WPR18LA215 · Cessna T337 G
Northern Air Cessna T337 G · Accident: system/component malfunction/failure (non-power) on approach
From Lewiston Nez Perce County Airport (LWS) to Lewiston Nez Perce County Airport (LWS)
Event
- NTSB case
- WPR18LA215
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Cessna T337 G
- Aircraft type
- Cessna 337
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N255
- Operator
- Northern Air
- Onboard fatalities
- Unknown
- Route
- From Lewiston Nez Perce County Airport (LWS), Lewiston, IDTo Lewiston Nez Perce County Airport (LWS), Lewiston, ID
- Aircraft age
- About 43 years (built 1975)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Approach
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- System/component malfunction/failure (non-power)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft systems
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The pilot reported that he was returning to the airport after an uneventful aerial survey flight. When the pilot extended the landing gear, the system began operating but the gear did not extend. Multiple efforts to extend the gear, including assistance by the passenger and coordination with his company's maintenance personnel, were unsuccessful. The pilot then burned off excess fuel and conducted a gear-up landing at the airport. The airplane sustained substantial damage to the lower fuselage.
Postaccident examination of the airplane revealed that two main landing gear door actuators had hyperextended and allowed all hydraulic fluid to be lost. Detailed examination indicated that the right actuator had hyperextended in flight, while the left one hyperextended due to landing gear door runway contact during the gear-up landing. The actuator rod in each actuator was normally travel-limited and contained by a single internal snap ring, which acted as the mechanical stop and retention device for the rod inside the actuator cylinder. For undetermined reasons, the snap ring was liberated from its groove in the right actuator, which allowed the actuator rod to travel beyond its normal limit, which resulted in the loss of hydraulic fluid and operational failure of the landing gear. Postexamination reassembly and testing of the landing gear system indicated that the hyperextended actuators were the only mechanical deficiencies in the system.
The airplane manufacturer's maintenance manual specified the replacement of the snap rings (retainers) upon rebuild of the actuator. According to the airplane maintenance records, all three main landing gear door cylinders (actuators) were rebuilt with new "O-rings" about 4 years before the accident. The entry did not cite any additional details about the rebuilds, including whether new internal snap rings were installed. Discussions with the operator's director of maintenance indicated that the snap rings likely were not replaced during the actuator rebuild.
Review of industry documents revealed other occurrences of snap ring liberation and consequent landing gear system problems in this model airplane, and at least two different hardware options to prevent recurrence were available. One incorporated a new-design actuator that eliminated the accident failure mode, and one involved elimination of the subject actuators from the airplane. The operator reported that this modification was installed on the accident airplane when it was repaired after the accident. Either option would ensure against a recurrence of this accident scenario.
Probable cause
The liberation of an internal snap ring from a landing gear door actuator, which resulted in a complete loss of hydraulic fluid and a gear-up landing. Contributing to the accident was the failure of maintenance personnel to replace the snap ring during the last rebuild of the actuator.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR18LA215
- Event ID
- 20180809X51217
- Case number
- WPR18LA215
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: local date, investigation status. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 2018-08-09.
- API snapshot SHA-256: 32103b0b742b6d5075284302d726d934696074b5baf962a87742e83021044f42; retrieved 2026-09-16T08:04:11.363Z.