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.
