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AAIB BA38 B777 Initial Report Update 23 January 2008

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AAIB BA38 B777 Initial Report Update 23 January 2008

Old 13th Feb 2008, 21:16
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I am concerned about any airlines min fuel policy that requires Boeing crews to action the low fuel drill checklist as SOP on arrivals in response to a warning message of low fuel.
I believe the low fuel drill should now be regarded as an emergency drill and not a SOP drill and fuel loads increased to avoid the routine use of this drill.
I am also concerned about the use and legal deffinition of adequate fuel onboard as regards useable fuel on board... and the amount of non useable fuel on board.
I do not have the B777 figures but on the B767 there is considered 2000Kgs of fuel total (1000kgs in each wing tank) as unuseable...thus with adequate legal fuel crews are often landing with the low fuel state warning on and the drill actioned (possibly this may have been the BA038 situation) thus you are initially getting all your fuel/contamination feed to all your engines from one tank...I always considered this an emergency not a normal SOP QRH drill and to avoid I always loaded the unusable fuel figure as extra to the min CFP fuel.
Probably not a totally clear response but as I am old and retired and off to get my hot milk you will have to accept it as adequate.
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Old 13th Feb 2008, 21:24
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Originally Posted by Milt
There was a time when we were concerned about Cladisporeum (spelling?) which grew in aircraft fuel tanks at the water fuel interface producing a corrosive of integral tanks. Many wing skins had to be replaced. Fuel additives were developed to combat the problem.
Pretty close, Cladosporium Resinae. I'm sure this has nothing to do with this accident but it's still interesting to see what can be lurking in fuel tanks-usually in warmer climes- so it's another reason to keep doing those water drain checks.

Look at the link if you would like to find out more.


www.casa.gov.au/fsa/2005/oct/50-51.pdf URL]
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Old 13th Feb 2008, 22:03
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Qwatters, Post 521 of the previous thread.
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Old 13th Feb 2008, 22:13
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Ref water drains, when I check the sump drains on 74s when in for service checks, there is very little water in the tanks, tne most I have ever drained would be 250mls tops and that when tanks have settled for at least 24 hours.
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Old 13th Feb 2008, 22:22
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Originally Posted by r75
Ref water drains, when I check the sump drains on 74s when in for service checks, there is very little water in the tanks, tne most I have ever drained would be 250mls tops and that when tanks have settled for at least 24 hours.
Have you ever done a fuel drain on an A/C that has been sitting in freezing temperatures for 24 hours? Is it possible that ice might stay in the tank and not drain out? Was a fuel drain even required?
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Old 13th Feb 2008, 22:53
  #366 (permalink)  
 
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bvcu
Thanks for your input, I guess water checks every 50 hrs or so is acceptable, re r75.
gerryfoley
Low engine oil temperature is a relative term, engine oil is very HOT, it has just lubricated and cooled the turbine bearings.
r75
Thanks for your observation, I suspected as much.
Being a rumour site, there was a story that crews were praised if they landed at minimum fuel as every tonne left in the tanks had cost one tonne to transport it with associated hi costs/lo profit.
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Old 14th Feb 2008, 01:21
  #367 (permalink)  
 
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Gentlemen and ladies,

Various scenarios have been posed on this thread that involve some type of fuel contamination. Whatever caused the two engines to misbehave, the only evidence we have so far indicates that one was stricken only 8 seconds before the other, and that their malfunctions were similar.

Although it is theoretically possible for a common-cause fuel contamination to develop to a critical point in two separate tanks at the same moment, even after a long flight and a complete descent, reason suggests this is improbable.

Therefore, these scenarios are all predicated on the assumption that, at the very least, the fuel crossfeed must have been open at the time of these failures.

I know of no evidence so far that this was the case.
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Old 14th Feb 2008, 04:33
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I can't see contamination causing the pitch up that occurred when Land 3 annunciated.
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Old 14th Feb 2008, 05:20
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Sheets of Ice

Turin said (in the earlier thread)
think about 10 years ago Continental had an issue with their early 777s in that during winter ops from NWK the fuel temp never dropped sufficiently to allow any suspended/solid water to thaw and therefore be drained during normal routine checks. Result was a very large, thick sheet of ice in the base of the fuel tanks which would often give erroneous tank qty readings.
Would such a "sheet of ice" form atop/in or at the bottom of AVTUR/JP4/JP5 etc? Would suspended particulate matter or FSII (anti-ice additives such as PRIST) affect that?
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Old 14th Feb 2008, 06:28
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but my understanding is that fuel temperature is kept above a minimum figure due to heat exchange with the hydraulic circuits routed through the tanks.
I believe the warming effect is very marginal. The primary purpose of the heat exchangers is to cool the hydraulic fluid, not warm the fuel.

Note that the heat exchanger for the Left hydraulic system is in the left wing tank and the heat exchangers for the Right and Centre hydraulic systems are in the right tank. The fuel temperature sensor is in the left tank, reportedly because the temperature will be slightly lower (because there is only one heat exchanger). The heat exchangers are mounted on the bottom of the tanks, inboard of the engines.
I believe the specific gravity of frozen water (ice) is .92, so still a lot more dense than fuel (and would drift to the bottom of the tank), so perhaps the heat exchangers might help to defrost the ice if it was present in the tanks.

I don't know how reliable the (ultrasonic) water detectors are in the fuel tanks. We have had a number of failures of ultrasonic potable water level detectors (on our 747-400ER's), so I'm not a big fan of ultrasonic-type devices.

Rgds.
NSEU
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Old 14th Feb 2008, 06:44
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Although it is theoretically possible for a common-cause fuel contamination to develop to a critical point in two separate tanks at the same moment, even after a long flight and a complete descent, reason suggests this is improbable.
I don't see why this is so improbable. The fuel comes from the same source and it is subjected to the same temperature conditions (give or take a few degrees). The fuel pump inlets in each wing are in similar positions. If the descent had been mostly at idle power, then the problem may have been brewing for some time before substantial quanties of fuel/thrust were required.

Perhaps airplane attitude put the fwd and aft pump inlets at the same levels, too, adding to the probability that both inlets might get blocked with slush/ice?
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Old 14th Feb 2008, 09:16
  #372 (permalink)  

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Planning landing at Heathrow with 30 min in the tanks is legal and would justify the official statement “adequate fuel”.
It would also justify (if officially confirmed in a coming update … !?) that crossfeed was open and flaps limited at 20, in order to follow a probable requested low fuel procedure 262 287
An open crossfeed could justify than both engines took fuel from the same wing tank, and therefore, as officially stated, one eng had to wait 8 sec longer than the other one to develop identical symptoms.
They landed with over 10 tonnes of fuel. Low fuel was not an issue.

2- Which fuel quantity does trigger a LOW FUEL EICAS MSG ?
Less than 2,000kgs in either wing tank.

Will the AAIB simply publish the actual FOB at the time ???
Why wouldn't they?

At what altitude the Boeing low fuel drill was actioned on BA038 and if the flaps were ever retracted to 20degrees.
The low fuel procedure wasn't actioned. The flaps were retracted from the selected landing setting but I am not entirely certain of what the settings were (before and after).

If BA B777 min fuel policy often causes crews to action the Boeing min fuel drill on arrival prior to landing...
Define often? In 20 years in BA and 5 years on the B777 I have only had a low fuel advisory once (that was on the B777) after extensive unexpected holding on a gin clear day in the USA.

Seems you need to save a lot of fuel by your min fuel policy to equal the cost of a total B777 W/O.
And your point is?

Fuel loads should be increased to totally avoid the SOP use of the low fuel state drill as it has been proven both engines will quit if run off a common contaminated tank.
OK, you pay.

The low fuel state drill should be reclassified as an emergency recall drill and its use now avoided as a SOP.
It does not need to be because it is rarely used and never caused an incident yet (that I am aware of). Its use is not an SOP, responding to any EICAS advisory or warning is.

I can't see contamination causing the pitch up that occurred when Land 3 annunciated.
When did that event happen and how do you know it did?
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Old 14th Feb 2008, 11:51
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Fuel Flow behavior

This may sound too simple, but suppose we know the speed fuel travels through the lines. With that information, we will know the distance fuel traveled in 3 and 8 seconds. Maybe we will get to the point where fuel flow changed it's behavior.

Just a thought, I am just a light twin Sunday driver.

Regards,

Rob
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Old 14th Feb 2008, 16:24
  #374 (permalink)  
 
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Originally Posted by M.Mouse
Why wouldn't they?
Your question is fair, I'm just surprised they haven't done it already, just to put things clear, especially when an airplane is lacking some power 2 miles short final.
You state "over 10 tons of fuel" and also that "the flaps were retracted" ... I personally haven't seen any official statement on that until now.
I want to remain cautious on any information we got up to now, official as well as unofficial, but to restrain the thinking to a possible logic, and that's why I rather use "would" or "could".

What about this ?:

Somewhere in final the low fuel procedure is applied.
As noted by triple-scan, the stronger center fuel pumps drain what remained in the center fuel tank, it could be a mixture of fuel and water or newly melted ice. Fuel flow (should I say Mixture flow ?) is adequate but mixture quality is poor, not poor enough for a dual eng fail but poor enough to only "produce thrust at an engine speed above flight idle"

What I say here may be well stupid ... but who cares ?
The only way to fully save the day would have been in an instinctive reaction, to turn all center fuel pumps off.

... Let's see if in the next months the low fuel procedure is slightly altered ... ?
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Old 14th Feb 2008, 16:40
  #375 (permalink)  
 
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Quote:
"but my understanding is that fuel temperature is kept above a minimum figure due to heat exchange with the hydraulic circuits routed through the tanks". - "I believe the warming effect is very marginal. The primary purpose of the heat exchangers is to cool the hydraulic fluid, not warm the fuel."

Thanks, NSEU.

Despite the steep temperature transfer gradient, the large differences between surface areas of the hydraulic lines/exchange devices and the tanks coupled with other factors would militate against the fuel retaining a significant degree of thermal energy. Pretty obvious when you're less silly than me!
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Old 14th Feb 2008, 17:26
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M M

It seems that ol' CCC has'nt a clue when it comes to fuel policies.
Even on B747-400's, 10 tonnes was regarded as plenty fuel (long haul ops) and 30 mins as minimum in tanks when landing (4000kgs), so where the statement "adequate fuel"?????

All these armchair pilots !!!!!

C
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Old 14th Feb 2008, 17:40
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Yo' CONFiture

Have you no knowledge of Boeings?? Let me remind you that it was criminal NOT to switch off the Centre tank pumps when the tanks were empty, lest they burn out (fuel cooled) TWA 800 !!!!

Why would you switch on pumps that have been off for a long time, and as far as I know, Low fuel ops DID NOT include switching on the centre tank pumps, if that was the case. This is the first time I heard of a possible Low fuel ops!!!! 10 tonnes on a heavy twin???? Lotta fuel!!!

C
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Old 14th Feb 2008, 18:21
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I think CONF has nailed it. It would really interesting to know if the crossfeed was opened before or after the failure happened.
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Old 14th Feb 2008, 21:08
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Fuel/Oil heat exchangers:

Quoting NSEU:
"Note that the heat exchanger for the Left hydraulic system is in the left wing tank and the heat exchangers for the Right and Centre hydraulic systems are in the right tank. The fuel temperature sensor is in the left tank, reportedly because the temperature will be slightly lower (because there is only one heat exchanger). The heat exchangers are mounted on the bottom of the tanks, inboard of the engines."

Hi, i am new to this forum. Not sure if the RR engine is similar to the GE engine regarding engine fuel distribution but i assume that the basics are the same:

After the fuel temperature has been (slightly) affected by the heat exchangers quoted above, it will eventually reach the engine fuel pump. The pump pressurizes the fuel and sends it through the main (engine fuel/oil) and IDG fuel/oil heat exchangers. After the fuel goes through the heat exchangers, it flows back to the pump where it goes through the fuel filter element.

After the fuel goes through the fuel filter element, it goes to the hydromechanical unit (HMU) (RR = FMU). The HMU meters the fuel. The fuel goes from the HMU to the fuel flow transmitter and then back to the HMU. The HMU distributes the fuel into the fuel supply manifolds. The fuel supply manifolds send the fuel to the fuel nozzles.

The HMU gets more fuel from the pump than the engine needs. The fuel that the HMU does not use goes back to the pump. This fuel is called bypass fuel.

With engines at or near flight idle during approach this means that comparitively more bypass fuel flows between the HMU and the pump which would mean that this bypass fuel is relatively warm when compared to an engine demanding increased amounts of fuel at higher power settings. The chance of ice build-up in this part of the system seems highly unlikely to me with engines at flight idle. With fuel being circulated like this for some time during descent, any ice accumulation would be at or near the pump inlet, not beyond the pump outlet.

Downstream from the fuel filter (on GE engines), a small amount of fuel also goes to the servo fuel/oil heat exchanger and then to the HMU. The servo fuel/oil heat exchanger increases the temperature of the servo fuel before it goes to the HMU. The HMU uses servo fuel pressure to move internal valves and engine air system components.

Furthermore, with regards to the hydraulic oil-to-fuel heat exchangers in the wing tanks, these heat exchangers have more work to do during approach with the aircraft maneouvring and selecting flaps and gear in this flight phase. This, together with a relative low amount of fuel in the tanks the heat exchange to the fuel should also have increased when compared to cruise conditions.
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Old 14th Feb 2008, 21:29
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Green Dot.....interesting post.

In the descent from cruise the engines would have been at Low Idle ( Gnd idle ) until any Flap/Slat or Gear selection, then this triggers the higher Flight idle speed.
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