Why you should always do a full run up

[bstratt]

Our plane came out of annual last Friday afternoon and one of my partners flew 1 1/2 hours Friday night to check it out.

Saturday morning I left for Black Hills in SD, with a refueling stop at Sioux Falls. After refueling at Sioux Falls I taxiied out and in my usual fashion did a full run up - surprise - the engine ran extremely rough on one of the mags. Thought I may have fouled it and tried to burn it off but nothing worked. Told ground I had to taxi back to the FBO as I had a mechanical problem (note we had new Slick mags put in as part of the annual and I wondered if one was a lemon). When I pulled up to the FBO and the line guy came out to see what was the matter I said I had a problem and could he send a mechanic. While waiting for the mechanic I pulled the cowl cover off and started to check around. Ground wires for the mags were firmly attached at both ends, then - well look at that - the lower rear right side spark plug wire was completely disconnected from the plug and hanging loose. The one in front of it I could spin the nut with my fingers. Mechanic showed up and re-installed and tightened both wires and checked all the others which were okay. Plane was fine after.

I can only surmise that the mechanic doing the annual attached them all by fingers and then went around tightening and forgot the lower two. As it passed the mag check leaving DPA that morning I figure the nut must have vibrated off.

 

[ScottM]

Sounds about right. I am with you and always do a full run up. I would rather be surprised at the hold short line than just after lift off.

 

[JohnR]

That's maddening. Even a visual check under the cowl wouldn't show the leads "finger tight." I guess you really have to check everything, especially after maintenance.

 

[Tom-D]

That's maddening. Even a visual check under the cowl wouldn't show the leads "finger tight." I guess you really have to check everything, especially after maintenance.

That's what I love about owners assisted annuals, The tools they find are theirs and poor maintenance is theirs too. The IA can't see torque either.

I lost a 4 inch snap on screw driver after one of my owner assisted annuals the owner buttoned up. I looked for it 2 days and never found it, 2 years later I see it in the owners tool box.

 

[sba55]

Wow, this seems to be the time for unlucky annuals. Just had one of those myself.

Personally, I don't see the point in run-ups. I do an inflight mag-check in cruise and another one right before landing. On departure, I'll put the JPI on normalize, quickly check both mags while taxiing out, and get on with it. That way, I'm usually ready to go before I get to the runway, and they're already waiting for my IFR release.

-Felix

 

[RotaryWingBob]

You're right, Barry. At some point I was doing some advanced dual and did a whole bunch of off-airport landings. My CFI made the point that even though you haven't shut down, if you are going need a max performance takeoff, you should should do a mag check prior to spooling up from ground idle. It's good advice.