Sierra Blanca, TX, USA
N997TD
Gates Learjet 24D
The twin-turbojet, transport-category airplane was destroyed when it departed controlled flight during descent into its final destination and impacted terrain. The flight was cleared to descend from FL 390 to 10,000 feet, and the flight crew established a 4,000-foot/minute descent. As the airplane descended through FL 219, air traffic control requested the pilot contact approach control. However, the pilot read back an incorrect frequency and spoke an unintelligible word. The controller attempted to correct the pilot; however, no additional communications were received from the flight crew. Located within a pause in the pilot's last transmission, a 1680 Hz frequency could be heard for 0.1 seconds. There are only two systems in the airplane with aural warning systems within that frequency range; the cabin altitude warning, and the overspeed warning (both systems were destroyed during the accident sequence). Shortly after the last transmission from the pilot, radar data depicted the airplane climbing back up to FL 231 before entering a steep and rapid descent. A performance study indicated that just prior to the loss of control, the airplane exceeded its maximum operating airspeed of 300 knots calibrated. However, according to the manufacturer, the airplane had been successfully flown at airspeeds up to 400 knots calibrated without loss of control. The right wing and sections of the right horizontal stabilizer/elevator separated from the airplane just prior to its impact with terrain and were located approximately 200-250 feet from the main impact crater. No anomalies with the airframe or engine were found that would have led to the loss of control. A cockpit voice recorder was installed in the accident airplane; however, it did not record the accident flight.
HISTORY OF FLIGHT On December 10, 2001, at 1821 mountain standard time, a Gates Learjet 24D transport category, twin turbojet airplane, N997TD, operating as Turbodog 36, was destroyed when it impacted terrain following an uncontrolled descent near Sierra Blanca, Texas. The airplane was registered to and operated by Air Cargo Express Inc., of Fort Wayne, Indiana. The airline transport rated captain and the commercial rated co-pilot sustained fatal injuries. Night visual meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan was filed for the 14 Code of Federal Regulations Part 91 positioning flight. The flight originated from the Harlingen Valley International Airport, Harlingen, Texas, at 1700, and was destined for the El Paso International Airport, El Paso, Texas. It should be noted that unless otherwise indicated, all times are in mountain standard time (MST). According to radar and communication data obtained from the Albuquerque Air Route Traffic Control Center (ZAB ARTCC), they provided air traffic control service during the descent portion of the flight from a point approximately 115 miles southeast of ELP. At 1809:26, ZAB cleared the pilot to descend "at pilot's discretion" from Flight Level (FL) 390 to 10,000 feet. The pilot acknowledged, stating "we'll take it nice and slow." At 1814:42, ZAB instructed the pilot to turn left ten degrees for separation from ELP departing traffic. The pilot acknowledged. At 1817:28, ZAB asked the pilot to "increase rate of descent if you can." The pilot replied that they would increase the descent by 1,000 feet/minute and asked at what altitude he could expect to turn back direct to ELP. The controller replied "about 25 [thousand]." The pilot replied that "would be no problem, we're coming down about 4,000 feet/minute." At 1819:10, ZAB cleared the flight direct to ELP, and the pilot acknowledged. At that point, radar data depicted the flight descending through FL266. At 1821:06, ZAB instructed the pilot to contact ELP approach control (the flight's mode C transponder depicted the airplane at FL219). The pilot acknowledged with an incorrect frequency and uttered an unintelligible sound. The controller attempted to correct the readback, but no response was received and the pilot never contacted ELP approach control. During this exchange the transponder's mode C function indicated the airplane climbed to FL225. The airplane continued to climb to FL231 and at 1821:20 no mode C was received from the airplane. The final radar contact was 37 nautical miles from the El Paso very high frequency omnidirectional range (VOR) navigational facility along the 103-degree radial. The flight crew did not contact ELP TRACON, and no distress calls were received. A search for the airplane was initiated and, at 2000, local authorities located the accident site on a private ranch. PERSONNEL INFORMATION The captain held an airline transport certificate with type ratings in the Douglas DC-3 and Learjets (both the 23/24 models and the 35 model). He also held a commercial certificate for single-engine airplanes with type ratings for the Lockheed B-34 and the Douglas B-26 (the latter two aircraft are considered vintage airplanes and the pilot was only permitted to fly them in visual flight conditions). According to records provided by Air Cargo Express Inc., the captain was hired on November 3, 2000. At the time the captain was hired, he had accumulated a total of approximately 20,000 hours, of which 10,000 were in multi-engine aircraft, 10,000 hours were in jet-type aircraft. The pilot reported accumulating 10,000 hours during night conditions. On June 8, 2001, the captain underwent his most recent FAR Part 135 airman competency/proficiency. At the time of the accident he had accumulated approximately 20,650 hours. Additionally, he held a first class medical certificate that was issued September 11, 2001. The medical certificate contained the following limitation: "Holder shall wear corrective lenses while exercising the privileges of his/her airman certificate." According to Air Cargo Express' flight and duty log, the captain did not work on the 8th and 9th of December. Prior to that, the captain logged 8.0 hours of duty time, of which 6.4 hours were flight time on December 7, 2001. On December 6, 2001, the pilot logged 7.3 hours of duty time, of which 6.2 hours were consumed while flying. On August 1, 2000, the co-pilot was issued a commercial pilot certificate. He held single-engine land, multi-engine land, and instrument airplane ratings. According to records provided by Air Cargo Express Inc., the co-pilot underwent initial second-in-command ground training on June 24, 2001. As of July 11, 2001, he had accumulated a total of 1,400 hours, of which 150 hours were in multi-engine aircraft, 20 hours were in jet-type aircraft, and 100 hours were during night conditions. On July 11, 2001, he underwent his most recent FAR Part 135 airman competency/proficiency check. At the time of the accident he had accumulated approximately 1,715 hours, of which approximately 315 hours were in the Lear 24. Additionally, he was issued a second-class medical certificate on June 26, 2001. The medical certificate contained the following limitation: "Must wear corrective lenses." According to Air Cargo Express' flight and duty log, the co-pilot did not work during the four days preceding the accident. AIRCRAFT INFORMATION The 1972-model airplane (serial number 247) was powered by two General Electric CJ610-6 turbojet engines (left engine serial number 251-657A, and right engine serial number 251-299A), which were rated at 2,950 pounds of thrust each. Photographs of the airplane taken prior to the accident revealed it was painted navy blue on the bottom 1/3rd of the airplane, encompassing the belly and wings. Three painted stripes; one navy blue, one gold, and another navy blue, topped the solid blue belly paint and were separated by white paint. The remaining top 2/3rds of the airplane was painted white, with the exception of the registration number and company logo. The wing tip tanks displayed a similar paint scheme as the fuselage, but to a smaller scale. The Learjet 24D's elevator and ailerons are operated mechanically through a system of cables, pulleys, push-pull tubes, and bellcranks. The rudder is operated through a system of cables, pulleys, and bellcranks. The aileron, rudder, and stabilizer trim systems are electrically driven. The flaps are operated utilizing a system of hydraulic pressure, actuating cylinders at each flap, and interconnecting cable that synchronizes the flaps through their range of travel. The spoilers are operated utilizing a system of hydraulic pressure and actuators at each spoiler panel. The airplane was established on an FAA approved airworthiness inspection program (AAIP). At the time of the accident, the airplane had accumulated approximately 7,970 total flight hours. According to the maintenance records, on December 7, 2001, at an aircraft total time of 7,966.4 hours, the aircraft had its emergency gyro battery deep-cycled, and its left engine replaced. The installed left engine serial number was 251-657A and had a total time of 6,968.0 hours, and a total time since overhaul of 3,954.7 hours. On October 31, 2001, at an airplane total time of 7,860.1 hours, an overhauled yaw servo unit was installed. On October 30, 2001, at an aircraft total time of 7,857.9 hours, maintenance personnel complied with the 2,400-hour replacement of the primary control cables, and conducted a detailed inspection of the flap system. The airplane underwent its last AAIP inspection on September 10, 2001, at an aircraft total time of 7,763.7 hours, when a 300-hour Phase A1-A6 inspection was completed on both the airframe and the engine. During that inspection the #1 navigational transmitter and captain's directional gyro were replaced, and the horizontal-to-vertical stabilizer gap fairings were replaced along with the main landing gear wheels. On August 9, 2001, at an aircraft total time of 7,663.6 hours, the co-pilot's directional gyro was replaced. On June 12, 2001, the spoiler attachment bolts were replaced. On June 12, 2001, at an aircraft total time of 7,516.2 hours, the captain's vertical gyro was changed, the co-pilot's attitude indicated was replaced with a serviceable unit, and the autopilot control panel was replaced. On May 21, 2001, at an aircraft total time of 7,464.4 hours, the airplane and engines underwent a 300-hour Phase A1-A6 and a 600-hour Phase B1-B6 inspection as per the Air Cargo Express AAIP. During the aforementioned inspection, the stabilizer actuator was replaced with an overhauled unit (part number 2581037-47). According to Air Cargo Express' airworthiness status record, on the morning of the accident, the airplane had accumulated a total of 7,966.4 flight hours. The left engine accumulated a total of 6,968.0 hours and 7,163.0 cycles, and 3,954.7 hours and 3,847.0 cycles since its last overhaul. The right engine had accumulated a total of 7,666.3 hours and 8,222.0 cycles on the morning of the accident, and 5,072.9 hours and 4,284.0 cycles since its last overhaul. METEOROLOGICAL INFORMATION At 1751, the weather observation facility at the El Paso International Airport, El Paso, Texas (located approximately 48 miles west-northwest of the accident site), reported a few clouds at 25,000 feet, visibility 10 statute miles, temperature 51 degrees Fahrenheit, dew point 30 degrees Fahrenheit, wind from 140 degrees at 10 knots, and an altimeter setting of 29.75 inches of mercury. On December 10, 2001, the U.S. Naval Observatory's Astronomical Applications Department recorded sunset and the end of civil twilight at El Paso to be 1702 and 1729, respectively. The moonrise occurred at 0333 on the morning of the 11th. A meteorological study was conducted by the NTSB utilizing information obtained from the University of Wisconsin's Space Science and Engineering Center's McIDAS (Man computer Interactive Data Access System), the National Oceanic and Atmospheric Administration (NOAA), and the National Weather Center (NWC). According to the information gleaned from these services, the cloud tops were near 10,800 feet, the freezing level was near 11,000 feet, no turbulence was displayed between 20,000 and 25,000 feet in the accident area, no mountain wave activity was diagnosed or forecast between 10,000 and 39,000 feet near western Texas, nor were there any AIRMETS, SIGMETs, or Convective SIGMETs issued for Texas during the accident time. FLIGHT RECORDERS The accident airplane was equipped with a Fairchild A100 cockpit voice recorder (CVR) that had sustained severe structural damage during the accident. The CVR was taken to the NTSB's Vehicle Recorder Lab in Washington, D.C. The internal recording tape also sustained substantial damage and was extracted and repaired. Although audio information had been recorded, it became evident that the audio recorded was not audio from the accident flight. Specifically, there was a female and male crew recorded (the accident crew consisted of two males) calling for the before taxi and before takeoff checklists, prior to takeoff from an airport in the Chicago area. After listening to the first 15 minutes of the tape, it was determined that the accident flight had not been recorded. A flight data recorder (FDR) was not installed on the accident airplane, nor was one required by regulation. WRECKAGE AND IMPACT INFORMATION The accident site was situated at 031 degrees 32.67 minutes north latitude and 105 degrees 37.331 minutes west longitude. The accident site consisted of an impact crater that measured 17 feet by 30 feet. The main impact crater was excavated to a depth of 6 feet when a rock layer was met. The northeast, northwest, and southwest quadrants of the crater were excavated 6 feet until undisturbed dirt was met. The southeast quadrant of the crater was excavated 4 feet until undisturbed dirt was met. Debris comprising of soil and fragmented components of the airplane, were located in a fan distribution emanating outward from the crater to the north-northwest and ending approximately 1/4 miles from the crater. The right wing separated from the aircraft at near wing station (WS) 25.0, and was located 250 feet south of the main impact crater. Wing skin at the separation was bent downward. The wing's leading edge metallic strip displayed a smeared sky blue paint in the spanwise direction. The forward portion of the right wing tip tank, between tip tank stations (TTS) 46 and 83.85, came to rest 385 feet south-southwest of the main impact crater. The forward section of the right tip tank, between TTS 0 and 46, was located 150 feet south-southeast of the main impact crater. The left wing was fragmented and located throughout the fan distribution north-northwest of the main impact crater. The largest section of left wing, which consisted of an outboard section from WS 125 to WS181, was located 225 feet north of the main impact crater. The forward section of the left wing tip tank, from TTS 0 to 46, was located 385 feet north of the main impact crater. The right horizontal stabilizer was located 200 feet southeast of the main impact crater. The left horizontal stabilizer was fragmented and located throughout the fan distribution. The entire lower section of left horizontal stabilizer skin was located 210 feet northeast of the main impact crater. The vertical stabilizer was fragmented within the fan distribution. The largest section of the vertical stabilizer was located 124 feet northwest of the main impact crater. All flight control surfaces were accounted for at the accident site. The horizontal stabilizer trim actuator nut-screw assembly was measured at 0.5 inches from the full nose down mechanical stop position. According to Learjet, this measurement equates to approximately -1.39 degrees (near the full nose down travel point). The horizontal stabilizer trim limits are -0.50 to -7.50 degrees nominal. This measurement equates to a trimmed position for a speed of 280 knots +/-40 Knot Calibrated AirSpeed (KCAS), for an airplane weighting 9,000 lbs, loaded 25% Mean Aerodynamic Chord (MAC), and at an altitude of 22,000 feet. The right aileron remained attached to its wing attach point. The left aileron was recovered in sections and the trim tab (located on the left aileron only) deflection was not measurable. The aileron trim tab nominal deflection is +/- 8 degrees. The aileron system control continuity could not be established. The rudder was fragmented and located throughout the fan distribution. The rudder trim tab was separated from the rudder and its deflection was not measurable. Rudder trim tab nominal deflection range is +/-15 degrees. Rudder system control continuity could not be established. Both elevators separated from their respective horizontal stabilizers. Each elevator separated into three sections. The left-hand outboard section of the left elevator, from the tip to approximately butt line (BL) 60, was located 700 feet southeast of the main impact crater. The center section of the left elevator, between approximately BL 33 and BL 60, was located 225 feet north of the main impact crater. The inboard section of the left elevator, between approximately BL 33 and BL 1, was located 490 feet southeast of the main impact crater. The right-hand outboard section of the right elevator, between the tip to BL 60, was located 77 feet south-southwest of the main impact crater. The center section of the right elevator, between BL 33 and BL 60, was located 157 feet southwest of the main impact crater. The inboard section of the right elevator, between BL 33 and BL 1, was located 415 feet south-southwest of the main impact crater. Elevator system control continuity could not be established. The right flap assembly was separated from the right wing. The right flap actuator measured 2.45 inches. Nominally, 2.0 inches is fully retracted. The left flap was found fragmented throughout the fan distribution and the left flap actuator measured 2.30 inches. This measurement equat
loss of control during descent for undetermined reasons.
Source: NTSB Aviation Accident Database
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