By Andy Pasztor and Robert Wall
Aviators around the globe have long recognized potential hazards
of malfunctioning flight-control sensors similar to the one
implicated in last month's Lion Air jet crash. Now, investigators
are examining how plane maker Boeing Co. heeded those earlier
warnings.
The latest investigation has expanded to delve into whether
Boeing -- as well as regulators specifically responsible for
certifying the sensor system -- fully incorporated those earlier
safety lessons into the final design of the Boeing 737 MAX 8, the
model that crashed in Indonesia, according to industry and
government officials.
The Federal Aviation Administration, which oversaw the design
and testing of the suspect sensor and related hardware, has said it
is reviewing risk analyses and pilot-training requirements
originally developed by Boeing. These actions are part of the crash
investigation led by Indonesian authorities, according to the
agency.
In a statement Sunday, Boeing said it "continually learns from
its fleet experience, which includes closely following aircraft
incidents and airworthiness directives that are issued, and then
strives to incorporate lessons learned into its designs and
recommended procedures." The company also reiterated it continues
to provide technical assistance to investigators examining the Lion
Air crash.
Called angle-of-attack indicators, the system sends data to
flight-control computers about how high or low a plane's nose or
wings are compared to level flight. But if erroneous information is
transmitted in certain situations while pilots are flying manually,
the plane's computers will automatically and repeatedly push the
nose down. Investigators have said publicly this is what they
believe occurred on Lion Air Flight 610, because some apparent
problem with the sensor system incorrectly indicated the plane was
on an excessively steep climb at a relatively slow speed.
On MAX 8 models, under certain conditions, pilots may be unable
to pull the plane out of a dive unless they react quickly and
proceed to the most relevant portion of their emergency checklist.
One fundamental question is how the FAA gave the green light for a
system in which one malfunctioning sensor -- called a "single point
failure" in engineering lingo -- can lead to a catastrophic
dive.
Investigators haven't determined exactly what role erroneous
angle-of-attack data played in the Lion Air tragedy, and other
potential malfunctions or factors may have contributed. In
addition, since the crash, Boeing has said its flight manuals and
training materials adequately addressed the risks, privately
telling pilots and airlines that any pilot who follows required
procedures can avoid a crash, according to government and industry
officials familiar with the discussions.
In addition to sensor hardware, investigators also are looking
into operation of separate software used to digitally process
signals from sensors.
As far back as 2013, however, regulators on both sides of the
Atlantic issued safety directives mandating emergency pilot
responses to ensure that failures of the same type of sensors on
long-range Airbus SE A330 and 340 models didn't result in an
uncontrolled dive. Concluding that in some cases an aircraft's nose
couldn't be raised even with maximum pilot manual commands,
regulators ordered that suspect parts be replaced.
The following year, the European Aviation Safety Agency issued
an emergency order revising certain cockpit procedures to deal with
blocked angle-of-attack sensors on thousands of Airbus wide-body
and narrow-body jets. And just last month, U.S. regulators
increased the number of Airbus A319 and A320 models included in a
different safety directive also focused on the dangers of blocked
sensors.
Those previous actions primarily covered angle-of-attack sensors
that were blocked or rendered temporarily inoperative by icing. The
Lion Air probe is assessing other potential causes for problems
with the sensor.
Regarding Boeing aircraft, the FAA in 2013 proposed a safety
directive mandating inspection and possible replacement of
angle-of-attack sensors affecting a total of more than 1,000 747
jumbo jets and older 737 models. The agency determined
malfunctioning sensors could result in false stall warnings to
pilots during takeoffs.
As the latest investigation gains steam, safety experts
increasingly are paying attention to the same category of dire
consequences that confronted Airbus crews: forceful, automated
nose-down commands while flying manually, which can be particularly
dangerous if pilots are surprised and confused about how to
counteract them.
Some of the data-processing units for angle-of-attack sensors
and others measuring airspeed on the Lion Air jet were manufactured
by Honeywell International Inc. A spokesman said the company has
been contacted by the National Transportation Safety Board and is
cooperating. The probe is expected to examine whether possible
problems with those units may have contributed to the crash.
The sensors themselves were supplied by a United Technologies
Corp. unit, which didn't respond to a request for comment.
Introducing new systems, even those meant to enhance safety such
as the MAX 8's stall-protection features, can come with pitfalls as
teething difficulties are addressed, according to safety
experts.
When a previous upgrade to Boeing's 737 plane entered service,
it also created problems. A British Midland 737-400 crashed in
England on Jan. 8, 1989, after an engine failure, killing 47 of the
126 people onboard. Investigators determined new cockpit
instruments, though not the cause of the accident, made it more
difficult for the crew to manage the situation. They recommended
enhanced training for pilots.
"The challenge for manufacturers is to introduce the sorts of
technology which have made aviation as safe as it is" while
simultaneously "minimizing the conversion training that is required
to fly different aircraft of the same family," said Graham
Braithwaite, who teaches safety and accident investigation at
Britain's Cranfield University.
--Andrew Tangel contributed to this article.
Write to Andy Pasztor at andy.pasztor@wsj.com and Robert Wall at
robert.wall@wsj.com
(END) Dow Jones Newswires
November 18, 2018 14:35 ET (19:35 GMT)
Copyright (c) 2018 Dow Jones & Company, Inc.
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