Breaker popping

[atn_pilot]

My new (to me) M20C has all of the lights and the fuel boost pump on the same "aux bus" breaker. Twice now that breaker has popped and refused to reset. Tonight I ended up having to land with no landing lights, something I haven't done in 15 years. Needless to say it was not a pretty landing.

 

Would I be correct in thinking that the fuel boost pump must be drawing too much of a load and overheating the breaker? The POH says to land with the pump on, but I'm wondering if maybe I should ignore that advice. Thoughts?

[N201MKTurbo]

The landing light is the biggest current draw. The breaker is probably old and weak. The proper thing to do would be to test the circuit breaker and measure the current draw of everything on the buss. Most mechanics don't have the instrumentation to do those tests, so you just end up changing parts until the problem goes away.

[MB65E]

I land with the pump on and lights on. But, I don't let the pump run on the ground. Once clear of the runway. I only turn it on below 1000ft. Considering the Dukes pumps are expensive I try to limit the use. Your pump could be drawing too much current. There is a 10 year calander life to the pumps as well. To be clear, was it the fuel pump braker or the buss braker?

Could be a loose or chafed wire with any of the circuits on that bus. With the hard failure of the circuit as you described, I'd brake out the multi meter and go to town. I'd actually check the landing light wires if was the bus braker. That's a high output lamp, if it's OEM, and the wires are usually in harms way and get banged up over the years.

A few questions:

Last OH of the pump?

What landing lamp is installed?

Good luck,

Sounds serious enough not to fly till sorted out.

-Matt

[N601RX]

I think he may be referring to the 50 amp breaker that supplies the entire Aux bus?  If it is wired like the slightly later models then the light, pitot heat, strobe, fuel pump, alternator field and a couple of other things are fed off the same bus but each device then has its own breaker/switch. if this is the case it is likely a faulty, loose or corroded circuit breaker.

[Marauder]

As was suggested above, I would start looking for chafed wires and at the breaker. I can't tell you the number of breakers I have replaced over the years because they just wear out.

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[carusoam]

From my 65C experience...

The landing light CB has a tendency to wear out. Used constantly for recognition, while flying...

The rubber IP mounts have a tendency to age and droop.

The IP sags and turns off the landing light.

The CB / switch is more expensive than expected and more of a PIA to replace than expected because of the bus.

But, I don't see how this is related to the OP's fuel pump...just an FYI I guess?

[HRM]

Tonight I ended up having to land with no landing lights, something I haven't done in 15 years. Needless to say it was not a pretty landing. 

 

Quit whining, real pilots don't need landing lights 

 

That said, if you have to have a landing light, investment in an LED will reduce all sorts of future issues:

 

• less drain on electrical system.
• less stress on CB (CB stays the same since it is just there to protect the wiring).
• better light, but you really don't need that part.

[M20C]

Have to agree with HRM...a new LED landing light is a great investment...Much less current draw... will allow you to continue using your old braker (assuming no shorts), and will last a LOOOONG time;-)

[Marauder]

Speaking of landing light issues. My 1975 F has some sort of relay in the switch circuit. When I switched over to the LED, it was working fine and over the weekend, I don't hear the relay click and the landing light no longer works.

Anyone know if I can do away with the relay? I suspect it was there for the large current draw of the incandescent bulb.

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[ArtVandelay]

Speaking of landing light issues. My 1975 F has some sort of relay in the switch circuit. When I switched over to the LED, it was working fine and over the weekend, I don't hear the relay click and the landing light no longer works.

Anyone know if I can do away with the relay? I suspect it was there for the large current draw of the incandescent bulb.

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I don't have a relay, on the back of the switch you will see its rating, I going to venture a guess it's like 2 or 5 amps, take the total current draw of you landing lights, if less than switch rating, then you don't need it.

[atn_pilot]

I'm going to have a local A&P take a look at the wiring, and probably go ahead and switch out the light to an LED while I'm at it. I figure Aircraft Spruce probably has one, and they're right on the field here at FFC.

[Marauder]

I don't have a relay, on the back of the switch you will see its rating, I going to venture a guess it's like 2 or 5 amps, take the total current draw of you landing lights, if less than switch rating, then you don't need it.

I have the very special machine gun version of the light switch. I don't have a panel mounted Klixon like some of you guys. Or the toggle type. I actually have a little button on the end of the throttle.

[M20C]

They do...I'm in T-18 @FFC!

I'm going to have a local A&P take a look at the wiring, and probably go ahead and switch out the light to an LED while I'm at it. I figure Aircraft Spruce probably has one, and they're right on the field here at FFC.

[ArtVandelay]

I have the very special machine gun version of the light switch. I don't have a panel mounted Klixon like some of you guys. Or the toggle type. I actually have a little button on the end of the throttle.

Ahhh, well then if that is a generic switch like this one:

http://www.aircraftspruce.eu/push-button-swtch-spdt-black-2-post.htm

Then it's rated for 1 amp, a PAR 46 whelen needs 2.6 amps, so the answer would no. The risk is that pushing more amps then the switch is rated for could cause it to heat up, I would just replace the relay.

[atn_pilot]

They do...I'm in T-18 @FFC!

I'm down at the lowly tiedowns at P-68, next to the v-tail Bonanza. If you see me out there, stop and say hi! I'm number 33 on the wait list to get one of those T-hangars.

[jamesm]

 Could be that  circuit breaker/ switch intermittent ? I just had replaced my "Nav" light switch/circuit breaker it was  intermittent.

During annual I had reach in through pilot's window to check it .. and it and it worked fine but when the IA had checked by climbing up on the wing the switch / breaker tripped in my case the AUX breaker was ok. Depending  on the year of  your M20C ... as you have to  already pointed out.  AUX breaker essentially is in series with all switches/circuit breakers above the pilot's left knee.  Barring any high resistance contact(s)  any of the switches/circuit breaker above the pilot's knee  (i.e. Boost Pump, Landing light, Nav Light, Beacon, Glide slope(if installed), marker beacon(if installed) ,Pitiot heat (if installed) ....)  should have been effected  if the the AUX breaker tripped.

[Guest]

My new (to me) M20C has all of the lights and the fuel boost pump on the same "aux bus" breaker. Twice now that breaker has popped and refused to reset. Tonight I ended up having to land with no landing lights, something I haven't done in 15 years. Needless to say it was not a pretty landing.

 

Would I be correct in thinking that the fuel boost pump must be drawing too much of a load and overheating the breaker? The POH says to land with the pump on, but I'm wondering if maybe I should ignore that advice. Thoughts?

If my memory is correct that is a 50 amp breaker, I would investigate further before further flight. Tripping once with a normal reset is one thing, but failure to reset or immediate tripping after resetting is concerning.

I've seen small bits of instrument mounting hardware dropped and land on the electrical buss cause all kinds of weird things.

Clarence