Digital Averaging - The Smoking Gun Behind 'No Fault Found'

Air Safety Week, Feb 24, 2003

The "digital averaging" technique and the NFF problem should be recognized for what they are:

1. Proof that airborne intermittency is as dangerous as wiring shorts and arcing, and can easily lead, at worst, to deadly accidents and, at best, to perplexing system aberrations.

2. Proof that testing methods employing digital averaging devices exclusively may be bogus and, like the problem of bogus parts, provide no proof of a component's reliability.

In any case, by eliminating NFF problems, the airlines could save half or more of their current avionics repair costs while enjoying the benefits of more flights departing on time and with a tremendous boost in safety, reliability, and confidence at a time when it is so badly needed.

Byline: Brent Sorensen spent 29 years working for the U.S. Air Force testing avionics and researching the causes and symptoms related to avionics aging and "No Fault Found" issues. Related to this effort he developed numerous testing and process improvements through the use of emerging computer and digital technology. Later in his career he worked on projects to reduce NFF and maintenance costs associated with fighter aircraft.

(ASW note: Sorensen's company manufactures analog testing technology, but the notoriously endemic and systemic nature of the NFF problem warrant discussion even from an advocate who has a business interest in a solution. It could be argued that intermittency and NFF are the same thing. Other views of Sorensen's thesis, will be presented in next week's issue) >> Sorensen, e-mail Brent.Sorensen@usynaptics.com <<

Syllogism of Risk

* Aging failure events manifest themselves as random intermittent failures for which there are no established testing protocols and no testing standards.

* With no testing standards, there is no testing.

* With no testing, there is no sustained reliability.

Source: Sorensen

Digital vs. Analog Analogy

"In a nutshell, the difference between digital and analog testing equipment/sensors parallels the difference between one of those three-way lamps that can be clicked to 75, 100 and 150 watts versus a rheostat where one can raise or dim the light smoothly over the full range of voltage (and read off the exact voltage with a sufficiently graduated dial). Or, why some music aficionados prefer analog vinyl records to CDs, in that the analog recording may capture the full uninterrupted range of musical notation vs. 'databursts.' "

Source: Lee Gaillard

Digital Averaging - The Smoking Gun Behind No Fault Found

In the realm of testing and diagnosing avionics equipment and failures, generally "higher" accuracy digital instruments are usually sought after as somehow being synonymous with higher quality. Quality in a measurement, however, may have more to do with delivering accurate and useful information than simply delivering more digits to the right of the decimal place.

A case in point may be the NTSB's (National Transportation Safety Board) investigation into the crash of Flight 587, an American Airlines [AMR] A300-600 that crashed Nov. 12, 200, in New York, killing 265 persons.

The NTSB examined the flight data recorder (FDR) and discovered that expected information ... was missing on some channels due to what [was] described as "digital averaging." Digital averaging also is employed heavily in the testing and maintenance of avionics equipment as well as the aircraft's wiring.