Date: February 24, 1989
Type: 747-122
Registration: N4713U
Operator: United Airlines
Where: Honolulu, Hawaii
Report No. NTSB-AAR-90-01
Report Date: April 16, 1990 Pages: 68

Executive Summary:

On February 24, 1989, United Airlines (UAL), flight 811, a Boeing
747-122 (B-747), N4713U, was being operated as a regularly scheduled
flight from Los Angeles, California (LAX) to Sydney, Australia (SYD)
with intermediate stops in Honolulu, Hawaii (HNL) and Aukland, New
Zealand (AKL).  There were 3 flightcrew, 15 flight attendants, and 337
passengers aboard the airplane.

The flightcrew reported the airplane's operation to be normal during
the takeoff from Honolulu, and during the initial and intermediate
segments of the climb.  The flightcrew observed en route thunderstorms
both visually and on the airplane's weather radar, so they requested
and received clearance for a deviation to the left of course from the
HNL Combined Center Radar Approach Control (CERAP).  The captain
elected to leave the passenger seat belt sign "on."

The flightcrew stated that the first indication of a problem occurred
while the airplane was climbing between 22,000 and 23,000 feet at an
indicated airspeed (IAS) of 300 knots.  They heard a sound, described
as a "thump," which shook the airplane.  They said that this sound was
followed immediately by a "tremendous explosion."  The airplane had
experienced an explosive decompression.  They said that they donned
their respective oxygen masks but found no oxygen available.  Engines
No. 3 and 4 were shutdown because of damage from foreign object
ingestion.

The airplane made a successful emergency landing at HNL and the
occupants evacuated the airplane.  Examination of the airplane revealed
that the forward lower lobe cargo door had separated in flight and had
caused extensive damage to the fuselage and cabin structure adjacent to
the door.  Nine of the passengers had been ejected from the airplane
and lost at sea.

The issues in this investigation centered around the design and
certification of the B-747 cargo doors, and the operation and
maintenance to assure the continuing airworthiness of the doors.

The National Transportation Safety Board determines that the probable
cause of this accident was the sudden opening of the improperly latched
forward lower lobe cargo door in flight and the subsequent explosive
decompression.  Contributing to the cause of the accident was a
deficiency in the design of the cargo door locking mechanisms, which
made them susceptible to inservice damage, and which allowed the door
to be unlatched, yet to show a properly latched and locked position.
Also contributing to the accident was the lack of proper maintenance
and inspection of the cargo door by United Airlines, and a lack of
timely corrective actions by Boeing and the FAA following the 1987
cargo door opening incident on a Pan Am B-747.

The Safety Board issued three safety recommendations as a result of
this investigation that addressed measures to improve the airworthiness
of the B-747 cargo doors and other non-plug doors on pressurized
transport category airplanes.  It also issued recommendations affecting
cabin safety.