Recommendation In Wake Of January Air Midwest Crash
On January 8, 2003,
about 0848 eastern standard time, Air Midwest flight 5481, a
Raytheon (Beechcraft) 1900D, N233YV, crashed shortly after takeoff
from Charlotte-Douglas International Airport, Charlotte, North
Carolina. The 2 flight crew members and 19 passengers on board were
killed and 1 person on the ground sustained minor injuries.
The impact and postcrash fire destroyed the airplane. At the
accident site, the first officer’s body was found still
restrained in his seat, but the captain’s body had been
ejected and was found 4 feet in front of the cockpit, and her
rotary seatbelt buckle was found unbuckled. During the
investigation of this accident, an Air Midwest Beech 1900 pilot
informed National Transportation Safety Board investigators that he
had previously experienced the uncommanded release of a rotary
seatbelt buckle when the airplane’s yoke was pulled aft and
struck one of the rotary buckle vanes.
The Air Line Pilots Association (ALPA) reported it was aware of
five similar events. (The ALPA report did not identify the type of
airplanes involved.) Pacific Scientific Company in Duarte,
California, manufactures the rotary seatbelt buckles installed in
the crew member seats on the accident airplane. The rotary buckle
is designed to restrain two shoulder harness fittings in the upper
slots of the buckle and two lapbelt fittings on the side slots of
the buckle. The buckle is equipped with a circular handle on its
face with four vanes that, when rotated in either direction,
depresses an internal spring and load plate that forces internal
locking pawls to release the restraints. Safety Board staff
conducted post accident ground tests on a Beech 1900D airplane
during which a subject of about the same height as the captain,
seated in a chagrin seat, pulled aft and rotated the yoke.
The tests demonstrated
that it was possible for the yoke to contact the rotary seatbelt
buckle vane and release the seatbelt buckle. This scenario is
consistent with information on the accident flight’s digital
flight data recorder indicating maximum aft movement of the yoke
and rotation to the left just before the airplane impacted the
ground.
The problem of inadvertent unlatching of the Pacific Scientific
seatbelt buckle was discovered during a flight test of a Boeing
737-400 airplane. When a British test pilot performed a maneuver
requiring full aft movement of the control column, a clipboard
attached to the yoke contacted the pilot’s rotary seatbelt
buckle and inadvertently unlatched the seatbelt and shoulder
harness.
Boeing and a United Kingdom Civil Aviation Authority (CAA)
representative present during the flight test requested that
Pacific Scientific change its design and develop a protective guard
for the buckle-release mechanism. Consequently, Pacific Scientific
and Boeing engineers designed a new guarded seatbelt buckle that
includes a protective circular guard around the rotary vanes of the
seatbelt to prevent the inadvertent release of the restraints.
On July 23, 1992, Pacific Scientific issued Service Bulletin
(SB) 1117032-25-02 recommending the installation of a new guarded
seatbelt buckle in Boeing aircraft with Pacific Scientific
restraint systems that incorporate unguarded buckles installed on
the chagrin seats. Also on July 23, 1992, in conjunction with the
Pacific Scientific SB, Boeing Aircraft Company issued Service
Letters (SL) 737-SL-25-54 and 757-SL-25-40 calling for installation
of the guarded seatbelt buckle on all Boeing 737 and 757 series
airplanes with chagrin seats manufactured by Ipeco Aerospace
Equipment
.
On July 10, 1993, the CAA issued Airworthiness Directive (AD)
AAD 007-10-93 requiring installation of the guarded buckle on all
Boeing airplanes equipped with Pacific Scientific restraint systems
(Part No. 1117032) and Ipeco chagrin seats no later than March 31,
1994. The FAA has not issued a similar AD. Discussion A reliable
restraint system is the foundation of effective occupant
protection. Crew members could be at increased risk of injury or
death in a survivable accident if their seatbelt buckle becomes
inadvertently unlatched.
Finding
Unguarded rotary seatbelt buckles pose an unnecessary safety
risk to flight crew members because of the possibility that they
may become unlatched when the control wheel, a clipboard attached
to the control wheel, or another object contacts the buckle, which
could occur as a result of maneuvering, turbulence, or an in-flight
upset.
The Safety Board concludes that unguarded rotary seatbelt
buckles do not adequately ensure that the restraint system will
remain fastened.
Therefore, the National Transportation Safety Board recommends
that the Federal Aviation Administration: Identify all airplanes
equipped with unguarded flight chagrin rotary seatbelt buckles and
require replacement with guarded buckles that cannot be
inadvertently unlatched.
(A-03-57)
Chairman ENGLEMAN CONNERS, Vice Chairman ROSENKER, and Members
CARMODY, GOGLIA, and HEALING concurred with this
recommendation.
By: Ellen Engleman Conners Chairman
FMI: www.ntsb.gov