NTSB Factual Report

On March 27, 2008, at 1808 central daylight time, N23661, a Boeing 737-524 airplane, operated by Continental Airlines, sustained minor damage during the landing at George Bush Intercontinental Airport (KIAH), Houston, Texas. Visual meteorological conditions prevailed at the time of the incident. The scheduled domestic passenger flight was being operated under the provisions of Title 14 Code of Federal Regulations Part 121, on an instrument flight rules flight plan. The captain, first officer, three cabin crew, and 113 passengers were not injured. The cross-country flight departed from Will Rogers International Airport (KOKC), Oklahoma City, Oklahoma, at 1656.

According to the Pilot/Operator Aircraft Accident/Incident Report form submitted by Continental Airlines, the flight had departed KOKC with the knowledge that the anti-skid system was inoperative. The anti-skid system had been placarded inoperative and was included for flight permissions on the minimum equipment list (MEL). Prior to the flight and several times during the flight, the captain and first officer discussed the procedures to be utilized while operating the airplane with the anti-skid system inoperative. These procedures included utilizing minimal braking to avoid damaging a tire.

Prior to landing, the fight crew compensated their landing speed due to wind information reported and ensured that the auto brake system was off, as required by the checklist for an inoperative anti-skid system. Upon touchdown, the captain stated that he almost immediately felt a shudder. The captain suspected that they had a flat tire and took control of the airplane. The captain reported that he did not apply brakes during the event, as the airplane was slowing rapidly. He reported that he maintained runway centerline by utilizing the tiller. The airplane came to a stop towards the end of the runway and the flight crew and passengers disembarked from the airplane utilizing air stairs.

According to a Federal Aviation Administration (FAA) inspector who responded to the scene, the airplane touched down in the touchdown zone of runway 26R, and came to rest on the runway approximately 2,000 feet from the departure end of the runway. A small fire was noted on the right main gear and the Houston Aircraft Rescue Fire Fighting (ARFF) responded and extinguished the fire. An examination of the airplane revealed that all four main landing gear tires had blown. The landing gear wheels, brakes, and tires were secured for further examination.

The wheels, tires, and brakes were examined at Honeywell’s facility in Houston, Texas, on April 3, 2008. Each wheel and tire assembly was disassembled and examined. Wheel assembly three and four exhibited damage from extended contact with the runway. Tires one and two were "severely blown out throughout the entire circumference of the tire" with little tread area remaining. Tires three and four exhibited a flat spot where initial contact was made with the runway surface. An examination of the four brake assemblies revealed no anomalies aside from damage created by contact with the runway.

According to the 737 Flight Crew Operations Manual, when operating with the anti-skid inoperative, the locked wheel protection is not available during the landing. The checklist guides the crew to turn the auto brake select switch off, not to arm the speed brakes, and not to apply brakes until the nose wheels are on the ground the speed brakes are extended. The quick readiness handbook (QRH) further details that the speed brakes are to be deployed manually immediately upon landing and to brake with caution.

The airplane was equipped with an L-3 Communications Fairchild Model FA2100 Flight Data Recorder (FDR). The FDR unit was removed from the airplane and sent to the National Transportation Safety Board Vehicle Recorders Laboratory in Washington, DC, for data extraction. Data from the accident flight was extracted and one minute and 40 seconds of data from the landing event was plotted. Parameters included in the plot were the left and right brake pressure, and the nose gear weight on wheels sensor. According to the data extracted, there was an increase in left and right brake pressure, to a level of 3,000 pounds per square inch (the upper limit of the pressure range) at the same time the nose gear weight on wheels sensor was activated. The pressure decreased to 1,200 pounds per square inch, and then to zero pounds per square inch several seconds later. This pressure increase and decrease is consistent with the application of brakes upon landing. Additional study of the FDR data revealed that the speed brakes were not extended and the thrust reversers were not used for this landing.

NTSB Probable Cause

The flight crew's improper landing technique for an inoperative anti-skid system resulting in locked brakes and four blown main landing gear tires.