Go or no go

patmike

patmike

Pre-takeoff checklist
Joined
May 1, 2011
Messages
175
Location
New Britain Ct.
Display Name
Display name:
pat
I'm trying to figure out if I'm being to cautious or not. I've been flying the same plane (Aero AT-4) for 2 years from the same fbo that I got my license from over a year ago so I think I have a pretty good read as to whats normal with the plane. It has been getting a lot of use and has almost 2300 hrs. and it's due for an engine change. Today after my pre-flight Started the engine and the alternator failure light was on and voltage was at 13.8 normally it has always been 14.3. I shut down went inside and asked one of the instructors what he thought, he said he noticed it had been different but to be sure ask one of the mechanics which I did and he said that it was fine, that it would go out after the engine got up to 3000 rpm. So I got back in started up taxied out did the run up but the engine gauges where acting strange oil pressure was at the high end of the range but acceptable but when I throttled up oil pressure went down. I waited a while to see if everything stabilized which it did but with the avionics on the voltage was down to between 12.8 to 12.5 so I took off went around the pattern did a full stop landing taxied back to the end of the runway turned the fuel pump back on for takeoff but the fuel pressure gauge was bouncing around. it was bouncing in the green range but it wasn't stable and voltage was down to 12.1 that was it for me. Told the the desk guy what was going on and he said he would inform the airport manager to see what he wanted to do. question is was I wrong to pull the plug on the flight?
 
Always err on the side of caution.
When a trusted plane feels off, turn it off.
 
If you don't feel good about it, then pull the plug on the flight.
 
Planes were designed to be "fixed" on the ground not in the air. You did the right thing.
They may be putting off the inevitable for as long as they can.
 
You were on battery power only, if the alt. was working you should be the 13-14 volt range.
 
Did anyone check the alternator breaker? Did you look to see if the belt was intact and tight? :dunno: The alternator obviously wasn't on. 14.3v is what the alternator puts out, 13.8 is a fully charged 6 cell battery. That reading combined with the Alt light tells you you have a problem. You don't have to take off and fly to get an alternator to put out full production, if the light doesn't go out and voltage come up by 1500rpm, you have a problem.
 
Wait, so your engine gauges were funky for a while and your volts were low...and then you took off?? :confused:
 
Thanks for all of the input. As of right now the plane is still on the schedule and someone was scheduled to fly it after me and tomorrow, so I must be full of it.
 
Don't let it bother you, Pat. Better to be cautious.
 
Henning said:
It's not like it's gonna die and fall out of the sky, worst that happens is he loses the radio.
Click to expand...
I must be missing something then. What does the weird behavior of the engine instruments have to do with the alternator failure?
 
azure said:
I must be missing something then. What does the weird behavior of the engine instruments have to do with the alternator failure?
Click to expand...

All the gauges described are electrical and could be explained by a dropping bias voltage, or are the result of measuring electrical equipment.

The OP now knows what a discharging electrical system looks like. Next was radios and flaps.
 
Last edited:
1) A broken ring terminal on the alternator of my Cirrus caused several engine instruments to jump about. Noise in the electrical system can do that.

2) "If in doubt, sit it out."

You done good. Except for the taking off part.
 
MAKG1 said:
All the gauges described are electrical and could be explained by a dropping bias voltage, or are the result of measuring electrical equipment.
Click to expand...
Possibly, but I don't see how that explains the oil pressure going DOWN when he throttled up, particularly if it went up again when he throttled down. Admittedly, he didn't say whether it did or not.
 
If the oil pressure gauge is electric (which it probably is) it could be picking up interference from the failed alternator.

The voltage was continuing to drop, so you made the right call to stop. I probably wouldn't have taken off at all though.
 
azure said:
Possibly, but I don't see how that explains the oil pressure going DOWN when he throttled up, particularly if it went up again when he throttled down. Admittedly, he didn't say whether it did or not.
Click to expand...

Yes, that's what it did. It went from having an over pressure warning above 72 psi at idle (still in acceptable range) to in the 50's anything above idle like 3000 rpm.

StinkBug said:
If the oil pressure gauge is electric (which it probably is) it could be picking up interference from the failed alternator.

The voltage was continuing to drop, so you made the right call to stop. I probably wouldn't have taken off at all though.
Click to expand...

The engine monitor is TL Elektronic. it's about a 3x3 lcd screen with op ot egt's and cht's The fuel pressure is just a little analog gauge. It's bouncing around was the final straw for me. On the pre takeoff checklist it says fuel pump on pressure stable. Since it wasn't stable I stopped.
Whats making me doubt my observations and decision to stop is that they are still flying the plane. Isn't anybody else seeing the same thing I am? After being a race car driver I probably look at engine gauges more than most would.
 
It's never the wrong decision to call off a flight if you're uncomfortable with something. you made the right call.
 
Henning said:
They need electricity for the most part.
Click to expand...
Of course they do, that's not what I was getting at. I can see how erratic behavior might be due to the alternator malfunction (though I have to say I didn't observe anything of the sort during either of my two alternator failures). But the OP reported an oil pressure indication that dropped at higher RPM and went up at low RPM - if I'm reading his #20 correctly, the behavior was consistent and reproducible. How could alternator failure be responsible for that?
 
azure said:
Of course they do, that's not what I was getting at. I can see how erratic behavior might be due to the alternator malfunction (though I have to say I didn't observe anything of the sort during either of my two alternator failures). But the OP reported an oil pressure indication that dropped at higher RPM and went up at low RPM - if I'm reading his #20 correctly, the behavior was consistent and reproducible. How could alternator failure be responsible for that?
Click to expand...

very simple, an engine gauge is nothing more than a volt meter normalized for what ever sensor it is reading. as system voltage varies, as it will when an alternator is failing but still producing some voltage, the biased voltage it is showing on the gauge will vary with rpm. depending on how the circuit is designed, it will go up with increased base voltage or down with increased base voltage.


bob
 
old cfi said:
Planes were designed to be "fixed" on the ground not in the air. You did the right thing.
They may be putting off the inevitable for as long as they can.
Click to expand...


The Spruce Goose has walkways out to the engines inside the wings. A mechanic can work on the engine inflight!!:hairraise:

But you knew that.....
 
azure said:
Of course they do, that's not what I was getting at. I can see how erratic behavior might be due to the alternator malfunction (though I have to say I didn't observe anything of the sort during either of my two alternator failures). But the OP reported an oil pressure indication that dropped at higher RPM and went up at low RPM - if I'm reading his #20 correctly, the behavior was consistent and reproducible. How could alternator failure be responsible for that?
Click to expand...

I don't know the gauge circuit, so can't comment, but there are several ways that low voltage can turn a smooth gauge into a jumpy one.
 
kgruber said:
The Spruce Goose has walkways out to the engines inside the wings. A mechanic can work on the engine inflight!!:hairraise:

But you knew that.....
Click to expand...

So did the B-36. Al used to tell stories about fixing them in flight.
 
You must log in or register to reply here.
Back
Top