Rotax 912 Engine Failure

When we started flying four decades ago, we asked friend Jack, a very experienced pilot, aircraft mechanic, and computer science guru, "What are the odds of an engine failure in flight?"

He responded, "About once in your lifetime."

We just had that rare event and hope it is the only one for the remainder of our flying career. Here is the story.

The Flight

Departing at 6 am from the Aero Country airport north of Dallas, TX, a strong tailwind pushes us north to the Lee’s Summit airport near Kansas City, MO in four hours.

The new carburetors that we installed a few weeks ago on the Rotax 912 engine of our Zenith 601 HDS have cut fuel consumption. We burn just 12.2 gal in those four hours.

We refuel with 91 octane Mogas, help another pilot figure out the self service refueling system, and take off. It’s less than three hours to our final destination, the Boone Municipal airport north of Des Moines, IA.

Perfect weather, a strong tailwind, a purring engine. What could possibly go wrong?

In level flight, the water temperature climbs to 230 F. This is strange. The temperature usually hovers around 210 F, and goes to 230 F only during a steep climb. We reduce power. The temperature goes down to 210 F within maybe 30 seconds.

The speedy temperature reduction puzzles us, too. It normally takes several minutes to cool down the water again by a reduction of power.

Adding power again, the engine sounds different. It’s sort of a blaring sound. Never had this before.

We reduce power, add power, still that blaring sound. It’s getting louder, too. Clearly something under the cowl is . . . what? Breaking up, falling apart, blowing up?

The oil pressure and temperature are normal. The water temperature is back in the green arc. But the engine sound is frightening.

We reduce power to the point where we just can stay at altitude, around 2500 ft AGL (above ground level).

Maybe the engine is about to seize up, maybe something has broken off, who knows?

Taking Action

The thought surfaces that we likely must do an emergency landing. We look for a suitable meadow, a road. Nothing appealing is in sight.

A thought we never had before but have prepared for: It’s time to call for help. We dial the emergency frequency 121.5. "Mayday, Mayday. This is Experimental N314LB with engine about to fail."

Literally within three seconds we get a response by Air Traffic Control (ATC) asking us to verify the call sign and provide the location.

We look up the data for the nearest VOR, give the identifier, radial, and distance, even tell that we have ADS-B Out, something ATC likely knows already.

ATC gives us a transponder code, which we dial in. Then ATC points out options. There is an Interstate to the right, but with dense traffic. Farmed fields with much vegetation.

ATC also mentions two airports, one 5 miles away, the other 10 miles. We are too focused on the engine to look up the airports, in fact do not believe that we can make it there.

We emphasize to ATC that the engine may break up at any time. By now we are just 1500 ft AGL and concentrate on possible landing sites if the engine quits or worse.

Given that mental preparation for an emergency landing, we just don’t feel that we can spend time on airport selection.

Then we have the correct idea: ATC has all the information. We just should ask for it.

We request details about the two airports. The closest one, at 5 miles, is north of us and thus can be reached with a tailwind. That makes it the obvious choice.

We don’t want to figure out the heading to the airport since we want to remain focused on emergency landing sites. Instead, we make another smart decision. We just ask for the direction to steer.

ATC gives us the information in a snap, and we swing around into that direction.

Upon our question, ATC gives us the time required to reach the airport: four minutes. It’s a long time when a complete engine failure seems imminent.

To make it even worse, there are now trees below, and going for the airport might be the wrong decision.

But we are committed now. The engine is still turning at the reduced rpm. That gentle treatment seems correct even though it extends the time to reach the airport.

We pass over the trees and get to an expansive grass area surrounding the airport runway. Relief: We could land almost anywhere.

ATC gives us the winds of the Kansas City airport even though the airport we are approaching has AWOS (Automated Weather Observing System), as we learn later. But that service happens to be temporarily out of service.

But there is the windsock. We tell ATC that the wind looks fine with a moderate crosswind component, something we can easily handle.

We land, taxi off the runway, and tell ATC that we have done so. Then we realize that ATC cannot possibly receive that broadcast since we are too low for line-of-sight communication.

What do you know? There is a response. Incredulous, we ask how this is possible. As we learn later, ATC had asked another pilot to track us. He was nearby when we made the first Mayday call, and ATC asked him to keep watch over us. When direct contact with ATC was no longer possible, he began relaying our transmissions.

Wow, what a system! We thank ATC profusely. What a terrific help we got when a complete engine failure loomed!

Subsequent Contact with Air Traffic Control

Three weeks after the fateful flight, Lisa of Kansas City Air Traffic Control (ATC) contacted us. She is the Air Traffic Controller Association president for Kansas City International tower and approach control.

She told us that several people had been involved when we called for help on 121.5. Up to that time, our assumption had been that just one controller had assisted. 

To the contrary, it had been a complex operation. She proposed a Zoom session with all the people who had been helping during that fateful  flight. 

Let's look at the flight from the viewpoint of ATC. The narration is based on a summary by Lisa. Of course, any mistakes of interpretation should be charged to us. We include comments in parentheses.

The ATC Story

Mid-morning of that fateful day, Kansas City Center advised ATC that an aircraft had called on the Mayday frequency 121.5 in Kansas City airspace. The departure controller reached out on that frequency and located the aircraft in the Kansas City airspace south of the Cameron airport KEZZ.

The controller requested that the pilot switch to 118.4 for better communication. 

(We heard that request. By mistake, we just had pushed the button for switching frequencies, going back to the frequency with which we had opened the flight plan with Flight Service after the departure from Lee's Summit. Confused, we thought we were talking with Flight Service, and decided to go back to 121.5 and continue there.)

(This was a mistake, of course. We should have asked for clarification of the frequency information.)

The fact that the pilot continued on 121.5 posed a problem since it demanded that the controller handle just that single aircraft. 

This required a major reassignment of ATC personnel, including a controller who was on break. It involved initially two additional controllers, and later yet another one. 

(All this was unbeknownst to us: We focused on the terrain below for possible emergency landing sites and communicated on 121.5.)

As luck would have it, a VFR aircraft had just departed from KGPH, one of the so-called satellite airports in the larger Kansas City area. The controller requested that the satellite controller responsible for that airport contact the pilot and request that the plane act as spotter aircraft.

The pilot agreed to help, and the satellite controller sent the aircraft towards the aircraft in trouble. 

A terrific decision. In case of a crash, the spotter aircraft could immediately call in the precise location and thus direct rescue personnel.

(We weren't aware of any of this.)

The controller acted cool and reassuring. He advised that there were two nearby airports, Cameron KEZZ and Midwest National KGPH. 

(We completely discarded that information, feeling that the engine would never last long enough to get to either airport.)

He also pointed out that the Interstate was just off to the right. 

(Looking to the right, we felt great. This was the first landing possibility that seemed doable without a crash.)

He repeated the advice about the two airports, seeing the plane just making circles in a search of alternate landing sites. 

(We were caught up in the belief that the engine would quit at any moment, and kept looking for a landing site. A mistake, of course.)

(The gentle prodding of the controller to think about the two airports finally got us off the notion that we could never get there. This was the crucial point in time where we asked for details about the two airports.)

He then supplied information about the two airports, including the distance, of course. 

(It's at this point that we decided that we should offload all information gathering to the controller. It kept us focused on alternate landing sites, without the need to fiddle with the radios and looking for relevant information.)

A second controller gathered the information the pilot requested, and the controller passed it on.

(What seemed to us an amazingly quick response by the controller actually were two controllers working together.)

The information included current distance, wind conditions, and direction to steer, and a bit later the time needed to get there. 

(The wind conditions told us that for any reasonable landing we would have to go around the airport and approach the runway from the north.)

The controller checked for competing traffic near the airport. Fortunately there was none, and hence no need that the pilot switch frequency and announce the arrival and pattern legs on the airport frequency. 

(The thought didn't even cross our mind that we should switch frequencies. Instead, we just looked around carefully and checked whether any other aircraft were in the area. There were none.)

While all this went on, the spotter aircraft tracked the plane from above. When the plane was too low to connect with ATC via 121.5, the pilot of the spotter aircraft relayed the transmissions to the controller. That included telling ATC about the successful landing and taxiing to the FBO terminal.

When we learned about all this in the joined Zoom session with all personnel involved, we were just amazed: Four controllers and one pilot had worked diligently to assist. 

The word "grateful" doesn't begin to express the thoughts we have every time we go over this process again.

What We Learned in the Zoom Session

When things really go south and you realize that help is needed, go out to 121.5 and launch the  Mayday call. 

There isn't just one person who might help you. There is an entire organization that can step in and assist with things you aren't even thinking about, such as a spotter plane tracking your flight.

Do not believe that you will stay totally cool and rational. It may look like that to you, but you may overlook major items, both in your favor and against you.

The controller will objectively look at your problem and may give you advice you hadn't even thought about, let alone evaluated. 

That was the case for us. We were so caught up with the notion that the engine could quit at any time that we ruled out trying for any airport.

This was based on our understanding of the Rotax engine, the sounds it may make, the way it behaves when things are not normal. That understanding did not include the current case, as we see in a moment. 

Let's go on with the story. Envision that we have just landed at the Cameron Memorial airport KEZZ in Cameron, MO. We have taxied to the FBO and shut down the engine.

What’s Wrong With the Engine?

Eric of the Cameron FBO is most helpful. He allows us to move the plane into a hangar that has just been vacated.

Nephew-in-law Ryan flies in from Ames, IA with the family’s Cessna 150. He brings tools. Before he arrives, we have already looked over the engine, even have run it once more. Still the blaring sound, yet nothing seems amiss. We quickly shut down the engine again.

With Ryan’s tools, we pull the spark plugs and check for compression. We do not have a gauge, but sealing the opening for one plug at a time with a finger and turning the propeller by hand, we have the sensation that there is reasonable compression on all cylinders.

Ryan suggest that we run the engine for a few moments and check whether all exhaust pipes are hot. Lo and behold, the exhaust pipe of the #3 cylinder feels comparatively cool.

Not only that, as Ryan touches the pipe, he also moves it! We look closely. The pipe has separated from the cylinder!

Exhaust pipe of Cylinder #3

Since the pipe is well hidden by the right hand side carburetor and the water radiator, we didn’t see the problem when we inspected the engine.

Analysis

The pieces of the puzzle come together. When the exhaust pipe is disconnected from a cylinder, that cylinder runs hotter due to a certain interaction between the fuel/air intake and the exhaust gas. If you want to learn more about this, check the section "Valve overlap" of Wikipedia "Valve timing."

When we removed the spark plugs, we saw the effect of that increased temperature: The spark plug of the #3 cylinder had run hotter than usual, and that even at the low power setting.

The Rotax 912 engine originally didn’t measure water temperature, but instead sensed the head temperature of one cylinder and declared it to be the water temperature. Our 27-year-old engine is of that vintage.

The temperature probe happens to be installed on the #3 cylinder, exactly the one with the failed exhaust pipe.

This explains the increased water temperature reading we had in level flight, and also that the temperature dropped almost immediately when we reduced power.

Indeed, the water was still at 210 F, but the aluminum head of the #3 cylinder had gone up to 230 F. When we reduced power, the water quickly cooled the head back down to 210 F.

The blaring sound resulted from a partial discharge of the hot exhaust gas past the broken pipe.

It was a possibly life saving decision that we immediately reduced power since the escaping hot exhaust gas is like the flame of a propane torch. And that below one of the carburetors!

Conclusion

Babying the engine saved the day, as did the terrific ATC response to the Mayday call.

Repair

The Zenith factory in Mexico, MO once more helps. Roger says that they do not have the pipe in stock, but Travis produces a portion of the pipe overnight, and with more work we have a replacement part that Ryan helps install.

Repaired pipe

A test flight, and all is well again.

Flight from Cameron, MO to Boone, IA. Photo by Ryan White.

During the days of the repair, we check with Eric of the FBO at the Cameron airport about payment for the storage of the plane. 

He says that no payment is due since the previous tenant prepaid the rent for the entire month, but removed his plane a few days before we arrived. We thank him for the kind consideration.

What Have we Learned?

Prior to the Zoom session with the controllers, we had come up with the following three-part advice.

First, when things seriously go south, call for help immediately on the emergency frequency 121.5.

Second, rely on instinct when you react to the failure.

Third, stay focused on the biggest threat and ask ATC to figure out details of any plan and to give you easy-to-follow step-by-step instructions.

After the Zoom session we have much more nuanced advice, as described earlier. This means that a post mortem based only on one's own actions and thoughts may be woefully incomplete. 

So that is our final point: Much insight can be gained by talking with all people who were involved. 

A Well-deserved Award

In September 2023, the team of controllers who managed and coordinated the rescue effort received the 2023 Archie League Medal of Safety Awards: Central Region. The post includes a detailed description of the rescue process from the controllers' viewpoint. It's wonderful that the controllers received this recognition for their excellent work.

Have any questions or feedback? Please share your thoughts in the comments.