After 15 years and 800 flight hours, the Tyco (P&B) W31 breaker switch for my boost pump quit working. It gave me a little bit of warning, it was intermittent for a couple of flights where I could cycle the switch a couple of times to get it to work, and then last Saturday - nothing.
Some background:
I built and wired my RV-8 switch console in accordance with Vans wiring suggestions and main wire harness kit when I built the airplane in 2006--2007. I didn't know any better at the time - it turns out that these W31 breaker switches have a pretty bad reputation, as many of you know. But I have learned a few things. First of all, most people are quick to cite the AD's that are out for Cessna (AD 2005-20-25) and Beechcraft (AD 2008-13-17) airplanes that use(d) these. The AD required replacement with new switches. The FAA found that although the most common failure mode is to fail "open", they could also sometimes fail shorted so that the circuit could not be turned off, and the circuit protection of the breaker was inoperative. Occasionally they would get hot and even smoke.
Subsequent to those ADs, around approximately 2008--2009 I believe, the manufacturer modified the design of the breaker-switch so that the fail "short" mode was mitigated. So the new W31 breaker-switches you can buy today are not the same as the ones that came under the AD's. (source: 2013 FAA SAIB)
Some time later in 2013, the FAA released an SAIB (Special Airworthiness Information Bulletin) that provides more recent information on these breaker switches. They found that about 2% of the switches fail after 2000 cycles, and about 50% fail after 6500 cycles. So the FAA recommendation is to replace these breaker switches after 2000 hrs. I can live with that. I would not use these on a new build, but I'm not going to rip out the whole airplane wiring and start over to eliminate these W31s.
So - to the issue at hand - replacing the breaker switch in the RV-8 switch console. In my case, this is potentially pretty difficult because I didn't leave any slack in the harness to pull out the whole switch console to allow access to change a switch. Again, I didn't know any better at the time. So, today I came up with what turned out to be a pretty straightforward way to get at all the switches. Step one is to remove all the jam nuts and lock washers that hold the switches to the panel. this allows the whole switch assembly (they are all ganged together on the 'line' side with a copper bus strip) to float in space. Step two remove the 10 screws and remove the switch console panel, leaving the row of switches all exposed. Then it was pretty easy to replace the switch (I also replaced the avionics master and the alternator field switch - so all of the switches that are cycled at every flight have been replaced). Re-assembly was straightforward as well. Just poke all the switches up through the holes in the console, re-install the lock washers and jam nuts, and re-install the 10 screws that hold the console in place.
I was pretty relieved that this was not the job from Dante's seventh circle, and I can live with this set-up for another many years hopefully before any more of the switches fail.
Some background:
I built and wired my RV-8 switch console in accordance with Vans wiring suggestions and main wire harness kit when I built the airplane in 2006--2007. I didn't know any better at the time - it turns out that these W31 breaker switches have a pretty bad reputation, as many of you know. But I have learned a few things. First of all, most people are quick to cite the AD's that are out for Cessna (AD 2005-20-25) and Beechcraft (AD 2008-13-17) airplanes that use(d) these. The AD required replacement with new switches. The FAA found that although the most common failure mode is to fail "open", they could also sometimes fail shorted so that the circuit could not be turned off, and the circuit protection of the breaker was inoperative. Occasionally they would get hot and even smoke.
Subsequent to those ADs, around approximately 2008--2009 I believe, the manufacturer modified the design of the breaker-switch so that the fail "short" mode was mitigated. So the new W31 breaker-switches you can buy today are not the same as the ones that came under the AD's. (source: 2013 FAA SAIB)
Some time later in 2013, the FAA released an SAIB (Special Airworthiness Information Bulletin) that provides more recent information on these breaker switches. They found that about 2% of the switches fail after 2000 cycles, and about 50% fail after 6500 cycles. So the FAA recommendation is to replace these breaker switches after 2000 hrs. I can live with that. I would not use these on a new build, but I'm not going to rip out the whole airplane wiring and start over to eliminate these W31s.
So - to the issue at hand - replacing the breaker switch in the RV-8 switch console. In my case, this is potentially pretty difficult because I didn't leave any slack in the harness to pull out the whole switch console to allow access to change a switch. Again, I didn't know any better at the time. So, today I came up with what turned out to be a pretty straightforward way to get at all the switches. Step one is to remove all the jam nuts and lock washers that hold the switches to the panel. this allows the whole switch assembly (they are all ganged together on the 'line' side with a copper bus strip) to float in space. Step two remove the 10 screws and remove the switch console panel, leaving the row of switches all exposed. Then it was pretty easy to replace the switch (I also replaced the avionics master and the alternator field switch - so all of the switches that are cycled at every flight have been replaced). Re-assembly was straightforward as well. Just poke all the switches up through the holes in the console, re-install the lock washers and jam nuts, and re-install the 10 screws that hold the console in place.
I was pretty relieved that this was not the job from Dante's seventh circle, and I can live with this set-up for another many years hopefully before any more of the switches fail.
