FTW95LA170

The approach briefing, radios, instruments, and speed bugs were set up for a planned landing on runway 17R. The first officer, who was flying, inadvertently aligned the airplane with runway 17L and the flight was subsequently cleared to land on that runway. At 500 feet AGL, the glideslope aural warning sounded. At 100 feet, the ground proximity warning system's sink rate warning sounded, and the first officer added power. At 50 feet and over the runway threshold, airspeed deteriorated. The first officer applied additional power and the captain added maximum thrust and forward control yoke pressure. According to the crew, 'a hard landing was made.' A review of control tower tapes revealed the winds varied from 180 to 200 degrees and 10 to 27 knots. Moments before the flight landed, another landing airplane reported a 10-knot loss of airspeed at 100 feet. The airplane sustained damage to the pressure vessel and structural stringers.

On April 13, 1995, at 2226 mountain daylight time, a Boeing 737-4Y0, EI-CEU, was substantially damaged during landing at Denver, Colorado. There were no injuries to the 141 passengers, 4 cabin attendants, and two cockpit crewmembers aboard. Visual meteorological conditions prevailed.

The airplane was being operated by MarkAir, Inc., as flight 523, scheduled domestic passenger service from Kansas City, Missouri, to Denver, Colorado. According to a joint written statement submitted by the captain and the first officer, the flight proceeded uneventfully and the approach briefing, radios, instruments, and speed bugs (Vref, 136 KIAS; target speed, 145 KIAS; Vref+15, 151 KIAS, based on a landing weight of 112,000 pounds) were set up for a planned landing on runway 17R. The first officer was flying the airplane.

After the airplane had been positioned on the downwind leg, the crew was offered the option of landing on runway 16. This was accepted but when told they could expect a delay to that runway, they requested and were cleared for a visual approach to, and landing on, runway 17R.

ATIS (automatic terminal information service) indicated the winds to be from 190 degrees at 18 knots. A surface weather observation in effect at the time indicated the winds were from 180 degrees at 19 knots. The first officer, who was flying the airplane, lined up with runway 17L and when the mistake was realized, they requested and were cleared to land on runway 17L. This paragraph is based on the crew's enclosed statement. The airport was visible to the crew. The lights for runway 17L were set on high intensity; the lights for runway 17R were not visible. The airplane was aligned with the visible runway lights: PAPI (precision approach path indicator) lights and glideslope indications agreed with each other. When there was no localizer capture, the crew realized they were lined up with runway 17L. The flight was subsequently cleared to land on runway 17L. At 500 feet AGL (above ground level), the glide slope aural warning sounded and was cancelled because the radios had been tuned to the navaids serving the parallel runway. At 100 feet AGL, the GPWS (ground proximity warning system) sink rate warning sounded, and the first officer added power. At 50 feet AGL and over the runway threshold, airspeed deteriorated. The first officer applied additional power and the captain added maximum thrust and forward control yoke pressure. "A hard landing was made."

During its preflight inspection, the relief flight crew noticed damage to the airplane that included a compromised pressure vessel, a crushed tail skid, breaches in the skin with associated stringer damage, and a collapsed right main landing gear strut. The crew flying "did not suspect any external damage to the aircraft until arriving at the gate and being told by ground personnel."

The data from the airplane's digital flight data recorder (DFDR) was read out and evaluated. According to the group chairman's factual report, vertical acceleration spiked at 3.64 g's when the airplane contacted the runway. The report added that due to accelerometer characteristics and DFDR sampling rate, this value could be greater or less that the actual g's incurred. The factual report and the DFDR Data in Graphical Format are attachments to this report. Data supporting these documents are on record with the Safety Board's Office of Research and Engineering.

A review of the control tower audio tapes revealed the following (all times are approximate):

2218:41 Frontier 706, cleared to land, runway 17R. Wind 190 degrees at 16 knots.

2221:50 United 776, cleared to land, runway 16. Wind 190 degrees at 10 knots.

2222:01 MarkAir 523, cleared to land, runway 17R. Wind 200 degrees at 18 knots. Wind check for runway 16 approach end, wind 190 degrees at 25 knots.

2222:36 UPS 841, cleared for takeoff, runway 17R. Wind 200 degrees at 18 knots.

2223:37 Wind check, 190 degrees at 27 knots. Runway 17R, wind 200 degrees at 20 knots.

2224:12 United 358, cleared to land, runway 16. Wind 180 degrees at 25 knots.

2225:06 Cactus 491, cleared to land, runway 16. Wind 180 degrees at 25 knots.

2225:40 MarkAir 523, you're lined up with runway 17L. Cleared to land, runway 17L.

2225:49 United 776 reports a 10 knot loss of airspeed at 100 feet.

2226:23 Cactus 491 advises it will be "real careful."

2226:38 United 242, cleared for takeoff, runway 17R. Wind 200 degrees at 18 knots.

2227:02 MarkAir 523 is given initial taxi instructions.

The following is a portion of the recorded ATIS (automatic terminal information service) in effect at the time of the incident:

Denver International Airport, Automated Weather Arrival, Information Alpha, zero three five five zulu, temperature five five, dew point three zero, wind one eight zero at one niner, altimeter two niner eight five...