G1000 GMA1 Fail and Failed Path

tehmightypirate

tehmightypirate

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So, the other day I was about to return home from a x-country flight and went to start the engine of the Cessna 172 SP I fly. It was hot and the engine was running about 20 minutes prior so I performed a hot start without priming. The engine didn't catch. Upon the second try the engine again didn't catch and ended up being flooded at this point (bleh) but the G1000 lit up with a ton of red X's. All the engine instruments were out and I had the following errors:

GMA1 FAIL - GMA 1 is inoperative
FAILED PATH - A data path has failed

This was along with the usual errors of running the G1000 on the standby battery alone without the engine running.

I shut down all power including the standby battery, allowed the system time to reset, and then rebooted the G1000 on standby battery. Again no engine instruments and the same warnings. I then turned on BAT power and avionics BUS 1 and 2. All functionality was restored except I still received a FAILED PATH error. After some consultation with another pilot familiar with the G1000 and after consulting the quick reference guide we determined that it was safe to fly home as I did not require the standby battery functionality and the FAILED PATH error only indicated a data path connected to the GDU or the GIA 63/W has failed but they could still function using other data paths. All instruments worked correctly on the return flight and it was uneventful. The FAILED PATH error remained throughout the entire flight.

The plane was apparently serviced yesterday but I don't know what they replaced or did. Something involving the audio panel from the note left on the schedule. Haven't received any word from the flying club on this.

I checked the plane today and now the engine instruments all work on standby battery but the GMA1 FAIL and FAILED PATH errors still appear. With battery power and avionics Bus 1 or Bus 2 on (or both on) I receive a FAILED PATH error.

http://www.pilotsofamerica.com/forum/attachment.php?attachmentid=34878&stc=1&d=1404958665
The alerts shown on standby battery power.

http://www.pilotsofamerica.com/forum/attachment.php?attachmentid=34879&stc=1&d=1404958665
Page 2 of the alerts shown on standby battery.

My father and I were planning on taking it out this weekend and were curious if anyone could shed some light on the cause of this error. I assume the GIA 1 and 2 computers are still working normally. We plan to avoid IFR flight but we're curious how risky an IFR would be.
 

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I actually resized them when making the post but it then posted them full size... No idea, can't seem to fix it so I've changed them to just links.
 
You should only start the 172SP G1000 with the STBY BATT. Nothing else.

GMA1 FAIL – GMA1 is inoperative.

The audio panel self-test has detected a failure. The audio panel is unavailable. The G1000 system should be serviced.

I'm not sure if it's an LRU or not or how easily it can be serviced.
 
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I assume you mean start it on standby battery as well as master switch alternator and main battery. Which, yes, we did. The engine was never started with avionics bus 1 or 2 on. While the engine instruments were inoperative on standby battery we turned on bus 1 and 2 asap after engine start to get the engine instruments operational.
 
Why would you not prime a hot engine? That's how you get cool fuel in the fuel lines that the engine can run on, otherwise you have to crank a lot.
 
Cpt_Kirk said:
You should only start the 172SP G1000 with the STBY BATT. Nothing else.
Click to expand...
Care to shed some light on this statement?

From the 172S NavIII POH:

"STARTING ENGINE (With Battery)
...
3. STBY BATT Switch:
a. TEST - (hold for 20 seconds, verify that green TEST lamp
does not go off)
b. ARM - (verify that PFD comes on)
...
10. MASTER Switch (ALT and BAT) - ON"

Henning said:
Why would you not prime a hot engine? That's how you get cool fuel in the fuel lines that the engine can run on, otherwise you have to crank a lot.
Click to expand...
Same question.

From the 172S NavIII POH:

"NOTE
If engine is warm, omit priming procedure steps 12 thru 14
below.

12. FUEL PUMP Switch - ON
13. Mixture Control - SET to FULL RICH (full forward) until stable
fuel flow is indicated (approximately 3 to 5 seconds), then set to
IDLE CUTOFF (full aft) position.
14. FUEL PUMP Switch - OFF"

I've always started hot injected recips like this and never had an issue...
 
Henning said:
Why would you not prime a hot engine? That's how you get cool fuel in the fuel lines that the engine can run on, otherwise you have to crank a lot.
Click to expand...

From the expanded section of the procedures in the 172SP POH on starting engines:

In warmer weather, engine compartment temperatures may increase rapidly following engine shutdown, and fuel in the lines will vaporize and escape into the intake manifold. Hot weather starting procedures depend considerably on how soon the next engine start is attempted.Within the first 20 to 30 minutes after shutdown, the fuel manifold is adequately primed and the empty injector nozzle lines will fill before the engine dies. However, after approximately 30 minutes, the vaporized fuel in the manifold will have nearly dissipated and some slight “priming” could be required to refill the nozzle lines and keep the engine running after the initial start. Starting a hot engine is facilitated by advancing the mixture control promptly to 1/3 open when the engine starts, and then smoothly to full rich as power develops.

If the engine does not continue to run, set the FUEL PUMP switch to the ON position temporarily and adjust the throttle and/or mixture as necessary to keep the engine running. In the event of over priming or flooding, set the FUEL PUMP switch to OFF, open the throttle from 1/2 to full open, and continue cranking with the mixture in the idle CUTOFF position (pull full out). When the engine fires, smoothly advance the mixture control to full rich and retard the throttle to desired idle speed.
Click to expand...

In my case I should have done some minor priming as the engine started the first time but failed to continue running which indicates there was insufficient fuel flow into the injector lines to keep the engine running. The second time I started I did a quick priming but it was apparently too much and the engine flooded and failed to start on the second attempt. This was when I got the errors above.
 
So I finally got some follow up from my flying club and figured I'd document this in case anyone else runs into this problem and can't find any help on google.

The maintenance officer for the club claims that FAILED PATH error was there a long time ago. I highly doubt this as I check the messages page every time I fly and I had not seen it before. Anyway, he claims that alerts are stored in the G1000 until cleared (such as the terrain database error we've had in the plane for a while).

Anyway, if it's true that when they checked the system there was no issues then perhaps what can happen is if you have a failed start or some other strange situation the G1000 can throw a FAILED PATH error. Then upon resetting the system the G1000 will maintain that error until cleared even if the actual failed path condition is no longer present. Kind of like a check engine light in a car.
 
tehmightypirate said:
From the expanded section of the procedures in the 172SP POH on starting engines:



In my case I should have done some minor priming as the engine started the first time but failed to continue running which indicates there was insufficient fuel flow into the injector lines to keep the engine running. The second time I started I did a quick priming but it was apparently too much and the engine flooded and failed to start on the second attempt. This was when I got the errors above.
Click to expand...

Engines do not run until vaporized fuel gets between the electrodes of the spark plugs. These big bore engines love fuel, lots of it, to start on. With a fuel injected engine I always go full throttle, full rich, fuel pump on, flow indicating 1. Full flow now 2...3...4 and off. Throttle open 1/8-1/4 travel, mixture back to a lean ground run position, spin the starter one blade, left mag on two blades huff, three blades and she goes if she didn't take off on the second blade. Hot start, cold start, procedure is the same, really cold and I may add some more priming time and a blade or two and let it sit and the fuel vaporize a bit and try to light it. If it chugs and dies, I add more fuel and let it sit again, so also to allow that little chugs worth of heat to get in the head and piston top.

If I added a little too much fuel to a hot engine it takes no more than 2-3 extra blades to clear.
 
Henning said:
With a fuel injected engine I always go full throttle, full rich, fuel pump on, flow indicating 1. Full flow now 2...3...4 and off.
Click to expand...


So basically you always flood the engine? Because what you described is a really good way to do that. I guess started with a flooded engine always is one way to do it.
 
vince said:
So basically you always flood the engine? Because what you described is a really good way to do that. I guess started with a flooded engine always is one way to do it.
Click to expand...

Nope, just shy of flooded, best way to start an engine. I actually move excess fuel out and suck some fresh air in on that first blade before I hit the mag. But a little flooded is not a problem in a hot engine with two plugs, it will be ready to combust in a single cycle. The only time flooding is a problem is with a cold engine where the plugs stay wet with fuel and won't spark. A hot plug dries itself of fuel very quickly, in fact it's nearly impossible to flood a hot engine, especially with the one plug at the top of the cylinder. Also typically there isn't any fuel at the nozzle until after the count of two, so I'm not spraying all that much fuel into the engine, and it vaporizes very quickly.
 
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Seems a little risky to ride that close to flooding all the time and potentially dropping fuel out of the engine regularly. I'll stick with the Cessna POH recommendations. I belive my problem was not enough throttle and too slow on the mixture.
 
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