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Operations Manual Bulletin No. ILF2-40(R3), Dated April 1, 2001 (continued)
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Operations Manual Bulletin
for
International Lease Finance Corp.
The Boeing Company Seattle, Washington 98124-2207
Number: ILF2-41(R5)
Date: April 1, 1999
Document Effectivity: D6-30151-425
Subject: CENTER WING TANK (CWT) OVERRIDE/JETTISON AND HORIZONTAL STABILIZER TANK TRANSFER/JETTISON PUMPS
Reason: To inform flight crews of possible fuel pump damage that could create a potential fuel vapor ignition source. Revised for administrative purposes.
Information in this bulletin is recommended by The Boeing Company, but may not be FAA approved at the time of writing. In the event of conflict with the FAA approved Airplane Flight Manual (AFM), the AFM shall supersede. The Boeing Company regards the information or procedures described herein as having a direct or indirect bearing on the safe operation of this model airplane.
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
Background Information
Previously, Boeing issued Alert Service Bulletin 747-28A2212 (May 14, 1998 Rev. 2) to inspect CWT override/jettison pump inlet adapters and inlet check valves. This was followed by FAA Airworthiness Directive 98-16-19. Until completion of the required inspection, flight crews were instructed to select the CWT override/jettison pumps OFF on airplanes with over 20,000 flight hours when CWT fuel decreased to 7,000 pounds (3,200 kilograms).
Boeing recently received reports from two 747-400 operators regarding low-time removal of override/jettison pump motor/impeller assemblies installed in main tanks 2 and 3, and center wing tanks, due to low fuel pressure indications. To date, Boeing has received reports of twelve low-time removals of override/jettison pumps, all of which had accumulated less than 700 airplane flight hours. Visual inspection of the removed pumps revealed damage to the inducer and impeller, with related score marks on the inner diameter of the inlet adapter. This sustained metal-to-metal contact is a possible ignition source. Testing by the pump manufacturer, Hydro-Aire, did not result in ignition. The FAA has issued Airworthiness Directive T98-25-52.
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Operations Manual Bulletin No. ILF2-41(R5), Dated April 1, 1999 (continued)
The following procedures apply to pumps manufactured, overhauled, or repaired between July 1996 and November 1998. Operators can determine specific airplane applicability through methods published in FAA letter 98-140S-440, “Approval of Alternative Method of Compliance with Airworthiness Directive T98-25-52”, and respective Service Bulletins.
If CWT override/jettison pumps are to be used for flight, the center wing tank must contain at least 17,000 pounds (7,720 kilograms) prior to engine start. This ensures both CWT override/jettison pumps remain covered during rapid acceleration and high nose attitudes during takeoff and climb.
If CWT fuel is less than 50,000 pounds (22,700 kilograms) prior to engine start, the flight crew should select the CWT override/jettison pumps OFF when fuel in the center wing tank reaches 7,000 pounds (3200 kilograms). This ensures a potentially damaged pump remains covered by fuel, and is not exposed to fuel vapors during climb. The flight crew may select the CWT fuel pumps ON when stabilized in cruise, then select the CWT fuel pumps OFF when CWT fuel reaches 3,000 pounds (1,360 kilograms).
Airplanes with electric CWT scavenge pumps will scavenge some or all of the remaining 7,000 pounds (3,200 kilograms) of fuel. However, this scavenging will not occur until the reserve tanks begin to transfer. Based on a minimum scavenge flow rate of 1,700 pounds per hour, approximately 3,400 pounds (1,540 kilograms) of fuel will be scavenged within the two hour scavenge pump activation cycle. The remaining 3,600 pounds (1,630 kilograms) is unusable. The scavenge flow rate is a function of several variables (pump efficiency, discharge pressure, etc.). On some airplanes, the majority of the 7,000 pounds (3,200 kilograms) of CWT fuel may be scavenged within the two hours. Operator experience may provide different values for scavenged and unusable fuel.
All of the remaining 7,000 pounds (3,200 kilograms) of CWT fuel is unusable in airplanes with CWT jet scavenge pumps. However, in a low fuel situation, the CWT fuel pumps may be selected ON and all CWT fuel used.
If CWT fuel is greater than or equal to 50,000 pounds (22,700 kilograms) prior to engine start, the crew should select the CWT override/jettison pumps OFF when CWT fuel reaches 3,000 pounds (1,360 kilograms). Increased CWT fuel ensures both CWT override/jettison pumps remain covered during rapid acceleration and high nose attitudes during takeoff and climb. Under these conditions, CWT pump shutoff is not required until the cruise phase of flight.
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