Oakdale, CA, USA
N105RH
Hooker Zodiac 601XL
While entering the traffic pattern on the 45-degree entry, witnesses observed the amateur built airplane enter into a spin and impact the ground in a nose down attitude. One witness reported that the airplane was about 800 feet above the ground when he saw the wings "visibly vibrate." He saw the left wing collapse and fold rearward against the fuselage prior to the airplane entering into a spin. He further reported that he did not see anything depart the airplane. Other witnesses in the surrounding area, along with the first witness, reported that the engine sounded very loud, as if it were being revved up. They also reported that after the airplane had completed one full revolution to the right, the right wing collapsed and folded up against the fuselage. The Federal Aviation Administration (FAA) airworthiness inspector that responded to the site noted that the wings remained attached to the center section carry-through spar via their respective main spar bolts. The tail section remained attached to the empennage, with the rudder folded over the horizontal stabilizer. The entire airplane came to rest upright at the accident site. The cockpit area was thermally destroyed. The wing root areas sustained extensive thermal damage, as well as the entire tail section. The Safety Board IIC along with parties to the investigation inspected the airframe and engine at a later date following recovery of the wreckage. The airframe inspection revealed that the wings remained attached at their respective wing root attachment to center carry-through spar. Both wings' sustained severe thermal damage as a result of the post impact fire. The leading edge wing skins for both wings had separated from the wing spars and ribs about 6 feet from the wing tip inboard; the rivet holes were elongated and ovaled. Investigators noted that both wings and the associated main spars showed deformation about the longitudinal, lateral, and vertical axes of the wing with multiple "S" bends and twists in the main spars. The main wing aft attach points remained secured to the fuselage in the normal manner. The tail section remained attached to the fuselage, with damage consistent with impact forces. The engine inspection revealed no discrepancies that would have precluded normal operation. The degree of thermal destruction precluded a definitive determination of the sequence of failures within the wing structures.
HISTORY OF FLIGHT On February 8, 2006, at 1515 Pacific standard time, an experimental amateur built Hooker Zenith Aircraft Company Zodiac 601XL, N105RH, impacted flat open terrain in a nose down attitude about 1/4 mile northeast of Oakdale Airport (O27), Oakdale, California. The pilot/owner operated the airplane under the provisions of 14 CFR Part 91. The airplane was destroyed. The private pilot/owner and the certified flight instructor (CFI) were fatally injured. Visual meteorological conditions prevailed for the local area instructional flight that departed Modesto City-County Airport-Harry Sham Field (MOD), Modesto, California, about 1500. No flight plan had been filed. The wreckage was at 37 degrees 45.723 minutes north latitude and 120 degrees 47.823 minutes west longitude. Witnesses, who saw them boarding at Modesto, indicated that the CFI was seated in the left seat, and the pilot/owner was seated in the right seat. One witness, located about 1/2 mile north of the accident site, stated that he was outside on his break when his attention was drawn toward the direction of the accident airplane that was flying overhead towards Oakdale airport. The airplane was about 800 to 1,000 feet above ground level (agl). He stated that he heard a "very loud" engine and it sounded as if it were being "revved up" repeatedly. As the airplane flew to the southwest, he saw the wings visibly vibrate, and observed what he thought were pieces of metal separate from the airplane. The witness stated that the engine noise momentarily increased in pitch and volume before the "left wing collapsed and folded rearward against the" fuselage of the airplane. The nose pitched down and the airplane entered a spin to the right. The right wing collapsed upward and folded back against the fuselage. He stated that the airplane impacted the ground in a 45-degree angle, and exploded on impact. The witness further reported that the wings remained attached to the airplane, but folded back during the accident sequence. He added that he did not see any components separate from the airplane prior to impacting the ground. Additional witnesses from various locations surrounding the accident site reported that the airplane flew a wide arc to enter the traffic pattern. The engine sounded very loud, as if it were alternately being "revved up to full rpm and then going to idle." The left wing of the airplane collapsed upward, and it entered a nose down 60-degree spin to the right. The airplane completed one full revolution before the right wing collapsed upward and folded back. The airplane then struck the ground. A Federal Aviation Administration (FAA) airworthiness inspector from the Fresno, California, Flight Standards District Office (FSDO) responded to the accident site. He stated that the airplane came to rest in-between rows of trees in an orchard. The wings remained attached to the main spar running through the cockpit area. The skins of the leading edge of the wing sections for both wings separated from the wing spar, but were found in the main wreckage near their respective wings. The tail section also remained attached to the empennage and fuselage, and was folded over the horizontal stabilizer. Impact forces destroyed the airplane, and the cockpit area was destroyed in the post impact fire. According to the FAA accident coordinator, the airplane was purchased in Hemet, California. The airplane was delivered to Modesto on December 27, 2005, where it was not flown until the day of the accident. PERSONNEL INFORMATION Pilot/Owner (Right Seat) A review of FAA airman records revealed that the pilot held a private pilot certificate with an airplane single engine land rating. The last medical certificate of record was issued on January 18, 1988. It had the limitation that the pilot must have available glasses for near vision. An examination of the pilot's logbook indicated an estimated total flight time of 320.0 hours logged since February 7, 2005. According to FAA records, the pilot had a total time of 350.0 hours. Insurance records from December 13, 2005, obtained from the owner's estate, revealed that the pilot had a total flight time of 325 hours, and that he was currently working on a biannual flight review. He also indicated that he was going to utilize the Light Sport Airplane rules in place of a medical. Second Pilot/Certified Flight Instructor (CFI - Left Seat) A review of FAA airman records revealed the CFI held a commercial pilot certificate with airplane single and multiengine land, single engine sea ratings, and instrument airplane rating. The CFI also held a certified flight instructor certificate with airplane single and multiengine land ratings and instrument airplane rating. According to FAA records, the CFI had accrued 17,900 hours of total flight time. The CFI held a second-class medical certificate that was issued on May 24, 2004. It had the limitation that the CFI must wear corrective lenses. AIRCRAFT INFORMATION The airplane was an experimental amateur built 2002 Zenith Aircraft Company Zodiac 601XL, serial number 6-5301. An FAA Designated Airworthiness Representative (DAR) inspected the accident airplane and issued a special airworthiness certificate in the experimental category on April 19, 2005. According to FAA Form 8050-2 (Aircraft Bill of Sale), the accident pilot purchased the airplane from a private builder on December 13, 2005. The National Transportation Safety Board's investigator-in-charge (IIC) interviewed the previous builder/owner. He stated that the airplane was flown to Modesto on December 15, 2005, where the accident pilot/owner took possession of the airplane. Pacific Aircraft Service dated the last aircraft logbook entry January 24, 2006. The entry indicated that a copilot brake system was installed. The installation required that the control sticks and rudder bar be removed. After reinstallation of the system, the flight controls were checked for full travel and freedom of movement. Also repaired at the time were broken canopy latch cables. The airplane was equipped with a Jabiru model 3300A engine, serial number 33-A-639. The last engine logbook entry dated January 24, 2006, recorded an oil and filter change. The engine was test ran and checked for leaks. A Sensenich propeller model number AF6698, serial number W642K51 was installed new on March 3, 2005, by the builder. A review of the airplane's logbooks revealed a total airframe time of 60.1 hours on December 5, 2005. MEDICAL AND PATHOLOGICAL INFORMATION Pilot/Owner The Stanislaus County Coroner conducted an autopsy on the pilot on February 9, 2006. The FAA's Civil Aerospace Medical Institute (CAMI) Forensic Toxicology Research Team, Oklahoma City, Oklahoma, performed a toxicological analysis from samples obtained during the autopsy. The results of the analysis of the specimens were negative for carbon monoxide, cyanide, volatiles, and tested drugs. Pilot/Certified Flight Instructor (CFI) The Stanislaus County Coroner conducted an autopsy on the CFI on February 9, 2006. The FAA's CAMI Forensic Toxicology Research Team, Oklahoma City, performed a toxicological analysis from samples obtained during the autopsy. The results of the analysis of the specimens were negative for carbon monoxide, cyanide, volatiles, and tested drugs. TESTS AND RESEARCH Investigators from the Safety Board, the FAA, and the kit manufacturer, a party to the investigation, examined the wreckage at Plain Parts, Sacramento, California, on March 16, 2006, and again on November 16, 2006. The Safety Board IIC noted that the engine had sustained thermal damage due to the post impact fire. One propeller blade was attached at the propeller hub assembly, which remained attached to the engine. The propeller blade, wooden in construction, had impact damage, and was partially consumed by the post impact fire. There were no obvious mechanical malfunctions noted with the engine that would have precluded normal operation. The airframe inspection revealed that the wing spar was a center spar construction, with the wings attached at the root area with six main spar bolts on each side. Eleven of the main spar attach bolts were found in their normal position and remained connected by their respective retaining nuts and washers. Recovery personnel had disassembled the twelfth bolt during retrieval of the airplane. According to the build diagram specifications, the wingspan measured from wing tip to wing tip was 27 feet in length. The as measured length of the wings in the wreckage from wing root to a wing tip was 11.9 feet. The inboard section of both wings' leading edge were either thermally consumed or partially consumed in the post impact fire. Both wings were fire damaged at the wing root areas, with the bottom portion split open from impact forces. About 6 feet from the wing tip inboard, leading edge wing skin from both wings had separated from the wing spar and ribs. The rivet holes were elongated and oval shaped from the spar aft to the trailing edge of the outboard portions of leading edge wing skin that had not been fire damaged. Both sections were crushed and accordioned in appearance. Investigators noted multiple S-bends and distortions of the spars of both wings in multiple directions at the wing root areas. Investigators noted that both wings were displaced forward of their normal position along their lateral axis. The left wing front spar rotated aft, with a sharp bend about midspan of the wing near a support doubler. At that point, the wing spar rotated forward. At the center spar to wing root attachment area, the spar had a "U" shape to it with the opening of the "U" towards the bottom of the wing. The wing spar material from the wing root outboard to the support doubler had splayed apart. The center spar to the right wing root was bent down about 2 feet, then the front portion of the wing spar rated forward. About mid wing span the front wing spar rotated in an aft direction. The aft spar attach point was intact. Examination of the tail section revealed that the horizontal tail with two sections; the stabilizer (non-moving) and the elevator (which moves up and down to control the pitch), and the rudder remained attached to the empennage. The horizontal stabilizer remained connected to the tail assembly by two of the four elevator attachment brackets. The two attachments brackets were located on the right side (front and rear). The front and rear attachment brackets for the left side had separated. The bolt, nut, and retaining hardware had pulled out of the front left attachment bracket at a 45-degree angle. The bolt, nut, and retaining hardware remained attached to the horizontal stabilizer at the L-bracket. The left rear attachment bracket retained the bolt, nut, and retaining hardware and a portion of the L-bracket. The retaining hardware for the right front and rear attachment brackets were removed to facilitate inspection of the tail assembly. There were no other discrepancies noted with the tail section. Weight and Balance Information According to the manufacturer's build plans for the airplane, the maximum gross weight is 1,300 pounds, with a design load factor of +/- 6 G's. The airplane was equipped with standard fuel tanks (total 24 gallon), with 3 gallons of fuel considered unusable. The fuel burn was determined to be 5.5 gallons per hour. The Safety Board IIC contacted SkyTrek Aviation at MOD for fuel record information. SkyTrek personnel did not refuel the airplane the day of the accident, nor had they refueled the airplane during the preceding two months that it had been at MOD. The Safety Board IIC interviewed the ferry pilot who transported the airplane from Hemet, California, to MOD. He stated that 3 or 4 days prior to leaving for MOD, he flew the airplane for about 30 minutes and noted no abnormalities. According to his logbook entries, on December 23, 2005, he departed Hemet with full fuel tanks. Due to bad weather, he landed at Bakersfield (L45), California, and recorded a total flight time of 2.7 hours. He left the airplane at Bakersfield for a couple of days and returned on December 27, 2005, and departed for MOD. He stated that the weather had mostly cleared up, but that he had decided to "top off the tanks" just in case. The flight to MOD was recorded as 2.1 hours. The Safety Board IIC calculated the weight and balance for the airplane utilizing the following information: Basic Empty Weight 754.5 pounds Pilot 1 - 200 pounds Pilot 2 - 230 pounds (estimated weight provided by the Coroner 220-240 pounds) Baggage - 10 pounds Fuel - 12.45 gallons (74.7 pounds) The calculations yielded the following information: At 6.23 gallons of fuel, the airplane's gross weight was 1,289.5 pounds. At 9.34 gallons of fuel, the airplane's gross weight was 1,308.2 pounds. At 12.5 gallons of fuel, the airplane's gross weight was 1,326.7 pounds. ADDITIONAL INFORMATION The IIC released the wreckage to the owner's representative. Federal Aviation Regulation's (FAR) pertaining to airman medical requirements in regards to sport pilot can be found under FAR Part 61, subpart A - General, and subpart J Sport Pilots. Section 61.21b "Operation not requiring a medical certificate" Section 61.21c "Operations requiring either a medical certificate or U.S. driver's license" Section 61.53 "Prohibition on Operations During Medical Deficiency" Section 61.303 "If I want to operate a light-sport aircraft, what operating limits and endorsement requirements in this subpart must I comply with?" Section 61.315 "What are the privileges and limits of my sport pilot certificate?" The Safety Board IIC noted that registration paperwork submitted by the builder (Mr. Hooker) showed that the aircraft manufacturer was Zenith Aircraft Company. It should be noted that the correct aircraft manufacturer should have been Mr. Hooker as he built the airplane.
the structural failure of the wings for undetermined reasons.
Source: NTSB Aviation Accident Database
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