ASN Wikibase Occurrence # 354176
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| Date: | Tuesday 7 July 1998 |
| Time: | 07:40 LT |
| Type: |  Boeing 737-7H4 |
| Owner/operator: | Southwest Airlines |
| Registration: | N701GS |
| MSN: | 27836/6 |
| Year of manufacture: | 1997 |
| Total airframe hrs: | 1754 hours |
| Engine model: | Cfm CFM56-7B |
| Fatalities: | Fatalities: 0 / Occupants: 96 |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | Birmingham, AL -
 United States of America
|
| Phase: | Unknown |
| Nature: | Unknown |
| Departure airport: | Tampa, FL (KTPA) |
| (KBHM) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The flight data recorder showed that as the flight descended through 2,875 feet pressure altitude on approach to land, the no. 2 engine fuel flow increased followed by the EGT. The engine N1 speed was at 25.6 percent and decreased to 12.8 percent. Engine cutoff was performed 74 seconds after fuel flow increase began. An uneventful landing was made. Examination showed a broken wire in the no. 2 engine electronic engine control, hydromechanical unit, fuel metering valve resolver Channel B. The broken wire was due to damage that was incurred during the manufacturing process and caused unstable Channel B sine out voltage when the resolver was heated above 160 degrees Fahrenheit. The fuel control computer software locked on Channel B, disabled Channel A, and due to the unstable sine out voltage, commanded the fuel metering valve to go to a full open position. The large increase in fuel flow with the engine at idle speed resulted in the engine core stalling and heat damage to the low pressure turbine.
Probable Cause: The improper electronic control unit software logic that permitted the electronic control unit to lock on a failed hydromechanical resolver, which failed due to damage to a wire that was incurred during the manufacturing process, resulting in an uncommanded and sudden increase in fuel flow to the engine that damaged the turbine and caused the engine to lose power.
Accident investigation:
 |
|
Sources:
NTSB MIA98IA193
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 10-Mar-2024 19:52 | ASN Update Bot | Added |
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