On February 16, 1998, at 1240 central standard time, an Airbus A-320-212, N341NW, operated by Northwest Airlines, had an Engine Condition and Monitoring System (ECAMS) No. 1 fuel filter clog warning message about 200 miles from Memphis, Tennessee. The flight crew decided to divert the aircraft to Memphis, Tennessee. While turning inbound on the first turn in holding at 10,000 feet msl to burn off fuel to get down to the maximum landing weight, the No. 1 CFM56-5A3 turbofan engine experienced an uncommanded in-flight shutdown. The attempt to restart the engine was unsuccessful. An uneventful single-engine landing was made. There were no injuries to the captain or first officer, the five flight attendants, or the 110 passengers. The 14 CFR Part 121, Flight 1821, had departed Detroit Metropolitan Airport, Detroit, Michigan, en route to Mexico City, Mexico. Visual meteorological conditions prevailed and the flight was on an instrument flight plan. Use your browsers 'back' function to return to synopsisReturn to Query Page
The examination of the engine revealed a 4-inch long (circumferential) by 1-inch wide (axial) burn-through in the low pressure turbine case in the plane of the 2nd stage turbine stators at the 11 o'clock location. There was reported heat distress to the left engine pylon. The examination of the fuel pump filter revealed the presence of a bronze-colored material. The fuel nozzles were partially blocked by bronze-colored material in the nozzle jets.
The engine was removed from the airplane and shipped to SNECMA, where it was disassembled under the direction of the Bureau Enquetes Accidents. The engine was equipped with an Argo-Tech fuel pump, part number (PN) 714900-2. The fuel pump was removed from the engine and returned to Argo-Tech Corporation, Cleveland, Ohio, for disassembly and examination.
Northwest Airlines records show that the fuel pump, PN 714900-2, serial number (SN) 37001, had operated 17,208 hours time since new (TSN) and 6,972 cycles since new (CSN). The records show that the fuel pump had not been removed from the engine, SN 731-709, since the engine had been received by Northwest Airlines. The engine's records show that it had operated 17,208 hours TSN and 6,972 CSN.
The disassembly and examination of the fuel pump revealed the pump housing had gear pocket milling. The fixed and pressurized bearings, which are made of bronze, were worn. The fuel pump's filter bypass valve was found to have bronze-colored particles on both sides of the valve.
The drive and driven gears were both intact. The teeth of the driven gear were worn approximately 0.017 inches diametrically. The drive and driven gear were measured and compared to new parts as follows:
Feature New part dimension Actual dimension
Drive gear OD 3.2474-3.2480 inches 3.248 inches
Driven gear OD 3.2474-3.2480 3.231
The pump gear housing had gear pocket milling on the driven gear side. The housing was sectioned at the milled area and a measurement of the remaining wall thickness showed that it was 0.240-inches thick. The driven gear had wear that corresponded to wear on the quad-ring bolt bosses inside the housing. The remaining wall thickness at the quad-ring bolt boss was found to be 0.450 inches.
The fuel pump has four bearings: the fixed drive bearing, fixed driven bearing, pressurized drive bearing, and pressurized driven bearing, which are made of bronze. The fixed bearings did not move freely and were slightly recessed below the split line. All four bearings exhibited wear and material loss. The bearings from the pump were weighed for comparison to new bearings.
Part New part weight Actual weight
Fixed drive bearing 623.42 grams 623.7 grams
Fixed driven bearing 622.86 564.4
Pressurized drive bearing 602.13 570.2
Pressurized driven bearing 603.45 493.8
The fixed drive bearing had a dam wipe of 0.041 inches. The bearing face had minor scoring. The bearing bore was in good condition. The rear side of the bearing did not show any wear.
The fixed driven bearing had a severe dam wipe. The face of the bearing was worn. The bearing bore was worn 0.146 inches. The back side of the bearing was not worn.
The pressurized drive bearing had a severe dam wipe. The face of the bearing was worn. The bearing bore was scored.
The pressurized driven bearing had a severe dam wipe. The face of the bearing was worn. The bearing bore was worn 0.146 inches. The "O" ring and backup ring on the pressurized driven bearing were found to be cut and the "O" ring was also nibbled. (See NTSB Powerplants Group Chairman's Factual Report)
The fuel control, or hydro-mechanical unit (HMU), was inspected. The examination revealed no anomalies to the HMU that contributed to the main fuel pump failure. (See Woodward Governor Engineering Analytical Report)
Parties to the investigation included the Federal Aviation Administration, Northwest Airlines, GE Aircraft Engines, CFM International, Argo-Tech, SNECMA, and Woodward Governor Company.