Plane Crash

Instructor: Greg Alston Abstract This paper examines the in-flight
separation of the number two pylon and engine
from a Boeing 747-121 shortly after takeoff from the Anchorage
International Airport on March 31, 1993. The
safety issues discussed focus on the inspection of Boeing 747 engine
pylons, meteorological hazards to aircraft, the
lateral load-carrying capability of engine pylon structures, and aircraft
departure routes at Anchorage International
Airport during turbulent weather conditions. Shortly after noon on March
31, 1993 the number two engine and
pylon separated from Japan Airlines Inc. flight 46E shortly after departure
from the Anchorage International Airport.
The aircraft, a Boeing 747-121, had been leased from Evergreen
International Airlines Inc. The flight was a
scheduled cargo flight from Anchorage to Chicago-O\'Hare International
Airport. On board the airplane was the
flight crew and two nonrevenue company employees. The airplane was
substantialy damaged during the separation
of the engine but no one on board the airplane or on the ground was
injured. Flight 46E departed Anchorage about
1224 local time. The flight release and weather package provided to the
pilots by Evergreen operations contained a
forecast for severe turbulence. As fight 46E taxied onto the runway to
await its takeoff clearance, the local controller
informed the flight crew that the pilot of another Evergreen aircraft
reported severe turbulence at 2,500 feet while
climbing out from runway 6R. After takeoff, at an altitude of about 2,000
feet, the airplane experienced an
uncommanded left bank of approximately fifty degrees. Although the
desired air speed was 183 knots, the air speed
fluctuated from a high of 245 knots to a low of 170 knots. Shortly
thereafter the flight crew reported the number two
throttle slammed to its aft stop, the number two thrust reverse indication
showed thrust reverser deployment, and the
number two engine electrical bus failed. Several witnesses on the ground
reported that the airplane experienced
several severe pitch and roll oscillations before the engine separated.
Shortly after the engine separated from the
airplane, the flight crew declared an emergency, and the captain initiated a
large radius turn to the left to return and
land on runway 6R. The number one engine was maintained at maximum
power. While on the downwind portion of
the landing pattern bank angles momentarily exceeded forty degrees
alternating with wings level. About twenty
minutes after takeoff flight 46E advised the tower they were on the
runway. The aircraft was substantially damaged
as a result of the separation of the number two engine. Estimated repair
costs exceeded twelve million dollars. In
addition, several private dwellings, automobiles, and landscaping were
damaged by the impact of the number two
engine and various parts of the engine pylon and the wing leading edge
devices. The National Transportation Safety
Board (NTSB) determined the probable cause of this accident was the
lateral separation of the number two engine
pylon due to an encounter with severe or possibly extreme turbulence.
This resulted in dynamic lateral loadings
coming from many directions that exceeded the lateral load-carrying
capability of the pylon. It was later discovered
that the load-carrying capability of the pylon was already reduced by the
presence of the fatigue crack near the
forward end of the pylon\'s forward firewall web. As a result of this
investigation the NTSB made seven
recommendations to the Federal Aviation Administration (FAA),
including the inspection of Boeing 747 engine
pylons, the potential meteorological hazards to aircraft, an increase in the
lateral load capability of engine pylon
structures, and the modification of the aircraft departure routes at
Anchorage International Airport during periods of
moderate or severe turbulence. The NTSB also recommended that the
National Weather Service (NWS) use the
WSR-88D Doppler weather radar system to document
mountain-generated wind fields in the Anchorage area and
to develop detailed low altitude turbulence forecasts. In the course of the
investigation the NTSB explored virtually
every contributing factor contributing to the aircraft accident. These
included weather, mechanical failure, design
deficiencies, and human factors. The flight crew was properly trained and
qualified for this fight. None of the crew
members\' Federal Aviation Administration (FAA) records contained any
history of accidents, incidents, or
violations. The flight crew and the mechanics who had worked on the
airplane before the flight volunteered to be
tested for the presence of alcohol and both lawful and illegal drugs. All of
the test results were negative. The
investigation revealed that the flight crew was in good health. The
airplane, registration N473EV, was a Boeing
model 747-121, serial number 19657. The airplane