Accident McDonnell Douglas MD 500E (369E) N142MK, 21 Jan 2005
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ASN Wikibase Occurrence # 294155
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Time:16:30 LT
Type:Silhouette image of generic H500 model; specific model in this crash may look slightly different    
McDonnell Douglas MD 500E (369E)
Registration: N142MK
MSN: 187E
Fatalities:Fatalities: 0 / Occupants: 5
Aircraft damage: Substantial
Location:Pahoa, Hawaii -   United States of America
Phase: Unknown
Departure airport:Hilo International Airport, HI (ITO/PHTO)
Destination airport:
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The helicopter impacted small trees during an autorotational landing that was preceded by the in-flight separation of a tail rotor blade abrasion strip. According to the pilot, the helicopter developed a "sudden vibration in the tail rotor pedals followed immediately by a loud 'crack' or 'snap', and then an extremely loud banging noise and a sharp vibration in both airframe as well as the tail rotor pedals." The pilot made an off-airport autorotational landing to a clearing, but during the landing flare, the tail section snagged a tree. Post-accident examination of the tail rotor blades revealed that the leading edge abrasion strip debonded from one of the blades. Based on the surface finish, the debonding was most probably an adhesive failure at the interface with the abrasion strip. The cause of the bond failure is unknown, but could be the result of in-service conditions, a production problem, or undetected impact damage. The adhesive is the primary means of holding the strip to the blade, but there are also two rivets on the inboard end of the blade that serve as a secondary securing method. The abrasion strip fractured at the outboard rivet and the fracture surface revealed evidence of fatigue cracking indicating that the abrasion strip was completely debonded for a period of time. In addition, dark sooty deposits were visible in the bond area on both sides of the blade. Maintenance records indicated that the helicopter underwent a 100-hour inspection approximately 62 hours prior to the accident. The inspection calls for a visual examination of the tail rotor blades to ensure no separation of the bond around the edges or at the tip end of the blade exist. The inspection process calls for a dye-penetrant inspection or tap test only if a debond is suspected. However, detection of the debond during the visual only 100-hour inspection would depend on whether the separation intersected on the strip edges. The preflight examination procedures called for the pilot to visually examine the tail rotor blades to ensure there is no debonding along the abrasion strip-to-airfoil bond line. The pilot reported that he inspected the abrasion strip prior to the accident flight, but did not notice any evidence of an abrasion strip debond. The blade accumulated 2,379.7 total hours of operation, and 1,820.6 hours since its last overhaul.

Probable Cause: the in-flight separation of the tail rotor blade abrasion strip due to a degraded adhesive bond and fatigue fracture of the metallic abrasion strip. The ultimate cause for the degraded bond is unknown.



Accident investigation:
Investigating agency: NTSB
Status: Investigation completed
Duration: 1 year and 3 months
Download report: Final report

Revision history:

10-Oct-2022 17:58 ASN Update Bot Added

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