Fokker F.28 MK 4000 incident near Spokane, Washington, April 1, 1999
On April 1, 1999 at about 3:43 am local time, a Fokker F.28 MK 4000, registered N477AU, was involved in an incident near Spokane, Washington. It was a flight of an unrecorded kind under scheduled airline rules (Part 121). No one was hurt; 44 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
A chafed hydraulic line.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- April 1, 1999 · about 3:43 am local time
- Place
- Spokane, Washington · map
- Type
- Incident
- Injuries
- No one was hurt; 44 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Fokker F.28 MK 4000 F.28 MK 40
- Registration
- N477AU · no longer on the register · serial 11226
- Damage
- Not recorded
- Flight
- Flight of an unrecorded kind · scheduled airline rules (Part 121)
The NTSB's narrative final · quoted from the NTSB record
The flight crew reported that, while in cruise flight, the number 1 hydraulic (utility) fluid quantity dropped below the low red mark on the gauge. The flight crew switched to the secondary hydraulic system and diverted to a nearby airport, where a landing was made without incident. Maintenance personnel inspected the aircraft and found a hydraulic line to the flap drive motor was chafed through and leaking. The flight crew reported that this was the second time that day that the number 1 hydraulic system fluid level had dropped. Prior to the last departure, maintenance personnel had serviced the system with hydraulic fluid. On that occasion, the flight crew ran the engines and cycled the flight controls while maintenance personnel looked for leaks. No leaks were found and the aircraft departed on the next leg of the scheduled flight.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: airline transport pilot, flight instructor, commercial pilot
- Ratings: multi-engine land; single-engine land; instructor: airplane multi-engine; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane; rotorcraft: glider
- Flight time: 11,000 hours in all; 1,100 in this make and model
- Medical certificate: Class 1 (valid medical--w/ waivers/lim.)
- Seat: left
The aircraft
- Last inspection: continuous airworthiness programme
- Maximum gross weight: 71,000 lb
- Seats: 69
- Landing gear: retractable
- Engine: (type not recorded); 0 hours total
- Operator: Horizon Air
The flight
- Departed from: BIL Billings MT at 2:28 am
- Destination: SEA Seattle WA
- Flight plan: IFR
- Runway 0
- A second pilot was aboard
Weather at the time
- Light: night, dark
- Wind: from 340° at 7 knots
- Visibility: 10 statute miles
- Sky: broken clouds at 18,000 ft; not recorded
- Temperature: 37°F (3°C), dew point 21°F (-6°C)
- Altimeter: 29.00 inHg
- Observation at 3:56 am from GEG, 40 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 4 | |||
| Passengers | 40 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.