Boeing 737-7H4 N701GS

Summary

On 7 July 1998 at about 11:40 local time, a Boeing 737-7H4 registered N701GS was involved in an incident near Birmingham, Alabama, United States. 96 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

7 July 1998 at 11:40

Classification

Incident

Location

Birmingham, Alabama, United States

Coordinates

33.5693, -86.7105

Aircraft

Boeing 737-7H4

Registration

N701GS

Category

Airplane

Engines

2

Operator

Not recorded

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Tampa → Unknown

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

MIA98IA193

Nobody was injured.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.