Southwest B737 at Chicago on Apr 26th 2011, runway excursion on landing

Last Update: June 12, 2012 / 13:09:11 GMT/Zulu time

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Photo of Southwest Airlines C-GAQZ, Boeing 737-700 — Southwest Airlines C-GAQZ, Boeing 737-700 (Photo credit: abdallahh / Flickr / License: CC by)

Incident Facts

Date of incident
Apr 26, 2011

Cause
Runway excursion

Airline
Southwest Airlines

Aircraft Registration
C-GAQZ

Aircraft Type
Boeing 737-700

ICAO Type Designator
B737

The NTSB released their final report concluding the probable cause of the incident was:

The flight crew's delayed deployment of the speedbrakes and thrust reversers, resulting in insufficient runway remaining to bring the airplane to a stop.

Contributing to the delay in deployment of these stopping devices was the flight crew's inadequate monitoring of the airplane's configuration after touchdown, likely as a result of being distracted by a perceived lack of wheel braking effectiveness.

Contributing to the incident was the flight crew's omission of the Before Landing checklist, which includes an item to verify speedbrake arming before touchdown, as a result of workload and operational distractions during the approach phase of flight.

The NTSB reported the crew was advised to enter a holding as there were delays in the Chicago area due to weather and traffic congestion. ATC subsequently advised they could accept a RNP (RNAV RNP Y 13C) approach to runway 13C, the crew however mistakenly selected and briefed a different procedure, RNAV GPS (RNAV GPS Z) approach to runway 13C. While in the hold the crew assessed the landing distance available and correctly assessed the runway was sufficiently long for landing.

When the aircraft was released from the holding and received approach instructions the crew was confused and discussed the instructions amongst them, the confusion most likely resulting from selecting the incorrect approach procedure. The crew finally identified the mistake, found the correct approach chart and reprogrammed the FMS to the correct RNP approach procedure and amended some of the crossing altitudes in order to follow ATC instructions. The NTSB commented that this added workload to the crew.

After selecting flaps to 15 degrees the preceding arrival reported fair braking action on the runway, the crew heard that report and re-assessed the landing distance required and (correctly) found the landing distance available still sufficient. The crew adjusted autobrakes accordingly.

When the crew intended to set flaps to 25 degrees, the airspeed was too high, requiring the airspeed to decay further before flaps could be set to 25 degrees resulting in another distraction due to the flap overspeed. A rain showed passed over the aerodrome needing further assessments, and the minimum descent altitude was still incorrectly set and needed to be adjusted.

The flap overspeed occurred at a time the crew would normally have processed the "Before Landing" checklist, which included the "Speedbrakes - armed" task. The NTSB commented that the "Before Landing" checklist was not heard on the cockpit voice recorder and no mention of the speedbrakes. The flight data recorder indicated the speedbrakes remained not armed.

Shortly after setting the flaps to 25 the crew selected the flaps to 30 and 40 degrees.

The aircraft touched down within 500 feet past the runway threshold at 136 KIAS/ 143 knots above ground with 5600 feet of runway remaining, the captain perceived lack of deceleration assuming lack of brakes effectiveness and applied full manual braking. Speedbrakes did not deploy upon touchdown, the thrust reversers were not deployed. About 16 seconds after touchdown the thrust reversers were deployed which also deployed the speedbrakes per system design, at that point 1500 feet of runway were remaining. When the aircraft came close to the end of pavement the captain attempted to steer the aircraft onto the last taxiway to the left but was unable. The aircraft exited the runway at 30 knots above ground, both engines at or near maximum reverse thrust, spoilers deployed and brakes pressure at 3000 psi, the aircraft rolled onto grass and came to a stop 180 feet off paved surface and north of the runway's EMAS.

The crew subsequenty ascertained there was no fire, advised tower they were in the grass and announced passengers should remain in their seats. The passengers subsequently disembarked via mobile stairs.

The right hand engine ingested a taxiway light, the thrust reverser and inlet cowls were damaged. Two fan blades of the left engine were bent, the left and right hand flaps sustained aft damage, the NTSB analysed the damage did not meet the criteria for "substantial" however.

The captain (50, ATPL) had 10,500 hours of total experience with 7,000 hours in command, 7,000 hours on type with 5,000 hours in command on type. The first officer (50, ATPL) had 17,000 hours total with 7,000 hours on type.

The flight data recorder showed the aircraft performed as expected and per configuration. The speedbrakes were never armed or deployed by crew action, but deployed after thrust reverser selection as per system design. Extending the speed brakes would reduce lift and thus increase weight on wheels increasing brakes effectiveness, the lack of speedbrakes deploying caused a loss of 60% braking effectivity.

Analysis determined the aircraft would have stopped with 900 feet of runway remaining had the speedbrakes been armed and had they deployed upon touchdown, and with 1950 feet of runway remaining had speedbrakes and thrust reversers been deployed upon touchdown.