DEN05IA076

NTSB incident investigation · Boeing 737-322 · Denver, CO · May 17, 2005

Incident · No injuriesIncident investigationFinal report
Date
May 17, 2005, 08:56 local (14:56 UTC)
Place
Denver, CO
Injuries
187 uninjured
Phase of flight
Taxi
Aircraft
N305UABoeing 737-322N373UABoeing 737-322
Weather
Visual (VMC) · Day
Status
Completed · report October 27, 2005
Report
Approved by Office Director
Parties
Denver, Colorado
Case key
61512

From the NTSB’s public API. By law, NTSB reports can’t be used as evidence in lawsuits over the incident.

On this page

Probable cause

the improper use of procedure used by the ground personnel resulting in the right wing of the aircraft colliding with the left wing of another aircraft. A factor in this incident was the failure to maintain clearance by the flight crew of the other aircraft.

the pilot's failure to maintain clearance resulting in the left wing of the aircraft striking the right wing of an adjacent aircraft. A factor in this incident was the improper procedure performed by the ground crew (of the second aircraft involved).

Sequence of events

NTSB’s coding before 2008: each occurrence and phase of flight, and the causes and factors under it. The codes are defined in NTSB’s coding manual.

On ground/water collision with objectTaxi - to takeoff
Improper use of procedureGround personnelFactor
Clearance - not maintainedPilot in commandCause
Object - aircraft parked/standing
On ground/water collision with objectTaxi - pushback/tow
Improper use of procedureGround personnelFactor
Clearance - not maintainedFlightcrew of other aircraftCause
Object - aircraft moving on ground

Analysis

The two Boeing 737 company aircraft were involved in a ground collision while on the ramp. The first airplane, N305UA, was pushed straight back from its gate via a tug and wing walker. The airplane was disconnected from the tug and its engines were running. The pilots received hand signals from the tug operator releasing them from his guidance. The second airplane, N373UA, was being pushed back an adjacent gate via a tug and wing walker. The wing walker, who was positioned at the front of the right wing, stopped the pushback. The wing walker and tug operator had a brief discussion which resulted in the tug operator pulling the aircraft back toward the gate. The pilots of the first airplane visually cleared the area and began to taxi by turning to the west. During the turn, the left wing tip of the first airplane struck the right wing tip of the second company airplane.

The two Boeing 737 company aircraft were involved in a ground collision while on the ramp. The first airplane, N305UA, was pushed straight back from its gate via a tug and wing walker. The airplane was disconnected from the tug and its engines were running. The pilots received hand signals from the tug operator releasing them from his guidance. The second airplane, N373UA, was being pushed back an adjacent gate via a tug and wing walker. The wing walker, who was positioned at the front of the right wing, stopped the pushback. The wing walker and tug operator had a brief discussion which resulted in the tug operator pulling the aircraft back toward the gate. The pilots of the first airplane visually cleared the area and began to taxi by turning to the west. During the turn, the left wing tip of the first airplane struck the right wing tip of the second company airplane.

Factual narrative

See narrative for DEN05IA076A.

On May 17, 2005, at 0856 mountain daylight time, a Boeing 737-322, N305UA, operated by United Air Lines, flight 229, sustained minor damage when it collided with N373UA, another Boeing 737-322 operated by United Air Lines, flight 424, while taxiing at Denver International Airport (DEN), Denver, Colorado. Visual meteorological conditions prevailed at the time of the incident. Both flights were being conducted with instrument flight rules flight plans under the provisions of 14 CFR Part 121. The 2 pilots, 3 flight attendants, and 120 passengers aboard flight 229 and the 2 pilots, 3 flight attendants and 57 passengers aboard flight 424 were not injured. The flights were originating at the time of the accident, and were en route to San Jose, California and Minneapolis Minnesota respectively.

N305UA had completed a straight pushback from gate B19 via a tug and wing walker. The airplane was disconnected from the tug and its engines were running. The pilots received hand signals from the tug operator releasing them from his guidance. N373UA was being pushed back from gate B21 via a tug and wing walker. The wing walker, who was positioned at the front of the right wing, stopped the pushback. The wing walker and tug operator had a brief discussion which resulted in the tug operator pulling the aircraft back toward the gate. The pilots of N305UA visually cleared the area and began to taxi by turning to the west. During the turn, the left wing tip of N305UA struck the right wing tip of N373UA. N373UA was positioned a reported "5 to 10 feet too far west" at the time of the accident.

Post-accident inspection by airline maintenance personnel revealed that the left wingtip of N305UA and the right wingtip of N373UA had scratches, dents, and broken navigation lights and lenses. There was no structural damage found to either aircraft.

Aircraft · 2

Registration
N305UA
Reported as
Boeing 737-322
Category
Airplane
Serial number
23666
Airframe hours
53,316
Engines
General Electric CFM56-3-C1, 20,000 lbs thrust, turbo fanGeneral Electric CFM56-3-C1, 20,000 lbs thrust, turbo fan
Damage
Minor damage
Flight
Part 121
Registered owner
United Air Lines
Airworthiness certificate
Standard, Transport
Departed
DEN · Denver, CO
Destination
SJC · San Jose, CA
Flight plan
IFR
Airport
DEN · Denver International Airport

Matched to the registry by N-number and the event date; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.

Registration
N373UA
Reported as
Boeing 737-322
Category
Airplane
Serial number
24638
Airframe hours
45,202
Engines
General Electric CFM56-3-C1, 20,000 lbs thrust, turbo fanGeneral Electric CFM56-3-C1, 20,000 lbs thrust, turbo fan
Damage
Minor damage
Flight
Part 121
Registered owner
Wilmington Trust Co.
Airworthiness certificate
Standard, Transport
Departed
DEN · Denver, CO
Destination
MSP · Minneapolis, MN
Flight plan
IFR
Airport
DEN · Denver International Airport

Matched to the registry by N-number and the event date; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.

Flight crew · 4

As NTSB recorded them. NTSB leaves out names.

Role
Pilot, aircraft N305UA
Age
45
Injuries
None
Certificate
Airline transport
Airplane ratings
Multi-engine land
Instrument ratings
Airplane
Medical
Class 1, Without waivers/limitations
Last flight review
October 1, 2004
Seat
Left
Flight hours
6,192 in this make and model
Role
Co-pilot, aircraft N305UA
Age
50
Injuries
None
Certificate
Airline transport
Airplane ratings
Multi-engine land
Instrument ratings
Airplane
Medical
Class 1, Without waivers/limitations
Seat
Right
Flight hours
5,766 in this make and model
Role
Pilot, aircraft N373UA
Age
45
Injuries
None
Certificates
Flight engineer, Flight instructor, Airline transport
Airplane ratings
Multi-engine land, Single-engine land
Instrument ratings
Airplane
Medical
Class 1, Without waivers/limitations
Last flight review
September 1, 2004
Seat
Left
Flight hours
7,361 in this make and model
Role
Co-pilot, aircraft N373UA
Age
39
Injuries
None
Certificates
Flight engineer, Airline transport
Airplane ratings
Multi-engine land
Instrument ratings
Airplane
Medical
Class 1, Without waivers/limitations
Last flight review
July 1, 2004
Seat
Right
Flight hours
5,323 in this make and model

Weather

Conditions
Visual (VMC) · Day
Wind
220° at 12 knots
Visibility
10 statute miles
Lowest ceiling
13,000 ft broken
Temperature
66 °F, dew point 34 °F
Altimeter
29.51 inHg
Observed at
DEN

Other investigations on N305UA · 2

Matched to the same aircraft by N-number and date.