Clock: placard and log as inop

[455 Bravo Uniform]

I have the stock Cessna clock that has stopped working. Fuse and wiring are good, clock is inop.

Questions, after reading 91.213(d)(3)(ii)
-Doed the fuse need to be removed? It’s already inop, but not really deactivated, so thinking I would need to.
-Does a mechanic need to placard & log it as inop? I think I can do so, but thinking about what a pilot can/can’t do under maintenance regs.

In order to prevent POA arguments about needing a clock, just assume I have another one installed and working that meets the intent of the FARs (which I do).

 

[NoHeat]

91.213

excerpt:
Deactivated and placarded “Inoperative.” If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with part 43 of this chapter;

Maybe since the clock is neither working nor interfering with anything else, nothing needs to be done regarding deactivation. Hence, I'm guessing there's no maintenance, no requirement for an AP.

 

[Bell206]

-Doed the fuse need to be removed?

Technically it states "removed... or deactivated...." so yes the fuse should be pulled unless you have an ON/OFF switch to the clock.

-Does a mechanic need to placard & log it as inop?

No. So long as the deactivation falls under "routine pilot tasks" or under Preventative Mx a pilot can deactivate a system. Don't forget the placard and log entry.

 

[NoHeat]

Technically it states "removed... or deactivated...." so yes the fuse should be pulled unless you have an ON/OFF switch to the clock.

I'm curious about this. The intended function of a fuse is to prevent electrical fires, by avoiding too much current passing through the wiring. That's the reason that aircraft (and houses and other things) are equipped with fuses, to avoid fire. Its intended function is not to serve as an on-off switch, so I don't see why it would be required to use it that way.

 

[Bell206]

I'm curious about this... so I don't see why it would be required to use it that way.

The issue is the deactivation of the clock, i.e., removing its power, not the purpose of the fuse. Pulling a CB or selecting OFF on a power switch would also meet this requirement per previous guidance. The fuse merely provides an easy solution for the 91.213 requirement. Nothing more. You're other options to comply with 91.213 requirement would be to disconnect the clock power wires or remove the clock, both of which would require a mechanic.

 

[unsafervguy]

as bell said, the reg requires de-activation. why is the clock inop? can you be sure that the movement is not stalled and drawing more current than it would running? that could cause problems. hence, the requirement to "de-activate or remove". by removing the fuse, or pulling the C/B you are removing all power from the circuit and assuring that there is no electrical load on the circuit.

 

[denverpilot]

I'm curious about this. The intended function of a fuse is to prevent electrical fires, by avoiding too much current passing through the wiring. That's the reason that aircraft (and houses and other things) are equipped with fuses, to avoid fire. Its intended function is not to serve as an on-off switch, so I don't see why it would be required to use it that way.

It’s kinda hard to start a fire with a huge air gap in the circuit where the fuse used to be.

Cessna fuses of old for clocks are back in the tail inches from the battery box. For the most part....

And the wire is small enough gauge (on purpose) back there that it’ll also act as a fuse for the few inches it runs to the fuse holder, which is true of most wiring gauges used, besides the inline fuse.

It’s designed to melt and fail open fairly quickly with the current available from the battery.

Like most things in aviation — multiple design features to handle multiple failure modes.

Fuses have been known to melt juuuust right (on very rare occasions) to not open, but turn into a nasty melted short.

 

[Juliet Hotel]

I'm curious about this. The intended function of a fuse is to prevent electrical fires, by avoiding too much current passing through the wiring.

That is only one intended function of a fuse or circuit breaker. The other function is to serve as way to remove all power from the circuit. I suppose there are folks out there who like to leave the circuit breaker on when they wire up their new dryer outlet but I'm not one of them.

 

[denverpilot]

That is only one intended function of a fuse or circuit breaker. The other function is to serve as way to remove all power from the circuit. I suppose there are folks out there who like to leave the circuit breaker on when they wire up their new dryer outlet but I'm not one of them.

Using circuit breakers not rated for switching loads in aircraft as switches is generally disapproved and bad form.

Working on most light aircraft electrical systems, the correct way to remove power from any circuit is to disconnect the battery, not pull a breaker for the circuit.

If nothing else because even with the master off there’s usually live terminals back there in tight spaces that can be touched with conductive things.

Battery disconnect usually takes five minutes.