Pilot Debrief

BOEING 737-8K2 near Las Vegas, NV — 2022-02-04

Final reportENG22FA009
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Date
2022-02-04
Location
Las Vegas, NV, USA
Airport
LAS
Aircraft
BOEING 737-8K2
Registration
N817SY
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Landing

Probable cause

The fatigue failure of the right main landing gear initiated by liquid metal embrittlement by cadmium at arc burn locations in the outer cylinder tooling hole area. The arc burns were likely the result of operator error during stylus cadmium plating operations during overhaul.

NTSB narrative

Upon retracting the landing gear after takeoff, the flight crew received a right main landing gear (RMLG) red position indicator light, indicating that the RMLG was not in the up and locked position. The crew elected to return to the departure airport and the RMLG red indicator light remained illuminated until the crew selected the gear DOWN position for landing. During the landing roll, the RMLG collapsed, resulting in minor damage when the right engine impacted the runway. It is likely that the RMLG was partially fractured after takeoff which prevented it from retracting to the up and locked position. Examination of the RMLG revealed that the outer cylinder fractured through a tooling hole. Examination of the fracture revealed the presence of fatigue cracking that initiated at the intersection of the tooling hole inner diameter and the outer cylinder inner diameter. Four areas of arc burn damage were identified in the tooling hole area, two of which were at the crack initiation sites. Cadmium identified at the intergranular separation initiation sites indicated the crack initiated due to liquid metal embrittlement by cadmium at the arc burn locations before propagating in fatigue. The RMLG was last overhauled about 10 years before the incident, during which the outer cylinder was replated with cadmium after repair. It is likely that the arc burning in the tooling hole area was caused by a hand-held stylus cadmium plating operation performed in the tooling hole when the stylus (anode) made contact with the outer cylinder (cathode), initiating an arc. A nonconductive sleeve normally installed on the anode was either not present or deteriorated, allowing physical contact between the anode and cathode.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Crew could have performed more thorough checks on landing gear before takeoff.

NTSB coding

Evidence available

  • FDR / data
  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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