Boeing 737-522 incident near Denver, Colorado, April 24, 1993
On April 24, 1993 at about 2:20 am local time, a Boeing 737-522, registered N905UA, was involved in an incident near Denver, Colorado (Stapleton International airport). It was a flight of an unrecorded kind under scheduled airline rules (Part 121). No one was hurt; 133 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
THE PILOT-IN-COMMAND'S FAILURE TO MAINTAIN ADEQUATE SEPARATION FROM THE BOEING 757, AND HIS FAILURE TO STAY ABOVE THE PROBABLE PATH OF THE BOEING'S WAKE VORTICES, WHICH RESULTED IN THE VORTEX ENCOUNTER. FACTORS RELATED TO THE ACCIDENT WERE: THE CROSSWIND, AND AN INADEQUACY IN ATC PROCEDURES CONCERNING VISUAL APPROACHES OF AIRCRAFT, BEHIND AND DOWNWIND FROM APPROACHES OF HEAVIER AIRCRAFT TO PARALLEL OR ADJACENT RUNWAYS.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- April 24, 1993 · about 2:20 am local time
- Place
- Denver, Colorado · Stapleton International · map
- Type
- Incident
- Injuries
- No one was hurt; 133 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Boeing 737-522 · all 737-522s on the register
- Registration
- N905UA · no longer on the register · serial 25005
- Damage
- Not recorded
- Flight
- Flight of an unrecorded kind · scheduled airline rules (Part 121)
The NTSB's narrative final · quoted from the NTSB record
ON A VISUAL APPROACH TO RUNWAY 26L, UNITED FLIGHT 409, A BOEING 737, EXPERIENCED AN UNCOMMANDED ROLL OF ABOUT 23 DEG AT AN ALTITUDE OF 882' AGL. THE CREW WAS ABLE TO CORRECT THE ROLL & MADE A GO-AROUND TO AN UNEVENTFUL SECOND APPROACH & LANDING. THE BOEING 737 WAS FOLLOWING A BOEING 757, WHICH WAS ON A VISUAL APPROACH TO RUNWAY 26R. THE TWO RUNWAYS WERE 900' APART FROM CENTERLINE TO CENTERLINE & THE THRESHOLD OF 26L WAS OFFSET ABOUT 1300' EAST OF 26R. ACCORDING TO DATA FROM THE FLIGHT RECORDER, THE WIND AT THE ONSET OF THE INCIDENT WAS FROM THE NORTHWEST AT 5 TO 10 KNOTS. THE SURFACE WIND WAS FROM 360 DEGREES AT 10 KNOTS. THE TWO AIRCRAFT WERE 1.32 NAUTICAL MILES APART IN AN OFFSET TRAIL POSITION. BOTH AIRCRAFT WERE ON 3 DEG GLIDE SLOPES. THE WAKE VORTICES HAD SETTLED ABOUT 100' & MOVED LATERALLY TOWARD THE GLIDE PATH OF 26L. WEATHER DATA SHOWED EVIDENCE OF POSSIBLE INTERACTION BETWEEN WAKE TURBULENCE FROM THE 757 & AN OUTFLOW BOUNDRY, WHICH WAS MOVING THROUGH THE AREA.
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, commercial pilot, flight engineer
- Ratings: multi-engine land; single-engine land; instrument: airplane
- Flight time: 8,428 hours in all; 1,731 in this make and model; 198 in the last 90 days; 73 in the last 30 days; 1,731 as pilot in command
- Medical certificate: Class 1 (valid medical--no waivers/lim.)
- Seat: left
The aircraft
- Last inspection: inspection type not recorded
- Maximum gross weight: 119,800 lb
- Seats: 133
- Landing gear: retractable
- Engine: Ge CFM-56 (turbofan); 0 hours total
The flight
- Departed from: SAT San Antonio TX at 1:03 am
- Destination: DEN
- Flight plan: IFR
- Runway 26L, 10,004 ft by 150 ft
- A second pilot was aboard
Weather at the time
- Light: dusk
- Wind: from 360° at 10 knots, gusting 16
- Visibility: 50 statute miles
- Sky: broken clouds at 27,000 ft; scat at 8,500 ft
- Temperature: 59°F (15°C), dew point 19°F (-7°C)
- Altimeter: 29.00 inHg
- Observation at 2:50 am from DEN
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 5 | |||
| Passengers | 128 |
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.