Goodland, KS, USA
N31MC
Learjet 35A
According to the flight crew, they exited the clouds approximately 250 feet above ground level, slightly left of the runway centerline. The pilot not flying took control of the airplane and adjusted the course to the right. The airplane rolled hard to the right and when the pilot corrected to the left, the airplane rolled hard to the left. The airplane impacted the ground in a right wing low attitude, resulting in substantial damage. Further examination and testing revealed anomalies with the yaw damper and spoileron computer. According to the manufacturer, these anomalies would not have prevented control of the airplane. Greater control wheel displacement and force to achieve a desired roll rate when compared with an operative spoileron system would be required. The result would be a slightly higher workload for the pilot, particularly in turbulence or crosswind conditions. An examination of the remaining systems revealed no anomalies.
On October 17, 2007, approximately 1010 mountain daylight time, a Learjet 35A, N31MC, registered to Jagee Ventures, Inc., and piloted by an airline transport pilot, sustained substantial damage when it impacted terrain during landing at Renner Field (GLD), Goodland, Kansas. Instrument meteorological conditions prevailed at the time of the accident. The flight was being conducted on an instrument flight rules flight plan under the provisions of Title 14 Code of Federal Regulations Part 91. The pilot and co-pilot reported no injuries. The flight originated at Fort Worth Meacham International Airport (FTW), Fort Worth, Texas, at 0950 central daylight time. According to the telephone conversation with the flight crew immediately following the accident, the airplane exited instrument conditions at 250 feet above ground level on approach to runway 30 (5,499 feet by 100 feet, concrete) slightly left of the runway centerline. The flying pilot aligned the airplane with the runway centerline and experienced an uncontrolled left and right rolling motion. The pilot not flying stated that he noted that the aileron augment annunciator light had illuminated. According to the written statement provided by the pilot, prior to flying the instrument approach, it was briefed that the co-pilot would fly the approach and he (the pilot) would watch for the runway environment and "take the controls for the landing." He stated that when he had the runway environment in sight, they were "slightly to the left of center line" and he took control of the airplane, announcing the exchange verbally, and he made a "slight correction to the right." At this time the airplane "rolled excessively to the right" and he corrected to the left, at which time the airplane "rolled excessively to the left." According to the written statement provided by the co-pilot, the flight and instrument approach were without issues or anomalies. He stated that the airplane was fully configured to land and stabilized on the glide slope. As he approached the decision height, he was preparing to go-around when the pilot announced he had the runway environment in sight and took control of the airplane, as previously briefed. The airplane was to the left of the runway centerline and the pilot corrected to the right. At this time, the airplane "rolled much farther than was commanded." Correction was made to the left and back to the right, at which time, the airplane rolled hard again to the right. According to the Federal Aviation Administration inspectors and Learjet investigators, the runway and aircraft damage indicated that the right tip tank struck the runway at a very high right wing low attitude, crossing the runway at a 45 degree angle. The aircraft traveled off of the right side of the runway leveling out and contacting the ground. The aircraft then banked left with the left wing at a very high angle striking the left tip tank on the runway surface and breaking the left wing extension. The aircraft continued traveling left across the runway again off into the grass left of the runway at an approximate angle of 45 degrees. The airplane came to rest between the runway and the taxiway, adjacent to the airport terminal area. Examination of the airplane revealed that the left outboard wing section separated approximately three feet from the wing tip tank. The right tip tank fin was torn and the bottom of the tank exhibited forward to aft scratches. The fuel tip tank fuel cell was leaking. The weather at the time of the accident was reported as winds 330 degrees at nine knots; visibility 1.25 statute miles in mist; sky condition overcast 200 feet; temperature six degrees Celsius; dewpoint five degrees Celsius; altimeter 29.44 inches. On October 18, 2007, the Federal Aviation Administration (FAA) inspectors and investigators from Bombardier Learjet examined the airplane and its systems. A spoiler test box was installed and the spoilers were tested per the airplane maintenance manual. The aileron augmentation light illuminated with certain movement of the flight controls. The spoileron computer was removed from the airplane for further examination. On December 4, 2007, the spoileron computer was taken to Bombardier Learjet in Wichita, Kansas, and tested with the spoileron computer test panel. During initial examination, it was noted that the command limit was set clockwise to its farthest setting. It was also noted that the lock nuts on both potentiometers were loose. The left and right balance potentiometers were reset using the spoileron test panel. The unit was tested according to the vendor manual, with all results within test parameters. The left and right balance potentiometers were returned to their initial settings and the unit was retested. The spoilerons tracked consistently when tested in the air mode. The unit passed the remaining tests conducted. On December 17, 2007, National Transportation Safety Board, Bombardier Learjet, and FAA investigators examined the airplane and its systems. Aileron augmentation and yaw damper tests were conducted in various airplane configurations. During the aileron augmentation test, with the flaps set at 40 degrees, the spoilerons deployed to an unknown angle (motion was too rapid to measure) after five degrees of left aileron and immediately stowed. This was accompanied by an aug/ail light illumination in the cockpit. The spoilerons deployed and tracked normally with right aileron activation up to 14 degrees. The spoilerons stowed at 15 degrees of right aileron; this was accompanied by an aug/ail light illumination in the cockpit. The spoilerons were inoperative during airmode testing (with flaps at 20 degrees) and during computer power testing (with the spoileron computer circuit breaker pulled), as expected. Both yaw damper self-tests failed. The other yaw damper tests were within parameters. The yaw damper computer, two rate gyros, and two lateral accelerometers were removed for further testing. During the removal of the rate gyro, it was noted that the 7.5 degree wedge was not installed. On April 1, 2008, the yaw damper controller was tested in Wichita, Kansas, by Bombardier Learjet and L-3 Avionics Systems, under the auspices of the Federal Aviation Administration. The first functional test of the unit, as removed from the airplane, revealed the following: The primary and secondary centering voltages were high The primary rate gyro circuit did not function The primary cross feed did not function The secondary cross feed reacted slow The unit centering voltage potentiometers were centered and the unit was retested, revealing the following: The secondary centering voltage did not function The primary and secondary rate gyro circuits functioned properly The primary cross feed was functioned properly The secondary cross feed did not function properly Finally, the test set voltage was adjusted and the unit was retested, revealing the following: The primary and secondary centering voltages were high The primary rate gyro circuit did not function The primary cross feed did not function The secondary cross feed reacted slow Following the bench test, the settings were returned to their original configuration. Disassembly revealed that the J-6 pin 2 was pushed back and contacting the cover. No other anomalies or defects were noted. A review of the maintenance records, provided by Turbine Engine Specialists Inc, revealed that the "spoileron system" was not "working properly" and maintenance was initiated on October 2, 2007, addressing this issue in conjunction with other inspections and issues. The customer recalled the airplane while the spoileron system was being trouble shot and Turbine Engine Specialists reported that they "deactivated" the spoileron system in accordance with the Learjet minimum equipment list procedure. The circuit breaker was pulled and secured with a tie wrap and a decal was installed on the instrument panel indicating the system was deactivated. Neither the tie wrap nor decal were noted during the examination of the cabin of the airplane and both the spoiler and spoileron circuit breakers were in the closed position. According to the pilot, the "aug/ail" circuit breaker was pulled during the entire flight except for a short time in cruise flight when he attempted to reset the system. He stated that the system would not reset so he pulled the circuit breaker and it remained in that position for the remainder of the flight. He confirmed that the fuel load was balanced, the yaw damper was engaged, the flaps were "full", and the autopilot was not used during the approach. It was also stated that all cabin circuit breakers were reset following the accident. According to the Master Minimum Equipment List (MEL) for Learjet (including a Lear 35A) Revision 6, which was located in the accident airplane, the spoileron system may be inoperative provided the ground spoilers are operative, the airplane is operated at or below flight level 250, and the airplane is operated with a maximum crosswind limitation of 20 knots. There was no letter of authorization from the FAA for this MEL. According to Learjet, an inoperative spoileron system would not exaggerate control inputs or create control problems during landing. Learjet added that temporary flight manual change issued in July of 2007 states that "landing on a wide runway of sufficient length with minimum turbulence and crosswind is recommended" while operating with this system inoperative. The augmented aileron (spoileron) system was incorporated into the airplane design to improve handling qualities (roll axis) at lower airspeeds. When the flaps are retracted above 25 degrees the augmentation system is disabled, and only the speed brake function is operational. When the flaps are extended below the 25 degrees position, the augmentation system is active, and as the airplane is banked, the corresponding spoiler board is lifted to aid the lifted aileron. The automatic function of the system and spoiler deflection ratio is computer controlled, and includes limits of deflection based on aileron travel. The system will shutdown automatically if an anomaly is detected, leaving the aileron without augmentation, and a reduced roll rate. An enunciator panel warning light visually indicates a system anomaly. According to Learjet "this will result in a noticeable but manageable reduction in roll authority In other words, it will take greater control wheel displacement and force to achieve a desired roll rate when compared with an operative spoileron system. The result would be a slightly higher workload, particularly in turbulence or crosswind conditions." According to L-3 Avionics Systems, an inoperative rate gyro circuit could cause the affected yaw damper system to become inoperative. It was noted that the system does not provide an indication of a failed rate gyro circuit. In addition, the absence of the rate gyro wedge would result in the system being less effective at sensing and dampening the roll component of any oscillation.
The pilot's failure to maintain aircraft control during the landing.
Source: NTSB Aviation Accident Database
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