Airfoilmod
 

Entirely agree with your last post.

I thought the "possible problem" as identified by AAIB was an ice build-up on the inlet tubesheet of the FOHE. So the need would be to prevent ice release from upstream, not from within the FOHE. Once out of the tubes, the ice would immediately pass out of the FOHE.

If I read it right, the proposed RR interim fix addresses tube protrusion from the tubesheet, effectively making it smoother with less places for ice to catch and build up.

Sooty

Solution
 

Perhaps demoting the FOHE to a secondary system, an ancillary instead of a singular, and Flight Critical component. If I was to propose a fix:

Build a new, shorter HE that has a "Y" at either end, allowing the provision of a gate valve that can Divert Fuel AROUND the Cannister to a Flow Only Bypass that supplies the HP directly in Cold Cruise. If the HE is Bench Built and conforms to existing Entry Exit Plumbing, It could be fitted in a scheduled C or D break, for uninterrupted revenue and Plumbing redesign. I'll call my patent Atty. Interested?

AF

Solution to wrong problem, perhaps
 

Stopping the ice build-up in the FOHE is IMHO addressing the symptoms, not the disease. If there is sufficient incipient ice in the fuel flow, when the holes in the cheese line up it will find somewhere to accumulate.

Wouldn't it be better to stop the ice at source, or at least stop it being released into the engine?

Sooty

Incurable
 

The Problem isn't Ice, it's water. "In Spec." Fuel has it and at very low temps it takes shape as granular microscopic particles. As such, it does no harm. At Cruise, in VERY low temp. over many hours, the ice melts and refreezes in the FOHE. It can reaccumulate at the small bore exits to the HP's., cause cavitation and starvation, as discussed. Heating, melting at the entry and immediately refreezing downstream is the problem. Oil cooling is not necessary at this point, indeed, the Oil (mostly) bypasses the FOHE anyway., so why direct the Fuel through a periodically unnecessary Path?

The solution isn't water free Fuel, which is impossible anyway; but directing Fuel around vulnerability in the Fuel Path when it may create problems.

AF

How much money would need to be spent on having fuel that does not hold water and to have some sort of system on the fuel tanks to prevent water ingress through condensation etc.?

The Fuel Heater would be a simpler solution to the accumulation of ice.

Now the argument would be, where do you place the Fuel Heater, on the engine? At the front spar? In the tank? (I would go for the engine!)

(Non-pilot speaking)
But if you placed it in the engine - you have to pump the fuel there first ...?

My uneducated guess as to why fuel heaters were discontinued would be:
1) We have better fuel spec these days
2) We can save the weight and cost of these units
Followed by:-
3) It's worked well since we stopped installing fuel heaters ...

Humans usually have to learn things more than once.

Quick question and please excuse me for not going thru 115 pages to see it was already brought up:

Does the B777 have a fuel recirculating system to warm the stored fuel? My current bizjet does by recirc'ing fuel out of the oil cooler directly back into the wing tanks.

GF

And don't forget that the energy to heat the fuel is paid for in increased fuel burn. Only a small proportion of that comes back in the efficiency gain of hotter fuel for combustion

Heat Recovery
 

But the heat recovered by the necessary function of cooling the oil would otherwise be thrown away.

N T S B Issues Urgent Safety Recommendation To Address Engine Thrust Rollback Events
 

************************************************************
NTSB PRESS RELEASE
************************************************************
National Transportation Safety Board
Washington, DC 20594
FOR IMMEDIATE RELEASE: March 11, 2009
SB-09-11
************************************************************
NTSB ISSUES URGENT SAFETY RECOMMENDATION TO ADDRESS ENGINE
THRUST ROLLBACK EVENTS ON B-777 AIRCRAFT
************************************************************
Washington, DC - Following two engine thrust rollback events
on Boeing 777 aircraft powered by Rolls-Royce engines, the
National Transportation Safety Board issued an urgent safety
recommendation today calling for the redesign of a Rolls-
Royce engine component. The Safety Board also recommended
that, after the redesign is completed, the new system be
installed on all affected B-777 airplanes at the next
maintenance check or within six months.
These recommendations are being issued in response to the
findings in two investigations - an accident and an incident
- involving engine thrust rollbacks on Boeing 777-200ER
airplanes powered by Rolls-Royce RB211 Trent 800 Series
engines. In both cases a build-up of ice (from water
normally present in all jet fuel) on the fuel/oil heat
exchanger (FOHE) restricted the flow of fuel to the engine,
resulting in an uncommanded engine rollback.
The first event, which is still being investigated by the
UK's Air Accidents Investigation Branch (AAIB), occurred on
January 17, 2008, when a Boeing 777 experienced a dual
engine rollback on final approach and crashed short of the
runway at London's Heathrow International Airport. One
passenger was seriously injured, eight passengers and four
of the flight crew sustained minor injuries; the airplane
was substantially damaged.

The second event occurred on November 26, 2008, when a Delta
Air Lines Boeing 777 experienced a single engine rollback
during cruise flight over Montana while en route from
Shanghai to Atlanta. Normal operations resumed after the
flight crew followed Boeing's published procedure to recover
engine performance; the airplane landed safely in Atlanta.
Testing in support of the UK accident investigation led
Boeing to develop procedures to help prevent ice
accumulation, and to recover thrust in cases of ice
blockage. As more information from the Delta rollback event
was developed, Boeing modified the procedures, which became
the basis of an airworthiness directive issued by the
Federal Aviation Administration.
While the procedures may reduce the risk of a rollback in
one or both engines due to FOHE 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.
Because of these hazards, the Safety Board has determined
that the only acceptable solution to this safety
vulnerability is a redesigned FOHE that would eliminate the
potential of ice build-up. On February 23, 2009, Rolls-Royce
indicated that a redesign of the FOHE was underway, and that
they anticipated the redesign to be tested, certified and
ready for installation within 12 months.
"With two of these rollback events occurring within a year,
we believe that there is a high probability of something
similar happening again," said NTSB Acting Chairman Mark V.
Rosenker. "We are encouraged to see that Rolls-Royce is
already working on a redesign, and we are confident that
with the FAA and EASA (European Aviation Safety Agency)
overseeing the process, this flight safety issue - even one
as complex as this - will be successfully and expeditiously
resolved."
The NTSB has made the following two recommendations to both
the Federal Aviation Administration and the European
Aviation Safety Agency:
Require that Rolls-Royce redesign the RB211 Trent 800 series
engine fuel/oil heat exchanger (FOHE) such that ice
accumulation on the face of the FOHE will not restrict fuel
flow to the extent that the ability to achieve commanded
thrust is reduced.
Once the fuel/oil heat exchanger (FOHE) is redesigned and
approved by certification authorities, require that operators
of Boeing 777-200 airplanes powered by Rolls Royce RB211 Trent
800 series engines install the redesigned FOHE at the next
scheduled maintenance opportunity or within 6 months after the
revised FOHE design has been certificated, whichever comes
first.
The NTSB and AAIB will continue to work together closely on
both of the rollback events as each of the investigations
move forward.
Safety recommendation letter to the Federal Aviation
Administration:
http://ntsb.gov/Recs/letters/2009/A09_17_18.pdf
Safety recommendation letter to the European Aviation Safety
Agency: http://ntsb.gov/Recs/letters/2009/A09_19_20.pdf
Image: Ice accumulation on the inlet face of a Rolls-Royce
RB211 Trent 800 Series Fuel/Oil Heat Exchanger during
testing >>> http://www.ntsb.gov/Pressrel/2009/FOHEface.jpg
###
NTSB Media Contact: Peter Knudson
(202) 314-6100
[email protected]
************************************************************

NTSB Safety Recommendation
 

It's hard to imagine that the NTSB has sufficient data and risk assessment expertise to step in front of the public and say that the currently issued AD and incorporation schedule would not adequately minimize the risk.

It sounds more like a "me too" and I'm in charge.

NTSB
 

Is a BOARD. FAA is an AUTHORITY. The NTSB has forced FAA's hand. This isn't "me too", this is: "get busy". I think FAA determination will follow. Since the First mitigation didn't work (the "non-normal" one) there is great risk in merely "guessing" at a replacement, and NTSB has said it isn't acceptable anyway. The FAA diverges at great risk. The affected A/C I think will soon be parked. The NTSB's Move will temper the flack the grounding will engender, but those who complain will be criticized roundly. As I see it, it is appropriate for the Investigative Body (NTSB) to make findings of fact, then pass their work along to the rule making authority to direct a response by rule making. (FAA'S) job.

AF

Further reading
 

Of Ms. Osmus' letter reveals an opening left for the FAA. The NTSB anticipates a refit around maintenance schedules. This allows the FAA to come down authoritatively in ordering a fleet park.

There is some astonishing indictment of the as built FOHE as well. There are vast legal issues here, to put it mildly.

AF

Just about the time it took to redesign, test fly and put into production a complete new Mk of Spitfire and several Merlin supercharger & carburrettor upgrades :hmm:

....more than 60 years ago without CADM and with bombs dropping on one's offices and factories !

Harry
 

I think from first order to first flight was 15 months for the Mustang? I'll check that. Check That, make it 117 DAYS.

AF

Image: Ice accumulation on the inlet face of a Rolls-Royce RB211 Trent 800 Series F
 

Now THAT'S an occluded artery.

It's nice to see the NTSB and FAA agree with my guess from the 16th Feb 08!!

I've a good mind to name the ***** who questioned my basic understanding of aircraft systems when I put forward the idea of cold soaked system causing a restriction though the FCOC. I know it's correctly called a FOHE but I'm a bit stuck in my ways.

Where do I claim my prize?

Sorry for the cell phone interference brigade. You guys were banking on this weren't you?

:-)

C N N Article Regarding The Above N T S B Recommendation
 

WASHINGTON (CNN) -- Federal transportation safety officials Wednesday issued an "urgent" recommendation calling for a redesign of a component on some Boeing 777 aircraft engines -- a component blamed for two major mishaps in the past year.

Authorities have called for the redesign of an engine part in some Boeing 777s.


National Transportation Safety Board investigators said the Rolls-Royce engine component played a role in the January 17, 2008, crash of a British Airways jet near London's Heathrow Airport. Both the plane's engines lost power as the plane approached the runway, and 13 people were injured in the resulting crash.

Ten months later, on November 26, 2008, a Delta Air Lines Boeing 777 was in cruise flight over Montana when an engine lost power. That plane landed safely in Atlanta after pilots performed a procedure developed in response to the Heathrow crash.

In both cases, the NTSB said, a build-up of ice on a fuel/oil heat exchanger restricted the flow of fuel to the Rolls-Royce engines, reducing power.

"With two of these rollback events occurring within a year, we believe that there is a high probability of something similar happening again," NTSB Acting Chairman Mark Rosenker said in a news release.

The Federal Aviation Administration recently ordered operators of affected Boeing 777s to revise flight manuals to give pilots procedures to follow in certain cold weather conditions, outlining steps they should take if their jets experience a reduction of power.

But the NTSB said Wednesday the FAA action does not go far enough.
"The procedure has worked and it has been effective in significantly reducing the likelihood [of an incident]," said NTSB spokesman Peter Knudson. "But that's not enough. We need a permanent fix."
While the emergency procedures work, they add to the complexity of flying the plane and require a descent, which could be hazardous if the plane is not at a sufficient altitude, the NTSB said.

Some 56 aircraft in the U.S. fleet and a total of 228 worldwide are equipped with Rolls-Royce engines.

But the NTSB stopped short of recommending the planes be grounded. Knudson said the safety board believes the new procedures will significantly address the problem until Rolls-Royce has a new component ready for installation. Rolls-Royce indicated it can have a new system ready within 12 months, the NTSB said.

"We are encouraged to see that Rolls-Royce is already working on a redesign, and we are confident that with the FAA and EASA [European Aviation Safety Agency] overseeing the process, this flight safety issue -- even one as complex as this -- will be successfully and expeditiously resolved," Rosenker said.

The NTSB recommended that, once Rolls-Royce completes its redesign, the new system be installed on all affected Boeing 777's at their next maintenance check or within six months.

No one from Rolls-Royce was immediately available for comment.

"This is a serious matter for those airlines operating the 777 with Rolls-Royce engines," said Richard Quest, CNN's aviation correspondent . "There is a satisfactory temporary solution, but a long-term fix is what the NTSB is demanding."

"There is a satisfactory temporary solution..."
 

In school, "satisfactory" rates a grade of "C". Quest isn't much more optimistic than Rosenker or Knudson. I still think the NTSB, in not calling for "a grounding" has simply left the door open for their counterpart (FAA) to do so.

AF

From the NTSB press release posted above :-

"......... These recommendations are being issued in response to the findings in two investigations - an accident and an incident - involving engine thrust rollbacks on Boeing 777-200ER airplanes powered by Rolls-Royce RB211 Trent 800 Series engines. In both cases a build-up of ice (from water normally present in all jet fuel) on the fuel/oil heat
exchanger (FOHE) restricted the flow of fuel to the engine, resulting in an uncommanded engine rollback. ............" (my bold)


Fascinating.

According to this, the two investigations have been completed (at least they have specific "findings" and are factually known) as opposed to theories or speculation !

Likewise, they have supposedly explained where the additional water came to cause the problem.

Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.

.

READING, again
 

To Phil Gollin

Quote
Unforunately they haven't bothered to highlight other engine installations in other planes which need similar flight restrictions.
Unquote

This problem occurs specifically on the mentioned RR engine, due to its specific Fuel Oil Heat Exchanger design. Other jet engines on other aircraft have other designs of FOHE which have not exhibited this problem, so do not loosely assume that they also need restrictions. READ information please, when it is provided is such ample detail.

I think it is credible that the test rig investigations have moved forward substantially from the last official reports, particularly with another incident providing another dataset. This is supported by the image provided.

Because I don't think this is an issue any more. It looks from the details and the image that we are not looking at a big slug of ice collecting elsewhere and getting pulled down the pipes by the increased fuel demand, but rather it is small amounts of ice acreting at the entrance to the small diameter FOHE tubes. Increased (cold) fuel flow (as thrust was demanded) would then both cool the area and probably pull the ice into the tubes, blocking them.

EDIT: The above was based on the NTSB statement and the FOHE image, now looking at the AAIB report it is clear that the ice acretes on the pipework and is swept onto the FOHE inlet.

Leaving aside possibilities of ice in tanks not being detected or removed at sumping, there would still have been 5L or so (according to the AAIB) or water in the fuel. Looking at the FOHE image, I don't think you need anything near 5L of water to create a serious problem. Just the mechanism for small amounts to crystalise in a bad place - which is what appears to have now been established.

If you look back on the thread there are plenty of posts identifying the Trent plumbing as different, particularly in the location of the FOHE. The Trent 800 FOHE may well be different again, sufficiently for this not to happen on other Trents.
The publication of the image strongly suggests to me that they have got this ice acretion repeatable on the test rig, in which case testing other FOHEs could have already ruled out this particular problem.

This from a Seattle newspaper . . .
NTSB wants Boeing 777 engine redesigned

"Boeing engineers, working in the laboratory, determined that the heat generated by the Rolls-Royce fuel-oil heat exchanger is not adequate to prevent moisture in the fuel from freezing. When that happens, ice can form that blocks fuel to the exchanger, starving the engines."

Open Letter
 

To avoid Ice on FOHE, "Max Thrust is applied....". Sorry, isn't that what got This a/c into trouble in the First Place.??

To Avoid Ice on FOHE, "Idle Thrust is required...." Sorry, DELTA??

These "Mitigating procedures" were addressed. NTSB claims Another Incident (Accident) is "likely". Applied Power solutions are NOT working.

Will it now be "co-ordinated blending of high EPR followed by Idle, followed by" ....? A Secret Handshake?? Shaman? Tarot?

The way RR proposes to redo the HE frankly isn't too confidence inspiring either.

READ ##2204, 23, 42, 49, 54, 58, 59, ........ and others, ad, well, nauseum......

ReRead Osmus' letter. This isn't just "very cold temps". Neither is it "Chinese Fuel". Phil, this is a TRENT thing. Fuel has water in it, no mystery.

AF

To avoid the ice buildup, max climb thrust for step climbs had been mandated a couple of months ago in certain cold conditions.

This has proven to be insufficient in some cases. The Delta flight in question did two max. climb thrust step climbs.

To remove an ice blockage that has formed nonetheless, a few seconds of idle thrust will melt it away by changing the balance between hot oil (only a little less) and cold fuel (a lot less).


Bernd

bernd
 

I cannot even infer the point you may be making. The AD is working?

It is not? It may be working? Give it time? What is your point?

AF

Delta's Idle melting excursion cost 8,000 feet. Could it have been more?
Have you seen the terrain they were flying over? At 31,000 feet they could Glide what, 90 miles? Not enough. At 31k feet, they were at most 19,000 feet AGL, Get my point?

http://www.flightglobal.com/assets/g...x?ItemID=27976
:eek:

AAIB .pdf Report

airfoilmod,

sorry for being obscure.

You said in your post that both actions (max. thrust, and idle thrust) were to avoid ice build-up.

They aren't.

One was supposed to avoid it, the other to remove it.

And I also can't see how max thrust brought any aircraft into trouble. It was only that max. climb thrust (which is usually on the order of only 30% of maximum (takeoff/go-around-) thrust) didn't keep them out of trouble.

Or maybe I misunderstood the first part of your post.

I get the point, as does the NTSB, that the idle melting procedure is not optimal, to say the least. That is why the Trent 800 FOHE design is being changed. It may take a while. What to do in the meantime? Obviously I have no answer to that.


Bernd

OK
 

Thanks Bernd. On finals, it would seem, if not already established, that increasing thrust caused Rollbacks. If so, Demonstrably the fix doesn't work. Parsing "How Much Thrust" is a fool's game. I have alluded to vibration and Acoustics on enhanced EPRs many times; this may dislodge deposits upstream the FOHE, sending them down to the Face. It also may dislodge ice accreted at the Face, further blocking Flow. That Idle may melt accreted Ice and Open the Line is wonderful, but How much is anyone willing to gamble? If it doesn't work, what then Glide Idle?

AF

Very interesting report. Quite a few unknown unknowns are now known unknowns.

Reasonable to conclude from the evidence is the fact that Ice can migrate downstream to block the Face of the FOHE. Add to that the fact that Ice may have built up on the Face independently of additional "dislodged Ice". Yet the FOHE wasn't designed to be an Ice Melter; It is to be relied upon now to not only melt its own independent accumulations, but that released by "Thrust, Pitch, Turbulence"....etc.?? This is a type of Ice I suggested earlier, "Amoebic, migratory, slurry, etc." It seems to be too much for any makeshift lashup, (with respect).

AF

Post #2176 3 Feb. 09

Adapt Other FOHEs?
 

Since there have been no reported incidents with the other brand(s) of engines, it would seem prudent to consider the FOHE design(s) of those other brand(s). Could other FOHE designs not be adapted to fit the RR engines? Someone with specific experience with both/all types of B777 engines comment please.

Hitting your MAG
 

Airfoilmod sir, with the greatest possible respect you are showing your age here .............

In most (state) schools today raw results, such as the attainment of say a Grade "C", do not repeat not, rate as "satisfactory" or anything else; hitting your Mininimum Attainment Grade ("MAG") just might.

The Ofsted concept these days is more subtle and target driven as a function of your achieving "Value Added" cf datum MAG - datum MAG usually being defined as a function of a statistically derived average points score at the previous Key Stage.

On a personal note, the perception today is that in school all must win prizes and this mechanism is pretty good at diluting simplistic achievment driven elitism.

Do not expect me further to defend the current system...........

CW

Water quantities.

The AAIB Interim report no. 2 (my bold) states (page 7) that the

"... accident flight might have contained up to 70 ppm of dissolved and entrained (suspended) water ...."

whilst their post accident samples showed

".... Fuel samples taken from G-YMMM after the accident indicated that the water concentration in the fuel taken from the left main tank sump, APU line and Variable Stator Vane actuator was approximately 40 ppm ......".

However, the tests took place using 90 ppm something like 28 to 125% more than was in the crashed aircraft - as

".......the industry standard for continuous system operation tests, aiming to condition the fuel with 90 ppm of water. ......"

So, not only is the incident report rather cagey about what actually happened, but the tests do not seem (unless I missed something) truely representative of what happened. The report still doesn't explain where the additional water might have come from.

===========

However, it does look like there is a whole new bunch of research on fuel/ice mixtures to come about.

.

Young Chris, As I understand STAR, it is an "indexed form" plateau, sensitive to the augmented mean of specific prior record, adjusted for performance diminution caused by variable but "smoothe" forms. Graphically, a hyperbolic (sic) paraboloid, truncated at x and x-y, replacing that of which we cannot speak.

AF momentus continuum, continuum truncare

Phil, I beleive it does at least allude to where it came from...

The varied (and higher levels) of water can come from less than homogeneous distribution in the tank, but mainly from prior upstream ice melting, either from the boost pump screens or from pipewrok less far upstream.

As I took it to mean ppm at the point of interest e.g. in the pylon pipework or adjacent main tank pipework.

I believe they also inferred that concentrations could vary wildly from time to time in the fuel passing through the critical pipework sections, up to possibly 125ppm.

.. without of course re-reading or quoting directly.

probability of a grounding?
 

Would anybody be willing to make a guess as to the likelihood of the FAA ordering a worldwide grounding of the 777-200ER with the Trent 800 engine type until such time as a redesigned FOHE can be approved and installed? Nonexistent, small, moderate, significant...? Perhaps a silly question in which case my apologies, but it looks to this non-expert that the airworthiness directive now in place is far from ideal.

deScally
 

#2273 #2274..... Probability ??..... Moderate to Severe.

AF (my opinion) (Have you read the thread?)

airfoilmod; thanks for enlightening me. I had read the thread, just looking for some clearer opinion re: likelihood of grounding the fleet. I await the FAA's action with bated breath. Thanks again.