top of page
Search

19th of May 2020, Maintenance Error, Blog #652

Updated: Jun 2

A Boeing 737-800 was operating a scheduled passenger service from Victorville-Southern California Logistics Airport (California, USA) to San Diego International Airport (California, USA). After an uneventful take-off, the crew set course to San Diego, according to their filed flight plan.

The aircraft on approach to San Diego, not the missing panels and damage to the left-hand horizontal stabiliser (Source & ©: Yirina.net)


While climbing through an altitude of approximately 8000 feet, a loud bang was heard onboard the aircraft. As the crew scanned their instruments and indications no abnormalities were observed. As no cautions or warnings were presented the crew decided to continue to San Diego where the aircraft made an uneventful landing.


After the aircraft was parked a postflight inspection was performed and on this inspection, it was found that the dorsal fin and three panels were missing from the left-hand lower side of the vertical stabiliser.


The National Transportation Safety Board (NTSB) was alerted and launched an investigation. This investigation was done based on information, recovered aircraft parts and photographs provided by the aircraft operator. This was due to the restrictions in place because of the COVID-19 pandemic.

The missing parts were not recovered. Substantial damage was recorded at the;

  • Fuselage crown skin

    • Found dented, punctured, and gouged

  • Left horizontal stabiliser

    •  The leading edge, lower skin, and upper skin had multiple dents, gouges, and punctures

  • Right horizontal stabiliser

    • The front spar upper chord was fractured, the lower chord was deformed, and the web was gouged in two locations

  • The panel attachment structure on the lower left side of the vertical stabilizer

    • Found fractured and deformed in several places.

  • Attachment bolts were found missing at numerous locations

  • The attachment bolts that remained were not all secure

  • Three loose bolts were recovered on the interior ceiling panels beneath the dorsal fin location

Dorsal fins attachment points, with the relevant part numbers (Source & ©: NTSB)


Just under 3 months before the accident the aircraft had undergone maintenance in the affected area. As per the Aircraft Maintenance Program, every 24.000 flight cycles the fuselage skin under the dorsal fin was inspected for corrosion. For this inspection, the dorsal fin was removed. The maintenance manual task for the dorsal fin removal/installation indicated that the type and location of the bolts removed should be recorded. This was to ensure that each bolt would be returned to the same location from where it was removed. (The dorsal fin had different bolts with varying grip lengths.) Once the bolts were reinstalled, sealant was applied to the bolt heads. Based on the evidence provided the NTSB concluded that the probable cause(s) of this accident was;

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


As a result of this accident, the following mitigating actions were taken;

  • The operator revised the Aircraft Maintenance Manual to clarify the removal and installation procedures for the dorsal fin.

  • The Maintenance Organisation involved provided training to its staff on the maintenance procedures.

  • The aircraft manufacturer updated the dorsal fin removal and installation instructions in its 737-600/700/800/900 Aircraft Maintenance Manual by changing a note (with regards to bolt installation) to a caution, stating;

    • MAKE SURE THAT YOU MONITOR WHERE YOU REMOVE EACH FASTENER AT EACH LOCATION. THERE ARE DIFFERENT SIZES FOR THE FASTENERS. IF YOU INSTALL THE FASTENERS AT THE INCORRECT LOCATIONS, DAMAGE TO THE AIRPLANE CAN OCCUR.

    • MAKE SURE THAT YOU MONITOR WHERE YOU REMOVE EACH FASTENER AT EACH LOCATION. THERE ARE DIFFERENT SIZES FOR THE FASTENERS. IF YOU INSTALL THE FASTENERS AT THE INCORRECT LOCATIONS, DAMAGE TO THE AIRPLANE CAN OCCUR.

  • The Aircraft Illustrated Parts Catalog was amended

The bolts that remained in place (Source; NTSB © Operator)


The NTSB report, which served as the source for this blog can be accessed by clicking on the .PDF file below;


B737-800 Wrong Bolts 19May2020
.pdf
Download PDF • 5.27MB



588 views0 comments

Recent Posts

See All

Comments


Post: Blog2_Post
bottom of page