The International Cessna^® 170 Association

Many pilots are taught that during cockpit pre-flight inspections to check for unseated/"popped" circuit breakers/fuses and the assumption is made that they should be re-set prior to flight.

In truth, the technique should actually be taught that CB/Fuses should be "checked" and "considered"... and NOT re-set until maintenance has cleared them for re-set.

I recommend that CBs/Fuses not be used for temporary disabling of circuits without notations being attached for subsequent operators understanding of the purpose. In no case should non-essential CB/Fuses be reset in flight, unless the cause for the disruption is known and corrected. EVER!

So, I guess that rules out holding it in with your thumb until the gear cycle is completed. I remember being instructed by a company mechanic to do just that , "it won't hurt anything", I was told at the time. I remember the breaker getting pretty damn hot.

I wouldn't say it rules out something like that but it sure makes you think twice. CBs pop for a reason and resetting them can cause a fire which is a worse problem than losing the component powered by the breaker. An electric gear motor draws a lot of amps but usually does its job fairly quickly. I would sure consider holding a breaker to get the gear down done but if I started smelling smoke I would happily land gear up. The practice which led to the warning in the attachment was a habit in industry of pilots continually resetting CBs which in some cases resulted in a circuit welding itself shut causing a fire.
On a related topic, I recently discovered corrosion in my landing light fuse holder. Initially, I smelled a faint electrical burning smell followed by discovery of a very hot wire leading from the fuse holder. The fuse was hot on one end and not as hot on the other. Our local avionics shop is going to replace the fuse holder with a CB. I know its not original but it seems more reliable than a fuse. My landing and taxi light are off the same switch. The switch to the right is disabled. Would anyone recommend splitting the 2 lights and enabling the right switch?

Some years ago at my old airline we could reset the circuit breaker once. IIRC someone reset a breaker once and it fried the wires to the FO's pitot heat and started a fire in the console on the FO's right side inflight and melted a bunch of wires. After that only maintenance could reset a breaker unless it was during a preflight when accepting the aircraft AND the aircraft had just come out of maintenance.

Fuses are for the most part safer than circuit breakers.(IMHO) Circuit breakers that have been in place for years without cycling could become stuck or coroded & fail to unseat in time to do what they are intended to do which is protect the circuit & in turn the vessel or structure in which they are installed.Fuses on the other hand are faster to break the curcuit when both systems are in prime shape.When that fuse holder gets coroded the little bar that"blows" inside that little glass tube still has the same value that it had when installed fifty some odd years ago.Circuit breakers are a device of convenience (you don't have to carry any spares as long as every thing is working properly). Of course if you wrap a piece of gum wrapper around them or put a penny under the ones in your grandmothers basement fuse box in her hundred year old house that still has a fuse box you will be safer using curcuit breakers.When I was in the Navy,one of the things that happened during sceduled maint was the electricion had to cycle all the circuit breakers on the airplane by hand to insure that they were not stuck or coroded & nonfunctional.

There are two types of circuit breakers: "Trip Free" and "Non Trip Free". On the Convair T-29 aircraft they were colored differently and were used on different types of circuits. One type, if held down, would force the circuit. The other type, I believe, required coling down in order to be reset. "Electrical" George will probably remember which was which. I'm too old.

voorheesh wrote:... My landing and taxi light are off the same switch. The switch to the right is disabled. Would anyone recommend splitting the 2 lights and enabling the right switch?

I take it that you have a non-original panel equipped with a double-pole switch that is ON-OFF-BOTH/ON ? with the position to the right being both taxi and land lite on, and position to the left as taxi only? (or...vice-versa?... perhaps you meant it the other way?)

Cessna had several ways of providing taxi/land lights. The most common (in airplanes other than the ragwings) was a single switch with double poles, wherein one position was OFF, one was TAXI light only, and the last position was TAXI AND LANDing lights BOTH ON.

There is nothing "wrong" that I can see with seperating the land and the taxi lamps into separate circuits so that one OR the other could be energized. But I beleve most folks will find it "more illuminating" to be able to energize both SIMULTANEOUSLY as well. If one were to completely seperate the two circuits and utilize two separate switches that could be accomplished.... but at the expense of complicating cockpit switching/placarding a bit.

When Del and myself altered my land/taxi light system we kept the original OFF/TAXI/BOTH switching-scheme but separated the electrical circuits so that each had it's own circuit breaker. If I wished to operate only the LAND lamps I can simply disable the TAXI circuit breaker and place the switch into the LAND position.

So, if you wished to retain your present (or original) switching/placarding set-up.... all one would have to do is provide seperate circuit breakers for the two lamps and use solenoids. Here's a schematic of what we did to my airplane.
(The factory original switch (OFF/TAXI/BOTH) and placard were not altered. The land lamps remained GE-4509 and the taxi lamps were changed to 60-watt GE-4461, which have fresnel/fog lenses. The result is that while in taxi-only mode my electrical demand for the two lamps is less than previously (120-watts versus 200 watts). This is a much more visible lighting system for traffic-pattern work than previously due to the dual lamps being so widely seperated. Of course with all four lamps simultaneously on, the demand is much higher, 320 watts....but I only use that level of brilliance for the short period of short-approach and landing. I switch back to taxi-only after roll-out.)

Anyway, what I am suggesting is that is not necessary to install dual/quadruple lamps to utilize the same wiring schematic and thereby seperate the two circuits without having to alter your cockpit switch/placard. "Trip Free" circuit breakers will "trip" regardless of whether their mechanisms are held to the "on" position. They are preferred, in my opinion, but they cost more. (A circuit breaker which is restricted, such as when baggage or cargo is inadvertently laid against them will not protect a circuit.)
Holding a non-trip-free circuit breaker to prevent it's tripping is patently dangerous, in my opinion. If a mechanism requires that procedure then it is improperly maintained and/or designed and/or the wiring circuit is inadequate, and should be corrected.

I do not believe circuit breakers are "safer" than fuses, per se, but they are definitely more convenient. Corrosion will damage both systems equally. But fuses will almost always perform more reliably than circuit breakers in an overload-condition. (Although they have higher rates of failure in non-overloaded conditions, usually due to vibration. Fuse are definitely more difficult to re-set in flight and at night... but.... remember? we are not supposed to be doing that!

Would someone remind me what system is so important that a blown fuse/circuit-breaker MUST be reset inflight?
Landing gear? Nope. USe the alternate system or land gear-up. Better than an inflight fire.
Communications? Nope. Use the alternate system or continue per the FARs.
Navigation? Perhaps. But only if wx is widely-spread low-ifr. A vfr alternate is preferable to resetting a circuit. (As my old flight instructior once told me, "If you absolutely MUST have a radio (to survive) then you'd better not go, because that is when it will quit." Keep in mind that if your navigation radio system pops a fuse or c.b., then it's very likely a bad scenario within the radio and it won't work if re-set anyway. Are you sure you want to re-set it? Does your magnetic compass still work?

(I know. I know. Most of us will try at least one re-set. But that is the reason and purpose of this Safety Item thread: Think! How important is that circuit in reality?)

(And ....isn't this a great reason to carry a portable radio and/or GPS?)

I think I said that I think fuses are safer than circuit breakers, no big deal ,just an opinion anyhow. My 170B has the original fuse holder panel under the main panel & they are difficult to replace while standing on the ground & reaching in from the outside of the airplane much less while sitting in the left seat & trying to maintain an altitude,a heading and an attitude. Therefore are a LOT safer for ME because they prolly won't be replaced till I gitter on the ground & figure out why it blew.Had the main power lead to the alt chafe through at an adel clamp & ground out on take off from Arcadia Fla once & the cabin filled with smoke so fast it was amazing.Hit the master switch & popped the side window open & peeped out the opening to land straight ahead from about 15 or 20 feet.Lucky for me it didn't happen here at my place!!!!

P.S. The point being that that 60 amp breaker going to the alt never "popped". If it had been a fuse I am confident that it would have "blown" before that wire was fried.I also am pretty sure that if I hadn't turned the master switch off that there would have been more damage to the surounding wire bundle than there was.

The 60 Amp Breaker was in place to protect your general electrical buss, not your Alternator. When your ADL clamp wore through your main wire it did create the warm/hot short and heat enough to start a fire, but not enough to create a dead short. You killed the field with the master or battery switch. IMHO for breakers outway fuses, for ease of opening and convenience to isolate individual electrical circuits and later trouble shooting by the mechanic.

Re the earlier landing light question, my 1950 A model has one landing light switch that is on and off only. When on, both landing and taxi light are on. The switch to the right (the last one) does not move. In an earlier thread on this subj, someone said Cessna put an inhibitor on that switch to disable it. It sounds like I need to find a 2 pole landing light swich. Any ideas of where to get one or would a standard switch work in 170? Thanks for any advice.

voorheesh wrote:Re the earlier landing light question, my 1950 A model has one landing light switch that is on and off only. When on, both landing and taxi light are on. The switch to the right (the last one) does not move. In an earlier thread on this subj, someone said Cessna put an inhibitor on that switch to disable it. It sounds like I need to find a 2 pole landing light swich. Any ideas of where to get one or would a standard switch work in 170? Thanks for any advice.

OK, Harlow! NOW, I understand you.
You can disable the restriction on the switch and replace the switch with a double pole switch to accomplish what you ask. Or you can seperate the two functions into two switches, whichever suits you.

Zreyn wrote:P.S. The point being that that 60 amp breaker going to the alt never "popped". If it had been a fuse I am confident that it would have "blown" before that wire was fried.I also am pretty sure that if I hadn't turned the master switch off that there would have been more damage to the surounding wire bundle than there was.

Neither a circuit breaker or fuse would be expected to open when the short circuit is between the power source and the circuit protection device. The protection device will only open due to current which is flowing through the protection device.

Thanks George

Remember that all of the stock switches in a "Piano Key" system are single pole double throw switches and can be wired accordingly. My landng / taxi light switch was wired landing light down and taxi light up.