Investigation brief · generated 2026-10-09 · source: NTSB public docket and accident database
BOEING 737-8K2 — Las Vegas, NV, USA, 2022-02-04
NTSB number
ENG22FA009
Operator
Sun Country Airlines, Inc.
Registration
N817SY
Highest injury
No injury
Regulation
Part 121
Damage
Minor
Cohort
Part 121 airline
Recorder data
Tier 1 — decoded recorder tables
Every sentence below is taken directly from NTSB records — the accident database, the docket's recorder reports and the Board's findings — with its source noted. Nothing is paraphrased or inferred.
NTSB summary
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.
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.
Verbatim, NTSB determination.
Flight data recorder
Boeing 737-800 · N817SY — 270,149 samples, 103 parameters, 00:40:00.0 to 01:19:56.0.
Parameter
Max
at
Min
at
Final
at
Pressure altitude ft
9,512.0
00:52:58.7
1,516.0
01:18:48.7
1,597.0
01:19:55.7
Computed airspeed kts
216.8
00:58:46.7
45.0
00:40:00.7
45.0
01:19:55.7
Vertical acceleration g
1.2
01:18:59.8
0.1
01:18:59.1
0.9
01:19:55.9
Engine 1 N1 %RPM
94.2
00:42:26.4
21.2
01:19:26.4
22.0
01:19:55.4
Engine 2 N1 %RPM
94.2
00:42:32.9
5.1
01:19:55.9
5.1
01:19:55.9
Computed from the docket's tabular attachment; times as recorded (local or SRN as published).
Sequence of events (FDR factual report)
Time
Event
Page
00:40:28
The airplane departed Harry Reid International Airport (KLAS), Las Vegas, Nevada.
4
00:40:31
Nose and main landing gear warning parameters indicated "Warn", consistent with the crew moving the landing gear lever to the 'Up' position.
4
00:40:32
The nose and left main 'Gear Down' parameters simultaneously indicated 'Up'. The right main 'Gear Down' parameter remained in 'Down' status.
4
00:40:38
The right main 'Gear Down' parameter indicated 'Up'.
4
00:40:39
The nose and left main 'Gear Warn' parameters transitioned from 'Warn' to 'No Warn'. The right 'Gear Warn' parameter remained in 'Warn' status. The airplane continued to climb.
5
About 00:43:30
The airplane leveled off at about 9,500 feet MSL.
5
About 00:53:00
The airplane descended and leveled off at 7,500 feet MSL.
5
About 01:10:40
The airplane started to descend and maneuver back for an approach at KLAS.
5
01:14:37
The airplane was on approach for KLAS at an altitude of about 5,300 feet MSL. The right main 'Gear Warn' parameter continued to indicate 'Warn'. The nose and left main 'Gear Warn' parameters transitioned to 'Warn', consistent with the crew moving the landing gear lever to the 'Down' position. The airplane continued to descend.
5
01:14:44
The nose 'Gear Down' parameter transitioned from 'Up' to 'Down'. Simultaneously, the 'Gear Warn-N' parameter transitioned to 'No Warn'.
5
01:14:47
The left main 'Gear Down' parameter transitioned to 'Down' and simultaneously, the 'Gear Warn-L' parameter transitioned to 'No Warn'.
5
01:14:48
The right main 'Gear Down' parameter transitioned to 'Down' and simultaneously, the 'Gear Warn-R' parameter transitioned to 'No Warn'. The airplane continued to descend.
5
01:18:59
The nose, left main, and right main landing gear WOW all indicated 'Grnd (Ground)'.
5
01:19:00
The right main 'Gear Down' and right main 'Gear Warn' parameters transitioned to 'Up' and 'Warn', respectively. The recorded roll angle began to increase (right wing down).
5
01:19:04
Both engine's thrust reversers indicated full deployment. Air and ground speed continued to decrease.
5
01:19:19
The 'Eng2 Fire' parameter briefly indicated 'Fire'. One second later, the parameter transitioned back to 'No Fire' for about 26 seconds.
5
01:19:22
Both engine thrust reversers indicated they were no longer deployed. The recorded groundspeed was about 17 knots.
5
01:19:27
The recorded groundspeed was 0 knots.
5
01:19:47
The 'Eng2 Fire' parameter indicated 'Fire'. This indication persisted for the duration of the recording.
5
Extracted by claude-sonnet-5; 15 of 19 stated events verified against the raw recorder data.