High-impedance parts . . .
 

Could that possibly mean high-impedance parts or connections in the wiring close to the relays somewhere between the relays and ELMS?

Could fretting corrosion in connectors be a factor in this case? This kind of corrosion is often not visible to the naked eye. That is why there is an occasional misperception that there is no corrosion problem.

This was found to be a factor in the case regarding unscheduled closing of the shutoff valve i referred to in previous posts.


Regards,
Green-dot

Micro-muck
 

This is air pollution muck - NSEU - and its sink rate is very low within its water carrier.

Thanks for the 400Kg/hr figure. I was wondering how 'leisurely' the scavenge was.

If a dam of ice released a cascade of clean water into the water scavenge area, would 400kg/hr of water be enough to slow the engine? If so, the case against the dirty snowman collapses, and 'my' finger points to ice in the fuel.

Yes, 777fly, my outsider's view is showing its weaknesses.

The increase in volume of 4000Kg (about 320 - correction - 5000 litres) can only be supplied by adiabatic expansion if there is enough air in the tank to start with. If there is enough then there should be no contamination in the climb.

Edit3 - hope I'm on better form today ...
Tank capacity 100K litres, fuel upload approx 25k litres. Air to be expanded 75k litres. Expansion needed to replace fuel spent in the climb 5k litres. Estimate about 100mB (adiabatic) pressure change or 3000ft. There is an order of magnitude more air than needed to replace the fuel burned.
(OK - you professionals knew all this - I'm conceding as graciously as I can!)

Are the occasional 'water-in-fuel' warnings spurious? If not, 100+ gallons of water (and associated pollutants depending on where it came from) gets in some how.

NSEU may have exonerated the dirty snowman with his 400kg/hour scavenge rate for clean water. Could that cause the problem?

I think we should all remember that the scavenge system does not feed the remains of the center tank directly into the main tank boost pump pickups but rather it stirs up the fuel around the pickup.

If there were high-impedance points in the connections then the relay would probably fail to operate at all. After all it will require something in the region of 100mA to operate. ie around 3 watts.

Just toying with ball-park figures, but imagine a relay with a 28 volt coil. Number of turns required would result in around 1mH inductance and a self-resonant frequency around 1MHz.
What sort of field strength at 1 MHz would be needed to induce 3 watts in the coil??

P (dBm) = E (dBuV/m) - 20log F + Antenna gain - 77,2
Putting the relay coil and associated wiring as a 0 gain antenna and Power as 34 dBm the required field is 111 dBuV/m, or less than 1 V/m.

Do medium wave transmitters still exist?

According to the diagram provided in an earlier post (sorry - can't find it at the moment) the centre tank fuel scavenge outlet is at the outboard (high) end of the main tank. To get to the engines any water scavenged from the centre tank at this stage has to find its way back down to the main tank water scavenge pump which moves it to near the boost pump inlet.

(see post 461 Page 24 )

After all the theory and in depth physics, I wonder what the flight crew were doing as the speed decayed from 175 to 108 kts before the autpilot disconnected.:eek:

Reducing speed at 1knot per second?

pump cavitation
 

Pump output can be greatly diminished by cavitation and would give the results seen in this case.

The HP gear pumps show evidence of cavitation. Two of the principle determinants for the point at which cavitation occurs are pump speed and fluid viscosity.

A mixture of hydrocarbons such as jet fuel can have a temperature dependent change of viscosity while in the liquid state.

Cold high viscosity fuel along with an increase in pump speed at thrust demand may have lead to the cavitation.

Fuel that was not frozen but chilled to a high viscosity would have flowed through the large surface area filters without producing an alarm. And the boost pumps may have handled it without a problem too.

But how and why did it happen on this flight and not so many other flights?

I look back to a post on the previous thread (pg 20, post 394, by Glueball)
http://www.pprune.org/forums/showthr...310013&page=20

"The temperature probes in the 747-400, 777, and MD-11 are located where the bulk of the fuel is coldest. However, some fuel may be colder than the fuel measured by the probes, such as the fuel that is in contact with the lower wing skin. This creates a temperature gradient in the fuel tank from the wing skin to the location of the probe.
As fuel travels to the boost pump inlets, the bottom, cold layer flows through small flapper valves located on solid tank ribs next to the bottom wing skin. These valves are used to control fuel slosh. Thus, the cold fuel tends to flow toward the boost pump inlets."

Speculation ...

This flight started with fuel from a location that had cold weather. The initial FL resulted in a cold soak. The original flight plan was prudent for the conditions expected. The crew elected to honor a request from ATC to climb to FL348, ambient temperature approximately -65ºC. This was followed by a climb to FL380, -76C.

It seems to me that there was an extreme gradient between the coldest side of the tank and the fuel probe. While the the bulk of the fuel remained above the min. temp, I think that along the tank side, the fuel was chilled to the point that it congealed on the tank surface. Maybe it was still not frozen but perhaps so high in viscosity that it no longer moved with fuel currents to be remixed.

Once the tank surface warmed at arrival this high viscosity fuel would be released to flow toward the boost pump. Since the temp probe is not located at the pump inlet, it may have never seen this cold spot in the fuel.

Holes in the cheese ...

To reproduce this you have to cold soak the fuel. Expose the tank to extreme cold to get the required gradient, tank to probe, otherwise the crew will see the problem and correct for it. On arrival, a little more fuel in the tanks and the currents might not direct the cold spot to the pump or less fuel and the sloshing of flight maneuvers might remix the fuel. And the timing has to be just right. Early release of the cold spot gives a greater time for the remix of the fuel. A late release and the plane is on the ground before the cold spot gets to the pumps.

On this flight it all lined up. And it's going to be hell to prove. I bet it's a long time before we see a final report.

Code One . . . .
 

After digging into some background information i ran into an article in a "Code One Magazine" which may be of interest. Although a totally different type of aircraft, the article deals with a ground test to simulate a certain failure in the fuel system of a F-16. The similarity with the subject T7 is that its engine is also electronically controlled and the result of a simulation, engine rollback, comes remarkably close to what was experienced on G-YMMM. I know, totally different aircraft types but engine response seems not so different. Please read on . . . .

In this simulation the writer of the article, a senior experimental test pilot, describes the following:

Quote:
"Recently, I saw how the engine would quit in other than the normal airstart-test type of atmosphere. Although these tests were accomplished on the ground, I saw several things that I hadn't seen before, things I'd like to pass along. You can never know too much about the airplane.

I am sure that you are aware that there have been some as yet unexplained flameouts with the F110 engine. What we attempted to do was to try to induce as many potential malfunctions in the airplane as possible in order to shed some light on some of the past accidents/incidents. The airplane was tied down in the normal manner and then fully instrumented to record all the parameters of interest.
One large impression that I had was how tenaciously the engine will cling to life if it has fuel. On one test, we had artificially closed the master fuel shutoff valve to only five percent of capacity, that is, ninety-five percent closed. (There is no way that you can do this in your airplane without some really weird failure, or a plumbing change like we had for the purposes of this test.) The boost pumps were off and the refueling door was open so the system was depressurized. The engine was in idle and running just fine. The test point called for me to snap-accel the engine to ninety-five percent. The engine only briefly touched ninety-five percent, immediately rolled back to ninety-two percent, and hesitated there for a few seconds. It then rolled back to about eighty-seven percent for a few seconds. Subsequently it flamed out, but had an automatic restart accomplished in time to catch the rpm at eighty percent. It stayed there for another few seconds, and then flamed out again. The engine then auto-transferred to secondary engine control, or SEC, and got another auto restart at seventy-two to seventy-three percent. It maintained this condition for a little while and then flamed out again, with an auto restart in SEC at about sixty-five percent where it stayed for a while and then slowly continued to decay toward zero rpm. From this, and other similar runs, I feel that if the engine is operating properly, you have little fear of its quitting as long as the aircraft is providing fuel." Unquote



The article was written in 1990.

Here is the link to the complete article:

http://www.codeonemagazine.com/archi...out/index.html


In the simulation above it was elected to close the main shutoff valve for 95 percent, only 5 percent capacity, and the engine managed to retain RPM above idle several times for "a little while", even with boost pumps off and the fuel system depressurized (air refuel door open).

Focussing on the T7 dual engine roll back again, just suppose both spar valves had temporarily closed for, say, 80 percent (only 20 percent capacity remaining) with boost pumps on. Could that have resulted in engine roll backs to a stabilized thrust level above flight idle and cause cavitation at the engine pumps as the engines initially responded and then rolled back because reduced fuel flow did not meet engine demand?

I assume similar simulations such as mentioned above would have to be performed to find answers or are there other means (computer simulations?) to observe engine behaviour under such conditions?


Regards,
Green-dot

Change in procedures ?
 

Despite the lack of conclusive evidence in this case does anyone know if BA, or any other 777 operator has changed any procedures in the wake of this accident, and what that change might consist of ?

American 777 at LAX?
 

Has anyone heard anything more on the 777 rollback incident at LAX?

Blood tested?
 

Would people expect the BA crew to have their blood / fat tested after such an incident?

I have just started a thread on this subject which has been 'kindly' moved to Ground & Other Ops Forums - Questions! Thanks guys.

Blood yes - alcohol & drugs. Fat? :confused:

Vapour lock, not Carb-ice.
 

I may have been concentrating too much on the waxing and ice effects of very low outside temps during cruise .
...We are advised the uplifted fuel (stored and delivered at subzero temp) exceeded specs by a long chalk . being non waxing at temps down to -57 instead of only the normally expected -47ish
...The Chinese gave us a blend specially suited to their expected ISA minus 20 or worse. Its like our road fuel we get a more volatile blend in the winter.
...But how was this blend achieved? Was it just a generally lighter distillate? or was it by adding a much more volatile "additive"? With motor fuel it might be "quickstart" or alcohol.
.. The uplift was mostly in the CTW tank with the Wing tanks topped off.Fuel management in flight used a large proportion of the uplift at first., the remainder mixing with and somewhat diluting the original wing tank fuel.
...Finally descending into warmer UK temps at LHR, did this volatile cause gassing, cavitation, and loss of fuel pump efficiency when an extra demand reduced manifold pressures on the suction side of the pumps?

wilyflier:

Quote: " The uplift was mostly in the CTW tank with the wing tanks topped off".
This could not be the case. The aircraft would have arrived with, at a guess, 15000kgs (total) in the wings, assuming that there was no tankering. During refuelling the wing tanks have to be completely full before any fuel goes in to the centre tank. As the total wing tank capacity is about 58,000kgs, about 21500 kgs would have been put into each wing tank. The aircraft left with 79000kgs onboard, so about 21000kgs must have gone into the centre tank. In other words roughly the same amount of fuel was uplifted into each tank.

Vapour lock not carb-ice
 

Sorry about the sloppy refuelling Captain777
...My main thrust was higher volatility fuel and "vapour -lock" above normal propensity.

Fat test - why?
 

Cats Five - Fat is the long term storage place in your body for all the nasties that enter it either deliberately or by accident.

27 airline pilots were checked by UCL in 2006 and each and every one of them had abnormal amounts of toxic chemicals in them, which in turn produce mind bending effects.(sic)

Why not check for it as it could be relavent evidence and more importantly, it shouldn't be there.

DB :eek:

Fat test??! This topic is rapidly turning from speculation to pure fantasy.

wilyflier: Yours is as good a speculation as any other.

come on...a fat test is obvious, who would trust a skinny pilot ?

Vapour Lock #261
 

One of my suggested possibilities 300 posts (or so) ago. I also suggested the possibility of ethanol contamination as well, (explaining an unusually low fuel freeze point also: -57). This would increase "fuel" susceptibility to disastrous vaporisation at the HP pumps and consequent cavitation/damage to pump lobes. Although the AAIB tested samples, and they tested "OK", it isn't possible to have tested "all" fuel. Forgive the poor Physics memory, Wily. Something else that could have found its way into the tanks by mistake is Glycol, or DeIce fluid.

"Dear Willie,
Sorry I f****d-up the landing - it's because I'm a fat b@st@rd."

Faulty Software or EMI? Maybe, or Not?
 

There has been much discussion as to whether faulty software or Electromagnetic Interference (EMI) played a part in this accident. Before we can ascribe fault to either, we need to know just what the software does. The fuel control has multiple inputs but, presumably, only two outputs, fuel metering valve and inlet guide vane positioning, both of which have been reported by the AAIB to have functioned properly.

What else does the fuel control ultimately do? If the fuel control does more, can someone help us out here? If not, to blame the software or EMI looks to me like barking up the wrong tree. Again, apparently appropriate electrical signals reached the engines and individual parts of the engines responded accordingly but the engines just didn't produce the demanded power.

If there are no other fuel control outputs, it would seem that, since the high-pressure fuel pumps have been reported by the AAIB to work normally and there was enough fuel flow to keep the engines running at just above flight idle, it boils down to some characteristic of the fuel which reduced its ability to burn properly OR some flow restriction, presumably upstream of the high-pressure pumps.

Of course, there is a third possibility, the tanks simply started to run dry. :eek:

Skies fool,
At least I`ve done more good ones than bad ones
Hillyflier

Me too, Hilly -I just couldn't resist it. Dreambuster's "blame it on the pilots for fat-induced decision-making flaws" belongs to the 'Aliens' post!

Yes....indeed, I think someone has been on the blow :8. " While at 600ft, all I could think of was a fat juicy big mac....yyyyyummmmmmmmm, then all of a sudden we hit the ground....but it's not my fault, the burgers altered my mind...."

On the 29/02 on the french "rcoco.com" forum, one of the contributor joined to his post a report about the fuel scavenge system on the 777-300ER/777-200LR aircraft. I don't think that this (undated) report has been published here.
I believe it might be of some interest for most of you. And thank you for this very interesting discussion.
quote:

SUBJECT: 777-300ER/777-200LR Failure to Scavenge Fuel

/A/ Service Related Problem 777-SRP-28-0118
/B/ Fleet Team Digest Article 777-FTD-28-07002

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

SUMMARY:
Note: This message contains important information relevant to flight operations and airplane dispatch, please distribute accordingly.

Several 777-300ER operators have reported intermittent occurrences of airplanes landing with as much as 2200 lbs/1000kgs/300 gallons of fuel in the center tank. Boeing theorizes that this is an indication that the fuel scavenge system has malfunctioned. A failure such as this of the fuel scavenge system reduces the range of the airplane and could potentially lead to fuel exhaustion in the event additional failures occur which require use of all planned reserve fuel. To address this concern, Boeing recommends that 777-300ER and 777-200LR operators review their fuel reserve policy to ensure adequate reserves exist for each mission.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

DESCRIPTION:

The scavenge system is designed to transfer fuel from low areas of the center wing tank to the main tanks after the override pumps are shut off. Scavenging this additional fuel from the center tank increases the fuel available for engine use. The 777-300ER and 777-200LR airplanes have incorporated scavenge system design changes intended to increase the amount of fuel scavenged and reduce the amount of trapped unusable fuel in the center tank to approximately 3 gallons. These changes included relocating the fuel scavenge inlet further inboard, while the water scavenge inlet location remained unchanged. Additionally, the fuel scavenge outlet and float valve were moved further outboard to allow fuel scavenge to be initiated earlier in flight.

Several 777 -300ER operators have reported intermittent occurrences of airplanes landing with as much as 2200 lbs/1000kgs/300 gallons of fuel in the center tank. Boeing theorizes that this is an indication that the fuel scavenge system has malfunctioned. These instances have only occurred on long routes originating from colder climates and have led to the conclusion that an excessive amount of water is entering the fuel scavenge system and is freezing during scavenge operations. Because the water scavenge inlet was not co-located with the fuel scavenge inlets it is more likely for water to be ingested in the scavenge system. Additionally, as the outlet float valve location is further outboard in the main tank than previous, the scavenged center tank fuel has more exposure to the cold soaked main fuel tank prior to reaching the scavenge discharge. Indications are that the water in the scavenge system is freezing prior to discharging in the main tank. Frozen water (or ic!
e) in the scavenge system could result in a low rate of scavenge or no fuel scavenge.

Failure of the fuel scavenge system could result in airplanes landing with as much as 2200 lbs (1000 kgs) of fuel in the center tank. During mission planning and dispatch, this fuel in the center tank was considered usable fuel. However, failure of the fuel scavenge system in flight renders this 2200 lbs (1000 kgs) of fuel as unusable. There is no indication to the flight crew that the scavenge system has failed and the fuel is unusable. Failure of the fuel scavenge system essentially reduces the range of the airplane and could potentially lead to fuel exhaustion in the event additional failures occur which require the use of all planned fuel reserves.

Boeing review has determined that the failure to completely scavenge the center tank is the result of system configuration changes unique to the 777-300ER and 777-200LR airplanes. This issue has been placed in our Service Related Problem (SRP) process for resolution and is the subject of the REF /B/ Fleet Team Digest article.


DESIRED ACTION
===============
Boeing recognizes each operator establishes its own fuel reserve policy. Some operators choose to add additional conservatism to existing regulatory fuel reserve requirements. In addition, we note that not all routes and/or operators have shown a susceptibility to this condition. This may be because of environmental conditions, individual airline water sumping policies, or different operator fuel system procedures.

Boeing suggests 777-300ER and 777-200LR operators review their operation for exposure to trapped center tank fuel and their maintenance policy related to water sumping.

We recommend operators establish a policy to monitor center tank fuel quantity upon arrival of each flight. If trapped center tank fuel above 400 lbs (200 kgs) is discovered, we recommend a further review of fuel reserve and maintenance policies as noted above.

If operators chose to address this issue by uploading additional fuel, Boeing recommends operators notify their flight crews that additional fuel has been loaded to mitigate the potential for up to 2200 lbs (1000 kgs)of unusable fuel following failure of the scavenge system.

For operators who have seen the trapped center tank fuel condition and chosen to adjust their fuel reserve policy, we recognize it may be possible for this condition to be resolved on future flights due to a change in environmental conditions or maintenance practices.. If this situation arises, we believe it appropriate to adjust fuel reserve policies to original levels provided they continue the monitoring policy on a flight by flight basis for trapped center tank fuel.

Although these failure to scavenge occurrences have only been reported on the 777-300ER, any Boeing recommendations should also be applied to the 777-200LR as it has an identical center tank fuel scavenge system.


If further information is needed regarding the subject, please contact your local Boeing Field Service Representative. If your local Field Service Representative is unavailable, you may contact the appropriate Airline Support Manager or call the BCA Operations Center at (206) 544-75

unquote

original link:
http://www.rcoco.com/viewtopic.php?t...=asc&start=600

Regards.

Squawk_ident - scavenged ice from centre tank
 

Squawk_ident's post is interesting, especially where it says:
"Indications are that the water in the scavenge system is freezing prior to discharging in the main tank. Frozen water (or ice) in the scavenge system could result in a low rate of scavenge or no fuel scavenge. "

But the report does not comment on what effect such frozen water would have on systems 'down stream' of the scavenge system.

Seems to be an odd omission but I assume Boeing concluded that it was not worth comment.

regards

Trapped Fuel Indications
 

If there were fuel trapped in the center tank and if the fuel quantity system were working properly, the crew should have noticed it. AFAIK there has been no report that the crew noted anything less than sufficient fuel in the feed tanks to make a safe landing. If the feed tanks did run dry, that points to a fuel quantity indication problem. :sad:

Re post #608
 

I qoute from post #608:

"On the 29/02 on the french "rcoco.com" forum, one of the contributor joined to his post a report about the fuel scavenge system on the 777-300ER/777-200LR aircraft. I don't think that this (undated) report has been published here."

According the AAIB reports, BA38 was a 777-236ER.

It appears that this SB is valid only for the -200LR and not for the -200ER

Gelling
 

May seem irrelevant, but can we rule out the fact that the temperature was so cold the fuel was gelling and perhaps that led to the scavanging effect.

After impact etc this would possibly not be detected??

The Manager, OzJet, Safety & Security has posted the following:

My knowledge not being up to scratch on the subject, thought I would run it past you folks!

A matter of supply and demand . . .
 

Quoting Smilin Ed:

According to the AAIB report, engine fuel control systems functioned normally. However, if fuel flow (from airplane fuel system) to the engines is somehow restricted and cannot meet engine (control) demand, the engines will only accelerate to- and stabilize at the restricted fuel flow value, regardless of normally functioning fuel controls on the engines.


Green-dot

A330 Scenario, versus B777
 

Quote from ArcticLow [Mar02/19:06]:
....At 1000ft radio, the F/O takes control, states "Man Land 280 baro", but leaves the automatics in. At this stage, everything looks OK and they're just waiting to lose the last few knots of extra speed and so the power still hasn't come up fully. They've already discussed this and agreed that idle power is OK at 1000 but they'll go around if still not fully stabilised by 500 radio, as per SOP. At just under 750ft, the speed reaches the bug, the levers move forward to maintain target speed, but nothing happens. The levers go to climb power, still nothing. The F/O applies TOGA power, nothing. The rest is in the AAIB report. I don't know if this is what happened, but it's starting to look like a high probability hypothesis, on the available evidence. Thank God it wasn't a scarebus...
[Unquote]

For someone who claims not to be a pilot, you are remarkably well briefed. Perhaps by one of the Boeing Airways pilots on a long overnight flight?
He has certainly sold you the whole package -
1) If a Boeing has an incident/accident, it cannot possibly be caused by any fundamental problem with the aircraft. :rolleyes: Possibly rogue fuel? :ok:
2) If an Airbus has an incident/accident, it's because the designer was simply bonkers. := :{

Sound familiar? So, since you have begged the question, can I stay off-topic to speculate what MIGHT have happened if the Trent engines on an A330, for example, had behaved like the ones on G-YMMM did, at the same point on the same approach?

Unlike the B777, the A330 autopilot would be programmed to Go-Around mode as the pilot selected TOGA thrust. Because the aeroplane would be unable to comply, the AP would drop out almost immediately, and the FD demands on the PFD (ADI) would be of no help. The PF would switch it off (or ask the PNF to do it).

"Fly the aeroplane." The FBW would be doing just that. It would maintain 1-G flight in pitch, and zero-rate in roll; holding a steady descent path and keeping the wings level (if they were when the AP disengaged). Because of the shortage of thrust, the speed would be decaying, as per the B777.

Workload permitting, the PF might select the FPV display on his/her PFD. This, with the FD switched off, would display the "Bird", a symbol showing the drift and descent trajectory. This might be useful to check a steady profile is being maintained initially, even though the nose is being raised steadily as the speed falls. Because of this, the "picture" of the world outside the cockpit windows is starting to look very wrong.

Meanwhile, the aeroplane is still pretty much on the glide-slope. The FBW continues to run the stabiliser-trim in the "nose-up" sense. A decision must be made. The PNF's attempts to revive the engines have failed; we are going to undershoot the runway. What is the best (minimum-drag) speed on this aeroplane with landing flaps and gear extended? Haven't the foggiest idea, but we must be already below it! Time to trade height to stop the IAS going any lower. Slowing down equals MORE DRAG. We'll have to maintain this speed as long as we can. Tweek the sidestick forward a bit, then release. Down we go, is that enough?

We've got to get over the perimeter road – which has already disappeared somewhere under the nose – and into the field. The speed is still decaying slowly, unfortunately, but this aeroplane cannot be stalled. As the IAS drops to Alpha-prot, about 13% above stalling speed, the stabiliser stops trimming back; the stick must now be pulled harder and harder to stop the nose dropping. Can we keep a tiny bit of speed in hand to avoid hitting the ground too hard?

The rad-alt calls "ONE HUNDRED". Pull a bit harder. "FIFTY". Stick hard back - we've got to miss that road. We're close to Alpha-max (5% above stalling speed). Now, the aeroplane will descend of its own accord to avoid stalling. "TWENTY", BANG, we are down...

UPDATE: AAIB investigation into BA38 B777 crash at LHR
 

Smilin Ed said:

"There has been much discussion as to whether faulty software or Electromagnetic Interference (EMI) played a part in this accident."

EMI, like "pilot error" is something which leaves little or no evidence behind, and so is a convenient explanation for otherwise inexplicable events.

Modern airliners emit a lot of radio frequency radiation for many purposes, and their instruments and controls are made to tolerate quite high levels of EMI.

Also the AAIB should have noticed, and their report says:

The total fuel on board was indicating 10,500kg, which was distributed almost equally between the left and right main fuel tanks

Engine Compressor Guide Vanes?

Could I recommend we should look at the part that the engine guide vanes play in the scheme of things. They have received precious little attention so far no doubt because of the concentration in trying to determine a single source for a two engine event.

Presumably the engines compressor guide vanes angular control is by the FADECs which are in turn are driven by dedicated computerised software. Wonder where the FADEC software is physically located.

Can someone describe the Trent guide vane system? How many stages of vanes and are they all interconnected? Over what RPM range do they do their thing? Are they hydraulic, fuel pressure or bleed air driven? Are they anti-iced and what is likely to be the effects of malfunctioning or non functioning during engine acceleration?

Quote from grebllaw123d:
According the AAIB reports, BA38 was a 777-236ER.
[Unquote]

Hi, Are you are under the impression that the Boeing Service Bulletin only applies specifically to B777-300ER and B777-200LR?

Think you will find that Boeing dash-numbers ending in "0" or "00" are a kind of generic description. The second and third numerical digits merely indicate the airline.

Since I was a lad, all Boeing airplanes bought new by BOAC and BA have had dash-numbers ending in "36", e.g., B707-436, et cetera.

Chris

Editing PS: Ah, now I see what you mean, I think. Is it the "ER" designation you are querying? If so, I don't know. Sorry.

Chris, read post #608 the SB refers to 777-300ER and 777-200LR not 777-200ER.