Incident Overview
On May 4, 2009, at 1218 Mountain Daylight Time, an Airbus A320-211, registration N311US, operated by Northwest Airlines as flight 557, sustained a tailstrike during landing on runway 16L at Denver International Airport (DEN). The aircraft had departed from Minneapolis-St. Paul Airport at 1139 Central Daylight Time. The approach was visual, and the first officer was the pilot flying. The crew reported a stable approach at 1,000 feet above the runway threshold. The autopilot was disengaged at approximately 750 feet above touchdown, with auto-thrust and flight directors engaged. During the approach, the aircraft experienced a tailwind component that increased from about 7 knots to approximately 11 knots.
As the airplane passed about 50 feet above touchdown, the rate of descent was around 800 feet per minute. The first officer initiated the flare at about 45 feet and used larger-than-normal aft stick deflection to arrest the sink rate. During the flare, the automated “retard” call-out activated three times, but the thrust levers remained in the climb detent. The aircraft touched down on the main landing gear with a vertical load of 1.56 G. At initial touchdown, the thrust levers were still in CLB, and engine N1 increased from approximately 54% to 64%.
The aircraft then bounced. The first officer held full aft stick input and moved the thrust levers to idle during the bounce. Ground spoilers deployed, and the aircraft touched down a second time in an 11-degree nose-up attitude. The captain began adding nose-down stick input, but the pitch attitude increased to about 12.5 degrees nose up, exceeding the maximum pitch-up angle with gear compressed specified in the Airbus FCOM. A “dual input” call-out was recorded, and a loud bang was heard. As the captain’s input increased forward and the first officer relaxed back pressure, the nose wheel touched down. Thrust reversers and autobrakes were engaged, and the rollout was normal.
Injuries and Damage
Four flight attendants reported minor injuries. No other injuries were reported among the three flight crew and 147 passengers. The aircraft sustained substantial damage: heavy abrasions, dents, and perforations of the skin along the lower rear fuselage between frames 62 and 76. The aft galley drain mast, two antennas, and the APU air intake were damaged. The rear pressure bulkhead was buckled and cracked, and frame 70 had a crack and abrasions. Interior damage included minor frame deformation and damage to stringers, frame clips, fasteners, floor support strut fittings, and flange.
Flight Crew Information
The captain, age 49, had 14,619 total flight hours, with 2,677 hours as pilot-in-command on the A320. He held an Airline Transport Pilot certificate with type ratings in A320 and DC9. The first officer, age 48, had 5,901 total flight hours, with 200 hours in the A320. He held an Airline Transport Pilot certificate with type ratings in A320, DC-9, B707, and B720. An observer pilot was seated in the cockpit but was not performing any required duties.
Aircraft Information
The aircraft, manufacturer serial number 0125, was equipped with CFM56-5A1/F engines. It had approximately 57,600 total airframe hours. No relevant maintenance issues were recorded. At the time of the accident, the estimated landing weight was 140,000 pounds, and the center of gravity was within limits.
The aircraft was not equipped with an automated “pitch pitch” tailstrike warning feature available on some A320 and A321 models. The “dual input” feature had been recently incorporated, and a related Flight Operations bulletin was published.
Meteorological and Airport Information
The weather observation at 11:53 MDT reported winds from 240 degrees at 4 knots, visibility 10 miles, scattered clouds at 8,000 and 10,000 feet, and broken clouds at 20,000 feet. At 12:53 MDT, winds shifted to 330 degrees at 13 knots gusting to 17 knots. Doppler radar indicated some returns at 700 feet moving west to east at about 30 knots. Runway 16L at Denver International Airport is 12,000 feet long and 150 feet wide, with precision instrument markings and a 3-degree glide path. The runway was dry.
Recorded Data
The Digital Flight Data Recorder and Cockpit Voice Recorder were undamaged and provided valid data. The CVR recorded the “retard” and “dual input” call-outs but no automated tailstrike warning. Toxicological tests for the flight crew were negative.