Partial engine failure - lesson learned

[dutchroll]

Had a partial engine failure today departing in the Pitts which involved repeated huge "backfiring", accompanied by belches of black smoke (according to witnesses) and temporary substantial loss of power (followed by recovery each time) from about 100ft after takeoff.

 

I immediately turned onto the tightest downwind I've ever flown, pulled the power back a bit (which somewhat reduced the severity) did some quick trouble checks (boost pump on - already was, mixture, fuel on main, ignition switches, phew, at least I didn't skip my checklist actions before takeoff!) and had obviously caught the attention of tower who quickly asked "confirm Ops normal?" - answer "negative, rough running, returning for immediate landing". They immediately cleared me to land on any runway (good job ATC).

 

With much reduced power on a very tight base and final the backfiring stopped and the landing was uneventful, though with the significant noise I had quite an audience out the front of the hangars. The whole incident was probably 4 minutes.

 

So.....what was the problem and why do I feel like stabbing myself in the eyeball with a fork?

 

After a day attending to air system issues and the maintenance guys doing several engine runs I was heading home. I had abnormally low egt indications on #5 cylinder during the runup. It sounded good though, the other 8 cylinders were fine, and the mag drop was insignificant. I quickly sms'd the maintenance guys who were not far away from the runup bay and they replied that it sounded really good from outside. Bad probe? CHT was low on that cylinder but rising and coming within limits (warning sign ignored perhaps also influenced by get home-itis). So I made the fateful decision to takeoff.

 

Application of takeoff power was normal but we figure (will find out on Monday) that both plugs were totally fouled. The EGT indication was correct. The CHT was rising with heat produced by the perfectly functioning neighbouring cylinders. The mag check was normal because neither plug was operating, so switching each ignition off in turn made no difference. Giving this 436HP beast full power poured a gutful of fuel into the #5 cylinder which was fine for a very short time, but probably ignited the exhausted fuel mixture with a bang in the hot exhaust pipe very soon after takeoff. This probably produced substantial back-pressure, causing the instant power loss then recovery, until the next lot ignited in the exhaust with the same result. Reducing power reduced the fuel flow and consequent effect.

 

Ironically, if I didn't have an engine monitor (and many aircraft powered by these engines don't), the result would've been the same. However I did have one and it gave me 2 warning signs which I noted, but dismissed (abnormal EGT and slow rise in CHT in the same cylinder, in favour of the fact that it "sounded good" (and it truly did) and was a normal runup, with nothing out of limits.

 

Something I need to have a long hard think about when I finally stop hitting myself. I really need to pay more attention to the generous indications I have on the engine monitor rather than only being concerned with a flashing out of limits condition. EGT doesn't have this, but can tell me a lot.

 

 

[winsor68]

What do you imagine would have happened if the "partial" turned into a "full" during the circuit? Were you out of runway?

 

 

[gandalph]

A very enlightening post Dutch. Thank you! I'm sure I speak for all when I say we are VERY glad that you came back to tell us about it. And personally, it is so re-assuring to be reminded that making simple mistakes is not the sole territory of mugs like me.

 

 

[dutchroll]

What do you imagine would have happened if the "partial" turned into a "full" during the circuit? Were you out of runway?

Early during the circuit I would've had the ability to land on the cross strip, albeit with a fair crosswind. Would've needed some fancy manoeuvring, but achievable I think. Later in the circuit, because I deliberately kept it very tight, I could've turned an early base and touched down halfway down the runway, or just landed across both runways using the grass.

 

 

[M61A1]

Our machines will almost always tells us something, dropping little hints which seem so obvious after the fact. More than once I've got very sh1tty with myself for not listening properly in the first place.

 

Good outcome.

 

 

[facthunter]

The unburnt charge will explode in the exhaust where you have a collector ring depending on where the "cold" cylinder is. A backfire in the inlet manifold is extremely dangerous, because it can cause severe overcharging of another cylinder where the inlet valve is open . Taxiing for a long distance at idle or long warm ups cause sooting often as the idle mixture is normally very rich. Some pilots use a very lean taxy mixture, so lean that if you forget to enrichen it before take off the motor cuts out when you advance the throttle. Nev

 

 

[Oscar]

Blimey, DR - were you leaving Camden? I saw your plane at Dave Dent's place a few weeks ago - absolutely beautiful, glad it wasn't scratched!.

 

 

[Pearo]

though with the significant noise I had quite an audience out the front of the hangars.

There was an incident recently at YRED with an aircraft making the same noises. It every aviators worst nightmare, so I promise you every single person in that audience would have been standing there quietly geeing you on and hoping you got back on the ground safely. For you, it may have been sweating bullets, but those on the ground are doing the same on behalf of you!

 

Glad it all turned out ok for you!

 

 

[dutchroll]

The unburnt charge will explode in the exhaust where you have a collector ring depending on where the "cold" cylinder is.

Yes we strongly suspect that's what happened. It wouldn't have been a backfire I don't think, rather an afterfire. Fortunately!

 

Blimey, DR - were you leaving Camden? I saw your plane at Dave Dent's place a few weeks ago - absolutely beautiful, glad it wasn't scratched!.

Yep. Still not scratched!

 

 

[old man emu]

The thumping sound that was heard all over Camden Airport after your landing was Dave Dent's fundamental orifice puckering in and out.

 

OME

 

 

[Oscar]

Along with all of his lads.... they are a top mob of people and they LOVE their aircraft (well, not Jabs., but I know why, and I rarely disagree with their comments, TBH.) But they humour me and more importantly, they help me understand what, why and how to do things.. and having access to that depth of expertise is a resource of which no amateur should ever, ever underestimate the value.

 

 

[dutchroll]

The thumping sound that was heard all over Camden Airport after your landing was Dave Dent's fundamental orifice puckering in and out.OME

Lol. Yeah they were a bit saucepan-eyed when I taxied in!

Of course as we know, it wasn't their fault. Plug fouling is always a possibility after ground runs, and particularly so on the lower cylinders of a radial. The buck stops with me as PIC and I should've taken the #5 cylinder instrumentation warning signs more seriously (as I will from now until I fold up and pack away the logbook for the last time) instead of just going with a gut feel that it sounded normal.

 

As an aside, in the process of adjusting the air system relief valve and air charging system (which was why I was there) they noticed a very loose fuel primer line fitting at the solenoid valve in front of the firewall. They showed me this elbow fitting just flopping around! This hasn't been touched since engine installation at manufacture, so it most likely vibrated that way. God only knows how it hadn't sprayed or leaked fuel everywhere. Glad they picked that one up!

 

 

[fly_tornado]

Glad too hear you made it back to the ground safely

 

Is #5 the bottom cylinder?

 

 

[Oscar]

His playing around with the fuel system (against all the advice and warnings given him) killed Pip Bormann. I'd be surprised if there is ANYBODY in Australia who knows Pitts aircraft as well as Dave.... and therefore, what to look at.

 

 

[dutchroll]

Glad too hear you made it back to the ground safelyIs #5 the bottom cylinder?

Yep, #5 and 6 sit either side of the six o'clock position. #1 cylinder is right at the top, at the 12 o'clock position. Historically on the rare occasion I've had a single plug fouled (never had both before) it has usually been #6, but it's very noticeable of course on the ignition check. When they're both out, the ignition check is fine!

 

 

[Gnarly Gnu]

God only knows how it hadn't sprayed or leaked fuel everywhere.

Indeed; praise be to Him for your safety! Psalm 44...

 

 

[M61A1]

Indeed; praise be to Him for your safety! Psalm 44...

 

 

[Geoff13]

Indeed; praise be to Him for your safety! Psalm 44...

If he had been doing his job the bloody thing would not have broken down in the first place.!!!

 

 

[old man emu]

Serves you right for fitting an atheistic Commo engine you your palne!

 

 

[Gnarly Gnu]

Serves you right for fitting an atheistic Commo engine you your palne!

Haha, I've one of them too. In his case it's the plane that is the pitts.

 

 

[Ultralights]

Thought about doing an engine course? and learning exactly how to diagnose most engine issues with CHT and EGT readings?

 

 

[dutchroll]

Thought about doing an engine course? and learning exactly how to diagnose most engine issues with CHT and EGT readings?

I do actually have a whole bunch of info tucked away in a manual about EGT/CHT diagnosis. Might be reading that properly soon, although in this case I know what was indicated and what it meant, but mysteriously talked myself out of believing it. I certainly believed it a couple of minutes later, I can tell you!

 

 

[Teckair]

I am glad that turned out the way it did and it is so true take notice of the warnings you are given.

 

 

[facthunter]

Yes with both plugs sooted the rev drop test is not valid. I don't know how elastic your engine mounts are, but I'm surprised the engine didn't rock a bit with one pot out. Did you check your revs achieved on Take off? I know its C/S but it's on the fine pitch stop initially or your plane doesn't a have a usable prop safety speed. Nev

 

 

[cooperplace]

out of curiosity, what type of engine is this?