Fuel Tank Pumps Overheating!

[GlueBall]

Be mindful about keeping an adequate amount of fuel in tanks, especially on 74s. A newfound phenomena about Hydro-Aire (Burbank) fuel pumps capable of reaching temperatures of 1,100 degrees Fahrenheit has triggered an FAA/Boeing Airworthiness Directive: Ordering additional quantities than previously thought of minimum fuel to be maintained in tanks. Only 900 degrees Fahrenheit is necessary to initiate spontaneous combustion of fuel vapors.Emergency Airworthiness Directive (http://biz.yahoo.com/djus/021126/1300000602_1.html)

[Techman]

Whatever happened to the thermal-fuses I seem to remember from a long time ago. They would cut-off the pumps at around 400 degress F.

[Tuba Mirum]

GB, excuse a non-pilot butting in, but how useful a control is this when airborne? :eek:

[sharpshot]

This takes me back to 120.4's thread a few weeks ago:
What are these airlines who turn up on final at LHR on fumes going to do now?

Carry extra reserves one hopes?

[OVERTALK]

It's beginning to look like an Al Qaeda plot.

I still reckon that, because of the mis-wiring, the pumps are probably finding another earth (courtesy of the short or a further miswiring) - and running on continuously, wet or dry (the cockpit indicator would show it as OFF once power to it via its switch has been cut). Once you short something out it normally overheats; a conductor or terminal strip then melts (usually with a loud bang) and that's what's meant by "shorting out" (assuming CB doesn't do its job). However submerge that same part in fuel most of the time and it doesn't get hot enough for the electrics to melt (fuel rapidly dissipates the heat). What can happen (so the theory goes) is that (instead) the rapid heat build-up caused by the shorting permeates throughout the metal pump and, due to different coefficients of expansion the pump starts binding and so the heat build-up within it increases even more. However as long as it's submerged in fuel, there's enough cold-soak that there's no sufficient localised heat build-up such as to cause any electrical component to melt, "short out" - and so cut the current.

End result is a "blueing" of the metal indicating that extreme localised frictional heat has occurred - mainly due to the binding occurring whilst power remains on to a very hot pump (which is what they've found). And of course in any such shorting situation there would be no CB to overload and blow. Just a theory.

November 27, 2002 - FAA Issues 3rd Warning on Fuel Pumps

WASHINGTON (USA) - The Federal Aviation Administration is requiring about 3,500 Boeing jets to fly with extra fuel to prevent fuel pumps from overheating and possibly causing an explosion.

The FAA has sent airlines three safety warnings about the problem since August. The latest was issued last weekend after pumps in three planes overheated, the FAA said Tuesday.

The warning is intended as a precaution while the FAA figures out what's causing the problem with the pumps, made by Hydro-Aire Inc. of Burbank, Calif.

James McKenna, managing editor of Aviation Maintenance magazine, said the FAA doesn't ordinarily need to make a third attempt to ascertain what's wrong.

"That tends to unsettle the FAA,'' McKenna said.

No serious problems have been linked to the problem. However, if a pump overheats, the right mixture of temperature, oxygen and fuel can cause an explosion, McKenna said.

FAA spokesman Paul Takemoto said the extra fuel eliminates the possibility of an explosion.

"There's no danger of (the pumps) igniting fuel vapors if they're covered,'' he said.

The warning will remain in effect until the agency determines what causes the fuel pumps to overheat, Takemoto said.

The order affects about 1,400 planes - 737s, 747s and 757s flown by U.S. carriers. The FAA is also sending the advisories to its counterpart agencies overseas, covering another 2,100 jets.

The National Transportation Safety Board ruled that an explosion in the fuel tank of TWA Flight 800, a Boeing 747, caused it to crash off the coast of Long Island in 1996, killing 230 people. Vapors in the partly empty tank probably were ignited by a spark in the wiring, the NTSB said.

In August, the FAA ordered airlines to submerge certain Hydro-Aire pumps with fuel or, if not, to X-ray them to make sure they were properly wired. If they weren't, they had to be replaced.

Major U.S. carriers said they had few planes in which the suspect pumps were installed.

In September, the FAA found the problem potentially included every Hydro-Aire pump and ordered all fuel pumps submerged or X-rayed and replaced if faulty.

Then, last week, Boeing Co. received reports of overheating in fuel pumps that had been replaced on a Singapore Airlines 747 and on a Lufthansa 747.

The overheating of those pumps wasn't caused by faulty wiring, said Boeing spokeswoman Cindy Wall.

A pump on a third plane had been removed and was found to have overheated during an inspection.

"It's baffling,'' Wall said. "They've been working nonstop 24 hours a day trying to fix it.''

Hydro-Aire President Greg Ward said the company has made the pumps for 30 years without a problem. It's conducting an extensive investigation that includes chemical analysis of pump parts that overheated, checking airline service records and interviewing retired employees who worked on the pumps, he said.

"We're still piecing together clues,'' Ward said.

[FlapsOne]

Tuba Mirum

It's something you have to consider BEFORE getting airborne.

sharpshot

They're just gonna have to keep half a tonne of fumes over the pumps!!

As I understand it the fuel can still be used in the event of a diversion/emergency so it's not all exactly wasted extra 'baggage'.

Well, not all the time anyway.

[Belgique]

OVERTALK
Not Bad
Further thought:
I wonder whether Hydro_aire, during their pump redesign process, ignored the phenomenon of conductive silver sulfide build-ups, placed the pos and neg terminal strips too close together and they're consequently being bridged electrically and causing the pumps to run continuously. Whatever the mechanism, it has to be something that's allowing the pumps to both heat up electrically and then "run on" once dry (and also then heating further frictionally due to being overheated). That might make more sense as these pumps are supposedly "fixed" (or replacement) ones - i.e. without the original wire-shorting problems.

The suspicion of Hydro-Aire probably having repositioned positive and negative terminals stems from the root cause of the original shorting problem (too much wiring in close proximity).

[GlueBall]

Tuba the immediate precaution is to keep the fuel pumps fully submerged in fuel so as to preclude exposure of the pump housing with vapors (the air inside the tank above the fuel level). A spark is not required for ignition of vapors. Enough heat can cause spontaneous ignition.

[Cornish Jack]

Should be fairly simple to pick up the problem on the 47 Classics - FE just checks for an appropriate electrical load decrease on pump switch off. A bit more difficult on the -400 but can be done with a little organisation.

[kriskross]

I've had a full briefing on the problem, with pretty coloured pictures, and it looks to me just like downright poor design!!

It must be costing a lot of people a packet, and the safety implications are staggering

[Pilot Pete]

Another consequential problem is the lack of understanding by ground crew as to the requirement to leave 500kilos in the centre tank.

The load sheet seems to be incorrect 8/10 times. Our requirement is to turn the pumps off when the centre tank fuel gets down to 500k and thus not use it. We therefore require this 500k to be put into the ZFW (which is all explained before we start). Another problem is the addition of fuel. We supervise the 'dialling in' of fuel before uplift begins as we kept ending up with 500k more than required!

PP

[PickyPerkins]

Questions:
Just out of interest, at what power level is a typical fuel circuit breaker set to trip? i.e. with how many watts do they seem to be reaching 1,100ºF?

Does the whole pump body get "blued"?


http://home.infi.net/~blueblue/_uimages/pi.gif

[GlueBall]

Typical Fuel pumps run at 115VAC, 3 phase, and can draw up to about 3.45KW. (3450 W)
Just because a pump heats up internally does not necessarily trip respective circuit breakers in the cockpit. (A heating element on your stove top gets red hot without tripping a breaker). Usually fuel tank pumps are protected by thermal switches which are supposed to trip, as in the case when a pump is left running in a dry tank and overheats, etc... The question obviously is: Why did the Hydro-Aire pumps reach 1100 degrees without an automatic thermal cutout.

The Thai Airways B73-3 empty center tank explosion at the gate at BKK is believed to have been caused either by its pump overheating, or by arcing of electrical connections.

[Basil]

In order to allay any fears by those unfamiliar with this problem (on the B747):
1. It is not new.
2. The requirement is to keep the override/jettison pumps (booster pumps by another name) covered with fuel. That keeps them cool and excludes air & fuel vapour.
3. All the fuel in the centre tank may be used. When the contents reach a pre-determined minimum level, the main pumps are switched off and the centre tank emptied into number 2 tank by the scavenge pump which is not affected by the problem.
(so the bad boys can still arrive with sod all fuel but comply with AD 2002-19-52 :mad: )

[GlueBall]

TG 737 (http://airliners.net/open.file?id=151312&WxsIERv=Qm9laW5nIDczNy00RDc%3D&WdsYXMg=VGhhaSBBaXJ3YXlz&QtODMg=QmFuZ2tvayAtIEludGVybmF0aW9uYWwgKERvbiBNdWFuZykgKEJLS yAvIFZUQkQp&ERDLTkt=VGhhaWxhbmQ%3D&ktODMp=TWFyY2ggNCwgMjAwMQ%3D%3D&WNEb25u=QW5kcmVhcyBEYW1rZQ%3D%3D&xsIERvdWdsY=SFMtVERD&MgTUQtODMgKE=KGNuIDI1MzIxLzIxMTMpLiBUaGFpIGpldCBidXJudCBvdXQ gYXQgQmFuZ2tvayBhaXJwb3J0IHRoZSBwcmV2aW91cyBkYXkuIFBob3RvIHd hcyB0YWtlbiBmcm9tIGVuZCBvZiBiYWdnYWdlIGJlbHQu&YXMgTUQtODMgKERD=ODMzNA%3D%3D&NEb25uZWxs=MjAwMS0wMy0yNg%3D%3D&static=yes&size=M) after center tank explosion.

[nitro rig driver]

after reading the ad that faa issued,my impresion was that the blueing was on the bearing shaft,this is not what the thermal fuses are for (they are for an electrical overheat-ie a phase dropped out or the motor seized-fod in the impleler ????-which could be ice or spanners etc) and as such are removed from this equation
the ad also mentioned that the casing had melted in one removed pump indicating again the fault could be on the shaft on the pump motor/bearing,of course this could also be from running the pump excesivly with no load on (ie no fuel in impleller housing)
blueing on metal surfaces (that reach 1100 degs) that are rubbing will be from very localised heat

[PickyPerkins]

===== Quote ================
GlueBall Date : 29th November 2002 21:20 Typical Fuel pumps run at 115VAC, 3 phase, and can draw up to about 3.45KW (3450 W). …….The question obviously is: Why did the Hydro-Aire pumps reach 1100 degrees without an automatic thermal cutout?
==== End of quote =======

Thanks for the info that the pumps are 3-phase and that the circuit can supply up to 3,750 W.

From this info I assume/infer that when a pump runs dry, it:

(a) does NOT overspeed or otherwise run away, because its synchronous,

(b) ought to draw less current than when pumping, maybe an order of magnitude less power, and

(c) at this low power it could run progressively hotter because of lack of cooling, but fairly slowly, so that all parts of the pump would tend to warm up together.


From AD 022451 I see that:

(a) “… The cause of this overheating is believed to be friction between the pump parts; however, the specific cause of the friction is unknown at this time. …..”

(b) “……. The pump was found with the thermal fuses of the electrical motor winding open …..”, so that in at least one case the thermal fuse worked.

(c) “….. In addition, the aluminum bearing housing adjacent to the back side of the end plate had melted. ….”. Aluminum alloys melt about 1100ºF, so that seems to be good evidence of the temperature.

(d) “……. According to the pump manufacturer, bluing of the steel and/or Stellite materials is evidence of temperatures in excess of 1,100 degrees Fahrenheit. …….. Adjacent areas of the shaft were blackened. ……”. This suggests that most of the shaft did NOT reach this high temperature.


A back-of-the-envelope calculation suggests that if the pump were running dry, and if:

(a) enough friction developed to draw 3,750 W from the power supply, and

(b) the mass of the bearing, adjacent housing, and adjacent part of the shaft was about a pound, and that most of the electrical energy goes into this mass of metal, then that mass could reach 1,100ºF in about one minute (and without tripping the circuit breaker). Perhaps only a few ozs of metal would actually melt.


I wonder sometimes whether there is a little too much trust in the power of liquids to cool.

It is well known to the designers of steam boilers and boiling-water nuclear reactors that once a metal surface in water reaches about 50ºC over the boiling point of the water (I‘m working from memory), a continuous layer of steam is formed which effectively thermally insulates the surface, and the temperature may then jump several hundred degrees before another thermally stable state is reached.

I could imagine this happening to a binding shaft /bearing combination, particularly if only a limited amount of fuel were in contact with restricted flow. A test would have to be done to see if this could happen in practice. If there were no air it might even be safe, though there might be carbon deposits which might cause trouble later.


A nominally dry pump could still have pockets or valleys full of fuel, which could boil off and splash around onto a hot shaft/bearing.


I don’t understand the references to the “end plates of the priming and vapor section” and “scoring was found on the inducer housing of the pump”. Are these two different locations? Is the end plate a (the?) bearing?


Kriskross: A Question: Are the “pretty coloured pictures“ available anywhere for us to look at?


I don’t have any answers. Just questions. :)


Here is an extract from one of the AD’s:
==== Start of quote from AD 022451 ====
…… override/jettison pump ...... Since scoring was found on the inducer housing of the pump, the pump was disassembled, at which time evidence of severe overheating of the priming and vapor pump section was found. The Stellite (cobalt/chrome/nickel/iron alloy) end plates of the priming and vapor section of the pump were blued and cracked from thermal stress, and the steel pump shaft in that same area was also blued. According to the pump manufacturer, bluing of the steel and/or Stellite materials is evidence of temperatures in excess of 1,100 degrees Fahrenheit. It is believed that such temperatures could only be reached during dry running of the pump. ......... Adjacent areas of the shaft were blackened. In addition, the aluminum bearing housing adjacent to the back side of the end plate had melted.

The other pump was an override/jettison pump ........... The pump was found with the thermal fuses of the electrical motor winding open, which indicates an overheat condition in the motor section. Such overheating may be due to the pump rotor dragging or locking. Evidence of severe overheating of the priming and vapor pump section was found. The end plates of the priming and vapor section of the pump were blued and cracked from thermal stress, and the pump shaft in that same area was blued.
==== End of quote from AD 022451 ====


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[Belgique]

Now consider the case where a crew has smoke in the cockpit scenario and must urgently dump and land.

As I understand it, there's nothing to stop them from (per the checklist) dumping all that centre-section fuel. BUT the real hazard is that those faulty pumps are then running helter-skelter at the high jettison rate and will be pumping all that centre-section fuel overboard. Anybody see the flaw in that for a good old run-of- the-mill "smoke, so dump fuel and land ASAP situation"????? Very hot dump-pump dry-running in empty CWT? Nor sure if the CWT dump-pumps would shut off before the wing-tank levels reached the preset stop-dump levels (at some later date). Somehow doubt it.

So the jettison action would probably have the jettison pumps "running on" [dry] in an empty CWT. Not good. Would the ensuing fiery accident be put down to a CWT explosion or the smoke in the cockpit emergency - I wonder?

Is this a realistic concern?

[mono]

Overtalk, Belgique,

I think you may have misunderstood the AD and the shorting problem.

It would not be possible for a short in the pump itself to cause the pump to run dry. Because when the pump is switched off, the 3 phase power to the pump is switched off (NOT the earth) via a relay.

For the pump to run dry would require either a failure of the 3 phase relay, or for the crew to forget to switch the pumps off.

As for fuel jettison it is only necessary to dump fuel such that the a/c is below MLW not ALL the fuel.

[UNCTUOUS]

Don't think Belgique was inferring that any fuel dump would be
of "all the fuel". However in the case of a landing on a contaminated runway of marginal length (say), a crew might elect to dump to well below max landing weight. I assume that they could dump down to (for argument's sake) half wing-fuel tanks remaining (for an u/carriage problem for instance).

The question is whether:

a. that would empty the centre-section tank

b. whether the centre-section tank's jettison pumps would run on dry whilst the wing-tank fuel was dumping down to the selected (or preset) level.

c. in which case (a plus b) a hazard might exist from either the electrical shorting or the extreme overheating of the Hydro-Aire pumps.

[Lu Zuckerman]

For more information on this ongoing problem check this out.

:cool:
www.hydroaire.com/support/service.htm

[PickyPerkins]

-----------------
Lu Zuckerman
For more information on this ongoing problem check this out.
-----------------
Thanks for the pdf's. :)


I looked through and found drawings of typical pumps in e.g. 60-723-28-5Rev1.pdf (relating to cavitation problems) and an exploded view of the motor and pump in 60-721-28-3R1.pdf. (relating to wear of thrust bearings).

The latter was issued in 1999 and noted “…. bearing wear, in turn, may cause excessive rotor shaft end play, loss of pump performance, and internal damage to pump components. Approximately 20 pumps have been returned to Hydro-Aire with premature thrust bearing wear and damaged pump.“.

Presumably that has all been taken care of by now.

There is, of course, nothing yet covering the current problem, though superficially the current problem seems to have some aspects in common with the 1999 problem, e.g. friction between parts and internal damage.

X-rays showing where the wiring within the pump should be positioned are in motor-28-01.pdf.

http://home.infionline.net/~blueblue/_uimages/pi.gif

[GlueBall]

Belgique the necessity to dump fuel in case of smoke or fire is zero. We have all learned about that from SR111. The answer is to make an overweight landing. There no longer is any debate about that, at least not in my cockpit.

[Belgique]

Glueball

Possibly a little difficult to be hard and fast about what's appropriate...depends whether you've got any significant transit time to the nearest airfield (and how short that runway is and what sort of landing configuration you can achieve). Or it may be that a ditching is the only option in a mid-ocean scenario.

But apart from those factors, the point that I was making above is that the overheating fuel-pump AD says that there's no problem in going ahead with an emergency fuel dump (for whatever reason). My contention is that they may not have thought that one through. No one argues about Land ASAP but equally a large percentage of smoke in the cockpit scenarios are pretty low key stuff at the end of the day.

I'm just posing the question of where the greater threat lies - in the extremely overheating fuel jettison pump "running on" (dry) after dumping all centre-section fuel OR in the LAND ASAP smoke emergency that statistically will "pan" out to be, with hindsight, just a cooked component. It's not difficult to turn an incident into an accident. Smoke in the cockpit promotes all those rush factors that can lead you directly through that statistical portal.

[PickyPerkins]

I was once (a long time ago) a PAX on a 747 from OAK to PIT which got a fire warning light in the undercarriage area immediately on take off. Pilot didn't retract the u/c or flaps, didn't dump fuel (so far I could tell), went very slowly round the circuit (it seemed slow, and prabably was), landed very gently as soon as he got over the runway, didn't use the brakes, and let the a/c run the whole 10,000 ft to the reception committee complete in their shiny silver suits waiting at the far end of 29. Once the a/c had stopped we just sat for what seemed a long time. The PAX peered out of the windows at the suits, and the shiny silver suits peered back waiting the for the flames to show up. After 5 or 10 minutes everyine got tired of that and we taxied back to the gate. Turned out to be a false alarm, and after the FAA had signed off we were on our way after an hour or so.

My first indication that some thing was up was seeing a Flight Attendant getting a phone call and then anxiously talking to a another F/A, and both of them looking out of the window. Then I realized that we weren't climbing or retracting anything. Pilot then came on and said, "Folks, we got a red light on up here which shouldn't be on, and we are going right back to the airport. We should be back on the ground in about 10-15 minutes". He did not say it was a fire, nor that it was related to the u/c. Everything and everybody was very quiet after that.

One thing which struck me was how happily excited the flight deck crew were afterwards. It seemed to have made their day, and rightly so. They hadn't turned an incident into an accident.

http://home.infionline.net/~blueblue/_uimages/pi.gif

[Blacksheep]

Lots of un- or ill-informed commentary here. Please note that the problem is resticted to specific pumps in particular installations. For those unfamiliar with the Boeing "quiet, dark cockpit" philosophy I offer the following explanation.

Prior to starting the engines, all the fuel pumps are turned "On" in all of the tanks, but the centre tank pumps are designed to develop higher pressure than main tank pumps. They therefore overpower or "override" the main tank pumps, giving them their name - "Jettison/Override Pumps". The centre tank thus empties into the engine fuel feed system first, providing wing bending load relief, while the main tanks remain full. Once the centre tank empties, the main tank pumps take over the fuel feed without crew intervention. The centre tank "Low Pressure" lights illuminate telling the crew that the centre tank is exhausted, whereupon they switch the centre tank pumps "Off". This action also extinguishes the 'Low Pressure" lights and any EICAS message.

The part of the pump that has sometimes been found overheated, is the mechanical part which actually moves the fuel, rather than the electrical motor that drives it. The pump is both lubricated and cooled by fuel and is designed so that some residual fuel is retained in the priming section where the bearing is located. The pump is intended to be capable of running for up to 11 minutes without fuel being available at the priming inlet, and can in theory be left rotating for this long after the fuel is exhausted. Beyond that time, bearing failure might ensue and the pump is liable to overheat. The thermal fuses intended to protect against overheating should isolate the pump before excessive heat develops, but it seems that in some cases this didn't happen until after remote parts of the pump heated up to >1000 degrees Celsius - hence the Airworthiness Directive. Meanwhile the hot impeller housing contains fuel vapour and, in the event that the vapour happens to be mixed with air in the right proportions, this becomes a possible source of ignition. In the overheat cases identified so far, the fuel vapour seems fortunately to been too rich for this to happen, however this still may be the underlying cause of accidents such as TWA 800.

A possible reason for a pump to continue running after being switched off is a jammed pump relay. In this situation the crew would be unaware that anything untoward was happening, as the "Low Pressure" lights are wired through the cockpit switch, so that switch operation maintains the "quiet, dark cockpit" philosophy. A pump could therefore be running for considerably longer than 11 minutes without anyone being aware of it. I have encountered this condition on two occasions on the ground, once on a B737-200 and once on a B747-100 and I reported these findings to the FAA during the investigation into TWA800.

The AD requires that a minimum quantity of fuel remains in the centre tank at all times, to ensure that the Jettison/Override pumps remain immersed in fuel regardless of aircraft attitude in roll or pitch. Thus they remain cool even if they continue running after being switched off. The ultimate corrective action is yet to be determined, but will almost certainly require a change to the design of the fuel pumps and their control/indication circuits.

I hope that this heavily simplified explanation helps those of you unfamiliar with the affected fuel feed systems to better understand what the subject is all about.

**************************
Through difficulties to the cinema

[GlueBall]

What the engineers at Boeing could learn from its recently acquired Douglas subdivision is an age old Douglas fuel tank design edge: The DC-8 center tank fuel pump is inside the adjacent No.3 Main tank. How about that, huh?

[Blacksheep]

Not just Douglas, Glueball - almost everyone else BUT Boeing. Most of the British aeroplanes I worked with in the old days, had the fuel pumps outside the tank with just the plumbing inside. Thus, no heavy duty wiring passed into the wet area, just the very low-energy indication system components and wiring. Though I've been a "Boeing man" for decades now, I've always considered their fuel tank equipment to be a weak area. The tank harnesses are rubbish, the fuel feed systems are crude and the "Dry Bays" are anything but. Then again, Boeings are cheap and cheerful - thats why they've outsold everyone else. So far...

**************************
Through difficulties to the cinema

[PickyPerkins]

-------- Start quote -------
November 27, 2002 - FAA Issues 3rd Warning on Fuel Pumps .The warning is intended as a precaution while the FAA figures out what's causing the problem with the pumps, made by Hydro-Aire Inc. of Burbank, Calif. …….. Hydro-Aire President Greg Ward said …… It's conducting an extensive investigation that includes chemical analysis of pump parts that overheated, checking airline service records and interviewing retired employees who worked on the pumps, he said. …`We're still piecing together clues,'' Ward said. …."It's baffling,'' Wall said. "They've been working nonstop 24 hours a day trying to fix it.''
-------- End quote -------

If they have been “working nonstop 24 hours a day to fix it.'' for the last 45 days, surely its time for an update?

Cheers, http://home.infionline.net/~blueblue/_uimages/pi.gif

[Lu Zuckerman]

This may not apply to the subject covered in the above posts but it shows what goes on in the industry.

Many moons ago I was working as a consultant developing overhaul and repair procedures for helicopter servo systems. This company located in Burbank, California also overhauled other aircraft appliances including electric fuel pumps. When they got ready to assemble the fuel pumps they lubricated the bearings with WD-40 © which is not a lubricant although a lot of people think so. WD-40 is a water dispersant. That is what the WD means.

:D

[have another coffee]

It can't be too difficult to design some system where the centertank pumps switch off when the center tank reaches a predetermined level of fuel? Add a simple light if power is supplied to pumps with a three position switch to override the automatic switching. (auto-off-manual)
Apparently this is too much automation for a boeing aircraft called new-generation........

[Blacksheep]

It isn't too difficult, its just too expensive for what would be merely a temporary solution - remember that we have a potential ignition source, and simply keeping the pumps 'wet' is no more than a temporary solution. The design, development and certification process for an auto shut-off for each affected Boeing model would take at least as long as the ultimate fix. Note paragraph 'D' where Boeing state their intention to include an EICAS Advisory, warning crews to turn the pumps off, to prevent dry running. This is much simpler and cheaper than an auto shut-off.

For a hint of the magnitude of the job, here is Boeing's latest 'All Operators Wire' on the subject.

Quote:

----------------------------------------------------------------------
Investigation Status (Applicable to all affected models)
----------------------------------------------------------------------

OPERATIONAL RESTRICTIONS FOR AIRPLANES WITH CRANE HYDRO-AIRE
FUEL PUMPS - STATUS UPDATE
REF /A/ M-7200-02-02028 /C/
/B/ M-7200-02-01978
/C/ M-7200-02-01941
/D/ M-7200-02-01942
/E/ AD 2002-24-52
/F/ AD 2002-24-51
/G/ FTEI ARTICLE EM-02-00064
/H/ FAA AMOC LETTER 140S-02-384 DTD 6 DEC 02
/I/ M-7200-02-02033
/J/ BOEING SB 747-28-2255
/K/ FAA AMOC LETTER 140S-02-379, DTD 24 DEC 02 (ATTACHED)
/L/ FAA AMOC LETTER 140S-02-373, DTD 26 NOV 02
/M/ FAA AMOC LETTER 140S-02-377, DTD 29 NOV 02
/N/ 747-400 MT 28-037, DTD 20-DEC-02

Boeing and Crane Hydro-Aire are continuing to aggressively work
to identify the root cause of the subject fuel pump overheat condition. To date, no root cause has been identified.
Activities continue to focus on the following areas (further
information of each of these activities is detailed below):

- Laboratory analyses of the detail fuel pump components;

- Various heat generation tests on a complete fuel pump assembly
under dry (no fuel flow) and wet (fuel flow) conditions;

- Search of repair and overhaul records covering the past five
years for similar reports of overheat conditions;

- Review of all manufacturing processes, including sub-tier
suppliers, over the past four years;

- Evaluation of short-term and long-term solutions that would
mitigate the safety risk (without having a full understanding
of the root cause).

A. Laboratory analyses

The laboratory analysis is on-going with no new significant
information to provide at this time.

B. Heat generation testing

As discussed in ref /A/, recent testing has focused on
understanding the temperature characteristics as the fuel pump
transitions from wet to dry running. This testing, which was
performed prior to the holidays, was primarily accomplished to
simulate the Hydro-Aire fuel pump installation on DC-10 and MD-11 airplanes so that a potential overheat condition could be
evaluated for those airplanes. Similar wet-to-dry transition
testing is scheduled for next week, but with the test set-up
intended to simulate a 747 fuel pump installation. The results
of these tests will be used to facilitate the planned
incorporation of new EICAS messages on the 747-400, which will
alert the crew to shut-off the center wing tank (CWT) and
horizontal stabilizer tank (HST) fuel pumps to preclude dry
running. Further discussion on the planned EICAS changes is
provided below under the paragraph, "Information Specific to 747
Operators".

As also discussed previously, a thermal (spindle) test rig is
being developed which will test a primer impeller/side plate
assembly. This testing will characterize the effects of thrust
load versus temperature rise, impeller/plate material
differences, torque, and different FOD materials (size and
composition) on the overheating condition. A scheme is currently
being developed to simulate thrust loads. This testing is
scheduled to begin following completion of the transition testing
discussed above.


C. Search of repair and overhaul records

The results of the complete record search is being finalized and
documented. This process is now scheduled to be complete by 15
January 2003.

D. Review of all manufacturing / vendor processes

As noted, Hydro-Aire has been requested to extend the scope of
their review of the pump assembly processes, detailed parts, and
sub-tier suppliers to cover an additional two year period. The
prior review covered the past two years with no relevant
findings. This review is also now expected to be complete by 15
January 2003.

E. Evaluation of short-term and long-term solutions

Boeing and Hydro-Aire are continuing to evaluate proposed
solutions. It is expected that the results of the spindle test
discussed above will assist in determining whether a material
change to the primer impeller assembly is considered viable. The
test results will also be used as a basis for evaluating other
alternate solutions.

Changes to the airplane are also being considered to mitigate an
overheat condition. As discussed above, enhanced EICAS messages are planned for the 747-400 and a similar means of crew alerting is being investigated for the 737NG and 757 airplanes.


Information Specific to 747 Operators
-------------------------------------

A. AMOC Proposals

As stated in ref /A/, Boeing is pursuing additional operational
relief related to both the center wing fuel tank and the
horizontal stabilizer fuel tank (as installed).

The first proposal relates to minimum fuel loading requirements
in the center wing tank (CWT). The current ref /E/ and /F/
Certificate Limitations require, among other things, that a
minimum of 17,000 pounds (7700 kilograms) of fuel must be loaded in the CWT in order to use the override/jettison pumps in that tank. We have submitted an alternate method of compliance (AMOC) request to the FAA which would permit loading a minimum of 4000 pounds (1800 kilograms) in the CWT prior to engine start,
provided the override/jettison pumps in that tank are selected
off for engine start, taxi, and takeoff. The CWT pumps may then
be selected on during stabilized cruise conditions and must be
selected off again in accordance with the current limitations (at
or before the CWT fuel quantity reaches 3000 pounds (1400
kilograms).

The second proposal relates to operation with horizontal
stabilizer tank (HST) fuel. The ref /H/ AMOC eliminates the
requirement in the earlier AMOCs for a minimum of 100,000 pounds of fuel in the CWT at dispatch, but permits use of only the right HST transfer pump. Boeing has submitted an AMOC request to the FAA that will allow selecting the left HST transfer pump on, in the remote case the right transfer pump fails. This would
preclude the potential possibility of an overweight landing. The
existing fuel pump shut-off procedures contained in the prior
AMOCs for the left pump would still apply. This AMOC request
will also require a revised FUEL STAB XFR non-normal checklist to
address c.g. issues.

The FAA are still reviewing the above AMOC requests and we will
advise all affected operators once the AMOC approval letters are
received.

B. CWT Hydro-Mechanical Scavenge System Modification

The ref /I/ message advised that the ref /J/ service bulletin
has been released. This service bulletin is applicable to
747-400 airplanes with the hydro-mechanical scavenge system, and provides instructions to lock open the scavenge system float
valves located in the center wing tank to enable scavenging of
all residual fuel when operating under the ref /E/ operational
restrictions.

As noted in ref /I/, this modification requires a revised FUEL
STAB XFR non-normal checklist to accommodate the revised fuel
scavenging schedule. Operators electing to incorporate this
service bulletin should notify Boeing of their intent so that we
can expedite delivery of the operations manual bulletin and
revised checklist.

C. Defueling and Tank-to-Tank Transfer with Passengers On Board

Boeing has previously received AMOC approval letters for 737NG
and 757 airplanes and for 747-400 airplanes operating under the
ref /H/ Certificate Limitations. The ref /K/ FAA AMOC approval
letter permits defueling and transferring of fuel with passengers
on board using the noted limitations for 747 Classic airplanes
and for 747-400 airplanes operating under the ref /L/ Certificate
Limitations. Unfortunately, the FAA inadvertently omitted
reference to airplanes operating under the ref /M/ alternative
Certificate Limitations, so Boeing is still awaiting AMOC
approval for those airplanes.

D. Related Information

Boeing plans to introduce new/enhanced EICAS advisory messages on the 747-400 which will provide a cue to the flight crew to shut-off the CWT and HST fuel pumps to preclude dry running. The specific message nomenclature and logic is still being developed. The results of the fuel pump wet-to-dry transition tests will be used to determine if the shut-off trigger point can be lowered from the currently mandated fuel levels for the CWT and HST. The new IDS/EICAS software is scheduled to be available for both production and retrofit in early Mar 03.

Operation under the ref /H/ FAA AMOC approval letter, with only
one HST pump armed for dispatch, will set the STAB XFR SIG status message. This was noted during Boeing production flight test. The existing operations manual bulletins addressing the CWT/HST restrictions have been revised to include information on this status message. Operators using or planning to use the the ref /H/ AMOC should notify Boeing so that we can expedite delivery of this operations manual bulletin revision. The ref /N/
maintenance tip has also been released to address this issue.

Best Regards, from "Uncle Bill"... Unquote.

**************************
Through difficulties to the cinema

[GlueBall]

It has been said before: Put CWT fuel pumps into an adjacent main tank. End of story. End of engineering headache.

[PickyPerkins]

Its now about 134 days since they stated “working nonstop 24 hours a day to fix it” on the fuel pump problem.

Anybody know what is the latest news, and the current situation?

Cheers, http://home.infionline.net/~blueblue/_uimages/pi.gif