BA038 (B777) Thread
Join Date: Apr 2007
Location: moraira,spain-Norfolk, UK
Age: 82
Posts: 389
Likes: 0
Received 0 Likes
on
0 Posts
SLF choice of aircraft...
Dear Rainboe,
I think you fall into a great big hole in assuming that you
actually know what 95% of SLF think. Of course the majority
only want get from say Gatwick to Alicante, but of course
they can only travel on what is provided. In the same way that I can only vote for one or another party in a general election. So we rely on the authorities to make our travel
as safe as possible in whatever aircraft, and we expect them
all to be safe (whatever that means). For me, (Nowadays) I travel once or maybe twice a year northern to southern hemisphere and vice-versa, and short haul only to get to the long haul.
I always choose 747, not because I think it's safer, I do expect safety even in a 777, but I choose the 747 just because it is more comfy. So please don't dumb down people that you don't know, therein lies madness.
Kind regards ,John
I think you fall into a great big hole in assuming that you
actually know what 95% of SLF think. Of course the majority
only want get from say Gatwick to Alicante, but of course
they can only travel on what is provided. In the same way that I can only vote for one or another party in a general election. So we rely on the authorities to make our travel
as safe as possible in whatever aircraft, and we expect them
all to be safe (whatever that means). For me, (Nowadays) I travel once or maybe twice a year northern to southern hemisphere and vice-versa, and short haul only to get to the long haul.
I always choose 747, not because I think it's safer, I do expect safety even in a 777, but I choose the 747 just because it is more comfy. So please don't dumb down people that you don't know, therein lies madness.
Kind regards ,John
Join Date: Apr 2005
Location: Stockholm Sweden
Age: 74
Posts: 569
Likes: 0
Received 0 Likes
on
0 Posts
Someone mentioned that the FOHE is regulated. I don't remember this was mentioned in the report. Is it true? What other temperature probes are there to read out? Oil temperature maybe?
Second Law
Join Date: Jan 2008
Location: Wirral
Age: 77
Posts: 113
Likes: 0
Received 0 Likes
on
0 Posts
md80fanatic 1836
Sir, I bow to and respect your expertise on the mad dog but the additives used to scavenge traces of water in jet fuels do not dessicate in the manner you suggest.
The additives used are usually alcohol based derivatives of ethoxy ethane which use their OH groups to act as chemical bridges - using their OH groups, to Hydrogen Bond to the water molecules and simultaneously Van der Waals bond -with the rest of their structure, to the hydrocarbon fuel molecules.
Net effect of all this chemistry in action is to pull the water into solution in the fuel and not repeat not to accrete it into solid phase lumps.
http://en.wikipedia.org/wiki/Fuel_Sy...cing_Inhibitor
Hope this helps.
CW
Sir, I bow to and respect your expertise on the mad dog but the additives used to scavenge traces of water in jet fuels do not dessicate in the manner you suggest.
What was once a smattering of tiny manageable crystals of ice is quick becoming larger chunks that cannot always pass cleanly through the system.
Net effect of all this chemistry in action is to pull the water into solution in the fuel and not repeat not to accrete it into solid phase lumps.
http://en.wikipedia.org/wiki/Fuel_Sy...cing_Inhibitor
Hope this helps.
CW
Last edited by chris weston; 7th Sep 2008 at 19:33. Reason: insert 1836
Puzzling .....
Green-dot, Swedish Steve:
There are so many unknowns. Not disagreeing, just thinking on....
For an arrival in approx freezing temperatures, my calculations suggest a worst case of 500ml of new atmospheric water in the CWT (from here) which, by the same mechanism we see under the main tanks, will mostly be ice on the coldest inner surfaces of the tank. When the tank is subsequently partially filled with slightly warmer fuel, some of this ice will melt and run into the fuel as suspended droplets. With the aircraft at rest, it is not clear how much of this will collect at the sumping point.
Unless it freezes again, once the aircraft comes alive the scavenge system will deal with whatever water the warm fuel melted. But the ice will remain, presumably to accumulate over successive flights?
I believe there are reports (sorry - can't find references at present) of water-in-fuel warnings at start up which sort themselves out during taxi. The scavenge works. What is interesting is the amount of water needed to trigger such a warning, which as I recall is quite a lot. Such reports suggest that after fuelling, sumping was either not done, not done properly, or the water was somewhere else when the sumping was done, and only collected at the lowest point after start-up.
Given the effectiveness of the scavenge systems, the only time I can see water collecting to be sumped would be when a large amount of accumulated ice has melted after shutdown. The big question is can ice accumulate in this way?
There are so many unknowns. Not disagreeing, just thinking on....
For an arrival in approx freezing temperatures, my calculations suggest a worst case of 500ml of new atmospheric water in the CWT (from here) which, by the same mechanism we see under the main tanks, will mostly be ice on the coldest inner surfaces of the tank. When the tank is subsequently partially filled with slightly warmer fuel, some of this ice will melt and run into the fuel as suspended droplets. With the aircraft at rest, it is not clear how much of this will collect at the sumping point.
Unless it freezes again, once the aircraft comes alive the scavenge system will deal with whatever water the warm fuel melted. But the ice will remain, presumably to accumulate over successive flights?
I believe there are reports (sorry - can't find references at present) of water-in-fuel warnings at start up which sort themselves out during taxi. The scavenge works. What is interesting is the amount of water needed to trigger such a warning, which as I recall is quite a lot. Such reports suggest that after fuelling, sumping was either not done, not done properly, or the water was somewhere else when the sumping was done, and only collected at the lowest point after start-up.
Given the effectiveness of the scavenge systems, the only time I can see water collecting to be sumped would be when a large amount of accumulated ice has melted after shutdown. The big question is can ice accumulate in this way?
Controversial, moi?
I always choose 747, not because I think it's safer, I do expect safety even in a 777, but I choose the 747 just because it is more comfy.
Most people are only interested in how cheap the air fare is!
Join Date: Jan 2008
Location: EU
Posts: 33
Likes: 0
Received 0 Likes
on
0 Posts
1. Possible interim safety measures suggested by Boeing
I could not find it expressly referred to elsewhere in this thread but interim safety measures as reported last week to be 'in the pipeline' were:
"Boeing's [Nick] West said the initial instructions will be to periodically vary altitude when fuel in the main tank is below minus 10 degrees Celsius, and to advance the throttle to maximum for 10 seconds before the final descent when fuel has been below that temperature for more than three hours, clearing out any water buildup.
The instructions cover 220 777s powered by Rolls-Royce Trent 800 engines in service with 11 airlines worldwide, Boeing said. For 777 aircraft on the ground in freezing conditions, fuel pumps must be run at maximum for one minute each to prevent water buildup, the planemaker said.
In the U.S., the FAA will send a directive within two days covering 56 777s operated by AMR Corp.'s American Airlines and Delta Air Lines Inc., agency spokeswoman Alison Duquette said. The carriers will have 10 days to comply, she said."
see http://www.bloomberg.com/apps/news?p...HA6Kw&refer=uk (although seems to be mistaken reference to "frozen kerosene").
2. Earlier FAA leaked memo
The apparently leaked FAA memorandum dated 24 January 2008 disclosed back in February 2008 (see New BA 777 info - Airline Pilot Central Forums) seems to have been largely consistent with information only revealed in the latest AAIB interim report (eg see the fluctuating right hand engine P30 data). It seems that the reference in the memo to:
"• Ice in the fuel somehow limiting the fuel flow to the engines. A maintenance message indicating excessive water in the center tank was set during taxi on the two previous flight legs, although it cleared itself both times. The airplane was being operated in a high humidity, cold environment, conducive to ice formation."
was also correct in part - perhaps though the maintenance messages of excessive water must have been discounted for the time being by the AAIB (and therefore not mentioned in the interim report) as a result of the sumping on both 14 and 15 January 2008 - ie presumably prior to each of the two previous "flight legs" – which in revealing no excessive water allow any earlier excessive water messages to be set aside as erroneous or of no import? Would it be sensible to recommend that such a message is brought to the pilots' attention as an EICAS advisory message, given sump checks will not necessarily indicate for some time after an uplift of warm fuel into a cold centre tank what water may have been hidden away there as ice? Better to learn before the flight than after the flight when nothing that can do about it? What advice is there if a pilot searches out the relevant page in the course of a long cold flight and discovers such a message this week?
3. Any way for melted ice to go from centre tank to each fuel manifold, not via main tanks?
Given the possibility of centre tank ice from the volume of water implied by any excessive water message (ie potentially more than 627 litres – see http://www.pprune.org/3879461-post229.html - although in up to 79 tons of fuel) and the icing issues hinted at by the ongoing reporting requirements and proposed design changes in respect of the fuel scavenge pumps in related 777 series centre tanks (and for at least one operator apparently reported on 200ER), is there any other way in which ice from the centre tank might end up as a restriction in each feed line from the main tank without such ice causing water to be found at more than 40ppm in the main tanks themselves after the accident?
When the AAIB state (page 18) that "a low pressure in the fuel manifold would have led to air being drawn from the centre tank, via the jettison and override pump check valves", would this permit melted ice from the centre tank to pass directly to each fuel manifold (not via the main tanks)? If so, what would the pressure differential between each fuel manifold and the centre tank have to be to open the check valves? Is there a way for such differential to have occurred during the latter part of this flight and without a warning message, given the boost pumps were ON (implying it seems some positive pressure in each main tank feed line relative to the vented main tanks in the absence of any EICAS advisory of main tank FUEL PUMP low pressure) and the OJ pumps were OFF?
4. Icing scenarios
Icing even in the low flow scenarios outlined in the interim report certainly seems tricky to explain convincingly, unless the scenario also involves either:
- a lot more water in the flow available to accrete (taking into account back-to-back cold-soaked legs, centre tank unsumped water, etc) through the system, and/or
- an accretion "sweet spot" in each boost pump or a particular section of manifold common to each side of the system and no other spot to attract icing, so that the very low concentration of water in the slow fuel flow prior to its consumption by the engines can be sure to accumulate in sufficient volume to make the required restriction (and be dislodged as appropriate).
I could not find it expressly referred to elsewhere in this thread but interim safety measures as reported last week to be 'in the pipeline' were:
"Boeing's [Nick] West said the initial instructions will be to periodically vary altitude when fuel in the main tank is below minus 10 degrees Celsius, and to advance the throttle to maximum for 10 seconds before the final descent when fuel has been below that temperature for more than three hours, clearing out any water buildup.
The instructions cover 220 777s powered by Rolls-Royce Trent 800 engines in service with 11 airlines worldwide, Boeing said. For 777 aircraft on the ground in freezing conditions, fuel pumps must be run at maximum for one minute each to prevent water buildup, the planemaker said.
In the U.S., the FAA will send a directive within two days covering 56 777s operated by AMR Corp.'s American Airlines and Delta Air Lines Inc., agency spokeswoman Alison Duquette said. The carriers will have 10 days to comply, she said."
see http://www.bloomberg.com/apps/news?p...HA6Kw&refer=uk (although seems to be mistaken reference to "frozen kerosene").
2. Earlier FAA leaked memo
The apparently leaked FAA memorandum dated 24 January 2008 disclosed back in February 2008 (see New BA 777 info - Airline Pilot Central Forums) seems to have been largely consistent with information only revealed in the latest AAIB interim report (eg see the fluctuating right hand engine P30 data). It seems that the reference in the memo to:
"• Ice in the fuel somehow limiting the fuel flow to the engines. A maintenance message indicating excessive water in the center tank was set during taxi on the two previous flight legs, although it cleared itself both times. The airplane was being operated in a high humidity, cold environment, conducive to ice formation."
was also correct in part - perhaps though the maintenance messages of excessive water must have been discounted for the time being by the AAIB (and therefore not mentioned in the interim report) as a result of the sumping on both 14 and 15 January 2008 - ie presumably prior to each of the two previous "flight legs" – which in revealing no excessive water allow any earlier excessive water messages to be set aside as erroneous or of no import? Would it be sensible to recommend that such a message is brought to the pilots' attention as an EICAS advisory message, given sump checks will not necessarily indicate for some time after an uplift of warm fuel into a cold centre tank what water may have been hidden away there as ice? Better to learn before the flight than after the flight when nothing that can do about it? What advice is there if a pilot searches out the relevant page in the course of a long cold flight and discovers such a message this week?
3. Any way for melted ice to go from centre tank to each fuel manifold, not via main tanks?
Given the possibility of centre tank ice from the volume of water implied by any excessive water message (ie potentially more than 627 litres – see http://www.pprune.org/3879461-post229.html - although in up to 79 tons of fuel) and the icing issues hinted at by the ongoing reporting requirements and proposed design changes in respect of the fuel scavenge pumps in related 777 series centre tanks (and for at least one operator apparently reported on 200ER), is there any other way in which ice from the centre tank might end up as a restriction in each feed line from the main tank without such ice causing water to be found at more than 40ppm in the main tanks themselves after the accident?
When the AAIB state (page 18) that "a low pressure in the fuel manifold would have led to air being drawn from the centre tank, via the jettison and override pump check valves", would this permit melted ice from the centre tank to pass directly to each fuel manifold (not via the main tanks)? If so, what would the pressure differential between each fuel manifold and the centre tank have to be to open the check valves? Is there a way for such differential to have occurred during the latter part of this flight and without a warning message, given the boost pumps were ON (implying it seems some positive pressure in each main tank feed line relative to the vented main tanks in the absence of any EICAS advisory of main tank FUEL PUMP low pressure) and the OJ pumps were OFF?
4. Icing scenarios
Icing even in the low flow scenarios outlined in the interim report certainly seems tricky to explain convincingly, unless the scenario also involves either:
- a lot more water in the flow available to accrete (taking into account back-to-back cold-soaked legs, centre tank unsumped water, etc) through the system, and/or
- an accretion "sweet spot" in each boost pump or a particular section of manifold common to each side of the system and no other spot to attract icing, so that the very low concentration of water in the slow fuel flow prior to its consumption by the engines can be sure to accumulate in sufficient volume to make the required restriction (and be dislodged as appropriate).
Join Date: Nov 2001
Location: UK
Age: 70
Posts: 76
Likes: 0
Received 0 Likes
on
0 Posts
Just testing a thought here...wing tanks presumably will have an air gap over most of their enclosed surface near the end of a flight. Could a large flat sheet of condensation created ice have broken away, perhaps during the rapid descent to warmer air ?
Join Date: Feb 2008
Location: Wingham NSW Australia
Age: 83
Posts: 1,343
Likes: 0
Received 0 Likes
on
0 Posts
Aircraft types
Not only do few of the travelling public know what specific type they are flying in, they have no idea about those flying the thing. As long as the cabin is comfortable and the cabin crew helpful they are happy. Could be chimpanzee's flying the aircraft for all the pax care.
Join Date: Sep 2008
Location: Larger Antipode
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Rainboe:
And the other 5% are most likely to be frequent business travellers. You know, those who sit at the front of the plane (Just behind your little office door) and pay your salary.
Fact is, the belief that 2 engines cannot fail simultaneously has been disproven.
Let's face an uncomfortable truth! 95% of the great travelling public have no idea what they are travelling on.
Fact is, the belief that 2 engines cannot fail simultaneously has been disproven.
Join Date: Jan 2006
Location: Derby
Age: 42
Posts: 45
Likes: 0
Received 0 Likes
on
0 Posts
Fact is, the belief that 2 engines cannot fail simultaneously has been disproven.
Controversial, moi?
If we want to go down the road of pointless statements I believe that total engine failure has occurred on a B747 three times to date due volcanic ash. I do not believe that makes a four engine aeroplane intrinsically unsafe any more than an apparent fuel problem makes a B777 intrinsically unsafe.
Join Date: Jan 2008
Location: EU
Posts: 33
Likes: 0
Received 0 Likes
on
0 Posts
Here is some alternative speculation as to how a concentration of water in excess of 40ppm (ie in excess of water concentration found in main tanks) not derived from the main tanks might end up in each fuel manifold and thereby be a contributory factor to the suspected restriction in each feed line at late stage in flight:
1. Common cause - water in the centre tank after back to back long cold soaked sectors in humid conditions.
2. Otherwise normal operation - on return sector, any concentration of water in centre tank fuel transferred in first 2.5 hours by OJ pumps to each fuel manifold would not restrict the fuel lines (and would be consumed in the engines before it could become a contributory factor) due to the relative warmness of the centre tank fuel as compared to, say, the much faster plummeting temperature of the main tank fuel (which remains in the main tanks until about the time the OJ pumps are turned off) and the Critical Icing Temperature.
3. Common event - EITHER a concentration of water in remaining centre tank fuel at time switched off OJ pumps left a concentration of water beyond the OJ/jettison check valves in part of each fuel manifold connected to, but not subject to the cold slow flow from, the main tank feed, OR an event (relative low pressure in that part of each fuel manifold as compared to centre tank sufficient to overcome OJ/jettison check valves for a few seconds or more) after the OJ pumps were originally switched off leads to a concentration of water left behind in the otherwise empty centre tank flowing through the OJ/jettison check valves into the much colder mass of main tank fuel in each fuel manifold.
It is probable that water and/or ice may accumulate under certain normal certified operating conditions in the centre tank. However, given the circumstances of flights similar to BA038, arguably the bare results of general sump testing of the centre tank may be unrepresentative of the probability of this common cause becoming one of the contributory factors to this accident. For example, to what extent has sump testing been done in warm hangar or only several hours after uplift of warm fuel, in each case before further flight after the return from long back to back cold-soaked sectors in humid conditions? How much free water might be found in an empty centre tank but not come out of centre tank sump due to where it is located behind a baffle or at an alternate low point in centre tank (or it being frozen at the time, it not having been in a warm hangar)?
1. Common cause - water in the centre tank after back to back long cold soaked sectors in humid conditions.
2. Otherwise normal operation - on return sector, any concentration of water in centre tank fuel transferred in first 2.5 hours by OJ pumps to each fuel manifold would not restrict the fuel lines (and would be consumed in the engines before it could become a contributory factor) due to the relative warmness of the centre tank fuel as compared to, say, the much faster plummeting temperature of the main tank fuel (which remains in the main tanks until about the time the OJ pumps are turned off) and the Critical Icing Temperature.
3. Common event - EITHER a concentration of water in remaining centre tank fuel at time switched off OJ pumps left a concentration of water beyond the OJ/jettison check valves in part of each fuel manifold connected to, but not subject to the cold slow flow from, the main tank feed, OR an event (relative low pressure in that part of each fuel manifold as compared to centre tank sufficient to overcome OJ/jettison check valves for a few seconds or more) after the OJ pumps were originally switched off leads to a concentration of water left behind in the otherwise empty centre tank flowing through the OJ/jettison check valves into the much colder mass of main tank fuel in each fuel manifold.
It is probable that water and/or ice may accumulate under certain normal certified operating conditions in the centre tank. However, given the circumstances of flights similar to BA038, arguably the bare results of general sump testing of the centre tank may be unrepresentative of the probability of this common cause becoming one of the contributory factors to this accident. For example, to what extent has sump testing been done in warm hangar or only several hours after uplift of warm fuel, in each case before further flight after the return from long back to back cold-soaked sectors in humid conditions? How much free water might be found in an empty centre tank but not come out of centre tank sump due to where it is located behind a baffle or at an alternate low point in centre tank (or it being frozen at the time, it not having been in a warm hangar)?
Join Date: Dec 1999
Location: UK
Posts: 1,608
Likes: 0
Received 0 Likes
on
0 Posts
I think you're missing my point, which is, I conceed probably off-topic and anecdotal. The fact is, however, and the commercial side of the industry does need to deal with this, there is a growing PERCEPTION (Which is not the same as technically proven fact) amongst the travelling public that the 777 is not safe and that 4 engined planes are safer.
This is just melodrama. The incidence rate of the events encountered in this flight is so small as to be remote - as stated by the AAIB.
You clearly have little understanding of aircraft if you believe that a 4-engined aircraft would not be affected by similar common faults. Are we returning to posts from people who believe everything is dangerous if they do not fully understand it? I certainly hope not.
Join Date: Apr 2005
Location: Stockholm Sweden
Age: 74
Posts: 569
Likes: 0
Received 0 Likes
on
0 Posts
It is obvious to me that the centre tank contents is warmer than the wing tanks. The centre tank is emptied on every flight. The tank has packs under it, a warm cabin above it and a lukewarm freight hold in front of it. Even the wheel well behind it is warmer than ambient.
So why no save a few tons of fuel in the centre tank, and use it for the final descent and landing? All you have to do is turn off the centre tank pumps at say five tons remaining, and turn them back on at TOD. The higher delivery pressure of the OJ pumps would ensure the warm (how warm?) centre tank fuel is delivered to the engines, with reserve fuel in the wings to take over if necessary.
These warnings are not visible to the crew, but are stored in EICAS memory.
So why no save a few tons of fuel in the centre tank, and use it for the final descent and landing? All you have to do is turn off the centre tank pumps at say five tons remaining, and turn them back on at TOD. The higher delivery pressure of the OJ pumps would ensure the warm (how warm?) centre tank fuel is delivered to the engines, with reserve fuel in the wings to take over if necessary.
I believe there are reports (sorry - can't find references at present) of water-in-fuel warnings at start up which sort themselves out during taxi.
Junior trash
Join Date: Nov 1999
Location: UK
Posts: 1,025
Likes: 0
Received 0 Likes
on
0 Posts
So why no save a few tons of fuel in the centre tank, and use it for the final descent and landing? All you have to do is turn off the centre tank pumps at say five tons remaining, and turn them back on at TOD.
What happened is one of those accidents that aircraft designers/airlines rather than the pilots need to learn from, something that has been rare since the late 1970s.
Join Date: Jan 2008
Location: EU
Posts: 33
Likes: 0
Received 0 Likes
on
0 Posts
In summary, the holes in Swiss cheese (contributory factors) seem to me currently to be that within certified flight envelope:
1. Operational environment
- Long cold-soak sector.
- Back-to-back with another long cold-soak sector.
- Low fuel flow from main tanks at all stages of flight (never more than 30% or so of max certified flow).
2. Design
- Centre tank prone to accumulation of water and ice.
- Centre tank fuel scavenge which does not time-out.
- Introduction of centre tank water into very cold main tank fuel.
- Perhaps, areas such as suction feed prone to blockage by undissolved air.
- Fuel feed lines and/or FOHE prone to restriction by ice (whether accreted at site of blockage or not).
Swedish Steve, I agree but am guessing that the powers that be prefer not to keep much warmer centre tank fuel for landing:
- to ensure efficient wing loading in rest of flight;
- to make sure "independent" fuel supply to each engine in case supply to both is compromised on short finals (how unlikely is that!) not necessarily as a result of running out of fuel but perhaps using up dregs undiluted by main tank fuel and
- dependence on switching to main tanks close to landing (even automatically) and/or switching off OJ pumps (for TWA 800 reasons) is perceived to increase risk at time of potentially heavy workload?
1. Operational environment
- Long cold-soak sector.
- Back-to-back with another long cold-soak sector.
- Low fuel flow from main tanks at all stages of flight (never more than 30% or so of max certified flow).
2. Design
- Centre tank prone to accumulation of water and ice.
- Centre tank fuel scavenge which does not time-out.
- Introduction of centre tank water into very cold main tank fuel.
- Perhaps, areas such as suction feed prone to blockage by undissolved air.
- Fuel feed lines and/or FOHE prone to restriction by ice (whether accreted at site of blockage or not).
Swedish Steve, I agree but am guessing that the powers that be prefer not to keep much warmer centre tank fuel for landing:
- to ensure efficient wing loading in rest of flight;
- to make sure "independent" fuel supply to each engine in case supply to both is compromised on short finals (how unlikely is that!) not necessarily as a result of running out of fuel but perhaps using up dregs undiluted by main tank fuel and
- dependence on switching to main tanks close to landing (even automatically) and/or switching off OJ pumps (for TWA 800 reasons) is perceived to increase risk at time of potentially heavy workload?
Join Date: Nov 2001
Location: UK
Age: 70
Posts: 76
Likes: 0
Received 0 Likes
on
0 Posts
At the risk of being a nuisance and, I’m sure this has been discussed before on this thread, but there could be an explanation for large amounts of condensation ice breaking off the roof of both wings simultaneously – vibration through the wing caused when either the landing flaps were extended or the gear went down.
The ice would not melt when falling into the fuel due to its temperature. When the pumps started sucking the ice was drawn to the filters.
i.e. The ice was nothing to do with water in the fuel which was loaded.
Just a thought.
The ice would not melt when falling into the fuel due to its temperature. When the pumps started sucking the ice was drawn to the filters.
i.e. The ice was nothing to do with water in the fuel which was loaded.
Just a thought.