Salina, KS, USA
N333CG
Learjet 25D
During a test flight, the airplane encountered an elevator system oscillation while in a high-speed dive outside the normal operating envelope. The 17 second oscillation was recorded on the cockpit voice recorder and had an average frequency of 28 Hz. The aft elevator sector clevis (p/n 2331510-32) fractured due to reverse bending fatigue caused by vibration, resulting in a complete loss of elevator control. The flight crew reported that pitch control was established by using horizontal stabilizer pitch trim. The flightcrew stated that during final approach to runway 17 (13,337 feet by 200 feet, dry/asphalt) the aircraft's nose began to drop and that the flying pilot was unable to raise the nose using a combination of horizontal stabilizer trim and engine power. The aircraft landed short of the runway, striking an airport perimeter fence and a berm. The surface winds were from the south at 23 knots, gusting to 32 knots.
HISTORY OF FLIGHT On June 12, 2001, at 1300 central daylight time, a Learjet 25D, N333CG, operated by Avcon Industries, was destroyed on impact with terrain while landing at the Salina Municipal Airport (SLN), Salina, Kansas. The test flight was operating under the provisions of 14 CFR Part 91 and was on an instrument flight rules flight plan. The pilot and copilot sustained serious injuries. Visual meteorological conditions prevailed at the time of the accident. The flight departed Newton City County Airport (EWK), Newton, Kansas, at 1155. According to the flight crew, the purpose of the test flight was to establish a performance baseline prior to a modification to the aircraft. The purpose of the modification was the development of a new supplemental type certificate (STC) for the Learjet model 25 airplane. The test flight profile was to execute a high-speed dive to verify and establish the vibration and buffeting characteristics of the unmodified aircraft prior to a delta-fin modification to the aft-fuselage. The flight crew stated that the airplane was to be put into a dive, at 43,000 feet pressure altitude (Palt) and that they were to follow a predetermined altitude versus speed schedule until reaching 20,400 feet, where they would execute a 1.5-G recovery. The pilot in the left seat was the pilot-in-command (PIC) and flying pilot (PF). The copilot handled the radio communications and other related pilot-not-flying (PNF) duties. According to Avcon's safety assessment procedures, the test flight was determined to be a high risk and was performed with a minimum crew. The test plan noted, "Caution, Learjets may experience aileron buzz and Mach tuck at these high speeds and Mach numbers. Discontinue evaluation if characteristics become objectionable." The flight crew reported that during the high-speed descent, at approximately 24,000 feet, the control yoke began to vibrate rapidly for approximately 3-5 seconds after which elevator control was lost. The flight crew stated that they declared an emergency with the Federal Aviation Administration (FAA) Kansas City Air Route Traffic Control Center (ARTCC) and requested to divert to runway 17 (13,337 feet by 200 feet, dry/asphalt) at SLN. The flight crew stated that pitch control was established by using horizontal stabilizer pitch trim. The flight crew reported that during final approach to the runway the aircraft nose began to drop and that the flying pilot was unable to raise the nose using a combination of horizontal stabilizer trim and engine power. The aircraft landed short of the runway, striking an airport perimeter fence and a berm. The accident airplane was equipped with a cockpit voice recorder (CVR), which was recovered from the wreckage and sent to the National Transportation Safety Board (NTSB) CVR Laboratory in Washington, D.C., for readout. The CVR recording began at 1228:22 (hhmm:ss) and continued up to the point-of-impact at 1300:00. About 1229:35, Denver ARTCC cleared N333CG to descend from 43,000 feet to 14,000 feet. The following table was compiled from the CVR Group Chairman Factual Report, the test flight card, FAA aircraft radar track data, and ARTCC transcripts of voice communications. The table depicts the high-speed dive portion of the flight: Time (hhmm:ss) Altitude (feet Palt) Target Speed (Knots IAS) Actual Speed (Knots IAS) 1230:31 43,000 251 227 1231:05 40,000 268 266 1231:27 38,000 280 280 1231:44 36,000 294 293 1232:00 34,000 308 308 1232:18 32,000 323 322 1232:34 30,000 338 336 1232:41 29,000 346 1232:48 28,000 354 350 1233:02 26,000 369 367 1233:17 24,000 384 384 At 1233:31 a sound of an unidentified chattering noise starts and continues for a period of 17 seconds. The following selections are from the CVR Group Chairman Factual Report, which is included with the docket material associated with this accident investigation. The labels HOT-1 and HOT-2 refer to the hot-microphone source for the pilot and copilot stations, respectively. 1233:55 HOT-2 I think.... 1233:56 HOT-1 I think we lost our elevator. 1233:57 HOT-2 you okay? 1233:59 HOT-1 I think we lost our elevator. 1234:01 HOT-2 okay. 1234:02 HOT-1 I'm using the trim. 1234:03 HOT-2 all right t, keep using trim. 1234:13 HOT-2 okay, I'm gonna slow down. 1234:14 HOT-1 yeah. 1234:16 HOT-2 and we'll, go out here and experiment. I'm gonna go ahead and uh, declare and emergency. is the trim working? 1234:26 HOT-1 uh, trim's working but.... 1234:27 HOT-2 okay, okay. 1234:27 HOT-1 ... no elevator. 1234:28 HOT-2 okay, all right. okay, we're gonna go into Salina. long runway, okay? 1234:34 HOT-1 uh, yeah. 1234:36 HOT-2 all right... let me get'em on the other side here. let me get myself hooked up here. we're gonna go out and do some slow flight and all kind of stuff before we try.... 1235:03 HOT-1 yeah. 1235:04 HOT-2 ... and go in. Between 1235:52 and 1236:26, the copilot declared an emergency to Kansas City ARTCC, requested to land at SLN, and N333CG was cleared direct to SLN. At 1239:19 the copilot informs Kansas City ARTCC, "...we're flying on trim and uh, we'll proceed direct to Salina and uh try to make a, a landing using trim only." N333CG was cleared to descend to 9,000 feet msl. Between 1239:40 and 1248:03, the pilot and copilot discuss aircraft configuration for the landing and how the approach will be flown. 1243:39 HOT-2 and what do you think? Maintain about a hundred and fifty knots or so on, on final.... 1243:42 HOT-1 yeah. 1243:44 HOT-2 ... at, at least. 1243:44 HOT-1 yeah. and we got thrust reversers and we got the chute if we need it. 1243:48 HOT-2 yeah. 1243:48 HOT-1 I got the brakes. 1243:49 HOT-2 yep. 1243:50 HOT-1 we do have hydralics [unintelligible]. 1243:51 HOT-2 we got thirteen thousand feet. 1243:52 HOT-1 yeah. yeah. At 1243:59, Kansas City ARTCC cleared N333CG to descend to maintain 6,000 feet. Between 1243:59 and 1253:29, the pilot and copilot discussed approach speeds, aircraft landing weight, landing flap settings, and the copilot began transferring fuel from the aft-fuselage tank. At 1248:22, SLN tower tells N333CG, "... you can make a long final if you like straight in. give us a call five miles or right base your choice one seven." The copilot responded, "okay, we'll probably just circle out north and then try and set up a long straight in." At 1249:48, SLN tower cleared N333CG for the visual approach to runway 17. At 1253:29, N333CG was about 9.5 nm north of SLN and the copilot informed SLN tower that they are turning back toward the airport. Between 1254:38 and 1255:53, the flightcrew located runway 17 and discussed the landing approach. At 1256:45, the copilot reported being on a 3 nm final for runway 17 and SLN tower cleared N333CG for landing. At 1257:15, SLN tower reported the wind as 200 degrees magnetic at 20 knots, gusting to 27 knots. 1257:18 HOT-2 okay, I'd main about a hundred and seventy if you can. 1257:21 HOT-1 okay. 1257:25 HOT-1 eeh, don't get much slower than that. 1257:37 HOT-2 everything's lookin' really good. 1257:43 HOT-2 got about, we're about plus five right now which is fine. 1257:45 HOT-1 oh, okay. 1257:46 HOT-2 about one seventy five. I'm gonna start bringing the power back just a little bit. 1257:50 HOT-1 (unintelligible word) okay. 1257:55 HOT-2 I was trying to set up a real gradual descent here. 1258:05 HOT-2 got a little bit of a right crosswind, a little bit gusty. 1258:08 HOT-1 okay. 1258:08 HOT-2 twenty gusting to twenty seven, out of two ten. airspeed's looking good. we got a hundred and eighty. everything's lookin' good. 1258:14 HOT-1 yeah, that's good, that's okay. 1258:15 HOT-2 okay, we got about a four hundred foot per minute rate of descent. everything's lookin' good. 1258:38 HOT-2 'kay, (unidentified word). hundred and almost a hundred and ninety now. 1258:43 HOT-1 ah, okay. 1258:44 HOT-2 I'll pull back a little bit more on the power. 1258:59 HOT-1 my gear is down, yep. 1259:01 HOT-2 yeah, gear is down. 1259:09 HOT-2 okay, I got a hundred and nine. 1259:10 SLN Tower three charlie golf's in sight, wind again two zero zero at two zero gusts two seven. 1259:13 HOT-2 right. 1259:14 HOT-1 okay. 1259:15 HOT-2 okay, there's a hundred and ninety knots. a little bit of nose up trim, not much, okay. 1259:25 HOT-2 almost two hundred knots now. If we can slow 'er up just little bit. little bit slower. okay, keep 'er. 1259:40 HOT-2 little, nose up trim, nose up trim, nose up trim. 1259:45 HOT-2 okay, here we go. 1259:54 HOT-2 nose up trim, nose up trim, nose up trim, nose up trim, nose up trim, nose up trim. The CVR recording ended at 1300:00. A witness reported that the airplane came "in low, then started to pull up. The tail hit the ground then it started fishtail in the wheat [field], and landed inside airport fence." Another witness stated, "I witnessed a lear jet that appeared to be in normal landing configuration on an [approximately] 3 mile final to runway 17. At [approximately] 1.5 miles [north] of the runway the aircraft's nose pitched down [approximately] 30 [degrees] and impacted the ground." According to a statement provided by SLN airport rescue and fire fighting (ARFF), "As [the accident airplane] came into sight, we noticed the aircraft was really low. As it approached, the aircraft suddenly dove at a 45-degree angle." DAMAGE TO AIRCRAFT The airplane was destroyed during the impact with terrain and the airport perimeter fence. OTHER DAMAGE The airport perimeter fence was damaged when the airplane traveled through the fence. PERSONNEL INFORMATION Pilot-In-Command: The PIC was the flying pilot and was seated in the left cockpit position. The PIC held a commercial pilot certificate with airplane single-engine land, airplane multiengine land, airplane single engine sea, and instrument airplane ratings. He was type-rated for the Learjet. The FAA issued the commercial pilot certificate on February 2, 2000. FAA records indicate his last medical examination was completed on January 25, 2001, and that he was issued a second-class medical certificate with the restriction, "Must have available glasses for near vision." The pilot reported a total flight time of 19,000 hours, of which 16,500 hours were as PIC. He had accumulated 9,000 hours in single engine airplanes and 10,000 hours in multiengine airplanes. He had logged 1,500 hours in the Learjet model 25, of which 1,300 hours were as PIC. He flew 19 hours during the last 3 months, of which 4 hours were in the accident airplane. He had flown 8 hours during the last 30 days, of which 4 hours were in the accident airplane. He flew 2.3 hours during the last 24 hours, all of which were in the accident airplane. His last flight review, as required by Federal Aviation Regulation (FAR) 61.56, was completed on May 3, 2001, in a Learjet model 25. The PIC became a naval aviator on December 18, 1953, and was assigned to the Marine Fighter Squadron VMF-451 in El Toro, California. While with the VMF-451 he flew the FJ-2 "Fury" jet fighter in California and Japan. In January 1956 he was assigned to Cherry Point, North Carolina, where he flew the TV-2, FJ-2, and FJ-3 jet fighters. The pilot completed his military career with the Marine Air Reserve in St. Louis, Missouri, and Olathe, Kansas. While with the Marine Air Reserve he flew the FJ-2, F9F-8 "Cougar", F4D "Skyray", and F8U "Crusader" jet fighters. The PIC joined Learjet Incorporated in March 1965 and became the Chief of Production Flight Test in October 1965. Between October 1965 and March 1972 he flew Learjet models 23, 24, and 25 through the production flight test syllabus. In March 1972 he transferred to the Engineering Flight Test department and flew certification test flights for Learjet models 35/36, 28/29, and 55/55C. The pilot retired from Learjet Incorporated in 1991 and subsequently became a contract flight test pilot for Avcon Industries starting in 1995. The PIC had not completed any formal test pilot training. According to FAA documents, the pilot received an order of suspension of his commercial certificate on January 7, 1998, for violating an ATC altitude clearance resulting in a loss of safe vertical and lateral separation from a passenger airliner. His commercial certificate was suspended for 15 days, after which his certificate was reauthorized. The FAA documents indicated that he was PIC of a Learjet model 35 that was performing a certification test flight within an assigned altitude block (37,000 feet to 41,000 feet). While performing flight test maneuvers he lost control of the airplane and descended below 37,000 feet. The pilot requested a lower altitude clearance in order to regain control of airplane; however, ATC instructed the pilot not to descend below 37,000 feet. He reported that he was unable to maintain 37,000 feet. He did not declare an emergency. Copilot: The copilot was the pilot-not-flying and was seated in the right cockpit position. The copilot held a commercial pilot certificate with airplane single-engine land, airplane multiengine land, and instrument airplane ratings. He was type-rated for the Learjet. The FAA issued the commercial pilot certificate on August 24, 1997. FAA records indicate his last medical examination was completed on August 6, 1999, and that he was issued a second-class medical certificate with the restriction, "Must wear corrective lenses." The copilot reported a total flight time of 5,168 hours, of which 4,500 hours were as PIC. He had accumulated 3,160 hours in single engine airplanes and 2,008 hours in multiengine airplanes. He logged 470 hours in the Learjet model 25, of which 273 hours were as PIC. He had flown 40 hours during the last 3 months, of which 26 hours were in the accident airplane. He flew 20 hours during the last 30 days, of which 16 hours were in the accident airplane. He had flown 2.3 hours during the last 24 hours, all of which were in the accident airplane. His last flight review, as required by Federal Aviation Regulation (FAR) 61.56, was completed on May 3, 2001, in a Learjet model 25. The copilot was a naval aviator and served two tours during the Vietnam war flying the F-4 Phantom. He then spent two years at the Chase Field Naval Air Station as an Advanced Jet Instructor for the F-9 Cougar. After his retirement from the military, he worked for the Cessna Aircraft Company (1976 - 1982) in sales, management, and demonstration pilot positions. He then worked for Piper Aircraft (1982 - 1983) as a Regional Administrator and demonstration pilot. From 1984 - 1992 he worked as the Vice President and General Manager of Kansas City Aviation Center. From 1992 - 1996 he was the Vice President of Sales & Operations for Avcon Industries. Currently he is the President of Avcon Industries. While at Avcon Industries he has worked as a company test pilot, as well as in the research/development and production/maintenance divisions. The copilot had not completed any formal test pilot training. AIRCRAFT INFORMATION The accident aircraft was a Learjet 25D, serial number 262, registered to Butler National Inc., and was equipped with two General Electric turbojet engines. The original airworthiness certificate was issued on October 28, 1978. The airplane was issued a special airworthiness certificate on June 8, 2001, and was certified for experimental category operations. The airplane certification was further categorized as "research and development" and "to show compliance." On June 7, 2001, at 8,419.5 hours airframe total time, 300 and 600 hour inspections were completed.
The PIC's delayed remedial action during the elevator system oscillation, resulting in the failure of the aft elevator sector clevis due to reverse bending fatigue caused by vibration, and subsequent loss of elevator control. Factors contributing to the accident were high and gusting winds, the crosswind, the airport perimeter fence, and the berm.
Source: NTSB Aviation Accident Database
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