain or hazardous weather, or the inability to achieve maximum thrust during a critical phase of flight, such as during a missed approach.
So while the fix they’re using right now does work, it’s not satisfactory in the long term. So should we worry about stepping on a Rolls-Royce powered 777? I wouldn’t. But it is clear that there are problems and it’s good to see them being addressed sooner rather than later.
