Torquelink

Extract from Boeing MOM issued Thursday 26th Feb:

Rolls-Royce has developed a modification to the FOHE to mitigate the potential for a future fuel system ice accumulation and release event resulting in a restriction at the inlet to the FOHE. Information on the proposed modification is provided via the ref /E/ Rolls-Royce Worldwide Communication (WWC). As noted in ref /E/, the modified FOHE is similar to the existing unit except that the fuel tube inlets are flush mounted to the inlet face plate instead of being proud of the inlet face plate. Testing has demonstrated a significant improvement in the tolerance to the arrival of ice at the inlet face plate in respect of ice quantity and fuel temperature.

Boeing and Rolls-Royce are working with the FAA and EASA to determine the most expedient path to certify the proposed FOHE redesign. Pending certification of the redesigned FOHE, Rolls-Royce is targeting service bulletin release in the third quarter of 2009. Per the ref /E/ WWC, the plan for allocating modified FOHEs is currently being developed and will be communicated with each operator individually once available.

phil gollin

Fascinating -- but it doesn't actually address the process that MIGHT have caused the crash, or where the water came from.

Nor is it a set of rules that applies to ALL aircraft with all types of engine.

Keep these announcements in context.

.

airfoilmod

My 2 cents, as a non engineer type, still relates to fuel and extended periods of very cold and very stable cruise. Both incidents occurred after very long periods of cold soaked and static cruising. All fuel has water in it, the spec allows small amounts. If the a/c tanks fuel prior to launch, it may already contain minute crystalline frozen water, albeit in trace amounts. Dispersed throughout the a/c tanks in some homogeneous mixture, it can certainly collect in small or "restrictive passages" (FOHE).
Built up as a "powdery" rather than a "solid" mass, it may collect in such a manner over time, that it allows cruise thrust, the flow of fuel acting to prevent continued necking down of the constricted passages so affected.
Without being specific due to my limited expertise, I can envision this "snowy" mass preventing higher thrust levels, or, due to additional accretion, maintaining current thrust, causing unresponsive power.

In the case of BA038, sudden full demand may have redistributed this occlusive mass downstream, packed it up and caused cavitation.

For Delta, the plug may simply have shifted on its own.

Anticipating the hue and cry from true believers in ETOPS, it isn't hard to imagine roughly simultaneous faults, given that at periods of long cruise, the systems acclimate and perform as one, essentially, given that there is no discrepancy in design, one from the other. Modern machining, chemistry and refining contributes to non anomalous behaviour of systems.

Then again, the Trent FOHE may melt and allow the ice to refreeze downstream. Over time, (long cruise) this could compromise fuel flow in the traditional way.

Smilin_Ed

Were the Fuel Oil Heat Exchangers for either GE or RR engines specifically designed to warm the fuel as well as cool the oil or was increasing fuel temperature simply a fortuitous byproduct? (Actually, increased fuel temperature would incrementally improve thermal efficiency.)

lomapaseo

How so, got any numbers?

phil gollin

Airfoilmod,

Please don't get me wrong, I like more information. All I worry about is that people MAY be being misled by short-term ideas or solutions. What is needed is a full scientific answer with a proper engineering solution which applies to all aircraft and engine installations.

It may (!) be that only one aircraft/engine installation combination is found to be at risk, but that is so unlikely as to be ridiculous. I just want people looking at the "big picture", not just concentrate on little ones.

.

fcom

I regularly operate on the China to Heathrow route and in winter the fuel temp always goes to around -42c sometimes -49c after around 6 hrs of flight.The minimum temp the fuel can drop to is -40c if USA fuel used and -49c for other countries. The engines can be at flight idle for around 20 mins during the descent with temps a lot lower than the fuel would have been on short finals which would have been around -8c or even warmer.
I'm pretty sure if there was any ice present it would have accumalated long before then and most certainly flagged up in the descent.

Oluf Husted

Dear fcom,

I have earlier, 2/3, 8/4, 1-5/5 and 3-4/7 (July) 2008, been writing, on this thread, about my theory, that core-icing, due to an ineffective or "turned off" engine anti-ice system, had the engines hesitate, and after "landing" just melt away.

This can also have been the cause in Amsterdam (TK1951)

So have a look, and let me know, if you have had the same thoughts.

Oluf Husted www.whistleblowers.dk

answer=42

Might this thread, especially the discussion of water from condensation, be relevant to the discussion?

DC-ATE

Has a "final" report come out yet on this accident?

lomapaseo

is this for voting or only for expert opinions

At any rate the answer is No

apparently you don't understand anti-icing systems nor core icing.

However having formed an opinion and your own web site I doubt that you will change your mind seeking only support for your theory.

airfoilmod

On board with that. My feeling all along is that information is being grasped a little too tightly by AAIB. FAA and NTSB operate a little differently. I do not buy the "Unknown characteristics". I think it is a wheeze. As time marches on, the leakage from the authority (not AAIB) has firmed up what Cargill and others were saying from the very beginning.

So it's the Trent? Boeing says so. Commercialism and turf battles have no place vis a vis safety issues. If that's what's happening.

FrequentSLF

As a reader of this forum I found, with all the due respect, your post absolutely meaningless. If you do not agree with a theory you should explain the reasons why you do not agree.

Carnage Matey!

From that website:

Not on any high-bypass jet engine I've ever operated. Engine anti ice keeps the nacelles ice free but it certainly doesn't route air to to spinner or fan cone nor does it prevent fan blade icing. I suspect this may be but one of many inaccuracies on that site.

Edited to add I've just spotted a complete lack of understanding of the BA LAX-LHR 3 eng flight in there too.

Rightbase

The thread you quote says the amount of water that can accumulate is quite substantial.

Against - there was a limited time window for it to accumulate after the inspection.
For - water scavenge is of doubtful effectiveness below freezing.

Any accumulated 'water' could all appear at once as the empty centre tank thawed out during the descent, and be scavenged through the still frozen main tanks to be fed to the two 'independent' engine systems as ice 'droplets'.

vapilot2004

Oil cooling is a requirement, but the heat exchangers main purpose is to warm the fuel.

vapilot2004

Boeing hasn't said exactly that. It is the combination of the Trent engine and the airframe fuel system that will require tweaking. Engineering on both sides obviously missed some low-temperature and possibly fuel quality management gotchas.

CV880

40 odd years ago I worked for a DC8-50 operator that experienced ice blockage of the inlet to the Fuel Oil Heat Exchangers on engines 1 and 4 on one particular sector. I don't recall if there were any power reductions as a result but the indicated fuel pressure on 1 and 4 used to drop late in the 9.5 hr flight. Investigation revealed impact icing on the fuel inlet end of the heat exchanger core. Part of the problem was the fuel loaded at HNL contained too much water as the tank farm capacity back then did not allow sufficient settling time before use. Engines 1 and 4 only were affected because the coldest fuel was in tanks 1 and 4 toward the end of the sector.
The fix was to reverse the oil flow through the FOHE. The original design had the hot oil entering at the fuel exit end and the cooled oil exiting at the fuel inlet which I recall was supposed to be the more thermally efficient flow but by reversing the flow the hot oil went into the fuel inlet end of the core and stopped the ice from building up on the FOHE core.

sky9

CV880

That should sort the problem out for little more than a couple of dollars

Von Klinkerhoffen

I have to agree with lomapaseo , you are confusing nacelle icing with engine core icing , two completely different things . As for your website , at least try to get your facts right before trying to impress a group of professionals on a forum !!

Besides , how on earth does engine core icing explain the HP fuel pump cavitation exhibited by both engines ??