ASN Wikibase Occurrence # 230758
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| Date: | Saturday 16 November 2019 |
| Time: | 19:45 LT |
| Type: |  Agusta A109E Power |
| Owner/operator: | Sevenbar Aviation LLC |
| Registration: | N901EM |
| MSN: | 11614 |
| Year of manufacture: | 2004 |
| Total airframe hrs: | 9987 hours |
| Engine model: | Pratt & Whitney P&W 206C |
| Fatalities: | Fatalities: 0 / Occupants: 4 |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | Hancock County, Penobscot, ME -
 United States of America
|
| Phase: | En route |
| Nature: | Unknown |
| Departure airport: | Blue Hill, ME (ME15) |
| Bangor, ME (ME02) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The main rotor blade tip cap leading edge fractures initiated due to fatigue cracking with multiple initiation sites. At the time of the incident, the possibility of fatigue cracking of the leading edge of the P/N 709-0103-29-109 tip cap was a known issue, and Leonardo technical bulletin (bollettino tecnico, or BT) No. 109EP-85 and Federal Aviation Administration (FAA) airworthiness directive (AD) 2007-26-52 were previously issued to inspect for incipient cracks before they grew large enough to result in an inflight separation of the tip cap. These inspections primarily relied on visual inspection of the tip cap leading edge using magnification, and only required dye penetrant inspection of the leading edge if there are doubts about the presence of cracks or if damage other than a crack was found. It is possible that the fatigue crack on tip cap serial number L206 was present during its last inspection, but the visual inspection did not detect the presence of this crack. The crack on the tip cap leading edge remained undetected and propagated until the incident flight, when aerodynamic forces led to partial separation of the upper skin from the lower skin and core.
While a visual inspection method can detect surface cracks, variances in the inspection environment (such as lighting), inspector experience, and operators' maintenance practices can affect the success in detecting surface damage, such as a crack. After the initial issuance of BT No. 109EP-85 and FAA AD 2007-26-52, there continued to be a recurrence of partial and complete inflight separations of tip caps, with at least six known tip cap failures due to fatigue cracking. This indicates that reliance primarily on a visual inspection was not sufficient to eliminate the issue of detecting fatigue cracks before they resulted in a failure of the tip cap. A revision to BT No. 109EP-85 required dye penetrant inspection of the tip caps, which should provide a more reliable inspection method for identifying surface cracks.
Probable Cause: Fatigue fracture of the main rotor blade tip cap leading edge and subsequent partial separation of the tip cap, resulting in increased vibrations in the main rotor.
Accident investigation:
 |
|
Sources:
NTSB ENG20IA005
FAA register: https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=N901EM
https://flightaware.com/resources/registration/N901EM
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 19-Nov-2019 00:51 | Geno | Added |
| 19-Nov-2019 17:11 | Terry Smith | Updated [Registration] |
| 04-Feb-2021 12:26 | Aerossurance | Updated [Source, Narrative] |
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