Are we learning something from this?
I am really disturbed by the practices described in anecdotal comments about recycling the breakers for YD, pitch/trim, FIC, etc. From these remarks, one can infer that this practice is common, normal, and sometimes considered necessary.
This may be a case where 'old-time' practices have been carried forward without much-needed examination for relevance and safety.
As a pilot, I am familiar with the decision process that leads to go/no-go decisions when some piece of MEL equipment is 'a bit flaky' but seems essentially sound: If you can inspire it to work in a perceptibly proper manner, you sure want to do that rather than scrub the flight. I am also very familiar with the tweaks and prodding sometimes required to fully awaken an aircraft from a cold / hot / long / damp sleep.
But as a computer architect, controls maven, and systems guy, it scares the stuffing out of me to think that repeatedly cycling primary power to mission critical systems - when the systems are balky on startup - is a popular cure-all in operations with "modern" aircraft.
The "modern" qualifier is meant to distinguish between older aircraft systems that were often controlled by relays and other mechanical contactors, versus newer ones that are principally implemented and controlled by electronic circuits of a much more complex nature. In the days of relays, cycling power repeatedly was a crude but effective way to break through oxides on the contacts and to free up stuck or slightly welded contacts on mechanical actuators.
In these modern days of electronics everywhere, cycling power a lot on systems is just a way to make them wear harder and fail much sooner than they otherwise would.
Not only that, the inability of an electronics-implemented control system to function *PERFECTLY* on the first power-up means either
a) it was designed wrong,
b) it (or something attached to it) is broken,
or c) both.
This is especially true for computer / microprocessor-driven systems - which most of the referenced ones appear to be.
If a system has to be recycled four times before it operates correctly, that really means the system probably is only working ok a mere ten percent of the time at initialization, (if I remember the statistics computation). Further correct operation is far from a sure thing. To emphasize the seriousness of this, one need note that initialization is, by design, normally the MOST reliable process in the operation of electronic control systems, so general operation may immediately be less reliable than the startup.
Tolerating faulty systems - in the aero controls especially - really introduces a wild card into the understanding of whatever happens afterward.
In what other aviation context would one *commence* flight with a critical system known to be working incorrectly more than half of the time ???? !!!!!!!! Not many, I hope.
Footnote: A practical procedure I would suggest, consistent with the above: If a system is not operating properly on power up, and smoke is not billowing forth, then leave power on awhile and give it an appropriate time to warm up. Then pull the breaker, count to 10, and repower it. If still inoperative, write it up, with bells.
Last edited by arcniz; 7th Nov 2002 at 21:25.