Avionics Cooling Fan

[JoeMhama]

Cessna 172P

How important is the fan? The other day on preflight I found the circuit breaker out and it was obvious that the fan was not working. My boss wants me to continue flying it until next required mx-- (About 30 more hours).

The circuit breaker is also responsible for the strobes which are working fine, so I know for sure its the fan.

Im concerned about the heat build up possibly damaging the avioncs displays or worse starting a fire. Should I be this concerned? Or do as the boss says and keep flying it?

Any advice?

 

[U of I Tweak]

Not a mechanic but....

For what it's worth we have a 172 M that doesn't have a cooling fan. It's just got two vents that blow air onto the avionics (although one of them is capped and not doing anything.) However we have had some transponder problems that may be a result of overheating. In the near future we're going to be uncapping the one vent and adding some hose to direct air to the transponder. I've also heard that our particular model of transponder (the Cessna 300) is prone to heat problems. Our current solution is to leave it off until holding short of the runway, then power it up as we're rolling and shut it down on rollout to avoid it generating too much heat while there isn't a lot of airflow.

 

[westward]

airport

airport ops

 

[Amish RakeFight]

For what it's worth we have a 172 M that doesn't have a cooling fan. It's just got two vents that blow air onto the avionics (although one of them is capped and not doing anything.) However we have had some transponder problems that may be a result of overheating. In the near future we're going to be uncapping the one vent and adding some hose to direct air to the transponder. I've also heard that our particular model of transponder (the Cessna 300) is prone to heat problems. Our current solution is to leave it off until holding short of the runway, then power it up as we're rolling and shut it down on rollout to avoid it generating too much heat while there isn't a lot of airflow.

Doesnt the transponder need a little time to actually "warm up" before it can function properly. Or is this only applicable to older models.

 

[RichardRambone]

I would think it's very important. Those dang avionics can get real, real hot to the touch. I had smoke coming out from behind them one time on a trip to Cali. Too freakin hot and the fan WAS working.

 

[208Tech]

I figure that someone smarter than me decided that the avionics needed a cooling fan. I'm sure that everything will work just fine for awhile, but something bad will eventually happen. Maybe not today, maybe not for 29 hours, but someday.

Here is the real question: Is risking an avionics unit or two worth the extra 30 hours of operation? Only your boss knows the answer to that question.

 

[avbug]

The avionics fan is important, both to the life of the avionics, and their proper operation. Get them too hot, they don't operate properly, or quit.

Aside from that, you needn't even ask the question. Is the aircraft airworthy? If the fan isn't working, then the answer is no. If you can make it airworthy (meeting approved data, and being safe), fine...but can you?

If everything is not working, can it be deferred under a MEL? If you don't have a MEL, can it be deferred in accordance with 91.213? If it's installed, it's properly deferred or altered, or it's working. If it's neither, then you need to have an authorized approved publication or data permitting it so...if it's not working, it's not something you can sit on...it needs to be fixed.

Your avionics fan is important. It should be addressed.

What makes you think you've just done a comprehensive trouble-shoot and properly determined that the fan is causing that breaker to open? You haven't. You saw that the strobes work...but you still don't know anything about the problem. You only know that a breaker is opening.

A circuit breaker isn't there to protect the equipment in the circuit; it's there to protect the wiring. It doesn't open until the load exceeds what's safely designed for the wiring. Guess what happens when the load for a given wire run has been exceeded.

When a breaker opens, if you don't know the cause, then don't close it.

The concept that scheduled maintenance is coming, and therefore things should be let go until that hour arrives, is a ridiculous falacy, and one that can meet in loss of expensive equipment, or loss of critical components...things must be fixed when they break. Period.

Anything else is poor airmanship.

 

[Tonala2k]

Get it Fixed

I Like what AvBug said. We're just the pilots. We know the plane inside and out allowing us to make in-flight decisions and land the plane safely with minimal damage to any part of it. However, there's a reason I leave the cooking to my wife.

If the operator is concerned about excessive down time because scheduled maintenance is coming up, then bump up the maintenance.

No strobe ligths... that's fine. Not the best, but livable. No avionics cooling fan.. ask a mechanic, like you're doing now. A circuit breaker opening... get it checked out. Hopefully the over load is on only one breaker and you don't have a faulty one somewhere that should be opening.

This is a pilot's, not a mechanic's opinion.

Doesn't the transponder need a little time to actually "warm up" before it can function properly. Or is this only applicable to older models.

I've been told by my 80+yr old Chief pilot with nearly 30,000hrs that all Xponders need about 24sec in standby or they may give false altitudes.

 

[Weasel Keeper]

Imagine your computer as an important avionics box. Remove the heatsink fan from your processor. See how long it runs. Post back your reply fast because she's going to fail soon.

Follow Avbug's advice. If nothing else, at least make it official and write it up. Then if something happens it's off of your shoulders.

 

[Amish RakeFight]

I've been told by my 80+yr old Chief pilot with nearly 30,000hrs that all Xponders need about 24sec in standby or they may give false altitudes.

That doesn't seem long at all. I thought it might take a bit longer like a few minutes. Anyone know the science behind the required warmup period?