Second Century

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The first ever certified electrical aircraft, the Pipistrel Velis Electro, has been flying commercially for over a year now. And I am lucky enough to say that I have been it for over a year as well.

Obviously, some things are different on that aircraft. Before you get in you'll probably see a charging connected to the nose. And after opening the hatch that would normally give you access to the oil dip stick, you'll see a hose with purple battery coolant. Once inside there are less buttons and the engine start checklist is much shorter than usual. Which also applies to the run up. You'll get from ramp to runway in no time.

These differences during the normal procedures make flying the aircraft easier and safer. A real improvement. However, the most interesting differences can be found in the emergency procedures section of the Pilot Operating Handbook (POH). This article will discuss the differences in emergency procedures between the electrical Velis and regular piston aircraft.

How emergency operations in electrical aircraft differ from regular piston or jet engine aircraft is a topic that has not gotten much attention so far. I hereby would like to make a start.

Introducing the Pipistrel Velis

Since the Pipistrel Velis will be discussed in this issue, it is good to start with an introduction of the aircraft. The video below gives a nice impression of how it is to fly the Velis. The video actually shows a Pipistrel Alpha Electro. The Velis was originally build as the Alpha Electro and was renamed later on.

Introducing the Pipistrel Velis Electro

Emergencies in the Velis

Like a regular piston aircraft, the electrical Velis has a wide selection of emergency procedures and checklists. And just like the others, it has minor and major failures. Things that you have to take care of but do not directly affect your operation. Failures that force you to land right away. And everything in between.

Here I would like to focus on the failures that have a major effect on the execution of the flight and are unique to this electrical aircraft.

Engine communication failure

The most interesting failure in the Velis POH is the “engine communication failure”. Which was completely new to me. “Engine failure”, yes, I have practiced that many times. The same goes for a “Communication failure”. But what is this?

This failure is the throttle failing to communicate with the engine. Which means you cannot adjust the power setting anymore and that you'll have to continue the flight with the power setting you had at the time of the failure.

Like breaking the cable between the throttle and the carburetor and the butterfly valve is stuck in the last position.

When this happens, the POH advises you to do the following:

“Assess the power available to determine if it is possible to return to base or to reach an alternate airfield or a suitable landing area. When at gliding distance from the elected landing site and when ready for a power-out approach, switch the motor off”

When this happens during a gentle cruise there is a good chance that you'll be able to safely make it to your destination airport. You were probably planning on keeping that power setting throughout the rest of the flight. Switch the engine off at a proper height and distance to perform a glide-in landing and your safe.

Things are much different when it happens during a lower power descent or a climb. During a descent, there is probably no other option than to keep descending at optimal glide speed and find a place to land within gliding distance. Just like a 'regular' engine failure.

When an engine communication failure happens during a climb, there are several scenario's to think of. While cruise is at about 33% power, a climb is performed with 74% power. Meaning that you will run out of power much quicker, even in level flight. Where you can land depends on how much range the aircraft has while flying at 74% power.

Also keep in mind that when you fly at 74% power in level flight, the airspeed will significantly increase. Which can lead to exceeding the maximum speed of the aircraft (Vne).

What makes it more complicated is that during a high power setting, the aircraft is more prone to additional failures. Such as battery overtemperature and engine overtemperature. While at the same time it is more difficult to mitigate these types of failures than during cruise. The more power the engine generates, the more heat it generates too. And the same goes for the batteries. The remedy for these these failures is reducing the engine power to give the systems time to cool down, which is not possible.

So when this accumulation of failures happens, you have to remember that switching off the engine and continue in an emergency glide without power is the only remaining option.

Battery low

Another interesting emergency is the “NO GO-AROUND AVAILABLE” warning from the battery system. This warning goes off when the battery has less than 15% State of Charge (SOC). The POH states that with less than 15% SOC you will not have enough power available to finish another traffic pattern.

By taking 15%, Pipistrel is using a safety margine. In my experience, doing a circuit takes about 10% of battery capacity. This does however depend on the height at which the circuit is flown and its length, the quality of the battery and the ambient temperature. So, always take those factors into account. When you have to make a go around with 16% left, you want to be sure you'll be able to stick the landing.

However, when you are on the final approach of a normal flight, without any irregularities, and you only have 16% SOC left, you did something wrong. The POH states that “Standard mission planning must consider 30% SOC as minimum value at landing”.

Is electrical flying safer?

Using this type of technology in aviation is still very new and it is difficult to predict what the future will bring. Nevertheless, it is interesting to take the little knowledge we have and use it to make aviation safer in the future.

An important advantage that electrical aircraft have over regular aircraft is that they are much more 'digital native'. This means that the technology is build on a digital platform from the start. Making is easier to get detailed diagnostics of the issues that may arise during a flight.

Regular, highly mechanical, aircraft are increasingly using digital technologies as well, but not in the holistic way electrical aircraft can. Sensors are added too many parts of the engine to monitor its condition. Making flying more predictable and safer, but it is also adding more parts to a drive train that already has hundreds of parts that can break.

When the Velis has an engine communication failure, the software will detect this within a second. And, as we know with computers, there is a chance that restarting the system will fix the problem. When a piston engine does not respond to the throttle input, it will be difficult to tell what happend. Maybe the butterfly valve is stuck. Maybe the throttle cable is broken. And even if you do know the problem, fixing it in flight will be impossible.

I don't need to explain that digital systems can have their hick ups too. We have all screamed at our laptop at some point in time. Therefore, I will not end this newsletter by stating that getting into an electrical aircraft today is safer than getting to a piston aircraft. What I do want to state is that the technology on which electrical aircraft are based has the ability to provide better safety systems in aircraft.

When learning to fly an electrical aircraft you will have to learn new types of procedures to deal with new types of emergencies.

Or aren't these emergencies new?

As discussed, the mechanical connection between the throttle and the engine can break as well. You just couldn't see it before. Just like the no go-around warning. At some point, a kerosine fueled aircraft won't have enough fuel on board to do another traffic pattern as well. You just don't know when.

The digital native approach of electrical aircraft makes it possible to spot even more potential hazards than before. Giving the pilot, whether on board or remote, better possibilities to deal with the situation. Let's use this foundation, fix the stability issues in the software, and make flying safer than ever before!