ASN Wikibase Occurrence # 362161
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| Date: | Friday 23 April 1993 |
| Time: | 21:20 LT |
| Type: |  Boeing 737-522 |
| Owner/operator: | United Airlines |
| Registration: | N905UA |
| MSN: | 25005/1976 |
| Year of manufacture: | 1991 |
| Engine model: | GE CFM-56 |
| Fatalities: | Fatalities: 0 / Occupants: 133 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | Denver, CO -
 United States of America
|
| Phase: | Approach |
| Nature: | Unknown |
| Departure airport: | San Antonio, TX (KSAT) |
| (KDEN) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
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.
Probable Cause: 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.
Accident investigation:
 |
|
Sources:
NTSB DEN93IA044
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 17-Mar-2024 18:27 | ASN Update Bot | Added |
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