Emergency: What if?

So what if I had made all the right decisions and executed them perfectly? How different would the outcome have been? Is there anything to be learned by studying what happened?

I'll answer the last question first. You can always learn from others or your own experiences.

First let's go to the starting point of the emergency. What caused the propeller to feather and the engine to stop? Unfortunately that cannot be answered yet. The Transport Safety Board said their investigation of this incident will be limited to gathering and filing data. Evidently they feel their finite resources would serve aviation safety better if they were used on more common aircraft failure scenarios, especially since injuries were (relatively) minor and property damage was nil. I cannot fault them for that assessment but it does leave me as the sole driving force looking for a solution.

The uncommanded feathering of the propeller is key. Pitch is controlled by a mechanical linkage. The propeller stopped vertically so that I could only see one blade. But both blades had to be feathered otherwise there would have been massive vibration.

Looking at the pitch control mechanism, there are only 2 points of failure that could allow the prop to get to a feathered position without being commanded it from the cockpit:a spring and a bolt that attaches the prop control rod from the hub to the position lever. If either of those disconnected somehow, only aerodynamic forces on the prop blade determine the pitch.

Nevertheless, I would be surprised if Pipistrel would allow a design that could fail leaving the propeller feathered. More likely is that there was some variation in my installation that allowed this failure mode. I have contacted Pipistrel regarding the failure mode.

Now for how the emergency situation was handled. From the breadcrumb file, there was about six and a half minutes from prop failure to impact. In these situations there are no certainties, you are just trying to choose the way that maximizes the probability of a safe outcome.

It is clear that planning was better than delivery. If I had to do it again, I would still pick the wide upward grade. Trees would probably have been ok but more of an unknown for me.

It was good that I planned to establish a standard circuit about the flare/landing point. It was good that I was vigilant against succumbing to panic. It was also a good idea to seek solutions that did require great skill to perform in my adrenalin compromised state.

Getting diverted by the radio while wrong had little effect on the outcome in this case... only because there were over 6 minutes before impact. But it still would have been better to have declared the emergency, given the latitude and longitude from the beginning and, once sure they got that right, signed off from the radio and shut it down.

The fixation on the landing area was another matter. It allowed me to unwittingly drift too close and low to the landing site. It is hard for me to over-emphasize the shock, wonder and disgust I felt when I realized I had botched the circuit. In my gliding/instructing days circuits were my specialty. Every landing was a spot landing where I had intended it to be. Complications like other aircraft, winds or high lift or sink encountered were handled easily.

This time I ended up too high and too close on final for spoilers to be sufficient to get down to the threshold. That led to a snap decision to do a figure 8 bowtie to lose altitude while consuming less runway. Unfortunately I had never done this on final and I did not perform this higher skill maneuver as planned, ending far down the runway. From examining the breadcrumb file, full spoilers and full flaps would have used a bit less of the runway than actually consumed.

Let me be clear, the biggest mistake was allowing myself to get diverted from the planned action to an irrelevant analysis of the already selected landing site. The second biggest mistake was not realizing that I had allowed myself to drift from the task at hand. That is not as bad as blind panic, but it was pretty bad.

If things had gone as planned, almost everything would have been routine. I would have reached final with full flaps and using spoilers to control the glidepath to the flare point. That would have led to a lower touchdown/impact speed and since energy varies with the square of the speed, less impact energy to dissipate.

Nevertheless, for this case, it is probable that there still would have been significant damage, although possibly less destruction to the aircraft and perhaps no broken bones for me. Since the sandy surface was fairly soft, the wheels could have dug in or locked by sand being trapped by the wheel pants. This could have led to the aircraft flipping over to its back.Read more