Aviation Week & Space Technology - 3 November 2014

Henry Canaday Washington

Chasing

‘No Fault Found’

Better data analytics, fault isolation

and predictive maintenance tools

target rogue avionics units

R

epairing or replacing avionics

components is hardly the big-

gest cost in maintenance. Avion-

ics do not wear out regularly like some

other aircraft systems. They just break

down, often unexpectedly.

Unexpected maintenance is more

expensive than scheduled repairs. And

there is another frustrating mainte-

nance problem that seems to afict avi-

onics components disproportionately.

An avionics line replaceable unit

may be removed because a pilot or

mechanic finds something faulty in its

performance. But when it gets back to

the shop, it tests as perfectly good, or

is “No Fault Found.” These NFFs cost

labor time to remove, logistics costs to

move—often long distances—expensive

time to test on costly equipment and re-

quire burdensome increases in invento-

ries. Far worse, NFFs may cause very

expensive delays or flight cancellations,

apparently for no good reason.

NFFs are common in avionics and

can be a major portion of components

sent to shops for inspection. A numeri-

cally smaller problem is the really bad

behavers. Sometimes called “rogue”

units, these are components sent to

shops repeatedly and frequently for ex-

actly the same reason, but they always

perform like stars on the test bench.

The entire industry has been fight-

ing NFFs and hunting rogue units for

some time. Effective approaches re-

quire the collaboration of many par-

ties, the airlines that remove NFF

units, the internal or third-party shops

that test them and manufacturers of

both individual components and the

aircraft of which they are parts.

Arinc 672, “Guidelines for the Re-

duction of NFF,” lays out the problem

in conceptual terms. But NFFs and

rogues must be tracked to their causal

lairs by extremely detailed practical

steps. Some airlines and shops work

very hard to gain even incremental

progress. Others don’t try very hard.

Jim Saltigerald is an Air Wiscon-

sin reliability analyst who is active in

drafting the next version of Arinc 672.

“Speaking from an airline perspective,

in some circles NFFs are regarded as an

unavoidable phenomenon, whose finan-

cial impact is less than that of trying to

find NFF reduction remedies,” he says.

Saltigerald disagrees with this pas-

siveness. He estimates that avionics

components removed as faulty for any

reason and found NFF in airline shops

can be half or more of avionics com-

ponents sent to shops if no corrective

actions are taken. Based on experience

at Air Wisconsin, he believes that rate

can be cut by half or two-thirds.

To do that, Saltigerald recommends

initially focusing on low-hanging, or

high-cost, NFF fruit. Concentrate first

on NFF items that cost a lot, even if

they are infrequent. Next, work on

NFFs that are low-cost but frequent.

The last priority is the low-cost, low-

removal frequency NFFs. “Don’t chase

stuf that has no value, you want to get

the biggest bang for the buck.”

Air Wisconsin began using this

three-tiered approach in 2005. It first

found the top 10 NFFs in terms of total

cost to its operations. Seven of the 10

had double-digit removal rates annu-

ally, up to 29 NFF removals per year

for a single component type. The car-

rier has reduced those rates to four to

six removals per year. Now only four

out of its 10 worst NFFs are removed

15-20 times per year. The rest are in

the single-digit NFFs.

So progress can be made, but it’s

not easy. Better troubleshooting helps.

Saltigerald says NFF problems can

trace to the piece-part level, the line-

replaceable-unit level, the system level

or the aircraft level.

Air Wisconsin designated a core

team to deal with NFFs, based at its

headquarters and linked to the entire

maintenance environment. Members

came from flight operations, mainte-

nance control, line operations, compo-

nent management and shop operations.

MRO Edition AVIONICS

MRO22 AVIATION WEEK & SPACE TECHNOLOGY MRO EDITION NOVEMBER 3/10, 2014 AviationWeek.com/mro

Air Wisconsin designated a core team

from flight operations, maintenance

control, line operations, component

management and shop operations to

deal with No Fault Founds.

AIR WISCONSIN

圀漀爀氀搀䴀愀最猀⸀渀攀琀圀漀爀氀搀䴀愀最猀⸀渀攀琀

圀漀爀氀搀䴀愀最猀⸀渀攀琀