ELTOPIA, WA, USA
N5360V
Hiller UH-12E
The pilot reported that he had just taken off to the south. About 30 seconds into the flight, a control paddle departed the helicopter, and control was lost. The helicopter crashed in a cornfield and rolled inverted, after which the pilot exited. Post-crash examination revealed that a flight control rotor blade departed the helicopter. The spar from the blade separated from a fatigue crack, which originated near one of the outboard retention bolt holes and propagated nearly all of the way around the spar on both sides. The NTSB materials laboratory determined that the fatigue cracking initiated from corrosion pitting. FAA Airworthiness Directives in effect at the time of the accident required inspection of the spar tube, cuff, and bolt holes every 100 hours to detect corrosion and cracking in accordance with a Hiller service bulletin. This service bulletin required a visual inspection for corrosion of the inside surface of the cuff and the inner and outer surfaces of the spar tube. This visual inspection was to be followed by a dye-penetrant inspection of the spar and the cuff to detect any cracks. Although logbook entries (of less than four months and 70 hours time in service before the accident) cited compliance with the relevant AD and service bulletin, no evidence was found of dye penetrant residue, zinc chromate primer, or the required sealant material during NTSB materials laboratory testing.
HISTORY OF FLIGHT On July 7, 1998, approximately 0615 Pacific daylight time, a Hiller UH-12E agricultural helicopter, N5360V, registered to and being operated by Jack Gillette Flying Service, and being flown by a commercial pilot, was destroyed during a collision with terrain in a corn field immediately following takeoff near Eltopia, Washington. Following the ground impact, the helicopter was consumed by a post-crash fire. The pilot sustained minor injuries. Visual meteorological conditions existed, and no flight plan had been filed. The flight, which was to have been conducted for the purpose of dispensing an insecticide, was to have been operated under 14CFR137. The pilot reported that he had just taken off to the south. About 30 seconds into the flight, a control paddle departed the helicopter, and control was lost. The helicopter impacted the ground and rolled inverted, after which the pilot exited (refer to photograph 1 and DIAGRAM I). AIRCRAFT INFORMATION An inspector from the Federal Aviation Administration's (FAA) Spokane Flight Standards District Office (FSDO) examined the helicopter's logs and records, and also conducted a post-crash examination of the helicopter at the accident site. He reported that the helicopter's total time in service was 8,600.2 hours, and 69.1 hours of service had accumulated since following the last inspection. A review of the helicopter's logbook revealed that an annual inspection had been accomplished on March 11, 1998, at a total airframe time of 8,531.1 hours. The annual inspection signoff contained an entry stating in part "-C/W AD 97-10-16 DYE CHK CUFF & SPAR TUBE AS PER PAR A & SB 36-1 REV 3-" (refer to ATTACHMENT L-I). The most recent inspection in the logbook which immediately preceded the March 11, 1998, inspection, was recorded as an annual on March 4, 1997, at a total time of 8,305.6 hours. Additionally, a register of Airworthiness Directive (AD) compliancy notes was maintained with the helicopter's log records. One page of this listing showed that AD 97-10-16 had been complied with on 2/3/98, at a total time of 8,531.1, and again at a total time of 8,631.1 hours. This entry was signed off, as in the helicopter's logbook, with an Inspection Authorization (IA) identification number of IA1982827 (refer to ATTACHMENT ADL-I). Airworthiness Directive (AD) 97-10-16 (effective date 6/26/97) states in part: "To prevent separation of the control rotor blade assembly and subsequent loss of control of the helicopter, accomplish the following: (a) Within the next 100 hours time-in-service (TIS) after the effective date of the AD, unless previously accomplished within the last 100 hours TIS, and thereafter at intervals not to exceed 100 hours TIS from the date of the last inspection, or at the next annual inspection, whichever occurs first, inspect the blade spar tube and cuff for corrosion or cracks, or elongation, corrosion, burrs, pitting or fretting of the bolt holes, and repair, as necessary, in accordance with the Accomplishment Instructions of Hiller Aviation Service Bulletin No. 36-1, Revision 3, dated October 24, 1979," (refer to ATTACHMENT AD-I). Hiller Aviation Service Bulletin (SB) No. 36-1, Revision 3, (dated October 24, 1979), provides specific procedures and corrective actions for the inspection of the retention bolt holes and control rotor cuffs (refer to ATTACHMENT SB-I). Among the procedures outlined, the SB specifically addresses the following procedures: "A. Remove the two bolts attaching the control rotor blade spar to the cuff and withdraw the blade from the cuff." "B. Inspect for corrosion on the exterior and interior of the spar tube as well as-" "C. Remove rust spots by-" "D. Dye-penetrant inspect the spar area which fits inside the control rotor cuff, paying particular attention to-" "E. Inspect spar tube retention bolt holes for elongation, corrosion, burrs,-" "F. If burrs are found, deburr bolt holes, paying particular attention to-" "G. Dye-penetrant inspect the outer seven (7) inches of the control rotor cuff paying particular attention to the four bolt holes. If cracks are found-" "H. If the control rotor attach bolts (AN174-26) show signs of wear or rust, they should be replaced.-" "I. Protect the spar tube by lightly coating areas of bare metal with two coats of zinc chromate primer." "J. Reinstall-" "K. Apply sealant material between bolt head or nut and cuff, covering the edges of the washer for the purpose of-" "L. Upon compliance, make appropriate entry in helicopter log book." WRECKAGE AND IMPACT INFORMATION The control paddle was subsequently recovered some distance from the main crash site. Post-crash examination by the Spokane FSDO inspector revealed that the yellow control paddle blade cylindrical spar tube had separated at a bolt hole inside the main rotor cuff (refer to photographs 2 and 3). The separation surfaces displayed corrosion. The yellow spar tube and cuff, along with the opposing blue spar tube and cuff, were shipped to the Safety Board's metallurgical laboratory in Washington, D.C., for further examination. TESTS AND RESEARCH Metallurgical examination revealed that the blue blade and yellow blade spars were both separated, with the inboard end of each spar retained inside the cuff. The separation of the yellow blade spar occurred through both of the outboard retention bolt holes, while the separation of the blue spar occurred through only one of the outboard retention bolt holes, with the rest of the fracture occurring further outboard toward the tip of the spar. BLUE BLADE SPAR The blue blade spar was significantly deformed adjacent to the outboard fracture face. The direction of deformation was consistent with downward motion of the outboard end of the blade, and a small buckle was noted on the underside of the spar. A corresponding bend was noted on the inboard side of the spar, at approximately seven o'clock (with twelve o'clock in the up position), where a section of the spar material was folded over the edge of the cuff. The fracture spiraled around the spar, with the fracture surface oriented along the shear plane, consistent with an overstress separation. The outside surface of the spar had not been painted or primed where it had been inserted into the cuff, and significant corrosion pitting was evident in this area. The inside surface of the spar on both sides of the fracture had been brushed with a yellow-green material, consistent with the application of a chromated primer. No sealant material was noted on the retention bolt heads, nuts, or washers. Both priming of the surface and sealing of the bolts is required by Airworthiness Directive 97-10-16. YELLOW BLADE SPAR The separation of the yellow blade spar was on a transverse plane, intersecting both of the outboard retention bolt holes. The majority of the bottom half of the fracture surface was flat (intersecting the surface of the spar at a 90 degree angle) and smooth in appearance. Most of the upper half of the fracture surface was also smooth, but it was on a slightly angled plane. The small portion of each of these fracture surfaces were shiny and angled along the shear plane, consistent with an overstress separation area. The bottom half of the fracture surface near one of the retention bolt holes showed a distinct semi-circular area, consistent with a fatigue origin at the outside edge of the spar. A similar origin existed on the opposite side of the same retention bolt hole. The fatigue origins were located at the corner between the outside surface of the spar and the bolt hole. Away from the retention bolt hole, on both sides of the spar, multiple crack arrest markings were seen. Examination of the wall of this same retention bolt hole on the inboard side revealed material which had been displaced both inward and outward, past the level of the inside and outside surfaces. Examination of the inside and outside surfaces of the spar in this same area revealed cracks running radially outward from the surface of the hole and a slight elongation of the hole in the inboard direction. The displaced material and the presence of these radial cracks are consistent with crushing damage of the bolt against the inboard surface of the retention bolt hole. The inside surface of both the outboard and inboard sides of the spar had been brushed with a yellow-green coating, consistent with a chromated primer. Like the blue spar, no paint or primer was noted on the outside surface of the outboard side where it had been inserted into the cuff, nor was paint or primer observed on the outside surface of the retained side when removed from the cuff. The outside surface of the spar on both sides of the fracture contained a significant amount of corrosion pitting. No sealant material was noted on the retention bolt heads, nuts, or washers. The outboard fracture surface was examined with ultraviolet light prior to cleaning. No fluorescent crack-detection media was noted on the fracture surface. Energy-dispersive spectrometry (EDS) of both sides of the fracture surface showed no trace of phosphorous, a material commonly found in dye penetrant solutions. The inboard fracture surface was cleaned with Endox to remove oxidation buildup, then examined with a scanning electron microscope (SEM). The fracture surface in the vicinity of the origin area on both sides of bolt hole was damaged, so no exact origin location could be determined. Examination near the origins revealed scattered corrosion pitting on the outside surface. The fracture surface away from the origin contained microfissures, consistent with fatigue, over a large portion of the surface. Refer to attached Materials Laboratory Factual Report #99-68. ADDITIONAL INFORMATION The spar spars and cuffs were returned to the owner via registered mail on February 18, 1999. The helicopter's logs and records were shipped via certified mail to the owner on March 2, 1999.
Fatigue of the control rotor blade spar and failure of the maintenance inspector to follow the procedures set forth in the airworthiness directive.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
