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Fuel Tank Pumps Overheating!

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Fuel Tank Pumps Overheating!

Old 3rd Dec 2002, 17:26
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Question Additional knowledge????

For more information on this ongoing problem check this out.


www.hydroaire.com/support/service.htm
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Old 3rd Dec 2002, 20:44
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-----------------
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.


Last edited by PickyPerkins; 25th Jan 2005 at 15:17.
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Old 5th Dec 2002, 00:02
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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.
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Old 6th Dec 2002, 15:05
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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.
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Old 7th Dec 2002, 16:11
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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.


Last edited by PickyPerkins; 25th Jan 2005 at 15:18.
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Old 10th Dec 2002, 05:26
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Lightbulb

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.

**************************
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Last edited by Blacksheep; 10th Dec 2002 at 05:49.
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Old 12th Dec 2002, 01:01
  #27 (permalink)  
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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?
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Old 12th Dec 2002, 07:25
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Wink

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...

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Old 9th Jan 2003, 18:54
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-------- 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,

Last edited by PickyPerkins; 25th Jan 2005 at 15:19.
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Old 9th Jan 2003, 19:19
  #30 (permalink)  

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Question High industry standards?????

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.


Last edited by Lu Zuckerman; 9th Jan 2003 at 23:17.
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Old 10th Jan 2003, 08:59
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Lightbulb

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........
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Old 13th Jan 2003, 06:37
  #32 (permalink)  
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Lightbulb

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

Last edited by Blacksheep; 13th Jan 2003 at 06:52.
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Old 13th Jan 2003, 15:30
  #33 (permalink)  
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Hello Boeing People

It has been said before: Put CWT fuel pumps into an adjacent main tank. End of story. End of engineering headache.
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Old 26th Feb 2003, 18:10
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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,

Last edited by PickyPerkins; 25th Jan 2005 at 15:20.
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