Stapleton International Airport
Aircraft Accident/Incident Report

Denver, Colorado 80207
Friday, April 23, 1993 20:20 MDT

NTSB Narrative Summary Released at Completion of Accident

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.

NTSB Probable Cause Narrative

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.

Event Information

Type of Event Incident
Event Date 4/23/1993
Event Day of the Week Friday
Time of Event 2020
Event Time Zone Mountain Daylight Time
Event City DENVER
Event State COLORADO
Event Country --
Zipcode of the event site 80207
Event Date Year 1993
Event Date Month 4
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude
Event Location Longitude
Event Location Airport STAPLETON INTERNATIONAL
Event Location Nearest Airport ID DEN
Indicates whether the acc/inc occurred off or on an airport On Airport
Distance from airport in statute miles --
Degrees magnetic from airport --
Airport Elevation 5333
Weather Briefing Completeness Full
Investigator's weather source Weather Observation Facility
Time of the weather observation 2050 Mountain Daylight Time
Direction of event from weather observation facility (degrees) 0
Weather Observation Facility ID DEN
Elevation of weather observation facility 5333
Distance of event from weather observation facility (units?) 0
Time Zone of the weather observation MDT
Lighting Conditions Dusk
Lowest Ceiling Height 27000
Lowest Non-Ceiling Height 8500
Sky/Lowest/Cloud Conditions Scattered
Sky Condition for Lowest Ceiling Broken
Visibility Runway Visual Range (Feet) 0
Visibility Runway Visual Value (Statute Miles) --
Visibility (Statute Miles) 50
Air Temperature at event time (in degrees celsius) 15
Dew Point at event time (in degress fahrenheit) -7
Wind Direction (degrees magnetic) 360
Variable Wind Indicator Unknown
Wind Speed (knots) 10
Wind Velocity Indicator Unknown
Wind Gust Indicator Unknown
Wind Gust (knots) 16
Altimeter Setting at event time (in. Hg) 29
Density Altitude (feet) 5000
Intensity of Precipitation Unknown
METAR weather report --
Event Highest Injury None
On Ground, Fatal Injuries 0
On Ground, Minor Injuries 0
On Ground, Serious Injuries 0
Injury Total Fatal --
Injury Total Minor --
Injury Total None 133
Injury Total Serious --
Injury Total All --
Investigating Agency NTSB
NTSB Docket Number (internal use) 5032
NTSB Notification Source --
NTSB Notification Date Apr 24 1993 12:00AM
NTSB Notification Time 800
Fiche Number and/or location -used to find docket information IMAGE
Date of most recent change to record Dec 11 2000 1:14PM
User who most recently changed record dbo
Basic weather conditions Visual Meteorological Cond
FAA District Office --

Aircraft Involved

Aircraft #1

Aircraft Registration Number N905UA
NTSB Number DEN93IA044
Missing Aircraft Indicator N
Federal Aviation Reg. Part Part 121: Air Carrier
Type of Flight Plan filed IFR
Flight plan Was Activated? --
Damage None
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name BOEING
Aircraft Model 737-522
Aircraft Series Identifier 737-522
Aircraft Serial Number 25005
Certified Max Gross Weight 119800
Aircraft Category Airplane
Aircraft Registration Class U.S. Registered/U.S. Soil
Aircraft is a homebuilt? No
Flight Crew Seats --
Cabin Crew Seats --
Passenger Seats --
Total number of seats on the aircraft 133
Number of Engines 2
Fixed gear or retractable gear Retractable
Aircraft, Type of Last Inspection Unknown
Date of Last Inspection --
Airframe hours since last inspection --
Airframe Hours --
ELT Installed No
ELT Activated Unknown
ELT Aided Location of Event Site Unknown
ELT Type --
Aircraft Owner Name UNITED AIRLINES
Aircraft Owner Street Address P. O. BOX 66100
Aircraft Owner City ELK GROVE
Aircraft Owner State IL
Aircraft Owner Country
Aircraft Owner Zipcode 60666
Operator is an individual? --
Operator Name
Operator Same as Owner? Yes
Operator Is Doing Business As --
Operator Address Same as Owner? Yes
Operator Street Address
Operator City
Operator State
Operator Country
Operator Zip code
Operator Code UALA
Owner has at least one certificate Yes - certificate holder
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation Unknown
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not Scheduled
Indicates Domestic or International Flight Domestic
Operator carrying Pax/Cargo/Mail Passenger Only
Type of Flying (Per_Bus / Primary) Unknown
Second Pilot on Board Yes
Departure Point Same as Event No
Departure Airport Code SAT
Departure City SAN ANTONIO
Departure State TX
Departure Country
Departure Time 1903
Departure Time Zone MDT
Destination Same as Local Flt crash at destination city
Destination Airport Code DEN
Destination City
Destination State
Destination Country
Specific Phase of Flight Approach
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record Jan 2 2001 10:30AM
User who most recently changed record dbo
Since inspection or accident --
Event Location Runway Number and Location 26L
Runway Length 10004
Runway Width 150
Sight Seeing flight No
Air Medical Flight No
Medical Flight --