Precursors

American Airlines, Boeing Model 747-100 series airplane, N743PA, San Francisco, CA - September 18, 1970.

Shortly after takeoff (at approximately 500 feet), the No. 1 engine sustained an uncontained failure of the second-stage turbine disk rim. The turbine blades and rim fragments penetrated the high-pressure turbine (HPT) case, engine cowling, and adjacent airplane structure. All fluid lines, electrical cables, and pneumatic ducts in the pylon area were severed, causing an intense fire which extended over the top of the left wing and lasted approximately three minutes. Two fuel tank access plates on the bottom of the wing inboard of No. 1 pylon were also penetrated by turbine fragments. Although there was no ignition of the fuel which was leaking from these two access plates, the flames propagating over both the top and bottom of the wing posed a definite danger of ignition. No fatalities resulted from this incident.

United Airlines, Boeing Model 747-100 series airplane, N4714U, Honolulu, HI - November 16, 1984.

During takeoff roll, the No. 7 tire exploded as the result of a wheel bearing failure. A fragment penetrated a fuel tank access panel on the right wing, and large quantities of fuel were spilled but never ignited. The airplane was evacuated, with some serious injuries, but no fatalities. The ability of a relatively low speed tire failure fragment to penetrate any part of the wing should have been recognized as a potentially hazardous condition.

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