Lancair Columbia 300 (IO-550 N/A).
5 min. after a sea level takeoff, experienced 150-200 sudden rpm loss and immediate recovery...3-5 sec.
All systems seemingly perfect before and after event.
Engine totally smooth running during event.
LOP mag check on descent...all normal.
Sumped 3 qts after landing ...only very slight debris in active tank...none in other or fuel strainer.
Disassembled gascolator strainer, no debris found.
Flown 2 times since...no recurrence.
Fuel totally clean now.
Conditions were perfect vfr, no turb. No moisture in tanks, nothing out of the ordinary.
flew :50 on same tank prior to event and no fuel added.
Anyone heard of this especially on Columbias?
Any suggestions or suspicions
Don't like mysteries in planes...

JPI 1 sec. data shows no anomolous readings at event point.

The last time this happened to me I had a crack in a cylinder head. Just a sudden loss of power followed by immediate recovery. I'm thinking a slug of water. Did not happen on subsequent flights later that day.

Happened a few days later in the same scenario to the new owner. We grounded the aircraft and my mechanic found the crack using soap bubbles deep in the cooling fins.

Good luck.

--paul

Tach error?

I had (possibly) a similar issue that I chased for quite a while, over a year.

I would describe mine as feeling like someone smoothly but quickly pulled the red knob to ICO and back where it was in about a second. Over time it happened boost pump on, boost pump off, climbing, level, descending, minutes in, hours in, but always full power. When it happened 400AGL I grounded it and the shop said it was the fuel spider. A rebuilt fuel distributor seemed to make it go away for a year or so but it reappeared yesterday as a matter of fact. Clicked the boost pump on and it went away. Thinking it’s vapor lock maybe.

I had this type of experience one day while climbing through 7000 ft. Everything was smooth as silk and then suddenly a rough engine for a second or two followed by back to smooth. This happened twice in about 60 seconds. I turned back to my home airport and landed without any repeat occurrences.

I used my engine monitor data to identify which cylinder was stumbling and then used a borescope on that cylinder. We found what looked like a patch of carbon buildup had blown free. It seems that perhaps that chunk of carbon had fouled a spark plug for a moment and that's what caused the roughness. I did lots of test runs on the ground and then over the top of the airport without any repeats of the problem and I haven't had it happen again since. This happened a couple months after I bought the plane from the previous owner. My theory is that he may have been running the engine too rich and that caused the carbon build up. With the change to proper leaning and lean of peak ops, some of that junk broke free.

Thanks John.
I run LOP most of the time and have little carbon.
Plane came out of annual 3 flight hours before where an extremely thorough borescope was done with great compressions. Engine data combed by Savvy with no clues...but we are not the only ones...
Thanks much for the respospnse.

I agree with Bob’s thought. When I have experienced fuel pump cavitation (vapor lock) on my Baron the symptoms are exactly as the OP described. Low boost overcomes the cavitation. There is an excellent article on Mike’s CSOBeech website written by Jack Letts on the subject. Jack is an expert in the field and used to be here on BT. He fortunately survived an accident years ago but I don't think he’s posted since.

Thx Sven.
The Columbia has an arm feature on the boost pump that turns it on automatically with loss of FP. So no low boost is used for all normal ops.
Also, I've been flying this plane and engine for 500hrs over 8 years and it has never done this before. The engine pump has never needed supplementation.
Something has changed.
The Columbia and probably all Beech products have some kind of slosh box for immediate fuel supply feed so the pickup is never uncovered due to fuel moving around the tank.
The entry of fuel into that box has a flapper door that if blocked could easily cause fuel starvation for any length of time.
This is just a logical theory based on the design of the tank. Do you know if there is a similar design in Barons?

Also, the above description, pulling mixture out and in, is exactly what I used to describe the event.

Eliot, Barons with baffled main tanks have that feature which addresses the conditions that cause fuel unporting on the ground or in flight. That is a different issue all together from cavitation. I have experienced cavitation many times - for me it’s typically after a wings level climb out on a hot day from Van Nuys to a cruise altitude over 10,000 feet. Since it is fairly predictable, I am ready to put one of the aux fuel boost pumps on low as soon as I see the fuel pressure start to fluctuate. I keep the pump(s) on low boost until I have reached target altitude, then continue with cowl flaps open until things cool down. Works like a charm!

Thx Sven.
I will keep a closer eye on FP from here on to see if it could be the offender.
Since normal for the Columbia is no boost pump it should be easy to pick up.
The data did not show any variation on my event.
We do have a low boost circuit we call vapor suppression but never use it except when switching tanks.

Test pilot time...
Thx

I had this happen one time in a T210; running really rough and I thought it was going to quit.

I switched tanks, hit the boost pump and richened the mixture. Problem went away and never repeated itself.

Thanks Bill..that is very helpful.
How long after that event were you flying that plane ?
Did it have a lot of time to do that again ?
Eliot

Don't remember exactly, but it was fairly early on a fairly long trip, so it had plenty of time to repeat.

I was just trying to zero in on what large time frame it occured and how much time in months or weeks it has had since then to recur.
Min happened about 3 weeks ago, was only 3-5 seconds long and I flew an hour and a half after that and then 2 local test flights after that with no recurrence.
Thx