Pilots at the controls of an American Airlines Boeing 757 en route from
Seattle to New York on September 22 had to switch to backup battery power after
they lost all electrical power while in cruise flight over Michigan.
Those batteries are designed to supply power to the airliner for only
about 30 minutes, but the jetliner stayed airborne for over two hours until the
flight deck crew made an emergency landing at Chicago O'Hare International.
But as Flight 268 approached, the two pilots found that several flight
control systems and engine thrust reversers were not working to sufficiently
slow the B-757-200 during touchdown. The pilots had drained the battery backup
system, leaving inoperable the vital systems that help stop a jet.
The jetliner skidded down the length of the runway and due to
obstructions off the end of the runway, the captain elected to veer the airplane
off the left side of the runway into the grass. The airplane came to rest with
all three main landing gear off the left side of the pavement and the nose of
the airplane approximately 100 feet from the end of the blast pad pavement,
which extends nearly 400 feet past the departure end of the runway. None of
the185 passengers or seven crewmembers was injured.
The full story of what happened on that transcontinental flight from was
not known until late October, when the National Transportation Safety Board
(NTSB) released its preliminary report on the potentially disastrous event.
The NTSB preliminary report gave this chilling account of what happened:
On September 22, 2008, at 1342 central daylight time, a Boeing 757-223
(N197AN) operated by American Airlines as Flight 268, diverted to Chicago O'Hare
International Airport (ORD) due to electrical system anomalies.
During the landing on runway 22R (7,500 feet by 150 feet), the airplane
veered off the left side of the runway resulting in minor damage to the landing
gear. There were no injuries to the two flight crew, five flight attendants, or
185 passengers.
The flight originated from the Seattle-Tacoma International Airport
(SEA), Seattle, Washington, at 0802 pacific daylight time, with an intended
destination of the John F. Kennedy International Airport (JFK), New York, New
York.
While en route the flight crew received an AIR/GRD SYS message, an
illumination of the standby power bus OFF light, and several advisory and status
messages on the engine indicating and crew alert system (EICAS). The flight crew
then referenced the quick reference handbook (QRH) regarding the AIR/GND SYS
message. The flight crew then followed the procedure referenced in the QRH for
STANDBY BUS OFF by turning the standby power selector to the BAT position. The
QRH procedure also referenced that, "The battery will provide bus power for
approximately 30 minutes."
The airplane systems stabilized with several items inoperative and the
captain contacted maintenance technical support and subsequently elected to
continue the flight on battery power. The flight crew then reviewed the MAIN
BATTERY CHARGER procedure referenced in the QRH.
Approximately 1 hour and 40 minutes later, while in cruise flight, the
battery power was depleted at which time several cockpit electrical systems
began to fail. The flight attendants discovered that public address (PA) and the
cabin/cockpit interphone systems were inoperative. A flight attendant wrote a
note and slipped it under the cockpit door to inform the flight crew of their
communication problems.
The airplane was over western Michigan and the captain elected to turn
around and divert to ORD.
While aligned with the runway to land, the flight crew declared an
emergency with the control tower as a precaution.
As the airplane neared the runway on final approach, the flight crew
discovered that the elevator and standby elevator trim systems were inoperative.
The captain then assisted the first officer on the flight controls and the
approach to land was continued. The systems required to slow the airplane on the
runway appeared to indicate normal, and with the elevator control issues the
flight crew did not want to perform a go-around to land on a longer runway.
Pitch control of the airplane was difficult so the flight crew elected to stop
the flap extension at 20 degrees.
The touchdown was smooth despite the control issues, however, the thrust
reversers and spoilers did not deploy. The captain attempted to manually deploy
the thrust reversers, but still was not sure if they deployed. The captain was
concerned about the brake functionality and accumulator pressure so he made one
smooth application of the brakes, which did not "perform well." Due to
obstructions off the end of the runway, the captain elected to veer the airplane
off the left side of the runway into the grass.
As the airplane touched down approximately 2,500 feet down the runway
witnesses heard loud pops. Skid marks from the left main gear were evident near
the point of touchdown and 165 feet further down the runway skid marks from the
right main gear were present. These skid marks were visible for the entire
length of the runway up until the airplane departed the pavement. The airplane
came to rest with all three main landing gear off the left side of the pavement
and the nose of the airplane came to rest approximately 100 feet prior to the
end of the blast pad pavement which extended 397 feet past the departure end of
the runway.
After coming to a stop, the flight crew was not able to shut the engines
down with either the fuel cutoff valves or by extending the fire handles. The
engines were subsequently shutdown by depressing the fire handles. The
passengers were then deplaned through the L1 and R4 doors using portable stairs.
Post incident investigation revealed a failure of the B1/B2 contacts in
the K106 electrical relay. With the standby power selector in the AUTO position,
this failure would have resulted in a loss of power to the battery bus and the
DC standby bus, which would have resulted in the AIR/GND SYS message and
illumination of the standby power bus OFF light that the flight crew received.
With the standby power selector in the BAT position, as selected by the
flight crew, the main battery provided power to the hot battery bus, the battery
bus, the AC standby bus, and the DC standby bus. In addition, the main battery
charger was not receiving power, and thus the battery was not being recharged.
When main battery power was depleted, all 4 of the aforementioned buses became
unpowered.
The incident remains under investigation by the NTSB, the Federal
Aviation
Administration (FAA) and American Airlines. American and its pilots
union, the Allied Pilots Association, declined to comment while the case remains
under investigation.
