Flying can be daunting at times. To be frank, you’re going to be thousands of feet in the air cooped up in a metal tube with no choice but to trust the pilot if things go south.
Thankfully, commercial aviation is still one of the safest ways to travel. In 2018 alone, the amount of road traffic deaths was an astonishing 1.35 million according to WHO’s global status report as compared to the 523 deaths (which is already a high compared to previous years) from plane crashes.
Unsurprisingly, most of these aviation accidents happen in general aviation due to pilot error where most of these planes are either single or twin-engine planes.
So then are twin engines safer than single-engine planes?
Twin-engine piston planes are not safer than single-engine planes. Although this goes against the common perception, the loss of one engine will cause extra drag, which together with the loss of the other engine’s thrust, easily can cause the pilot to lose control over the plane.
Add to this that a twin-engine airplane is twice as likely to encounter an engine failure, since it has not only one, but two engines, and you might start to question the safety of it!
Table of Contents
The Difference Between Airliners and Piston Planes
Before going into the meat of the article, we must establish the difference between losing an engine in an airliner, versus losing one in a smaller piston airplane, such as the Baron Beechcraft 58.
Airliners that operate with two engines, such as the Boeing 737, can fly and take-off with only one engine, although performance will be severely limited.
Smaller piston airplanes can also fly with one engine, but as we’ll discover in this article, they will be much harder to control, which can lead to serious crashes. In addition, it’s not even guaranteed that the airplane will be able to maintain altitude with one of its engines inactive, let alone gain altitude, due to the increase in drag by the inactive engine!
All this will be dealt with in the content below, so be sure to continue reading!
What Makes Twin-Engine Planes Less Safe?
Logically speaking, in the event of an engine failure in the air, a single-engine plane would essentially become a glider whilst a twin-engine plane would be able to divert to another nearby airport making it a safer option. Right?
Well, this holds true to some extent, but the issue is more complicated than this. Let’s look at some of the issues with twin-engine planes!
Redundancy
With most modern twin-engine aircraft, multiple layers of flight computers are needed to ensure that the thrust output and a variety of other parameters of both engines are kept the same.
This is called a redundancy (or a backup) system, which essentially ensures that if one system fails, more systems can still support the safe operation of a flight.
Redundancies are great but come at the disadvantage of added weight which results in having to carry more fuel to travel the same distance.
Drag and the weight of the second motor
In the event of a dual engine failure, although rare, a twin-engine will fall faster and harder than a single-engine aircraft due to the added weight of both the additional engine and the redundancies.
Even though all pilots with a multi-engine rating are trained to handle situations like these, twin-engine planes are still not as good gliders as a single-engine aircraft due to the extra drag and weight of the extra engine and all its added redundancies.
For instance, would one of the engines fail, you’re left with a 500-pound motor that will add drag and reduce airflow over the wing.
However, to mitigate the added drag, some airplanes are equipped with a safety feature called “feathering”. This is a feature that will reduce the angle of attack of the propeller blade and make it stop spinning or spin much slower. This significantly will reduce the drag, as the propeller isn’t turning and stopping the flow of air as much!
Below you see an airplane engine that is not feathered, and therefore spins with the air-flow. This obviously causes a lot of drag, and is often referred to as “windmilling”.
In the image below, right after the engine fails, the propeller is feathered, making the propeller stop spinning, which means that much less drag will be induced!
Can you continue to fly or climb with one engine?
Many people believe that you may continue to fly as you would normally, as soon as one of the engines fail. However, it’s not that easy…
Due to the increased drag caused by the inactive engine, there is no guarantee that you will be able to maintain altitude, let alone climb, using only one engine. Of course, the exact outcome depends on the situation you’re in, but it’s important to remember that a second engine does not mean that your flight will remain uninterrupted.
If you thought that a twin-engine airplane loses 50% of its vertical power in the event of an engine failure, unfortunately, you’re wrong.
In general, an piston aircraft that loses one engine will experience a loss in vertical performance of 80-90%.
Again, this has to do with that the thrust producing engine now hinders the air-flow, and the extra added weight of the second engine, which normally supports itself.
However, regardless of the exact conditions, a twin-engine airplane will usually keep you aloft for longer periods of time, and give you some extra time to find a suitable airport or landing site.
Pilot Experience and Asymmetric Thrust
Pilot experience is another monumental factor when deciding whether the twin is a safer option. With twin-engine aircraft being faster and more powerful, the speed at which mistakes and emergencies happen is compounded.
When an engine fails on a twin-engine aircraft, adverse yaw happens quickly especially at low speeds with high power settings which can catch pilots off guard, especially during the take-off and landing phase which are the most critical phases of flight.
In short, adverse yaw is a result of asymmetric thrust, which means that most or all of the thrust is coming from one side of the plane, thus causing it to yaw towards the other side.
In the case of an engine loss, it’s paramount that this is taken into account, as it otherwise may lead to something called a VMC roll!
VMC roll
The VMC roll is extremely dangerous, and the fact that nearly all twin accidents in some form are caused by an abuse of the VMC speed (minimum control speed), couldn’t be a more clear indicator!
So what is a VMC roll?
Well, as you lose power on one of the engines, you will have to compensate for the added drag by adding extra rudder input. However, as the plane slows down, you’ll have to add more and more rudder to keep the airplane flying straight.
If airspeed is not gained by lowering the nose, or you don’t decrease the throttle on the working engine, this will turn into a VMC Roll, which will have catastrophic consequences.
In the image below we see a twin-engine airplane that does exactly this, and crashes to the ground as a result.
Here is another video that explains this in much more detail!
So are Twin Engine Planes Really Safe?
That said, it is not that twin-engine aircraft are unsafe due to these few factors, it is more that they CAN be unsafe due to these factors.
Safety in aviation is priority and flight training always puts safety.
In the case of professional pilots, this means that they are properly trained, and much more likely to take the right course of action, would one engine fail.
However, for hobby pilots who might get their multi-engine rating and don’t fly that much afterward, experiencing an engine loss, especially during the take-off or landing, could have catastrophic consequences, if the right actions aren’t taken!
So in short, as long as you understand the dangers of flying a twin-engine, and manage to respond quickly enough in the case of an emergency, twin-engine planes will be safe to fly!
Pros and Cons of a twin-engine Planes
Twin-engine aircraft are great to fly, they generally move much faster than single-engine aircraft and are much more powerful, making for a very fun and thrilling experience for a new pilot.
That said, twin-engine aircraft have their own set of challenges like what we’ve briefly mentioned above.
Let’s look at some of the positives and negatives of a twin-engine aircraft.
Pros
Redundancy
The extra engine not only provides for more speed and power, but it also serves as a backup in case one engine fails. With the correct setup, the second engine will give you some extra time to find a place to land.
This extra engine also provides for ETOPS/EDTO certification. We’ll talk about this more below.
Performance
Needless to say, 2 engines give you more power and with that more speed and better climb performance. In case you would need to escape bad weather, this could work to increase safety!
Although there are some single-engine with rather insane performance (like the Pilatus PC-21 with a top speed of 320kts), twin-engine aircraft generally are the better performing category.
Space
With more power comes the ability to carry more load and thus more space can be incorporated into the aircraft in general.
You will notice that most twin-engine aircraft can carry a heavier useful load than a similar single-engine aircraft.
Weather
Generally, a bigger than most single engines, twin engines tend to fare better in bad weather. That said, they should still not be flown into bad weather on purpose, however, they generally handle things like turbulence better due to the added power keeping the plane more stable.
Cons
Cost
This is probably the biggest downside for most ‘wannabe’ twin-engine owners. The cost of owning a twin-engine aircraft is significantly higher than a single-engine aircraft (sometimes a few times more!).
Not just the cost of the aircraft itself, the operating costs like fuel, oil, and maintenance are also a lot higher since there are 2 engines with a much more complex system compared to a single-engine aircraft.
Training
Training to fly an aircraft is already expensive, to begin with. What’s more, in order to fly a twin-engine aircraft, a pilot needs to go through multi-engine training in order to operate a multi-engine aircraft
This extra training is usually about 10-20 hours of extra training, which can be quite tedious and expensive for already struggling pilots.
Does More Engines = Safer?
Before 1 or 2 engine aircraft became more of a norm, most commercial aircraft had 3 or 4 engines. This was before the 1980’s when most of these aircraft still had some reliability issues.
Therefore, in order to reduce the risk involved in flying long haul on twin-engine aircraft, most commercial flights were bound to flight paths that were at most 1 hour away from their diversion airports, based on piston reliability at that time. Unsurprisingly it was not uncommon for multi-engine aircraft to complete a flight with a failed engine.
As time went on, the reliability of the twin-engine continued to improve as technology advanced. This rule then proved to be rather restrictive. ICAO came up with ETOPS (extended twin-engine operations).
Essentially, ETOPS is a certification that requires the airline and the aircraft to comply with certain standards in order to fly further than the 1-hour ruling.
The ETOPS certification essentially gave operators the chance to fly further if they managed to meet the standards, which included things like flight crew training and maintenance. The ETOPS approved routes essentially saved money and time for the operators, in turn, bringing them more profit. 
ETOPs was fundamental to the aviation industry as it proved that by maintaining proper standards, twin-engine aircraft could outperform its 3 or 4 engine counterparts.
This is why most commercial airliners today are able to fly with just 2 engines. In fact, most of the safest commercial jetliners today are twin-engine aircraft i.e A320, B737 etc.
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