Analysis 135 Aircraft Accident Report
scenarios using vertical stabilizer structural models, conducted three postaccident static
lug tests, and evaluated certification documents.
No deviations from the original design and materials specifications were found in
the vertical stabilizer (including the repair to the left center lug area that was made during
manufacturing) that would have contributed to the vertical stabilizer separation. Also, a
detailed inspection of flight 587’s wreckage, including an extensive examination of the
vertical stabilizer main attachment fitting fractures, revealed that each main attachment
fitting had features that were consistent with overstress fracture and exhibited no evidence
of fatigue features or other preexisting degradation. Fracture features and damage patterns
on the right forward, center, and rear lugs were consistent with overstress failure under
tensile loading. The right rear lug, in particular, had fracture features that were consistent
with failure in the cleavage-tension mode. Fracture features and damage patterns on the
left forward, center, and rear lugs had features that were consistent with the vertical
stabilizer bending to the left after separation of the lugs on the right side.
Safety Board investigators conducted an airplane performance study to describe
the motion of the accident airplane, identify the causes of the motion, and calculate the
resulting aerodynamic loading on the vertical stabilizer.
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The airplane performance study
revealed that the first officer’s cyclic rudder pedal inputs, which began about 7 seconds
before the vertical stabilizer separation, led to increasing sideslip angles that, along with
the continued rudder deflections, produced extremely high aerodynamic loads on the
vertical stabilizer. The airplane performance study indicated that, at 0915:58.4, when the
vertical stabilizer separation began, the aerodynamic loads on the vertical stabilizer were
about two times the loads defined by the limit load design envelope (see figure 15).
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Given the aerodynamic loads at the time that the vertical stabilizer separated, it can
be determined that the vertical stabilizer’s structural performance was consistent with
design specifications and had exceeded certification requirements. However, to determine
if stresses in the vertical stabilizer at the time of failure corresponded to a material failure,
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On March 5, 1966, British Overseas Airways flight 911, a Boeing 707, departed Tokyo for Hong
Kong with 124 people and the cabin crew aboard. Because of the clear weather at the time, the pilot asked
for and received an amendment to the scheduled flight plan that would allow his passengers an up-close
view of Mt. Fuji. Shortly after the airplane began its descent toward the mountain, witnesses reported seeing
the airplane trailing white vapor and shedding pieces. The witnesses also reported that they saw a large puff
of vapor that came from the airplane’s vertical stabilizer and that the airplane pitched up and entered a flat
spin. The witnesses further reported that the vertical stabilizer assembly and engines were missing, the
outer wing had failed, the forward fuselage broke off, and the airplane continued in a flat spin until it crashed
into the base of Mt. Fuji. All of the airplane occupants were killed. The report on this accident indicated
that, when approaching Mt. Fuji, the airplane was violently impacted by a severe mountain wave, which led
to vertical stabilizer failure and subsequent in-flight breakup. (A U.S. Navy aircraft, which was dispatched
to search for the flight 911 wreckage, encountered extreme turbulence near the area of the crash. In fact, the
G meter installed on the U.S. Navy aircraft registered +9 to -4 Gs during the flight.) The report also
identified the white vapor as jet fuel flowing out of the airplane after separation of the engines.
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For more information about the airplane performance study, see section 1.16.2.
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Limit load is the maximum load to be expected in service, and ultimate load is limit load multiplied
by a safety factor of 1.5. During public hearing testimony, an FAA airframe engineer stated that airplanes
are expected to experience limit load only once in their lifetime and are never expected to experience
ultimate load. For more information, see section 1.6.4.1.1.