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)
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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 January 2003 at 06:52.