AOPA Pilot Magazine - May 2020 - 86

P&E

SAVVY MAINTENANCE

Corrective
maintenance
Event criticality

FAULT

Predictive
maintenance

Scheduled
maintenance

Condition-based
maintenance
Too early

Too late

CONDITION-BASED MAINTENANCE has been a huge step forward compared with traditional scheduled maintenance. Predictive maintenance is the next big step forward.

The core principle of reliabilitycentered maintenance is that most
preventive maintenance should be performed only when genuinely necessary.
It accomplishes this by doing away with
most scheduled preventive maintenance
(including most TBOs) and replacing it
with a program of condition-based maintenance. This means doing away with
time-based maintenance in favor of a program of inspections designed to assess the
condition of critical aircraft components
and to determine when their condition
has deteriorated to the point that failure
might be imminent. Component repair,
overhaul, or replacement is not performed
until a condition inspection indicates it is
required. As a result, work is performed
only when demonstrably necessary, as
opposed to at an arbitrary time interval
when some aeronautical engineer calculated that it might possibly be necessary.
Reliability-centered maintenance has
been a huge step in the right direction,
but it's still less than a perfect solution.
It requires regular condition inspections that are not inexpensive and may
be somewhat invasive-they involve taking things apart and putting them back
together-and so are not completely free
of maintenance-induced failure risk.
Perhaps we can do even better.
During the two decades I've been
working to bring the benefits of reliability-centered maintenance to owner-flown
86 | AOPA PILOT May 2020

GA, another quiet revolution that started
with the airlines has been quietly trickling
down the aviation food chain. It's called
predictive maintenance and is based on a
technology known as predictive analytics.
PREDICTIVE ANALYTICS

Modern air transport aircraft and engines
are built with thousands of sensors that
measure air data, critical engine operating
parameters, vibration levels, electrical and
hydraulic system parameters, flight control and landing gear positions, fluid levels
of all kinds, cabin pressurization and environmental parameters, and just about
every other measurable aspect of the aircraft. Measurements from these many
sensors are digitized by the aircraft's data
acquisition unit and then either transmitted to ground stations in real time or
captured continuously by a quick-access
recorder and extracted once the aircraft
is on the ground, via the cellular network
or on flash memory cards.
Predictive analytics-also known as
predictive failure analysis-employs computer algorithms to process this mass of
digital data and detect patterns indicating
that some sort of preventive maintenance
is necessary, or that evidence of some
incipient component failure has been
detected.
Detection of parameter degradation,
exceedance, or adverse trending-low
tire pressure, high electrical bus voltage,

decreasing oil pressure-is generally
pretty easy. Prediction of "rare events"-
contaminated fuel nozzle, damaged
compressor blade, failing engine bearing-
may require complex algorithms.
Boeing pioneered predictive analytics
16 years ago when it introduced a service
it calls Airplane Health Management
(AHM). Boeing's AHM monitors the
health of an airplane in flight and relays
that information in real time to airline personnel on the ground. When the
airplane lands and arrives at the gate,
maintenance crews are ready to make any
needed repairs quickly. AHM algorithms
also attempt to predict when aircraft components are in jeopardy of failing so the
operator can replace or repair them at the
next scheduled maintenance check.
Nowadays, virtually every airline that
flies Boeing's 777 or 787 uses AHM, and
Boeing is working to expand the service to earlier Boeing models as well as
to non-Boeing aircraft (e.g., intercontinental business jets). Last year, I had the
opportunity to see AHM in action when I
visited the Boeing Global Services office
in Englewood, Colorado, and to say I was
impressed would be an understatement.
This is very cool technology.
Not to be outdone, Boeing's archrival
Airbus has launched a predictive analytics service called Skywise in partnership
with Palantir Technologies, a Palo Alto,
California, software company that specializes in big data analytics. Recently Airbus
announced a partnership with Delta Air
Lines as the pilot customer for Skywise
Predictive Maintenance on Delta's A320
and A330 aircraft to assess the failure
probabilities of aircraft parts and anticipate the need for preventive maintenance
tasks. Delta is claiming a success rate of
more than 95 percent for pending failure predictions. According to Delta, the
carrier had only 55 maintenance-related
flight cancellations in 2018, compared
with more than 5,600 cancellations in
2010, and it credits predictive analytics
for most of this improvement in dispatch
reliability.
Jet engine manufacturers also have
adopted this technology. General Electric
presently appears to have the lead in

AOPA Pilot Magazine - May 2020

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