History of Flight
On May 16, 2009, at approximately 1548 Eastern Daylight Time, a Diamond Aircraft Industries GmbH DA 40, registration N323JT, operated by Waltzing Matilda Training LLC, experienced separation of the right main landing gear during landing at Norwood Memorial Airport (OWD), Norwood, Massachusetts. Visual meteorological conditions prevailed, and no flight plan was filed for the 14 CFR Part 91 instructional flight. The aircraft was substantially damaged; the certificated student pilot, the sole occupant, was not injured. The flight originated at OWD about 1543.
The student pilot reported that earlier that day he flew with his certificated flight instructor (CFI) and performed three touch-and-go and two full-stop landings, all uneventful. His CFI signed him off for his first solo flight and exited the aircraft. The student departed and remained in the traffic pattern for runway 10, turning onto downwind, base, and final. While on final approach with flaps extended, he maintained 75 knots and reduced power to 15 inches of manifold pressure when over the threshold. He leveled the aircraft, then applied aft elevator control input, resulting in a slow decrease in airspeed followed by activation of the stall warning horn. The aircraft landed with an indicated airspeed between 60 and 65 knots without bouncing, and turned left. He applied right rudder pedal input and right brake to correct but was unsuccessful. The longitudinal axis of the aircraft was not aligned with the runway, and while sliding approaching the edge of the runway, he heard a noise and felt a bump, which he thought was the landing gear breaking. After coming to a stop, he notified the tower and exited the aircraft. The student further reported that prior to the accident flight he had performed 39 landings.
The CFI stated that he flew with the student earlier that day practicing five normal and abnormal landings, which he described as "safe." The weather conditions were "prime" for the student's first solo flight; the wind was straight down the runway at less than 10 knots, and the windsock at the approach end of the runway indicated no wind. After receiving his endorsement for solo flight, the student started the engine and taxied to runway 10.
The CFI elected to stay on the ramp to observe the flight and was located approximately 400 yards away. He reported seeing the aircraft on final approach with flaps down and perceived that the ground speed was good and the pitch attitude was stable. The aircraft's first ground contact was located within 500 to 600 feet from the displaced threshold, and there was no float or bounce. The longitudinal axis of the aircraft appeared aligned with the runway at touchdown. Approximately 1 to 3 seconds later, he noted that the aircraft pitched up and the right wing raised, followed by the sound of screeching tires. He reported the pitch up wasn't "too steep," and the aircraft bounced no more than 1 to 2 feet. The aircraft veered off the north side of the runway, and the CFI reported a "very violent skidding turn (brakes alone would not cause such a violent turn)."
Personnel Information
The student pilot, age 31, was issued a Federal Aviation Administration third class student pilot medical certificate on March 31, 2009, with a limitation to wear corrective lenses. The National Transportation Safety Board Pilot/Operator Aircraft Accident/Incident Report submitted by the operator indicated the student pilot had 17 hours total time, all of which were in the accident make and model aircraft. Within the last 90 days and 30 days, he accumulated 8 and 7 hours, respectively. Other than the accident flight, he did not have any logged solo flight time.
Aircraft Information
The fixed tricycle gear, composite aircraft was manufactured in 2006 by Diamond Aircraft Industries, Inc., as model DA 40, serial number 40.714. It was equipped with Design Change Advisory MAM 40-123/e, which specified 18 mm thick landing gear struts. Design Change OAM 40-124, also incorporated, specified that smaller main landing gear tires (15x6.0-6) were approved for installation.
Review of maintenance records revealed the aircraft was last inspected in accordance with an annual inspection on October 31, 2008. The aircraft total time in service at that time was 174.6 hours, and at the time of the accident was 226.7 hours.
Further review revealed that on August 11, 2008, at aircraft total time 173.8 hours, a new right main landing gear tire (15x6.0-6) and new tube (6.00-6) were installed. On February 17, 2009, at aircraft total time 272.3 hours, a new right main landing gear tube (P/N 6.00-6) was installed. According to the manufacturer, the correct tube P/N based on the installed tire is 15X6.0-6.
Meteorological Information
A surface observation weather report taken at OWD at 1553, approximately 5 minutes after the accident, indicated wind calm, visibility 10 statute miles, overcast clouds at 6,000 feet. Temperature and dew point were 19°C and 12°C, respectively. The altimeter setting was 30.05 inches of mercury.
Airport Information
Norwood Memorial Airport is equipped with two asphalt runways designated 17/35 and 10/28. Runway 10/28 is 3,995 feet long and 75 feet wide.
Wreckage and Impact Information
Examination of the runway by a representative of the airframe manufacturer and an FAA inspector revealed skid marks corresponding to the left and nose landing gear tires, left of runway centerline, beginning approximately one-third down the runway. The skid marks from the left and nose landing gears depicted a left arc and were nearly continuous to the north edge of the runway. Two distinct skid marks associated with the right main landing gear were noted at the end of the skid marks near the north edge. A gouge in the runway surface associated with the right main landing gear wheel skid mark was noted; the right main landing gear skid marks were serpentine. The total length of the skid marks was 247 feet. The aircraft came to rest upright on grass off the north side of the runway, with the right main landing gear nearly separated.
Examination of the aircraft revealed that the right main landing gear remained attached only by brake hoses. A spanwise crack was noted in the upper wing skin of the right wing from the wing root outboard. The right main landing gear wheel assembly was broken into large pieces almost to the center where the two halves join. The outboard rim was scarred and abraded by the runway surface. The right main landing gear tire (15x6.0-6) was flat and exhibited sidewall damage appearing as cuts; there were no wear or skid marks on the tread surface. The inner tube had a 5-inch-long split along its inside centerline. The wheel fairing was severely damaged.
Inspection of the right wing revealed the outer main landing gear rib (P/N D41-5313-52-00_2-00) with attached main landing gear leg was torn out of the right wing center section. The aluminum retaining plate (P/N D41-3213-01-51), which secured the right main landing gear, showed bending damage in the forward one-third of its length. The right main landing gear leg (P/N D41-3213-12-50) was bent inward approximately 7 degrees at the lower radius and approximately 2 degrees about the vertical axis. The right outer main landing gear rib was retained for further examination.
Inspection of the left main landing gear tire revealed uneven wear (flat-spotting) and reduction of sidewall-to-tread radius on one-quarter of the tire circumference. Indications of high-temperature shredding of rubber on the outboard radius were noted; rubber fragments were noted on the sidewall/tread radius. Inspection of the nose landing gear tire revealed signs of skidding on the left tread surface only; the angle of abrasion was 90 degrees to the roll line.
Tests and Research
The right landing gear outer rib was submitted to the NTSB Materials Laboratory for examination. The rib, approximately 7 inches tall, was adhesively bonded at the forward and aft surfaces to vertical webs of the front and rear spar carry-through structures and to the inside surface of the upper wing skin. No mechanical fasteners were used to attach the rib to the spars or wing skin. The main landing gear leg was clamped between an upper nylon block and a lower rubber-cushioned aluminum bar at the bottom of the rib.
The rib bonding agent consisted of epoxy matrix material mixed with cotton fibers and fumed silica particles. No indications of improperly mixed or cured adhesive were found. A Diamond representative reported that the paste would have been brushed onto both the rib and spar surfaces, with expected bond thickness between 2 to 4 mm (0.08 to 0.16 inch); the bond thickness on the top of the rib was not strictly controlled. At the forward end, the adhesive layer remaining on the rib ranged from 0.09 to 0.21 inch thick. At the aft end, it ranged from 0.08 to 0.13 inch thick. Along the top surface, it ranged from 0.31 to 0.33 inch thick.
The aluminum bar at the bottom of the rib that clamped the right main landing gear leg was made of 3.1354 T351 aluminum (comparable to 2024 T351), with a minimum specified yield stress of 290 MPa (42 ksi). The bar was bent in a smooth arc centered approximately 1.2 inches back from its forward edge, with the forward end oriented at an angle of about 12 degrees. A localized linear indentation on the top surface approximately 0.95 inch back from the forward edge was consistent with downward force from the landing gear leg. The forward bolt hole was somewhat elongated. The forward bolt that held the clamping bar was bent at an angle of about 7 degrees, approximately 1.1 inch up from its bottom end. The aft bolt was not visibly deformed.
The space between the top of the main landing gear leg and the bottom recess in the rib was filled by a nylon block machined to fit. At the aft end of the rectangular slot in the block, the nylon above the leg retained some permanent deformation, with a small reduction in thickness and an increase in width of about 0.05 inch, consistent with an upward force from the leg in that location. The upper flange of the rib was cracked just aft of the upper forward corner; the crack extended transversely approximately 1.1 inch from the inboard edge. A triangular region of the flange behind the crack retained delaminations and upward permanent deformation, consistent with an impact on the interior of the flange aft of the crack.
The fractured adhesive bond at the forward end of the rib generally occurred near the interface between the adhesive and the rib, near the interface between the adhesive and the front spar, or through a void. The forward adhesive bond included relatively large voids estimated to occupy approximately 30 percent of the bonded surface area. A Diamond representative indicated that voids up to 8 mm (0.31 inch) are generally accepted without repair. At the top and bottom of the forward surface, fracture occurred near the interface between adhesive and rib, with lighter-colored areas indicating exposed glass fabric. The white areas away from voids are where fracture occurred near the interface between adhesive and front spar, as the adhesive surface showed imprints of a 2x2 twill fabric.
The fractured adhesive bond at the aft end generally occurred near the interface between adhesive and rib or rear spar. Voids were present but appeared consistent with expected size of 8 mm or less. On the lower three-quarters of the surface, fracture was near the adhesive-rib interface, forming a fan pattern of light and dark regions emanating from the inboard edge. The lighter areas were exposed glass fabric; darker areas predominantly associated with fracture in the matrix material slightly away from the glass fabric. The upper one-quarter showed fracture near the adhesive-rear spar interface, with imprints of 2x2 twill fabric and crushed/powdered adhesive.
The fractured adhesive bond at the top generally occurred near the adhesive-rib interface, with remaining fracture near the adhesive-wing skin interface. Beginning about 3 inches aft of the front and extending aft, adhesive was fractured at both interfaces, held in place by foam strips. Voids were present but consistent with expected size. About 1.75 inches aft of the front edge, a 0.5-inch-wide strip of accumulated interconnected voids was noted.
The fracture at the bottom forward lip occurred near the adhesive-rib interface, with parts at voids, including one void continuous with the large forward void. Voids estimated at approximately 35 percent of the bonded surface area. Other areas showed exposed glass fabric. The fracture at the bottom aft lip also occurred near the adhesive-rib interface, with light and dark areas; voids estimated at approximately 10 percent of the bonded surface area.
A Safety Board Materials Laboratory study indicated that the maximum bending moment did not occur at the forward attachment bolt but closer to the point of load application on the bar by the forward edge of the landing gear leg. Calculations indicated the maximum tensile stress in the bar was approximately 35.7 ksi, about 85 percent of the specified minimum yield stress.