Meridian, MS, USA
N196EC
EMBRAER EMB-500
The pilot reported that the approach was uneventful and that he noted no anomalies during the flight. However, after touchdown and immediately upon brake application, the airplane began sliding in a manner that the pilot said was similar to hydroplaning even though, at the time of the incident, the runway was dry. Postincident examination revealed that both main landing gear tires were deflated and had wear marks that were associated with the wheels being locked while the airplane was in motion. Examination of the recordable data revealed that just before touchdown the "ANTI-SKID FAIL" message was displayed on the crew alerting system, and the associated maintenance message, "BRAKE CONTROL UNIT FAIL," was recorded on the central maintenance computer. Examination and testing of the brake control unit (BCU) fault log revealed that the loss of the antiskid function was caused by a disagreement between two BCU internal components of the wheel speed reading of each wheel. Although the airplane was equipped with numerous brake system protections, after the loss of wheel speed data, the system's protections against skidding were no longer operational, and a wheel lock on both main landing gear occurred. The investigation could not identify the cause of the disagreement of the wheel speed reading.
HISTORY OF FLIGHT On April 5, 2013, about 1509 central daylight time, an Embraer EMB-500, N196EC, experienced an antiskid brake system failure immediately prior to touchdown at Key Field Airport (MEI), Meridian, Mississippi. The airline transport pilot was not injured and the airplane sustained no damage. Visual meteorological conditions prevailed and an instrument flight rules flight plan had been filed for the flight that originated from the Destin-Fort Walton Beach Airport (DTS), Destin, Florida about 1430. The airplane was registered to and operated by Progressive Aviation, LLC under the provisions of Title 14 Code of Federal Regulations Part 91 as a positioning flight. According to the pilot, after touchdown he applied the brakes and the airplane immediately began "sliding similar to hydroplaning." The airplane subsequently slid approximately 2,800 feet down the runway before coming to a stop. Examination of the main landing gear revealed that both tires had deflated. The airplane's tires were replaced and the airplane taxied to a hangar without further abnormalities. Initial examination by a Federal Aviation Administration inspector revealed that both main landing gear tires had wear marks similar to being locked up while the airplane was in motion. PERSONNEL INFORMATION The pilot, age 45, held an airline transport pilot certificate with airplane multiengine land ratings, and a commercial pilot certificate with an airplane single-engine land rating. A second-class airman medical certificate was issued to the pilot on October 12, 2012 with no limitations. The pilot reported 2,500 total hours of flight experience and 250 of those hours were in the accident airplane make and model. AIRCRAFT INFORMATION The six-seat, low-wing, retractable landing gear, pressurized T-tail airplane was manufactured in 2010. It was powered by two Pratt & Whitney Canada PW617F-E turbofan engines that were aft fuselage mounted. A review of the pilot operating handbook (POH) revealed that the main landing gear brakes are a brake-by-wire system controlled by either the pilot or copilot seat rudder pedals. The rudder pedals actuate the pedal transducers that in turn send the brake inputs to the Brake Control Unit (BCU). The BCU, which is connected to the DC BUS 2, receives all brake interface signals and controls the Shutoff Valve (SOV) and both Brake Control Valves (BCV's) for braking capability. The POH states that "In case of main brake failure, the Emergency/Parking brake is available and must be used carefully to stop the airplane." The POH further states in part, "…the antiskid protection prevents tire skidding and maximizes brake efficiency according to the runway surface." The system controls the amount of hydraulic pressure applied to the brakes and, meters the wheel brake pressure in order to recover wheel speed and prevent tire skidding. The antiskid system is deactivated for wheel speeds below 10 knots. In addition, the antiskid protection is not available for the emergency/parking brake system. Besides antiskid protection, the brake system also includes touchdown protection, and as designed inhibits brake pressure from being applied if the brake pedals in the cockpit are being applied prior to touchdown. The touchdown protection receives input from the weight on wheel (WOW) proximity switch and is deactivated when wheel speed is above 30 knots or 5 seconds after WOW has sensed ground contact. The brake system is also designed with locked wheel protection. Locked wheel protection compares main landing gear wheel speed signals. Should one main landing gear wheel speed become about 30 percent lower than the reference velocity, which is the "highest of the two wheel speeds or the previous reference velocity decayed by 25 ft/sec," the system commands a full brake pressure relief, which would allow wheel speed recovery. The system becomes active about 30 knots. The airplane was not equipped with thrust reversers, spoilers, or leading edge slats. METEOROLOGICAL INFORMATION The 1458 recorded weather observation at MEI included wind from 340 degrees at 10 knots, 10 miles visibility, clear skies, temperature 18 degrees C, dew point 8 degrees C, and barometric altimeter 30.09 inches of mercury AIRPORT INFORMATION The airport was a publically owned airport and at the time of the incident had an operating control tower. The airport was equipped with two recorded runways designated as runway 1/19, and 4/22. Runway 1/19 was 10,003-feet-long and 150-feet-wide and runway 4/22 was 4,599 -feet-long and 150-feet-wide. The airport was 298 feet above mean sea level. At the time of the incident the runway was dry. FLIGHT RECORDERS The airplane was equipped with a cockpit voice and data recorder (CVDR) unit and a Central Maintenance Computer (CMC). Both units were downloaded at the aircraft, and data was transmitted to Embraer for analysis. A representative from Embraer sent an electronic file of the downloaded CVDR data to the NTSB Recorders Laboratory in Washington D.C. for further analysis and a copy of the CMC data to both the brake manufacturer and the investigator-in-charge. TEST AND RESEARCH Examination of the impact switch, associated with the cockpit voice and data recorder, revealed that it had been activated, which was required when it was exposed to a 5g deceleration. However, a review of all available recorded data did not reveal any exposure to the required level and the greatest recorded level was about 1.273g. The CMC was downloaded on scene and revealed that a "BRAKE CONTROL UNIT FAIL" was registered and the crew alerting system (CAS) message "ANTI-SKID FAIL" annunciation message was logged 2 and 1 seconds respectively prior to touch down. The wheel speed transducers were examined and tested; however, no fault errors or abnormalities were noted. The BCU, manufactured by Meggitt Aircraft Braking Systems, was removed and sent to the NTSB Recorders Laboratory for download. The download revealed fault codes associated with the test as well as an "Lt ws ga dsgree," "Rt ws ga dsgree," and no weight on wheels indications. The right side (RH) and left side (LH) wheel speeds indications were respectively 85.95 and 85.11 knots. The RH brake pedal application was 36% and the LH brake pedal application was 2%. The RH brake pressure indicated 182.23 psi and the LH brake pressure was indicated 50.26 psi. The BCU was taken to the manufacturing facility in Dayton, Ohio and examined under the supervision of the NTSB IIC. The BCU was examined and installed on a test bench and functionally tested. The BCU operated normally with no anomalies noted. For further information on the testing of the BCU reference the "ERA13IA192 – BCU Exam" report within the docket associated with this accident.
The failure of the main landing gear brake system’s antiskid system, which resulted in locked wheels during landing.
Source: NTSB Aviation Accident Database
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