Cessna Alternator Warning Light

This forum has been developed to discuss maintenance topics in Canada.

Moderators: sky's the limit, sepia, Sulako, North Shore

torquey401
Rank 3
Rank 3
Posts: 168
Joined: Thu Feb 28, 2008 5:56 pm

Re: Cessna Alternator Warning Light

Post by torquey401 »

.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

torquey401 wrote:.
Hear you 5/5 torquey401.

On a related note, I know of a number of aircraft that I would run and hide from too, or to put it more accurately, I do not approach in the first place, due to maintenance assistance being provided on them by certain exceptionally knowledgeable people.
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Cessna Alternator Warning Light

Post by Colonel Sanders »

When was the last time a pilot tried to kill an AME?

Not very often, considering how often the reverse occurs.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Cessna Alternator Warning Light

Post by Colonel Sanders »

Really?
Yes, really. When bad maintenance tries to kill a pilot,
hopefully there is a good pilot up front, whom is up for
flying a broken airplane safely back to the ground.

See the "swiss cheese" model of accidents/prevention.
I can't believe you've never heard of it before.

Sometimes the pilot isn't the greatest, and then you
have an accident.

And sometimes the maintenance is so horrible, you're
dead regardless of whom is up front:

http://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261
The subsequent investigation by the National Transportation
Safety Board determined that inadequate maintenance led to
excessive wear and catastrophic failure of a critical flight control
system during flight.

The CVR transcript reveals the pilots' continuous attempts for the
duration of the dive to regain control of the aircraft. At one point,
unable to raise the nose, they attempted to fly the aircraft
"upside-down". However the aircraft was beyond recovery; it
descended inverted and nose-down about 18,000 feet in 81
seconds, a descent rate exceeding 13,300 feet per minute,
before hitting the ocean at high speed.

These poor guys were thrown quite a curveball:

http://en.wikipedia.org/wiki/Aeroper%C3%BA_Flight_603
The pilots struggled to navigate the aircraft after the
failure of all the plane's instruments. With the pilots unaware
of their true altitude, the plane's wing hit the water and it
crashed shortly afterward. The cause of the instrument failure
was a maintenance worker's failure to remove tape covering
the static ports necessary to provide correct instrument data
to the cockpit.

Sometimes the problem is worse than poor maintenance -
poor design of the aircraft. It doesn't make any difference
to the poor pilot, who is suddenly flying a broken airplane.
Again.

You've probably never heard of the B737:

http://en.wikipedia.org/wiki/Boeing_737_rudder_issues
During the course of the investigation of Flight 427,
the National Transportation Safety Board (NTSB) discovered
that the PCU's dual servo valve could jam as well and deflect
the rudder in the opposite direction of the pilots' input, due to
thermal shock, caused when cold PCUs are injected with hot
hydraulic fluid. As a result of this find, the Federal Aviation
Administration (FAA) ordered that the servo valves be replaced
and that new training protocol for pilots to handle unexpected
movement of flight controls be developed
But a lot of people died until that problem was figured out,
when the pilots weren't up to that curveball.


And then there's the B777 whose fuel system sometimes
doesn't work:

http://en.wikipedia.org/wiki/British_Airways_Flight_38
The cause of the accident was ice crystals in the
fuel clogging the fuel-oil heat exchanger (FOHE) of each
engine. This restricted fuel flow to the engines as thrust
was demanded during the final approach to Heathrow.

Boeing identified the problem as specific to the Rolls-Royce
engine fuel-oil heat exchangers, and Rolls-Royce has
subsequently developed a modification to its FOHE

I could go on and on and on and on, but the point is that
for a pilot, if you keep flying long enough, sooner or later
you will be rewarded with a broken airplane, and Congratulations!
You are now a test pilot, flying an uncertificated aircraft, possibly
with hundreds of pax in the back.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

Colonel Sanders wrote:
Too bad we couldn't have just left the prop well enough
alone. Had to get it "maintained". What a clusterf__k.
I'm having a hard time trying to nail down what your stand really is here. In the same thread, you bemoan having to subject your airplane to "maintenance", and then as an example of homicidal AME tendencies, you use an incident where "well enough" was left alone until people died.
I could go on, and on, and on, and on .... but what
I have learned, over the decades is that the more
most AME's work on an aircraft, the faster it is
reduced to a heap of rubble.
There are some dud mechanics out there. Unfortunately, it's human nature to remember the painful experiences and forget about the smooth ones. You maybe remember the best hamburger you ever had. You definitely don't remember the 1000 pretty good ones you've had over your lifetime. But you definitely remember exactly where the ones that made you sick came from. Just because you get a bad burger once in a while doesn't mean every fry cook is incompetent or has it out for you.
Excellent point. When I am teaching a pilot, he learns
that an aircraft is most dangerous when it just comes
out of maintenance. That's when it will kill you. Ask
any experienced pilot - his most exciting flights will
come from bad wx, and bad maintenance.
Yes, there is absolutely an increased risk of mechanical issues arising with an aircraft coming out of any kind of maintenance. Even maintenance as simple as adding a quart of oil can lead to a really bad day. Excellent thing to drill into new pilots. I find it alarming how many pilots will receive a plane out of heavy maintenance and can't be bothered to so much as read the maintenance release in the logbook, ask what work was performed or even do a basic preflight inspection.
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Cessna Alternator Warning Light

Post by Colonel Sanders »

I find it alarming how many pilots will receive a plane
out of heavy maintenance and can't be bothered to so much
as read the maintenance release in the logbook, ask what
work was performed or even do a basic preflight inspection.
I remember watching a TV program about one of the super-duper
mega-expensive new fighters. Forget which one. Grizzled old
pilot selected for first (ever) flight of prototype does careful
walkaround. Gives ground crew a handful of tools that he
found, left in the cockpit. Any of them could have jammed
the flight controls.

Just to make my position clear: not all AME's are bad, but
there are enough of them out there to make it a statistical
certainty that if you fly long enough, one of the winners will
really try to make your day.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

Somehow I only saw the first example in your previous post. Having read the whole thing now (I was aware of all the incidents you referred to, btw) it would seem we do agree in principle.
What I don't understand is the chip on both shoulders attitude there seems to be between some pilots and maintenance personnel. We all have the same interests here.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

Fair enough.. you watch my back, I'll watch yours.

I just hope you give me back my Snap-on wrench after you give me shit about leaving it on your seat!
---------- ADS -----------
 
iflyforpie
Top Poster
Top Poster
Posts: 8132
Joined: Tue Apr 15, 2008 12:25 pm
Location: Winterfell...

Re: Cessna Alternator Warning Light

Post by iflyforpie »

AMEs have a thankless task keeping planes in the air flawlessly.

I mean, doing something like a line abreast formation outside loop is almost haphazard by comparison. How many arcseconds of sky are occupied by Pitts S2B vs empty space? But you leave one tool on an engine, one screw loose, one cotter pin off the plane.... :smt040
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Cessna Alternator Warning Light

Post by Colonel Sanders »

But you leave one tool
Try writing embedded software for a living sometime.

A few years back, I was contacted by a company in Italy
about some software I had written 20 years ago. They
had done some testing, and in a particular failure mode
with 3 interfaces, it wasn't using the redundant interfaces
correctly.

I dug up the code, and sure enough, I had a looping variable
that wasn't updated correctly and was causing their problem.

I fixed it, and off they went. Do people contact you about a
screwdriver you left someplace 20 years ago?

The systems I am working on these days cost a million bucks
a day for downtime, and if there's a problem, it can cost billions
of dollars - and it has, in the past, which I might hasten to add
was not my boo-boo, but that of the cross-town competition.

Try not to leave your pliers on the floor, and I will endeavour
to fly and repair an airplane as well as you can.
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Cessna Alternator Warning Light

Post by Colonel Sanders »

Oh yeah, another one recently.

Friend had a little Lycoming four which ran a little
rough. Lycoming 4's are not known for their smoothness
but this one was a little bit worse than usual. I took
it up and flew it and agreed with him that something
wasn't quite right. Didn't know what the problem was.

AME R&R'd the mags - serviced in Toronto, instead
of new. Sigh.

Didn't make any difference. AME put new plugs in.
Didn't make any difference.

So, I'm wondering if the high-tension leads have a
hole worn in them someplace. I'm looking at them,
and I notice that one of the springs on the end of
the wires - you know, that goes into the well in
the plug - was tangled slightly.

I carefully untangled it, put it back on, and my
friend test-flew it. Ran fine now.

My problem is that I'm just not very bright
compared to the average AME. I've only been
operating and fixing motorcycles, cars, tractors,
boats and airplanes for 40 years now, which
explains why I am so dense.
---------- ADS -----------
 
iflyforpie
Top Poster
Top Poster
Posts: 8132
Joined: Tue Apr 15, 2008 12:25 pm
Location: Winterfell...

Re: Cessna Alternator Warning Light

Post by iflyforpie »

I always try to go from easy to find to hard to find, cheap to expensive when troubleshooting.

Rough running engine, I will pull the prop through to do a dirty compression check, pull the plugs and look for lead or other contamination or bridging, then do an HT lead test, then check the timing, etc etc before I start pulling things off and asking for money.

I did pretty good this summer even though the fixes werent cheap. I could have sold a customer an entire fuel injection system for his 206 (that we just happened to have on the shop floor) but a few tweaks and his pressures were back in the proper ranges.

I did replace a carb on a 152 that would keep on stalling after startup, but the throttle shaft was very worn and leaning it out. It kept on stalling with the new carb as well--until I realized the owner was so used to the leaky old carb that he wasn't advancing the throttle enough to keep the engine going (no issues at full power, and primer, idle mixture, fuel vents, strainer, induction system, plugs, and timing were all good).

Had a 172 with a stuck valve. O-300 that sat for three years but ran for the last two. Ran rough, wouldn't make power. Did a quick leak down and found the valve welded in the guide (took a lot of hammering to get it unstuck after we pulled the jug). The stem was corroded and attracting carbon. I told the owner based on his last jug just to replace it, because it would be beyond limits if I sent it in. Got a new cylinder kit, but then he was wondering why there was no corrosion in the cylinder barrel. He sent it in anyways and the shop said yes, there is no corrosion in the cylinder, but you will have to go oversize if you want it back.

Our Skymaster lost an alternator at a remote airport. Flew out there, swapped regulators (even though the Skymaster has two regulators either which can run both alternators, I had a spare and it was a five minute job), checked for shorts, checked for power, serviced the battery (it was low on water), and then scratched my head. Had an idea and went to the alternator and started spinning the cooling vanes..... U/S alternator drive. Looked lustfully at the other Skymaster on the ramp next to ours, then did the puppy dog face to the owner of said aircraft who was helping us out.... scored a new alternator plus drive. Re and re in an hour (access is a biotch), dumped the oil and cleaned all of the rubber crap out of the screen, and had the aircraft flying before dinner.

The only return misdiagnosis was the 152, only because I was saving replacement of the carb as a last resort.
---------- ADS -----------
 
User avatar
Colonel Sanders
Top Poster
Top Poster
Posts: 7512
Joined: Sun Jun 14, 2009 5:17 pm
Location: Over Macho Grande

Re: Cessna Alternator Warning Light

Post by Colonel Sanders »

Diagnosing an unfamiliar, complicated system
perfectly, first time, every time is very difficult,
especially when the problem is not easily reproducible.

Anyone that says they've never made a mistake
is either a liar, or doesn't have any experience,
which is what we refer to as the "trivial solution"
in mathematics. Lacks utility.

Most of the time, when an experienced mechanic
diagnoses a problem, he's actually performing
pattern recognition, not actual diagnosis -
he's seen that problem before. See page 1 of
this thread where Culver10 mentions he's seen
this problem 3 times before.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

Colonel Sanders wrote:Do people contact you about a
screwdriver you left someplace 20 years ago?
Pretty tough to contact the perpetrator(s), but I have found a number of tools left in aircraft that we believe could only have come from the factory itself 20 or 30 years prior.
---------- ADS -----------
 
GyvAir
Rank (9)
Rank (9)
Posts: 1804
Joined: Mon Mar 12, 2012 7:09 pm

Re: Cessna Alternator Warning Light

Post by GyvAir »

Colonel Sanders wrote: So, I'm wondering if the high-tension leads have a
hole worn in them someplace. I'm looking at them,
and I notice that one of the springs on the end of
the wires - you know, that goes into the well in
the plug - was tangled slightly.

I carefully untangled it, put it back on, and my
friend test-flew it. Ran fine now.
In the spirit of sharing tips:

Those little springs are surprisingly temperamental. I've noticed that newly overhauled or inspected engines often come with some sort of DC4-like lubrication applied to the silicone portion of the lead where it inserts into the plug. (I forget what is actually called up in the MM) If that gets onto the end of the spring, it causes arcing between the spring and the plug contact and leads to a build up of insulating carbon/soot/slag on the spring and plug which in turn makes for a rough running engine.
---------- ADS -----------
 
pelmet
Top Poster
Top Poster
Posts: 7138
Joined: Tue Jun 14, 2005 2:48 pm

Re: Cessna Alternator Warning Light

Post by pelmet »

Big Pistons Forever wrote: Mon Aug 06, 2012 9:14 am
Colonel Sanders wrote:The Cessna "high voltage light" is a bit of a misnomer.

When it comes on, all it's saying is that the alternator
has been taken off-line, and isn't producing current
any more. That's all. Now, one cause of the alternator
being taken off line is over-voltage.
This is a very good point. Most pilots who fly the simple Cessna's, including most instructors :roll: , think if the light isn't on the alternator must be working. This is not true as there are many other failures which could cause the alternator to stop providing power. The only way sure way to know if the alternator is working is to monitor the ammeter. BTW if you are flying along and all of a sudden ATC says that they are no longer receiving your transponder the first thing you should do is check the ammeter. Transponders are very sensitive to voltage in the event of an alternator failure the first thing to drop off line as the battery voltage drops will be the transponder. Still far better to keep a good scan of the ammeter.

It should also be noted that later models (post 1978) have a "low voltage" light instead of the "high voltage" light. This light comes on any time the bus voltage is below 24.5 volts. If the alternator is working then the bus voltage will be 28 volts, so this light is positive indication that the charging system is not working. That is it will always come on regardless of what or how an element of the charging system has failed.
This is a quote from another forum. Would you agree with this?....

"The old generators had light that would come on when output voltage fell off, but alternators and their regulators were adapted from automobiles, where the alternator regulator was switched on by a small signal from the alternator's stator junction. In airplanes we need some means of shutting the alternator off manually, so the ALT switch does that. The result is that the high or low voltage light doesn't come on unless the ALT switch is turned off either manually of if the overvolt sensor does it. It will not light up if the brushes fail or the belt breaks or the wiring falls off or even if the alternator falls off the airplane altogether. Newer (!) airplanes, post 1978/79 or so, used electronic ACUs that would fire the light if the output voltage fell off, but we still fly many thousands of older airplanes without such stuff."
---------- ADS -----------
 
Heliian
Rank (9)
Rank (9)
Posts: 1976
Joined: Wed Apr 29, 2009 2:14 pm

Re: Cessna Alternator Warning Light

Post by Heliian »

pelmet wrote: Thu Apr 02, 2020 10:36 am
Big Pistons Forever wrote: Mon Aug 06, 2012 9:14 am
Colonel Sanders wrote:The Cessna "high voltage light" is a bit of a misnomer.

When it comes on, all it's saying is that the alternator
has been taken off-line, and isn't producing current
any more. That's all. Now, one cause of the alternator
being taken off line is over-voltage.
This is a very good point. Most pilots who fly the simple Cessna's, including most instructors :roll: , think if the light isn't on the alternator must be working. This is not true as there are many other failures which could cause the alternator to stop providing power. The only way sure way to know if the alternator is working is to monitor the ammeter. BTW if you are flying along and all of a sudden ATC says that they are no longer receiving your transponder the first thing you should do is check the ammeter. Transponders are very sensitive to voltage in the event of an alternator failure the first thing to drop off line as the battery voltage drops will be the transponder. Still far better to keep a good scan of the ammeter.

It should also be noted that later models (post 1978) have a "low voltage" light instead of the "high voltage" light. This light comes on any time the bus voltage is below 24.5 volts. If the alternator is working then the bus voltage will be 28 volts, so this light is positive indication that the charging system is not working. That is it will always come on regardless of what or how an element of the charging system has failed.
This is a quote from another forum. Would you agree with this?....

"The old generators had light that would come on when output voltage fell off, but alternators and their regulators were adapted from automobiles, where the alternator regulator was switched on by a small signal from the alternator's stator junction. In airplanes we need some means of shutting the alternator off manually, so the ALT switch does that. The result is that the high or low voltage light doesn't come on unless the ALT switch is turned off either manually of if the overvolt sensor does it. It will not light up if the brushes fail or the belt breaks or the wiring falls off or even if the alternator falls off the airplane altogether. Newer (!) airplanes, post 1978/79 or so, used electronic ACUs that would fire the light if the output voltage fell off, but we still fly many thousands of older airplanes without such stuff."
No, each system can be slightly different. Some older systems have a relay built into or next to the regulator to trigger a light if the regulator fails or if the alternator fails which in then trips the regulator. The "newer",like less than 40 years old aircraft, usually have a solid state vreg which incorporates a light output for high/low voltage.

Best thing to do is to install a volt meter and just monitor that for proper output. Ammeters are fairly useless in smaller aircraft on a regular basis as there isn't enough load to get an accurate reading off of the +/- gauge. Once charged, the draw is low and then if it failed, you wouldn't really notice the slight movement to the other side. Your battery isn't just there for starting, it needs to provide that backup power in case of alt/gen failure.
---------- ADS -----------
 
Post Reply

Return to “Maintenance”