Boeing 737 incident near San Francisco, California, December 25, 2010
On December 25, 2010 at about 4:20 am local time, a Boeing 737, registered N248WN, was involved in an incident during enroute (climb to cruise) near San Francisco, California (San Franciso airport). It was flown under scheduled airline rules (Part 121). No one was hurt; 122 people were on board or involved.
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- December 25, 2010 · about 4:20 am local time
- Place
- San Francisco, California · San Franciso · map
- Type
- Incident
- Injuries
- No one was hurt; 122 people were on board or involved.
- Weather
- not recorded
- Aircraft
- Boeing 737 7H4 · all 737s on the register
- Registration
- N248WN · registry record · serial 32509
- Damage
- Not recorded
- Flight
- Flight · scheduled airline rules (Part 121)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Fire/smoke (non-impact) during enroute (climb to cruise)
- Powerplant sys/comp malf/fail during enroute (climb to cruise) defining event
- Engine shutdown during enroute (climb to cruise)
The NTSB's findings
- cause Aircraft › Aircraft power plant › Engine fuel and control › Fuel distribution › Incorrect service/maintenance
- cause Personnel issues › Task performance › Maintenance › Installation › Maintenance personnel
The aircraft
- Maximum gross weight: 154,500 lb
- Seats: 139
- Landing gear: fixed
- Engine: Cfm CFM56 7B22 (turbofan); 0 hours total
- Operator: Southwest Airlines
The flight
- Departed from: SFO San Francisco CA
- Flight plan: IFR
- A second pilot was aboard
Weather at the time
- Temperature: 0°F (-18°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Cabi | 3 | |||
| Flight crew | 2 | |||
| Passengers | 117 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.