Friday, October 10, 2014

When "Black and White" is better than a Rainbow

Flying home from a committee meeting where we discussed miswiring,
I look up and find that the no-smoking and seat-belt wiring are reversed only on the indicators over my seat!
Miswiring, typically when two connectors are mistakenly swapped, can become a hazard to the airplane and airplane systems.

After British Midlands 737 crashed following shut down of the "wrong" engine, an airworthiness directive revealed a number of airplanes had miswiring.

I have long been concerned over any reference to color as a means to prevent miswiring, as the colors are difficult to maintain in all lighting conditions, and can be hard to describe.

I was on a project in 2004 creating a new generation navigation radio.  The face plate had a set of LED indicator lights to show certain status.  The LEDs were colored red and green.  Red and green are particularly difficult colors for some people to tell apart.  With good fortune, blue LEDs had just come onto the market, and these were very bright and easy to tell from red or green.  I appealed to change the green LED to a blue LED on the basis of accommodating a maintenance technician with limited color acuity.  Sadly, a decision to remain with red and green was levied on the basis that had been accepted in the past, that there was no mandate for change from the customer, and for fear of confusion over the change.  Everyone was sympathetic to the human issue.

Ten years later I found myself in a similar debate.

Bob Lehman from Honeywell found some great guidance (see the end) that led me to invent Proportionally Weighted Labeling, a method of labeling that is easy to discern in any lighting condition by persons with any degree of color-blindness, and has no sense of language or nationality, a truly universal labeling method.

Other codes are possible, but this set of five has a degree of elegance and simplicity I am quite attracted to.  You can quickly glance and tell which of the five codes very easily.

First have a look at proportionally weighted labeling (with corresponding color codes shown adjacent).

Color Codes shown across from Proportionally Weighted Labeling Codes for the KRFU connectors
ARINC 791 does not profess to be a match-maker, but it does take a dim view towards connecting a cable to the wrong LRU connector.

The failing in the perception of color by human beings under varying lighting conditions is well documented. 

Labeling technology largely embraces color coding as a legacy.

The KRFU has several identical coaxial connectors closely spaced, where access is inconvenient and difficult. 

ARINC 791 TNC Keying - Removed in Part 1 Supplement 2
ARINC 791 has abandoned use of keying. 

No supplier of keyed TNC connectors were approved at both Boeing and Airbus, and the cost to gain approval was considered prohibitive.

Restricting cables from reaching the wrong connector is not helpful, in that they are cumbersome. 

The AEEC subcommittee has appealed to the suppliers to prevent damage from occurring if mismated.

ARINC 791 provides for color coding as a concession to those suppliers so insistent.

KRFU TNC Color Code

KRFU (Optional DBS) TNC Color Code

I developed a set of requirements to base a new labeling standard
Human Considerations for Labeling

Having decided that a pattern of black and white bands would meet the objectives for human considerations, I set out to try literally hundreds of combinations.  It became apparent that filling in equally spaced "blocks" with white or black offered a simple tooling for various combinations.  The first variable was how many rows to use.  

I stumbled upon the use of nine rows and five patterns (the sixth being all white, not used) and was immediately attracted to it.

Proportionally Weighted Labeling is provided as a model of a modern labeling standard that overcomes all the shortcomings of color-coding while being highly tolerant to aging and damage.

Nine rows of equal height are filled either white or black.Five unique patterns are created, shown below in columns
(where the sixth is all white, and not used)
The proportionally weighted label is applied to each cable end.

Proportionally Weighted Labeling (receptacle and cable-end)

Please consider use of proportionally weighted labeling 
in any application

Please upgrade your labeling tooling 
to support proportionally weighted labeling.

Bob Lehman, from Honeywell, delivered the following presentation.

Bob references the following web site

Here is a useful chart that shows how color discrimination is an issue.

Airbus presented the following chart in opposition to proportionally weighted labeling

Airbus has no tooling that can easily produce proportionally weighted labels.  With no resolution, we reluctantly agreed to provide color codes as an alternative.

At least blue finally got to be used.

Can we black-ball color-coding and strike it from the white-list?

I object to the use of color to convey goodness or badness.  For example, black-ball or white-list.  It amazes me when my appeals on this point are not widely embraced, and these objectionable terms continue.  As a society, we have to accept that giving meaning arbitrarily can be difficult to understand in differing cultures.  But even further to avoid, is describing certain colors as being good or bad using terms that are easily aligned to human race.  There is a good list and a bad list.  There is an allowed list and a denied list.  It's not that hard. 

Peter Lemme

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