United Airlines Flight 724
Boeing 757-222 · Incident: airframe, component or system failure en route
From Seattle–Tacoma International Airport (SEA) to Denver International Airport (DEN)
Event
- NTSB case
- FTW98IA019
- 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
- 0
- 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
Boeing 757-222
- Aircraft type
- Boeing 757
- 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
- N581UA
- Operator
- United Airlines
- Onboard fatalities
- Unknown
- Route
- From Seattle–Tacoma International Airport (SEA), WATo 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
- En route · climb to cruise
- 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
- Minor
Cause areas
- Company maintenance personnel › Maintenance, replacement, improper
- Door, emergency exit › Not secured
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
As the airplane was rotated for liftoff from Seattle, the captain noticed that the EICAS (engine indication and crew alerting system) 'EMERGENCY DOOR' light had illuminated. According to the Airplane Fight Manual, if pressurization is normal (and it was), the crew need not take further action. During the descent for landing, a flight attendant said she heard a loud noise from the left side of the airplane. The airplane landed uneventfully at Denver. Inspection disclosed the left off-wing slide had separated from the airplane, causing minor damage to the access door, flap, and fuselage skin. The slide had been routinely replaced the previous evening by a mechanic using a flashlight and referencing the airplane maintenance manuals. After installing the slide, the mechanic closed the panel and placed the actuator handle in the horizontal position (as per instructions placarded on the maintenance access door). He said he had never received any training for installing the off-wing slide. There have been four similar incidents since the airplane entered commercial service, prompting the manufacturer to issue Service Bulletin (S.B.) 757-25-0182.
Probable cause
Maintenance personnel's failure to properly secure the left off-wing slide door after routine slide replacement, allowing an inflight separation of the slide. Factors were inadequate training of maintenance personnel and inadequate written instructions by the airplane manufacturer.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record FTW98IA019
- Event ID
- 20001208X08998
- Case number
- FTW98IA019
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (5)
- 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: d85b24602be1991da2eed3701382b2a5c7d32814710099cd97b823cc9d87e82a; retrieved 2026-09-18T17:20:26.362Z.
- The NTSB's operator name is blank for N581UA; the operator shown is the name the NTSB's other records give its FAA operator code, UALA.