Bristell B23 loss of power

Thanks for alerting @Gallois, much appreciated.

From the report here I understand that there was a loss of power and a smell of burnt oil. After investigation it appeared that oil was found in the exhaust of cyl number 3. Hope my French didn’t fail me..

Here’s the second event , very similar although it does not provide technical details. The reports were submitted 15 jan but I assume there was some time between the events, as you can’t just do an engine exchange in a heartbeat. Very awkward if indeed the same thing happened twice in a row.

aart wrote:

The reports were submitted 15 jan but I assume there was some time between the events, as you can’t just do an engine exchange in a heartbeat.

They were not on the same aircraft, were they?

I have read both, and One of the report mentions 1l of oil consumption during the 50m flight.
the second doesn’t mention this but smoke on the engine diring descend/landing.
Looks like a headgasket…

First:

Instructional flight on Bristell B23.

The first part of the flight is a local flight about flight manouvers, during which no anomalies are observed. The second part of the flight on return from the local flight consists of performing 2 circuits. The first circuit is performed by the instructor for demonstration. A STOP&GO is carried out, and the second circuit is planned to be executed by the student. Takeoff is undertaken with 1200m of runway remaining. The power setting is nominal, normal parameters, and rotation is performed at 50kt.

As soon as “airborn”, we observe initially what could be likened to a shimmy of one of the airplane’s wheels, except that this vibration amplifies slightly and clearly it is not shimmy. The airplane has difficulty climbing, and I announce “I have the controls” (as the FI). The priority is to maintain speed (64kt minimum), and I no longer have enough runway available to consider a landing on the axis. During the quick fault search (100ft/ground), I notice that the propeller RPM fluctuates and that the engine speed is not the expected speed in this initial climb phase (+ or – 5300 rpm Iso 5700).

I declare a PAN PAN “vibrations and engine power loss” with, if possible, a report in close downwind (or against QFU) depending on the remaining engine capacity. The decision to turn towards the downwind is made because the engine is still pulling. I decide to retract the flaps and try to maintain 70kt, which allows me to have a significantly better climb rate. Passing 90° of turn, my trainee informs me that he smells something burning, which I immediately notice. This acrid and irritating smell leads me to think of a burnt oil smell, but there is no smoke in the cockpit. I immediately declare a MAY DAY with a burning smell in the cockpit. Established at the beginning of the close downwind, 300ft/ground, I reduce engine power in order to preserve it, and immediately the smell begins to dissipate in the cockpit. Nevertheless, I remain ready to cut everything, now in a position that allows me to reach the field on any QFU. The engine holds, the smell is less and less present, I continue the downwind and perform a PTU (dead stick landing).
Normal landing and taxiway C clearance where the firefighters are waiting for us.
Comment from the declarant:
Abnormal oil consumption. After a 50-minute flight, the engine would have consumed approximately 1 liter of oil (following post-flight oil change). Oil is consequently found in the exhaust pipe of cylinder #3. See engine endoscopy photos. Note that the propeller governor is hydraulic and uses the engine oil circuit.

Second (thro0ugh translate)

Third training flight of the day on the same plane. The previous 2 flights were normal. The student is at the controls.

Takeoff on runway 18, initial climb at 150 ft AGL, I hear a muffled noise, I see the RPM drop from 5700 RPM to 5500 RPM. I perceive it as a partial power loss. I take control and check the position of the throttle and propeller control. The throttle is full open, the propeller control is full fine pitch. I inform the tower with the radio message: “F-ZZZZ, pan pan, power loss”. I turn onto a low altitude circuit at 200 ft AGL. On downwind, I smell an unusual odor. I notice a new loss at 5000 RPM, my plane is level at 60 kts, 250 ft AGL. ATC asks me to extend downwind to allow a PC-12 to line up and clear the runway. I have enough runway from my position, I will not conflict with the PC-12 and I reply “Negative, from my position, I’m going to the runway.” I perform a left-hand U-turn and land on runway 18.

Plane stopped on the runway, the tower informs me that smoke was observed during the descent until the aircraft stopped. I initiate the evacuation procedure and the ground engine fire procedure. As I was already committed to evacuate, I do not wait for the engine to stop, I turn off the engine ignition. Evacuation completed, the crew waits for the firefighters on the side of the runway. I inform the firefighters that the safety pin of the parachute is not in place. One of the firefighters takes care of putting it back. The firefighters do not observe any fire or smoke. After a wait requested by the firefighters, the plane is towed back to the parking area.

Thanks @gallois for reposting these two “retours d’expérience (REX)” from the FFA. I read them this morning and this reminded me of this report from the Swiss CAA (FOCA) listing similar issues on ROTAX powered airframes since 2021:

Repeated ROTAX engine failures

The report states that the causes for these engine failures have not been identified so far.

Hi everybody,

I’m one of the managers of the French Air Club involved in the 2 engine failures you are writing about.
The 2 mishaps are related to the same S/N, with two different brand new engines.
The first one incident, in August 2023, at 54 hours engine time since new. The engine was sent back to BRM, after two months it was sent back repaired by czech Rotax dealer. No words on the root causes for this failure, nothing. So, our Camo rightly refused to have this engine installed on the plane. We sent it back and obtained a brand new engine, with totally different S/N from the previous one.
The second incident happened in December 2023, with this second, brand new engine, at 48hrs engine time since new.
Now, our plane is grounded and we have a second aircraft, fully paid, that is waiting for us at BRM’s factory in Czech Republic.
We haven’t got ANY information on our first engine failure, neither from Rotax nor from BRM.
Now, we are waiting BRM to come to our place to throughly inspect the plane and tell us what the hell happened.
In the meantime, since the BeA (sort of French NTSB) and the DGAC (the French Aeronautical Authority) refused to do it, we decided to perform our own investigation with ALL Bristell B23/912-operators, in France, Germany, Switzerland, The Netherlands, Austria and the Czech Republic. We focused the investigations on Rotax 912-equipped aircraft, and I don’t know nothing on the reliability of 915 turbo-operated planes.
Besides BRM, I am the only person for now that knows how many B23 have been concerned by engine problems or failures, knowing the operators, the serial numbers, the fuel used, the number of hours at the time of the incident and if and how their problem was adressed by BRM or Rotax.
The situation is really serious, as there have been at least 8 major engine troubles on the whole population of B23/912 planes.
At least 5 total engine failures that required engine replacement or repair.
Rotax says that the actual exhaust system on the B23 might be related to some incidents as the back-pressures are to the limits of what Rotax requires. For this, BRM has been making a new exhaust system, together with Rotax, that is intended to provide with 15% more margin in back-pressure levels.
This exhaust system is not certified yet.
And now they came out with this UL91 story, and nobody was aware of. B23 operators and Rotax dealers have suddenly discovered that BRM thinks that UL91 might cause troubles with the engine, while UL91 is shown as possible fuel in the B23 flight manual and in Rotax documentations.
By the way, our investigations show that some B23 engine failures occurred on SP98 (mogas) fuelled engines.
On the other hand, there are 912-equipped B23 that have flown on UL91 for thousands of hours without any problem.
Should anybody be interested in more details, I will be happy to provide the anonimous results of my investigations (names, registrations and S/N won’t be shown for obvious privacy reasons).
Hope this can be of some help.
Safe flights!

Thanks very much @FlyingWolf for your report and for taking action!

As further food for thought, exhaust flow dynamics and octane performance of fuel are not unrelated to one another.

FlyingWolf wrote:

We haven’t got ANY information on our first engine failure, neither from Rotax nor from BRM.

That is really bad. BRM should communicate openly with yourselves about your failures. OTOH, it seems this message is not 100% accurate since somehow they have communicated about exhaust backpressure and UL91 fuel.