Horizon Air Flight 4339
Canadair CL-600-2C10 · Incident: airframe, component or system failure on approach
From Ontario International Airport (ONT) to Denver International Airport (DEN)
Event
- NTSB case
- DEN04IA060
- 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
- Incident
- 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
- Airline
- 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
Canadair CL-600-2C10
- Aircraft type
- Canadair CL-600
- 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
- N609QX
- Operator
- Horizon Air
- Onboard fatalities
- Unknown
- Route
- From Ontario International Airport (ONT), Ontario, CATo Denver International Airport (DEN), Denver, CO
- Aircraft age
- Not recorded
- 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 121: Air Carrier
- 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
- First occurrenceThe 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
- Airframe, component or system failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- None
Cause areas
- Hydraulic system, pump › Failure, total
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The captain reported that while in cruise flight at flight level 330, the crew received a master caution light and a hydraulic system 1 low pressure along with warning lights for the outboard ground spoilers, outboard spoilerons, and the outboard spoilers. The hydraulic fluid quantity and fluid temperature readings were good, but the system pressure was dropping. The crew ran the emergency checklist and continued their flight to Denver, using the backup (1B) system. On final approach and landing, the captain reported that they lost number 1 system pressure and quantity. The crew shut off the 1B system and continued to land. After landing, the crew shut down the number one engine and taxied to the gate. A post-incident examination of the airplane's number 1 hydraulic system showed that the hydraulic pump had come apart internally and seized. Metal fragments were found in the hydraulic filters and lines. Further examination of the hydraulic pump showed that several piston shoes in the pump's hanger and piston subassembly had come apart. The resulting metal fragments subsequently caused damage to the hold-down plate, the hanger, and other internal components of the pump, resulting in its seizure.
Probable cause
The total failure of the airplane's number 1 system hydraulic pump.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record DEN04IA060
- Event ID
- 20040413X00454
- Case number
- DEN04IA060
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
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: investigation status, coordinates, damage. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 12bb037aae6997e0d9a42448723d70e1bae87b0f122154e7737747bc945c9c19; retrieved 2026-09-18T15:27:28.603Z.