Sunday, September 30, 2018

Embraer ERJ-175, operated by SkyWest Airlines, N161SY: Incident occurred December 04, 2016 at San Antonio International Airport (KSAT), Texas

The National Transportation Safety Board did not travel to the scene of this incident.

Aviation Incident Factual Report - National Transportation Safety Board: https://app.ntsb.gov/pdf 


Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms

http://registry.faa.gov/N161SY




Location: San Antonio, TX
Incident Number: ENG17IA005
Date & Time: 12/04/2016, 1453 CST
Registration: N161SY
Aircraft: EMBRAER ERJ170 200LR
Aircraft Damage: Minor
Defining Event: Landing gear collapse
Injuries: 1 Minor, 54 None
Flight Conducted Under:  Part 121: Air Carrier - Scheduled 

On December 04, 2016, about 1453 central daylight time, N161SY, an Embraer ERJ170 200L, operated by SkyWest Airlines, experienced an uncommanded retractionof the nose landing gear during rollout after landing on runway 4 at the San Antonio International Airport (KSAT), San Antonio, TX. The aircraft was originally scheduled to land at General Mariano Escobedo Int'l Airport (MMTY), Monterrey, Nuevo Leon, Mexico. However, after departure from the George Bush Intercontinental Airport (KIAH), Houston, Texas the crew heard a loud "thud/pop" just aft of the flight deck. Because no warnings or indications were displayed on the flight deck, the crew decided to proceed to MMTY. When the landing gear was extended on approach, the crew received warning indications regarding the landing gear position and a "LDG GEAR LEVER DISAGREE" message. The crew declared a missed approach, retracted the landing gear per the quick reference handbook (QRH) procedures, and elected to divert to KSAT. Upon entering US airspace, the crew declared an emergency and performed a flyby of the control tower to verify landing gear position. The tower confirmed that the gear appeared to be in the down position. After touchdown on runway 4, during the landing rollout the nose gear retracted, without command, as the aircraft slowed to a stop. The crew and passengers evacuated the aircraft from the aft cabin doors via the evacuation slides. The airplane sustained minor damage. The flight was conducted under the provisions of 14 Code of Federal Regulations Part 121. Visual meteorological conditions prevailed and a Federal Aviation Administration (FAA) flight plan had been filed for the flight.

Pilot Information

Certificate: Airline Transport
Age: 38
Airplane Rating(s): Multi-engine Land; Single-engine Land
Seat Occupied: Left
Other Aircraft Rating(s): None
Restraint Used: 5-point
Instrument Rating(s): None
Second Pilot Present:
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 1 With Waivers/Limitations
Last FAA Medical Exam: 05/01/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent:
Flight Time:   2814 hours (Total, all aircraft), 685 hours (Pilot In Command, all aircraft), 189 hours (Last 90 days, all aircraft), 46 hours (Last 30 days, all aircraft), 11 hours (Last 24 hours, all aircraft)

Co-Pilot Information

Certificate: Airline Transport; Flight Instructor
Age:
Airplane Rating(s): Multi-engine Land; Single-engine Land
Seat Occupied: Right
Other Aircraft Rating(s): None
Restraint Used: 5-point
Instrument Rating(s): None
Second Pilot Present:
Instructor Rating(s):  Airplane Multi-engine; Airplane Single-engine; Instrument Airplane
Toxicology Performed: No
Medical Certification: Class 1 Without Waivers/Limitations
Last FAA Medical Exam: 01/01/2016
Occupational Pilot: Yes
Last Flight Review or Equivalent:
Flight Time:  862 hours (Total, all aircraft), 132 hours (Last 90 days, all aircraft), 27 hours (Last 30 days, all aircraft), 11 hours (Last 24 hours, all aircraft)

Aircraft and Owner/Operator Information

Aircraft Make: EMBRAER
Registration: N161SY
Model/Series: ERJ170 200LR 200LR
Aircraft Category: Airplane
Year of Manufacture: 2016
Amateur Built: No
Airworthiness Certificate: Transport
Serial Number: 17000569
Landing Gear Type: Retractable - Tricycle
Seats: 80
Date/Type of Last Inspection: 11/29/2016, Continuous Airworthiness
Certified Max Gross Wt.: 85517 lbs
Time Since Last Inspection:
Engines: 2 Turbo Fan
Airframe Total Time: 1307.3 Hours at time of accident
Engine Manufacturer: General Electric
ELT: C126 installed, not activated
Engine Model/Series: CF34-8E5
Registered Owner: SKYWEST AIRLINES INC
Rated Power: lbs
Operator: SKYWEST AIRLINES INC
Operating Certificate(s) Held: Flag carrier (121) 

The event airplane, an Embraer ERJ 170-200 LR, registration N161SY, serial number 17000569, was manufactured and delivered to the operator in 2016 and had accumulated 1,310 hours and 740 cycles. The NLG downlock springs were installed during manufacture and had accumulated the same time and cycles as the airframe.

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: KSAT
Distance from Accident Site:
Observation Time: 1851 UTC
Direction from Accident Site:
Lowest Cloud Condition:
Visibility: 10 Miles
Lowest Ceiling: Overcast / 1300 ft agl
Visibility (RVR):
Wind Speed/Gusts: 10 knots /
Turbulence Type Forecast/Actual: / None
Wind Direction: 20°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 29.8 inches Hg
Temperature/Dew Point:
Precipitation and Obscuration:
Departure Point: HOUSTON, TX (IAH)
Type of Flight Plan Filed: IFR
Destination: Monterrey, FN (MMTY)
Type of Clearance: IFR
Departure Time: 1153 CST
Type of Airspace: Class B; Class D 

Airport Information

Airport: SAN ANTONIO INTL (SAT)
Runway Surface Type: Concrete
Airport Elevation: 809 ft
Runway Surface Condition: Wet
Runway Used: 04
IFR Approach: None
Runway Length/Width: 8505 ft / 150 ft
VFR Approach/Landing: Unknown

Wreckage and Impact Information

Crew Injuries: 4 None
Aircraft Damage: Minor
Passenger Injuries: 1 Minor, 50 None
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 1 Minor, 54 None
Latitude, Longitude: 29.531389, -98.468333 

Injuries To Persons

One minor injury was reported by a passenger which occurred during the evacuation of the aircraft. 

Damage To Aircraft

Scraping damage was reported to the lower fuselage skin, forward of the nose landing gear bay and the nose landing gear doors. Minor scraping to the underside of the right-hand engine nacelle was also reported. During the aircraft recovery, a failed downlock spring was found lodged in a lightening hole in the nose landing gear yoke, which obstructed the downlock operation for the nose landing gear. 

Flight Recorders

The aircraft was equipped with two combination Cockpit Voice Flight Data Recorders (CVFDR) which recorder identical sets of voice and parametric data. One CVFDR was sent to the NTSB Vehicle Recorders laboratory in Washington, DC for examination. The CVFDR recorded relevant data for landing gear and hydraulic system for the incident flight, and several previous flights. Due to the successful download of the stored data the other CVFDR was not downloaded for the investigation. The Flight Data Recorder Specialist's Factual Report can be found in the pubic docket for this incident. 

Tests And Research

The NLG downlock springs were removed and shipped to the NTSB Materials laboratory in Washington, DC. The right NLG downlock spring was received intact. The left NLG downlock spring was received in two separate pieces. The NLG downlock spring separated in the ninth coil from the lower end due to progressive crack formation. No evidence of overstress was observed.

During a visual inspection, external surfaces of the downlock spring wire had small openings, which resulted in surface roughness measurements that were above the allowable limit set by Embraer. Cross-sections prepared through multiple downlock spring coils along the length of the spring showed intergranular cracking at the openings. The openings and cracking were associated with white etching microstructure of the wire that was consistent with retained austenite, while the base material of the coils had microstructure consistent with martensite, as specified. The amount of retained austenite in a circumferential surface layer of the downlock spring coils was above the allowable limit specified by Embraer per AMS 5678.

Two spring pieces (an end segment and a ring segment) were documented using radiographic images. The computed tomography (CT) slice images were examined, processed, and analyzed by the NTSB to evaluate the components. The results of the CT imaging were inconclusive in locating crack location in the spring segments.

The manufacturer provided information to the NTSB regarding additional NLG and MLG downlock springs that failed during operations. The spring from this incident was the only one which resulted in an uncommanded gear retraction on landing. Manufacturing records for the incident spring were reviewed and compared with other events. The manufacturer identified a suspect batch of raw material for the springs, common to multiple events and springs with higher than allowable amounts of retained austenite. The aircraft manufacturer performed multiple quality audits throughout the supply chain for the spring manufacturing process and shared the results with the investigative team. 

Additional Information

On March 1st, 2017, Embraer released a retrofit letter, in conjunction with service bulletins for the E170/175 and E190/195 fleet. The letter addressed an inspection and possible replacement of the NLG downlock springs manufactured from certain material batches.


NTSB Identification: ENG17IA005
Scheduled 14 CFR Part 121: Air Carrier operation of SKYWEST AIRLINES INC
Incident occurred Sunday, December 04, 2016 in San Antonio, TX
Aircraft: EMBRAER ERJ170 200LR, registration: N161SY
Injuries: 1 Minor, 54 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft incident report.

On December 04, 2016, about 1453 central daylight time, N161SY, an Embraer ERJ170 200L, operated by SkyWest Airlines, experienced a collapse of the nose landing gear during rollout after landing on runway 4 at the San Antonio International Airport (KSAT), San Antonio, TX. The aircraft was originally scheduled to land at General Mariano Escobedo Int'l Airport (MMTY), Monterrey, Nuevo Leon, Mexico. However, after departure from the George Bush Intercontinental Airport (KIAH), Houston, Texas the crew heard a loud "thud/pop" just aft of the flight deck. Because no warnings or indications were displayed on the flight deck, the crew decided to proceed to MMTY. When the landing gear was extended on approach, the crew received warning indications regarding the landing gear position and a "LDG GEAR LEVER DISAGREE" message. The crew declared a missed approach, retracted the landing gear per the quick reference handbook (QRH) procedures, and elected to divert to KSAT. Upon entering US airspace, the crew declared an emergency and performed a flyby of the control tower to verify landing gear position. The tower confirmed that the gear appeared to be in the down position. After touchdown on runway 4, during the landing rollout the nose gear collapsed as the aircraft slowed to a stop. The crew and passengers evacuated the aircraft from the aft cabin doors via the evacuation slides. During the aircraft recovery, a failed downlock spring was found impeding the downlock operation of the nose landing gear. The downlock springs from the nose landing gear have been retained by the NTSB for further examination. The airline transport pilot and passengers was not injured. The airplane sustained minor damage. The flight was conducted under the provisions of 14 Code of Federal Regulations Part 121. Visual meteorological conditions prevailed and a Federal Aviation Administration (FAA) flight plan had been filed for the flight.

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