Pilot Debrief

BOEING 737 near Victorville, CA — 2020-05-19

Final reportDCA20LA107
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Date
2020-05-19
Location
Victorville, CA, USA
Aircraft
BOEING 737
Registration
N820TJ
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Climb

Probable cause

Improper installation of dorsal fin attach bolts which caused the dorsal fin to separate during flight, substantially damaging the left horizontal stabilizer.

NTSB narrative

After departure, the air carrier airplane was climbing through an altitude of about 8,000 ft, at which time the flight crew heard a loud bang. Because the flight instruments and gauges showed nothing abnormal, the flight crew elected to continue the flight to the destination airport. The airplane landed uneventfully. Postflight inspection of the airplane found that the dorsal fin and three panels on the lower left side of the vertical stabilizer were missing, and that the left horizontal stabilizer was substantially damaged. Most of the dorsal fin, the vertical stabilizer panels, and 7 of the 14 bolts attaching the dorsal fin to the fuselage were not recovered. Of the seven bolts that were recovered, four remined installed, and three were found loose. Three of the four installed bolts remained attached to pieces of the dorsal fin structure. Examination of the photographs showed that the bolts installed in three positions on the left side of the dorsal fin were the correct part number. The bolt installed in a position on the right side of the dorsal fin was not the correct part number, and the bolt was longer than required. The photographs also showed remnants of old sealant at each of the bolt locations but no evidence that sealant was applied during maintenance of the dorsal fin in February 2019 (less than 3 months before the accident). The seven missing bolts for the dorsal fin structure became loose, had fractured, or were not properly installed.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Proper inspection and installation of dorsal fin bolts could have prevented the failure.

NTSB coding

Evidence available

  • CVR
  • FDR / data
  • 7 docket documents
View NTSB final reportView NTSB docket

Docket documents7

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