Loma Alta, TX, USA
N138BF
Sino-Swearingen SJ30-2
The corporate jet was in a descent to attain a Mach 0.884 target speed during an airplane type certification flutter test. The airplane (a unique test bed) had a known speed-dependent tendency to roll right which was attributed to wing and aileron twist deviations. As the speed increased during the accident flight, the pilot had to apply full left aileron to be able to maintain airplane control. The airplane completed the test point about 30-degrees right-wing-low, and subsequently began to roll to the right, "like a barrel roll...not real fast," that the pilot reported he could not stop. Although the manufacturer’s engineering analysis (which did not include any high-speed wind tunnel testing) predicted positive lateral stability up to Mach 0.90, lateral control was lost during the accident flight, and the airplane rolled about 7 times during a 49-second timeframe, from about 30,500 feet until a near-vertical ground impact. A review of telemetry data revealed that, just before the rolls began, the airplane's elevator moved to the 3.5 degrees trailing-edge-up (TEU) position, and the airplane's heading deviated right. Less than 1 second later, the rudder moved from 2 degrees trailing-edge-left (TEL), to 6.5 degrees TEL, and the combination of the TEU elevator and the left rudder input coincided with a marked increase in airplane's right deviation. Elevator-up deflection and rudder-left defection were maintained, with some variation in magnitude, to nearly the end of the data. Because the known speed-dependent tendency to roll right had created significant control problems on a previous flight, the ailerons were removed, modified and replaced, and a Gurney flap was added to the right wing. After the addition of the Gurney flap, the lateral trim margin improved to about 40 percent required (where 50 percent was neutral) up to 305 KCAS. It was then determined that flutter testing could continue to higher airspeeds if the pilot needed to apply a "small" wheel force to augment the trim. The pilot had been instructed to reduce airspeed if there was a problem during the flutter testing, and had done so during an uncommanded roll to the left on the previous flight. Telemetry data from the accident flight revealed that at initiation of the upset, the pilot attempted to level the wings and raise the nose, but the airplane continued to diverge from stable flight, and it continued to accelerate beyond the airplane’s demonstrated flight diving speed. It is undetermined if the pilot could have reduced the speed of the airplane in time, during the initiation of the upset, so that the airplane would not diverge. After the accident, the company conducted high-speed wind tunnel tests, and found that lateral stability decreased with increasing Mach and angle of attack (AOA). Lateral stability became negative (unstable) above Mach 0.83, and rudder input intended to augment lateral trim above a certain Mach could aggravate the situation. In addition, a TEU elevator input would increase AOA, and also result in deteriorated lateral stability. High speed wind tunnel data also revealed that roll authority deteriorated above Mach 0.86, and by Mach 0.88, the aileron upper and lower surfaces were both in separated flow regions. The follow-on flutter test airplane, which successfully completed the certification requirements, was equipped with vortex generators and thicker trailing-edge ailerons. It also did not require the external trim device needed on the accident airplane due to improvements in manufacturing.
HISTORY OF FLIGHT On April 26, 2003, at 1005 central daylight time, a Sino-Swearingen Aircraft Corporation (SSAC) SJ30-2, N138BF, serial number 002, was destroyed when it impacted terrain near Loma Alta, Texas. The certificated airline transport pilot was fatally injured. Visual meteorological conditions prevailed for the flight, which departed on an instrument flight rules flight plan from San Antonio International Airport (SAT), San Antonio, Texas, at 0911. The local test flight was conducted under 14 CFR Part 91. At the time of the accident, the airplane was undergoing flutter testing for Federal Aviation Administration (FAA) type certification. SSAC Report 30-2222, "Flight Flutter Certification Test Plan for SSAC SJ30-2," delineated the flutter testing requirements, which included the Federal Air Regulation (FAR) Part 23.629 requirement that the airplane be demonstrated to be free from flutter, control reversal, and divergence up to the "demonstrated flight diving speed" (Vdf/Mdf). The testing was to be conducted in two phases, with the first phase planned to clear the airplane to its "maximum operating limit speed" (Vmo/Mmo) of 320 KCAS/Mach 0.83, and the second phase, to clear it to its Vdf/Mdf of 372 KCAS/Mach 0.90. Phase 1 flutter testing had been successfully completed. The first flutter mission of phase 2, flight test number 230, was flown one day before the accident flight, with the same pilot onboard. The objective of that flight was to complete flutter test points 1-12 (Mach 0.844) and 1-13 (Mach 0.864). Test point 1-12 was completed, and subsequently, the airplane went into a uncommanded roll to the left, which the pilot recovered from. Afterwards, during test point 1-13, a discrepancy was noted between the pilot's displayed airspeeds and those reported by a chase plane pilot, so the pilot terminated the flight. After the flight, the pilot realized that he had incorrectly set up the airspeed display in the test airplane, and was flying faster than his airspeed indicated. In addition, the pilot reported, that during the flight, he had felt a "rumble" in conjunction with the left roll. In his notes, he had written, ".855", and immediately below that, "Abrupt LH Roll [space] Rumble", and beneath that, "Rudder Input?" According to the project's flutter consultant, a Designated Engineering Representative (DER), a possible explanation for the rumble was Mach buffet. However, to help confirm there wasn't an in-flight mechanical problem with the airplane, flight test personnel assigned a second SSAC pilot as a backseat chase plane observer for the next (accident) flight, flight test number 231. The chase plane was a contracted Northrop T-38 jet, N638TC, with a pilot and the second SSAC test pilot onboard. The accident flight was also being monitored in a telemetry van in Rock Springs, Texas, by the flutter consultant and three SSAC personnel. Prior to the test flight, a mission briefing, led by the accident test pilot, was conducted via conference call between the San Antonio-based personnel and the telemetry van personnel. According to a briefing participant, all of the flight test cards were covered, "including the test limitations, test set-up, test points, weight and balance, airspace operational considerations, aircraft limitations, maintenance actions since last flight, instrumentation status, and chase aircraft procedures." A number of witnesses also noted that the test points briefed were 1-14 (Mach 0.884), and 1-15 (Mach 0.894) if conditions permitted. An "SSAC Flight Briefing Guide" was also utilized, which included a review of hazard analyses, and abnormal/emergency procedures. During the briefing, the test pilot stated that he was responsible for safety of flight. The flutter consultant also stated that he had, during previous discussions, advised that for the purpose of flutter testing, if the pilot ran out of aileron/elevator trim, the tests could still be completed, even if the pilot had to hold aileron/elevator force to steady the airplane. He further stated, however, that the continuance of the testing would never override the pilot's decision as to whether the control forces were unacceptable or hazardous. According to the flutter consultant, after takeoff, the accident airplane climbed to 39,000 feet, and prepared for a shallow dive along an easterly track for flight test point 1-14. A telemetry lock was then obtained. However, when the airplane reached indicated Mach 0.875, the test pilot called "Mark" on the radio. [An optional test point "14A" (Mach 0.874) was listed on the flutter test card; however, on the previous day's flight, it had been crossed out.] After the "Mark" was received, the pilot initiated a single pulse input to the elevator. After checking the telemetry strips, the consultant then gave a "Go" for a single pulse to the aileron, followed by another "Go" for a single pulse to the rudder. Telemetry van personnel noted that all the modes excited were "well damped." Telemetry van personnel also reported that after the pulses were completed, the test pilot stated that the uncommanded roll to the left (which was experienced on the previous flight), did not occur. There was also no mention of a rumble. In addition, the chase plane pilots confirmed that there were no mechanical anomalies evident on the accident airplane. The flutter consultant further stated that the accident airplane subsequently turned back to the west and began to climb back to 39,000 feet to prepare for the [easterly] dive to the 1-14 point. Discussion between the pilot and telemetry van personnel included the fact that the 1-14 point might be the last one of the mission due to fuel concerns, particularly for the chase plane. Following telemetry lock, the airplane began a shallow dive. At indicated Mach 0.884, the pilot called "Mark." Each control surface was again pulsed by the pilot, and the responses were again "well damped." Following the final pulse, the pilot was cleared to the next test point, 1-15 (indicated Mach 0.894), "if flight conditions permitted the test pilot to do so." However, the pilot did not acknowledge the clearance, but instead, reported that the airplane was rolling to the right, and he couldn't stop it. In a written statement, the chase plane pilot confirmed that after the 1-14 test point had been completed, the test pilot was cleared to accelerate to the 1-15 test point, if able. At that time, the accident airplane appeared to be in a shallow right bank with the chase plane less than 500 feet above and 500 feet behind it. According to the chase plane pilot, "very soon thereafter," about 30,000 feet, the accident airplane began rolling to the right. The rolling maneuver appeared to be stable, and continued unchanged until ground impact. The accident airplane appeared to remain intact throughout the event, and no parts were seen departing the airframe. After the accident airplane began to roll, and the test pilot stated that he couldn't stop it, the chase pilot called, "get out" twice. The accident pilot responded that he couldn't get out, that there were too many "g's." The second SSAC test pilot, who had been in the back of the chase plane, also reported that the accident sequence began after the completion of the 1-14 test point. During the sequence, the chase plane was not close enough to observe the accident airplane's control positions; however, the second SSAC test pilot observed the accident airplane's nose to be "a little low," and in an approximately 30-degree right bank after test point 1-14 was completed. A few seconds later, the accident airplane entered a "barrel-roll type maneuver" to the right, then continued to roll, and increased its dive angle until ground impact. When the second SSAC test pilot saw the first roll, his first thought was, "what did he do that for?" Then he saw that the accident airplane "came around and made another barrel roll. It was not around a point like an aileron roll; and it was not real fast; it looked lazy." The chase pilot then mentioned the roll to the accident pilot, who replied that he couldn't stop it. The accident pilot did not say anything further about how the airplane was performing, or what he was experiencing. At some point during the sequence of events, the accident pilot transmitted information about the flight controls and/or aileron trim; however, witness accounts differed on what and when it was transmitted. According to the chase plane pilot, the accident pilot stated, "I can't let go" after he was cleared to test point 1-15. The flutter DER stated that the accident pilot advised he "could not release the wheel" shortly after the 1-14 aileron pulse, and a telemetry engineer, who was calling out airspeeds to the DER, stated that the accident pilot reported, "full aileron trim and I can't let go" when the accident airplane had accelerated to Mach .881, prior to the 1-14 pulses. PERSONNEL INFORMATION -- Accident Pilot -- The accident pilot held an airline transport pilot certificate, with ratings for the Boeing 707, 727, and 747, and Airbus 300. He also had combat experience in the Vought F8J Crusader, and served a total of 30 years as an active duty and reserve Naval officer. According to the pilot's resume, dated July 2, 1996, he had 12-13 years of flight test experience prior to joining SSAC, including experience at LTV (Ling-Temco-Vought) Aerospace, Douglas Aircraft, the U.S. Navy, and General Electric. He was not a test pilot school graduate. Between 1966 and 1969, the pilot flew A-1 Skyraiders, then transitioned to the A-3 Skywarrior. He subsequently flew EKA-3B conversion flights from a depot level rework facility, and later, F-8 Crusader and F-4 Phantom acceptance flights. In 1969, the pilot qualified as a Boeing 727 flight engineer for a major airline. Later that year, when he was furloughed from the airline, he qualified as an agricultural application pilot. He later became involved in a short take off and landing (STOL) conversion as both a "project pilot" and a flight demonstration pilot, and he also flew the F-8 Crusader in an operational reserve fighter squadron. From 1970 to 1972, the pilot was carrier-based, flying combat missions in Vietnam. He applied for the U.S. Navy Test Pilot School, but was shot down and captured about 1 week before selections were made. Once repatriated, the pilot pursued a college degree while concurrently serving as a fighter pilot instructor. The pilot subsequently completed two more tours of operational duty. In 1973, the pilot again qualified as a flight engineer on a Boeing 727, and flew with a major airline through 1974. Between 1978 and 1983, the pilot participated in flight testing a turbine-powered agricultural application airplane, involving liquid and dry material dispersing. Between 1983 and 1985, the pilot served as a System Safety Engineer at Douglas Aircraft Company for the development of a Navy T-45 training system. As such, he was involved in hazard analysis and system safety for three prototype airplanes, along with simulators and academics. He also participated in system safety and hazard analysis for the NASA propfan program. Between 1985 and 1988, the pilot was a flying flight test engineer on the McDonnell Douglas MD-80 transport airplane. Records indicate that, in 1989, the pilot was hired as an "experimental test pilot" at General Electric's Flight Test Operation - Mojave. As one of only two pilots, he was "involved in virtually all aspects of testing for the various CFM Series, CF-6 Series and GE-90 Series engines." Testing included "stabilization on a test point, low altitude Vmax speed points, wind-up turns, airstart envelope determination, V2 climb profiles, over-rotation tests, aircraft stall maneuvering, high AOA investigation, zero 'g', various operability trials and profiles, plus others throughout the test envelope." The pilot became rated in the Boeing 707, 747 and Airbus 300 at that time. The pilot also reported that he was a member of the Society of Experimental Test Pilots, and wrote the organization's Flight Readiness Review and Preflight documentation. According to SSAC records, the pilot joined the company in 1997, and was serving as chief test pilot when the accident occurred. Prior to the accident flight, he had accumulated 294 flight hours in the accident airplane, and 331 flight hours in airplane serial number 001. The pilot's logbook was not recovered after the accident, and according to an SSAC representative, the pilot always took his logbook with him on his flights. On July 3, 2002, the pilot's latest Federal Aviation Administration second class medical certificate was issued, and at that time, he reported 12,000 hours of total flight experience. The second SSAC pilot reported that the accident pilot did not have experience performing flutter tests, but as chief pilot, he wanted to do it. The second pilot, who did have experience with flutter testing, provided training to the accident pilot. "I checked him out - he wanted to do it - we went out and I demo'd it, and he did it. He understood it; he's an F-8 guy. If I had any qualms about it, he wouldn't have been able to do it." The second SSAC pilot also stated that the accident pilot knew to slow the airplane should he run into any difficulty. "We discussed it a lot (power idle). We talked and talked about throttles idle. In my mind, I know he did that." -- Second SSAC Test Pilot -- According to the second SSAC test pilot's undated resume, he had previously served as a test pilot at McDonnell Douglas on the MD-80 series and MD-11 certification programs. He also served as chief pilot, and was responsible for six test pilots and six loadmasters. The second test pilot reported 7,000 hours of flight time, with 3,000 hours of test pilot experience over a 15-year period. He was also a graduate of the U.S. Air Force Test Pilot School. -- DER -- Per a technical services agreement, the flutter consultant DER was hired to "provide oversight and guidance in the execution and documentation of flutter analysis" for certification compliance with FAR 23. In conjunction with the agreement, the consultant was "given authority as director of test preparation, test conduct, and analysis of results." According to the DER's undated resume, he had worked in the field of aircraft flutter and dynamics for over 30 years. He had also been employed by Boeing for 12 years as a specialist engineer in flutter and vibration, and was involved with the Boeing 707, 727, 737, 747, and served lead engineer for the YC-14 flutter group. Previously, he performed flutter work, as a dynamics engineer, for development of the British Aircraft Corporation (BAC) Concorde. He became an independent DER in 1981, and "supported engineering work on projects ranging from the Cessna 180 to the Boeing 747 aircraft, with engineering analysis, design and testing as required for individual programs." The DER also had several published papers to his credit, including "Transient Excitation and Data Processing Techniques Employing the Fast Fourier Transform for Aeroelastic Testing," "Effect of Stabilizer Dihedral and Static Lift on T-Tail Flutter," and "The Use of Transient Testing Techniques in the Boeing YC-14 Flutter Clearance Program." COMPANY INFORMATION According to a company representative, in May 1995, The Sino Swearingen Aircraft Company was formed as an international joint venture between Swearingen Aircraft, Incorporated, and Sino Aerospace Investment Corporation, Taipei, Taiwan. The Company's status later changed to a Corporation. The original proof-of-concept SJ30, serial number 001, was built by Swearingen Aircraft, Inc., in the early 1990s, and first flew on February 13, 1991. In the mid-1990s, due to market demands and the products offered by competitors, the airplane was reconfigured. It was lengthened considerably, the wings were changed from anhedral to dihedral, and a new avionics suite was installed. It first flew in the new configuration in November 1996. By the time of the accident, the company h
The manufacturer's incomplete high-Mach design research, which resulted in the airplane becoming unstable and diverging into a lateral upset.
Source: NTSB Aviation Accident Database
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