Northwest Airlines Flight 08
Airbus A330-323 · Incident: flight instrument malfunction/failure en route
From Hong Kong to Tokyo
Event
- NTSB case
- DCA09IA064
- 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
- Instrument Meteorological Cond
Airbus A330-323
- Aircraft type
- Airbus A330
- 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
- N805NW
- Operator
- Northwest Airlines
- Onboard fatalities
- Unknown
- Route
- From Hong KongTo Tokyo
- 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
- Non-U.S., Commercial
- 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
- En route · cruise
- 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
- Flight instrument malfunction/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
- Aircraft › Aircraft systems
Approximate · Estimated position: the centre of Kagoshima, the place the record names. Not the accident site.
NTSB narrative
Both aircraft were in normal cruise flight at high altitude, in the vicinity of convective weather conditions, and both flight crews were aware of the weather. Crew statements and recorded data for both flights did not indicate any airplane anomalies prior to the events. Shortly before the unreliable airspeed events, each airplane encountered a visible effect of the weather conditions, the Northwest crew reported seeing moderate rain and hail, and the TAM crew reported an abrupt temperature change and St. Elmo’s Fire. Within seconds both airplane’s autopilot and autothrust disconnected, master warnings and cautions were indicated, primary airspeed display was lost or fluctuated, and the airplanes transitioned into Alternate Flight Law. According to Airbus documentation and analysis, if an airspeed discrepancy of more than 20kts or an altitude discrepancy of more than 400ft is detected between one ADR and the two others, the subject ADR is rejected. Then if a discrepancy occurs between the two remaining ADR, all auto flight functions are lost and autopilot, flight director, and autothrust disconnect. Applicable procedures for both airplanes call for autopilot and autothrust to be OFF, and for the pilot to pitch to 5 degrees and set thrust levers to the CLB detent. Both flight crews turned the airplanes to exit the weather area and the airspeed indications returned to normal within a short time.
The behavior of the airplane systems is consistent with, and supports a brief and temporary blockage of two or more pitot probes likely by an accretion of ice crystals aloft. Existing airplane flight manual/QRH procedures were sufficient to prevent a dangerous situation from occuring, however the airplane would, as designed, be operating in a lower level of automation. The autopilot disengaged automatically as intended due to its airspeed monitoring function. The flight crew’s attempt to reengage the autopilot during the unreliable airspeed event, and erroneous altitude reading, followed by pilot side stick inputs, exacerbated the altitude excursion experienced by the TAM flight, however the airplane was not actually in danger of a stall.
Probable cause
Brief and temporary blockage of the pitot probes in cruise flight, most likely due to ice crystals aloft, leading to erroneous airspeed indications and airplane automation degradation as designed.
Contributing to the incidents were design features of the Thales AA probes which left them more susceptible to high altitude ice crystal icing than other approved pitot probe designs.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record DCA09IA064
- Event ID
- 20090706X72654
- Case number
- DCA09IA064
- 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: investigation status, 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: 0c6c13d9ed5f85f8c4e60625e680ecd3e8872afaf7ccc38fbc248f1c12671609; retrieved 2026-09-15T11:41:26.897Z.