NTSB Identification: SEA96IA074.
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Scheduled 14 CFR operation of HORIZON AIR
Incident occurred Sunday, March 31, 1996 in EUGENE, OR
Probable Cause Approval Date: 02/28/1997
Aircraft: Dornier DO 328-100, registration: N334PH
Injuries: 27 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

The flight crew reported that as the airplane was climbing between 14,000 feet and 16,000 feet in light icing conditions, they felt a moderate shudder. The autopilot disconnected, and the airplane immediately rolled 15 degrees to the left. An emergency was declared, and the flight was diverted with no further incident. After landing, examination revealed that a section of the left wing de-icing boot had delaminated. When pressure was applied to the system, a bubble was created. When pressure was off, the delaminated plies were stretched beyond their elastic limits and would not return to the normal shape, thus creating wrinkles. Examination of the plies revealed that there was no evidence of contamination. The separation occurred between the adhesion coat and the knit fabric. The manufacturer of the boot reported that this mode of failure was consistent with an elastromeric construction that had reached the end of its useful life. The outer delaminated plies were found to be unusually durable, which resulted in a large bubble instead of the normally expected 'burst' of the outer plies.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

delamination of the wing de-icing boot, due to the boot reaching its life limit.

Full narrative available

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