By Andy Pasztor and Jon Ostrower
Nearly four years after Boeing Co.'s 787 Dreamliner entered
commercial service, federal regulators are moving to combat a
potentially dangerous software glitch they said can cause a total
loss of electrical power that would endanger the aircraft.
A Federal Aviation Administration safety directive that became
public on Thursday reveals that Boeing's laboratory tests
discovered that under certain circumstances, all of the 787's power
systems can suddenly shut down entirely during a flight.
Such a problem, which the FAA said risks "loss of control of the
airplane," can occur after a jetliner remains connected to onboard
or ground-based electric power without a break for a stretch of 248
consecutive days, the agency said. The FAA is ordering airlines to
shut down power systems periodically to alleviate the hazard.
Boeing said such shutdowns are part of regular maintenance, and
it would be rare for a jet to have power uninterrupted for so long.
The plane maker roughly a week ago recommended that airlines
voluntarily turn off power systems at least every four months.
During the early stages of the plane's introduction, Boeing
drafted an internal report concluding that Dreamliners experienced
most of their reliability problems just after being powered up. The
company recommended adding additional time before flights to deal
with erroneous "nuisance" messages.
As a result, many airlines made efforts to keep aircraft powered
over unusually long stretches to avoid some nagging technical
headaches and keep their Dreamliners flying on schedule.
According to the FAA document, a 787 "that has been powered
continuously" for about eight months can trip software causing all
four of its main generator control units "to go into fail-safe mode
at the same time." The result, according to the FAA, can be "a loss
of all AC electrical power regardless" of the phase of flight. Such
a scenario can develop if the control units were powered up at the
same time.
In the event of such a failure, the aircraft would revert to
battery power momentarily before deploying its ram air turbine, a
wind-driven propeller that generates a small amount of emergency
power.
The FAA's move is a minor headache for Boeing and its global 787
operators, but underscores the turbulent journey to maturing the
jet's advanced electrical systems.
The FAA's move is the latest complication for Boeing and its
global 787 operators involving the jet's electrical systems. In
January 2013, after two Japanese carriers experienced fire or smoke
emergencies with advanced lithium batteries, the FAA pressured
Boeing and all 787 operators to ground the planes for several
months until design changes were made to the batteries and their
containers.
In its latest directive, which isn't related to those battery
problems, the FAA is requiring mechanics to temporarily turn off
electrical systems on aircraft to briefly "deactivate" them. For
some 787s, that could be required by the end of next week.
Released on the Federal Register's website Thursday, the
directive applies to more than two dozen Dreamliner aircraft
currently flown by U.S. carriers. But foreign regulators are
expected follow the FAA's lead and apply it to about 230 other 787s
flying world-wide. Longer-term fixes to revise the problematic
software are expected later this year.
The Dreamliner's need for power is extraordinary: its advanced
electrical system generates nearly twice as much juice as Airbus's
double-deck A380 superjumbo jet despite being half its size.
United Continental Holdings Inc., the largest 787 operator in
the U.S. and an early customer for the jet, last year replaced many
ground power units where the aircraft was operating, including its
Houston hub. The earlier units, which sit at the gates and connect
to the power-hungry aircraft, were unexpectedly switching off,
causing a loss of power on the aircraft. When the aircraft was
repowered, nuisance messages would have to be cleared before a
flight could be operated.
Boeing and United said that software and hardware changes to the
aircraft have now significantly reduced those messages.
But previously, United said its ground crews would leave a small
onboard generator, known as the auxiliary power unit, running as an
"alternate power source for [the 787] to ensure stable electrical
power while on the ground."
On other aircraft, such units typically are only operated in an
emergency or immediately after landing and just before pushing back
from the gate.
A Boeing spokesman said the laboratory testing that revealed the
potential shutdown problem was unrelated to the earlier nuisance
messages or any reliability or other in-service issues with the
Dreamliner fleet. In a statement, Boeing said all airplanes have
performed a power cycle as part of maintenance activities,
eliminating the risk of losing power from all the generators at the
same time.
Boeing said a software update to solve the issue would be
provided to airlines starting in the fourth quarter of this
year.
Write to Andy Pasztor at andy.pasztor@wsj.com and Jon Ostrower
at jon.ostrower@wsj.com
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