Unbelievable, double electrical failure...

[iflyforpie]

I thought I would put this here instead of maintenance. Hopefully y'all don't mind...

So here I was, bored at work, wasting time on AVCANADA and such; when a local pilot comes in with a problem on his Seneca. He was IFR, in cloud, enroute from Seattle to Invermere, and he had experienced a double alternator failure.

Right alternator and regulator replaced only three months ago, left one only two years old and about a couple hundred hours on it.

Down in the US, the A & P who installed the R/H alternator could only get 12.5V by setting the regulator to its maximum setting. Hmm….





The owner was flabbergasted. He is absolutely convinced that the system wasn’t adjusted properly and wasn’t paralleling and he wants me to set it up properly so he can feel safe amongst the clouds again. But he does not want me to condemn any components because they are all pretty much brand new. Sure…

So I get the manual and find the procedure; pretty simple really. As the regulators are accessed from the front baggage door you obviously can’t run the left engine. So you take the paralleling wire out and run the right individually; setting it up to 13.5V. You then compare the field voltages of the left and right regulators and set the left so the voltage is zero compared to the right. Put it all back together, bing bang boom you’re done.





Well… I could only get 11.5V out of the right with the engine running and a 30AMP load on the alternator—the regulator was still pegged at the top. Hmm…interesting.

We closed the baggage door and ran the left engine with the regulator pegged… still 11.5V.

We switched regulators and tried again… still nothing. Nothing common in both systems was at fault either (master switch, master contactor, battery, etc).

I traced every wire in both systems and found nothing wrong. I tested the field coils of the alternators and they were still giving continuity and good resistance. Diodes were still good as well.

Finally, unsure of my test equipment and at the end of my rope, the owner relented and I pulled both alternators and regulators to be bench checked.





Just packaging them up, I noticed that the drive gears on each seemed to operate freely of the rotor through the rubber drive coupling. Looking at them, they looked perfect. I’ve seen rubber couplings fail before. It’s usually followed by removing every plug and screen in the engine to get that non-magnetic shit out; and praying to God that none of it has found its way into an oil gallery.

Two alternator couplings failing at the same time—what are the odds?




The owner went to Calgary and picked up a couple new ones--$1200 a piece! I guess they are so expensive they don’t get replaced at engine overhaul or alternator replacement. The reason why the right alternator couldn’t achieve voltage when it was installed was because the coupling was slipping all along. You'd think it would have been checked though...

There is no non-destructive way to test these couplings. Aside from the slipping action, they looked perfectly serviceable.

So watch out. The odds are slim, but they are there...

[6ftsnipe]

good find. These stories are great for all pilots and ames.

[Cat Driver]

[CPLMike89]

...and its a great way to stay in shape!

[GoinNowhereFast]

Ahh, the old Family Guy quote that has no relevance to the topic being discussed.

[CPLMike89]

well at least i didnt buy my PPC..

[b1ngnx33]

Nice story.

Thanks.

[Hedley]

This is why, when you're flying IFR, you have a Garmin
196/296/396/496/etc powered up and running off aircraft
power.

So, if you lose aircraft power, you still have some nav (now
running on internal batteries).

Yes, I know that many people here will argue that to comply
with regulations, in such a circumstance you should immediately
turn off the portable GPS because it is "not approved" for IFR
use.

However, truth be known, you can fly a pretty good overlay
non-precision approach with a VFR GPS. Which is what I would
do in this situation, even though it might contravene regulations.

[Mach .28]

rare but does happen....


User Name: Ridley, Rod
Date: 2007/02/21
Further Action Required: Yes
O.P.I.: Maintenance & Manufacturing
Narrative: a Piper Navajo, was inbound to Saskatoon when the pilot squawked 7600 radio failure while approaching the airport. He commenced an IFR approach and landed safely at 0106z. The pilot later called Tower and advised that the aircraft had a complete electrical failure.

User Name: Ridley, Rod
Date: 2007/02/26
Further Action Required: Yes
O.P.I.: Maintenance & Manufacturing
Narrative: UPDATE TSB reported that the PA-31, was en route to Saskatoon, when the crew noted a left alternator warning light. Efforts to bring the alternator on line were not successful. About 30 NM north of Saskatoon, the crew noted that the right alternator had failed without a warning, and that battery power was diminishing. The crew advised ATC and received vectors for an ILS Runway 09 approach at Saskatoon. During the approach, all electrical power was lost. The crew continued the approach, broke out of cloud at about 300 feet agl, and landed without further incident. Maintenance made some repairs, and the aircraft was ferried to the operator's base for further rectification.

User Name: Ridley, Rod
Date: 2007/03/12
Further Action Required: No
O.P.I.: System Safety
Narrative: UPDATE Maintenance and Manufacturing reported that the Director of Maintenance states the field fuse was blown on the left hand alternator and troubleshooting the right hand side proved that the alternator relay was unserviceable. The fuse and alternator were replaced on L/H side. The alternator relay was removed and replaced with a serviceable unit on the R/H side. The aircraft was returned to service. An SDR was submitted.

[iflyforpie]

This is why, when you're flying IFR, you have a Garmin
196/296/396/496/etc powered up and running off aircraft
power.

So, if you lose aircraft power, you still have some nav (now
running on internal batteries).

Yes, I know that many people here will argue that to comply
with regulations, in such a circumstance you should immediately
turn off the portable GPS because it is "not approved" for IFR
use.

However, truth be known, you can fly a pretty good overlay
non-precision approach with a VFR GPS. Which is what I would
do in this situation, even though it might contravene regulations.

I have pretty much sold him on a 496 with XM weather. I don't think it is contravening regs when you are experiencing an emergency and using what tools you have available to get down in one piece... but then I don't have any Tribunal experience.

[Cat Driver]

I don't think it is contravening regs when you are experiencing an emergency and using what tools you have available to get down in one piece...

The regulations should be the last thing on your mind in any emergency.

[Hedley]

Telling the truth in public is a very bad habit, . - you
will surely be punished severely for it.

[Rudy]

Ban multi-engine IFR!

[Cat Driver]

Telling the truth in public is a very bad habit, . - you
will surely be punished severely for it.

I already have been, however I very much doubt any TCCA inspector would want to try again.

[foxmoth]

i have never understood why GPS units are not mandated to have internal batterys so you can still get somewere if you have total electric failure. why is this overlooked?

[c170b53]

Probably more important to get one with a rapid screen refresh rate.

[Tubthumper]

Ifly4pie, was it a Seneca II?

[iflyforpie]

Ifly4pie, was it a Seneca II?

Yes...

[Tubthumper]

Well, that says it all. Piper added extra stuff in after the Seneca I, without improving the electrical handling capabilty for the extra stuff. I had to deal with a few things in it, but Airtids (....where are you?) has better stories than I do.

[iflyforpie]

This plane is loaded to the gills with all kinds of electrical gizmos (full stack, full de-ice/anti ice, stormscope, three axis autopilot, Sandel HSI, engine analyzers, HID lights, on and on...).

The 60A alternators were upgraded to 70A to handle the extra load. Kind of funny that Piper didn't go to a 28V system like everyone else had by 1980--the year this plane was built. Our '66 Skymaster is 28V and we rarely have electrical issues...