Air Canada Flight 791
Airbus Industrie A320-211 · Incident: system/component malfunction/failure (non-power) en route
From Toronto Pearson International Airport (CYYZ) to Los Angeles International Airport (LAX)
Event
- NTSB case
- CEN11IA649
- 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
Airbus Industrie A320-211
- Aircraft type
- Airbus A320
- 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
- C-FGYL
- Operator
- Air Canada
- Onboard fatalities
- Unknown
- Route
- From Toronto Pearson International Airport (CYYZ), TorontoTo Los Angeles International Airport (LAX), Los Angeles, CA
- 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 129: Foreign
- 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
- 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
- Minor
Cause areas
- Aircraft › Aircraft structures
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The first officer's (FO) windshield cracked during cruise flight. The crack subsequently progressed into multiple multidirectional cracks that obscured the FO’s view through the window. The flight crew was unable to determine the severity of the cracks and diverted without further incident. A postincident examination of the windshield revealed an area of arcing located along the electrical bus bar at the lower edge of the windshield, near the forward corner. This location coincided with the area in which the power and sensing element wires were routed around the structural glass plies. The area of arcing was surrounded by a cloudy and degraded interlayer, which was consistent with the presence of moisture. A section of the moisture seal was worn and appeared to have been repaired, resulting in moisture ingress. The moisture degraded the interlayer and electrical system resulting in a discontinuity that led to electrical arcing and failure of the heating system causing the windshield cracking. The latest windshield revisions, with part numbers NP-165331-1/-2, are available and include enhancements that reduce the potential for moisture ingress and its subsequent effects on the electrical system.
Probable cause
The infiltration of moisture into the windshield heating layer that induced arcing in the heating system that subsequently cracked the windshield.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CEN11IA649
- Event ID
- 20110917X35742
- Case number
- CEN11IA649
- 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. 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: 6cb238540ceba842cf60d3cf8cde2c24b633cfef6b73f4bd8300ee211fc38508; retrieved 2026-09-15T16:44:59.927Z.