No Fault Found - NewsWatch V.3
Commercial
Airlines form No Fault Found (NFF) Working Group
ARINC,
along with several supporting commercial Airlines, has recently
formed a No Fault Found (NFF) working group to develop a set of
coordinated NFF reduction guidelines. The purpose of this project is to share information and
to provide a standardized approach to reducing NFFs.
This effort may turn out to
be the largest and most comprehensive attempt yet to
examine the root causes of NFF and to develop viable
solutions. Judging from the preliminary briefings delivered at
the last Avionics Maintenance Conference (AMC) concerning the need
for additional intermittence testing equipment, we think they are
finally going to have some successes with this endeavor. More details...
Air
Force effort at NFF reduction delivering surprising results
Total
Quality Systems (TQS) of Ogden,
Utah is taking a slightly different approach to reducing F-16 NFF
problems. Rather than simply blaming tech
orders or technicians, they are focusing on the root
cause, or intermittence factor of the equation. They
have developed a three-pronged approach that includes
serialized data tracking of aircraft and Line Replaceable
Unit's (LRU's), test platform data comparisons, and
environmentally profiled intermittency testing. TQS's Defense Repair Information
Logistics System (DRILS), first
identifies LRUs coming in for depot repair as possible NFF
suspects based on their failure history. These suspect
black-boxes are then given special treatment with a functional
test and a test-data inspection process they call ATE
Insight, which compares presently tested
parameters against testing norms, looking for any failing or even
borderline failure values. Those boxes passing this
test successfully are then tested for any intermittent conditions in
the chassis interconnections, wiring, or flex cables using their
Intermittent Fault Detection and Isolation System (IFDIS) which is an
array of three IFD-3000's
from Universal Synaptics
which can simultaneously monitor over 750 circuit interconnections
for any nano intermittencies. The Unit Under Test (UUT) is
then subjected to thermal and vibrational stimulus while the
health of all the interconnections are simultaneously
monitored. Preliminary success using this system has been
excellent, with multiple latent intermittencies being found in
nearly 100% of the suspect boxes tested to date. TQS continues to
improve and further develop this process so you might want to keep in
touch with them. More...
Intermittents
continue to haunt NASA and the space shuttle program
More than
two years since the fateful Columbia accident, and after more than
two years of working on the investigating
board's recommendations, NASA again suffered a launch delay due to
an intermittent. The mysterious problem responsible for the three
week delay was apparently an intermittent glitch that
appeared during tanking tests, which before a diagnosis was
made, returned to a semi-good status without NASA ever discovering
the root problem or fixing it. The intermittently faulty
fuel-level sensor circuitry that failed is one of four that would
cut off the shuttle's three main engines if at least two showed that
hydrogen fuel was running low. A premature cutoff might damage the
engines, force the shuttle to make an emergency landing or leave it
short of its desired altitude.
Should environmental launch conditions
cause intermittent conditions to reappear inadvertently, the
shuttle's safety would again be compromised. We salute
NASA's extensive, precautionary efforts to try and resolve the problem.
Perhaps more
troubling to NASA than having an intermittent defect slip
past preliminary testing this time, is the fact that intermittence is
becoming a significant issue in all their aging electronics. The
Columbia Accident Investigation Board cautioned NASA
about their testing processes which previously failed to find
two other mission's intermittent problems (the explosive bolt
jettison systems that hold the shuttle to the main tank and the
explosive bolts that hold the entire stack on the launch pad). In
both of the previously cited cases, double redundancy in the explosive
bolts had diverted a disaster, but it reflects rather poorly on NASA's
ability to detect this intermittence and certify its testing practices
as being adequate to insure safe and reliable launch
operations. These nearly back-to-back-to-back
intermittent failures in critical systems point to a definite
need for them to take a more in-depth look into what they are
really testing...and what they are testing it with.
In
Universal Synaptics' efforts to upgrade NASA's and United Space
Alliance's testing practices we have found a few enlightened
employees and managers who understand the inadequacy of their
digital (averaging)
ATE and other instruments to find intermittencies. Some have
reverted back to using their old Simpson-260 analog swing-needle ohmmeters to test for
intermittence. While in theory, and often in-practice, the
Simpson-like meters are indeed superior to the best digital-based
measurement devices due to their all-the-time analog testing
capabilities, they still suffer from a lack of sensitivity to
short duration intermittencies and can only effectively test one line
at time. In addition, because of the at-rest inertia of
their ancient meter movements, wide-opens of a short duration may
only appear as a nearly imperceptible "blip". In the
case of one-shot events, or should the operator blink,
the detection will be lost. In reality, a $2.00 test light
from Radio Shack is a superior testing means, limited only by the
user's eye-flicker repetition rate which or about 1/30 of a
second. Forget finding the more numerous one-shot events with
this too.
By means
of comparison, our IFD-3000
is 10,000 times more sensitive to even one-shot intermittencies
than either of these two old analog standbys, and it can do it on
an unlimited number of lines simultaneously, and it can monitor the
circuits under test continuously for days if desired without missing a
thing.
Equipment-Reliability Institute
publishes new book on reliability testing
World-renowned reliability
testing instructor, consultant, and author, Wayne Tustin has
published a new book on testing for reliability. He devotes
chapter 24 of his book to the need for intermittency/NFF
testing in a maintenance environment and discusses the need for testing
using all-test-points all-the-time technology found in
the IFD-3000 to achieve a nearly 100% test coverage for these
randomly occurring, intermittent events, which
are not testable with other equipment. We invite you to
take a look, or sign up for one of his many courses taught
throughout the world. More...
The
Achilles Heel of Modern Electronics
Evaluation
Engineering magazine published an article on the effect
of unreliable circuit inter-connections in otherwise
reliable electronic devices. It details the
problem that digital measurement devices have in detecting
intermittence in these electromechanical devices and shows why
the IFD-3000 dominates all other testing methods for it's
detection. More...
Other
Suggested No Fault Found Articles
Avionics Magazine:
How
Parts & Systems Age
Avionics
Magazine: No Fault
Found Frustrations
Aviation
Maintenance Magazine: Finding
No Faults
Air Safety
Week: Digital
Averaging & No Fault Found
Avionics
Magazine: The
Digital / Analog Coin Toss
Universal
Synaptics: Digital
Averaging... The Smoking Gun
Avionics
Magazine: When
the Average Isn't Good Enough
Test &
Measurement World: Defeat Intermittents
Aviation
Maintenance Magazine: No-Fault
Finder
Universal
Synaptics: An Analyzer
For Detecting Intermittent Faults
Contact: contact@usynaptics.com
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