Individually Owned: 150,657
Corporate Owned: 137,281
San Franciso Airport
Aircraft Accident/Incident Report
San Francisco, California
Friday, December 24, 2010 20:20 PST
NTSB Narrative Summary Released at Completion of Accident
The CFM56-7B24 turbofan engine experienced an inflight fire after departure. The flight crew reported an engine fire warning, discharged a fire suppression bottle and diverted where a successful single engine landing was performed. The airplane taxied to the gate where all the passengers deplaned. There were no reported injuries. Preliminary examination of the engine revealed sooting on the engine cases from the compressor aft flange to approximately six inches beyond the turbine rear frame aft flange, but no significant thermal damage. Detailed examination of the engine revealed that the lower, most forward of the four bolts that secure the fuel manifold cover to the fuel manifold was missing while the other three had low torque values. Due to the missing attachment bolt and low torque on the three remaining bolts a gap between the two surfaces occurred that allowed fuel to leak. A review of photographs taken before the engine was released from the Celma overhaul shop reveals that all four bolts were present at that time, but based on the torque values during the investigation, they were likely not properly torqued at overhaul. These original low torque values allowed the bolts to back out over time until one eventually fell out. Pressurized fuel within the cavity was then able to pry the loose-fitting fuel manifold cover open at the location of the missing bolt and leak past its integral packing, creating the leak and subsequent in-flight fire. Examination of other 737 airplanes with CFM56-7B24 engines revealed no broader field problem.
NTSB Probable Cause Narrative
The probable cause of the undercowl in-flight engine fire was the insufficient installation torque of the bolts that secure the fuel manifold cover to the fuel manifold. Engine vibrations and fuel pressure cycles caused the bolts to gradually loosen further until one bolt lost all its tightening torque and fell out. The internal fuel pressure then forced open the fuel manifold cover at the location of the missing bolt, causing a gap between the two mating surfaces which allowed fuel to push past the integral packing, resulting in a fuel leak onto the hot engine cases where it ignited resulting in a fire.
Event Information
| Type of Event | Incident |
| Event Date | 12/24/2010 |
| Event Day of the Week | Friday |
| Time of Event | 2020 |
| Event Time Zone | Pacific Standard Time |
| Event City | San Francisco |
| Event State | CALIFORNIA |
| Event Country | -- |
| Zipcode of the event site | -- |
| Event Date Year | 2010 |
| Event Date Month | 12 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | -- |
| Event Location Longitude | -- |
| Event Location Airport | San Franciso |
| Event Location Nearest Airport ID | SFO |
| Indicates whether the acc/inc occurred off or on an airport | -- |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | -- |
| Weather Briefing Completeness | -- |
| Investigator's weather source | Unknown |
| Time of the weather observation | |
| Direction of event from weather observation facility (degrees) | -- |
| Weather Observation Facility ID | -- |
| Elevation of weather observation facility | -- |
| Distance of event from weather observation facility (units?) | -- |
| Time Zone of the weather observation | -- |
| Lighting Conditions | -- |
| Lowest Ceiling Height | -- |
| Lowest Non-Ceiling Height | -- |
| Sky/Lowest/Cloud Conditions | -- |
| Sky Condition for Lowest Ceiling | -- |
| Visibility Runway Visual Range (Feet) | -- |
| Visibility Runway Visual Value (Statute Miles) | -- |
| Visibility (Statute Miles) | -- |
| Air Temperature at event time (in degrees celsius) | -- |
| Dew Point at event time (in degress fahrenheit) | -- |
| Wind Direction (degrees magnetic) | -- |
| Variable Wind Indicator | -- |
| Wind Speed (knots) | -- |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | -- |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | -- |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | None |
| On Ground, Fatal Injuries | -- |
| On Ground, Minor Injuries | -- |
| On Ground, Serious Injuries | -- |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | 122 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 31704 |
| NTSB Notification Source | FAA SWA CMO |
| NTSB Notification Date | -- |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | -- |
| Date of most recent change to record | Aug 6 2013 2:50PM |
| User who most recently changed record | broda |
| Basic weather conditions | -- |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N248WN |
| NTSB Number | ENG11IA011 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Part 121: Air Carrier |
| Type of Flight Plan filed | IFR |
| Flight plan Was Activated? | Yes |
| Damage | None |
| Aircraft Fire | In-flight |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | BOEING |
| Aircraft Model | 737 |
| Aircraft Series Identifier | 7H4 |
| Aircraft Serial Number | 32509 |
| Certified Max Gross Weight | 154500 |
| Aircraft Category | Airplane |
| Aircraft Registration Class | -- |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | 2 |
| Cabin Crew Seats | -- |
| Passenger Seats | 137 |
| Total number of seats on the aircraft | 139 |
| Number of Engines | 2 |
| Fixed gear or retractable gear | Fixed |
| Aircraft, Type of Last Inspection | -- |
| Date of Last Inspection | -- |
| Airframe hours since last inspection | -- |
| Airframe Hours | -- |
| ELT Installed | Unknown |
| ELT Activated | Unknown |
| ELT Aided Location of Event Site | Unknown |
| ELT Type | -- |
| Aircraft Owner Name | Southwest Airlines |
| Aircraft Owner Street Address | P.O. Box 36647-1CR |
| Aircraft Owner City | Dallas |
| Aircraft Owner State | TX |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 75235 |
| Operator is an individual? | No |
| Operator Name | Southwest Airlines |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | P.O. Box 36647-1CR |
| Operator City | Dallas |
| Operator State | TX |
| Operator Country | USA |
| Operator Zip code | 75235 |
| Operator Code | SWAA |
| Owner has at least one certificate | Yes - certificate holder |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | -- |
| Operator Certificate Number | SWAA304A |
| Indicates whether an air carrier operation was scheduled or not | Scheduled |
| Indicates Domestic or International Flight | Domestic |
| Operator carrying Pax/Cargo/Mail | Passenger Only |
| Type of Flying (Per_Bus / Primary) | -- |
| Second Pilot on Board | Yes |
| Departure Point Same as Event | Yes |
| Departure Airport Code | SFO |
| Departure City | San Francisco |
| Departure State | CA |
| Departure Country | USA |
| Departure Time | -- |
| Departure Time Zone | -- |
| Destination Same as Local Flt | -- |
| Destination Airport Code | -- |
| Destination City | -- |
| Destination State | -- |
| Destination Country | USA |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | May 14 2013 5:14PM |
| User who most recently changed record | reih |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | N/A |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |