If you are a detailed-oriented person or an AVgeek for example, probably you have already noticed small, white lines with spiral designs painted in the center of the engine. If not, we are sure that next time you won't miss a chance to check these kinds of paintings on an aircraft you are waiting for to get ready for boarding.
In this article we will try to clarify the reason why these lines are being painted inside of the aircraft engine and what is their main purpose. So, let's get started.
Allegedly, the first time that these white lines were painted happened back in the World War II, when a certain number of aircrafts produced by Messerchmitt got these markings. It is believed that these spirals helped maintenance technicians to determine the direction of the large fan disk, because the fan could rotate backwards under the influence of the wind, while the engine was not working or not working with a full power. Furthermore, there is another theory that these spirals were used to distract allied gunners, but it is just a legend and these kind of lines were painted for the safety reasons just like today.
Like in the most cases when we talk about aviation, the main purpose of white spirals is safety. In this particular case, the point is to keep all ground handling staff safe and secure while an aircraft is parked on the parking position. By observing these safety, white lines ground handling staff can easily see if the engine is on and determine the speed of the engine fans.
You might be wondering what's the point to look at these lines when you can easily hear if the engine is running or not?
We can agree with your observation, but just partly and under certain circumstances, because it is a quite different situation when there is only one aircraft parked and when there are multiple aircrafts parked next to each other, including other aircrafts driving on the taxi way. In addition, the fact is that the ground handling personnel always wear or at least should wear hearing protection, because the noise of an aircraft engine can potentially be a dangerous threat to their hearing and it can cause a lot of damage. Anti-collision lights and painted endings on the fan, e.g. on Dash Q400, are being installed in order to prevent human injury or aircraft damage.
One thing is for sure, and that is the fact that the aircraft engine is usually involved in the accidents that occur as a result of the lack of attention or safety rules violation while the aircraft is parked on the ground. Even a smaller engine at idle has a dangerous zone of around 3 meters, within which there is the risk of being sucked into the aircraft engine. All in all, better safe than sorry. We think that it is always a better choice to invest a couple hundred euros in these kinds of things if there is the slightest chance to avoid a human injury or an aircraft damage.
Usually one more question pops up when we talk about white spirals and that is do birds see them and can these spirals reduce the number of aircraft accidents caused by birds?
We will just mention a theory that states how these spiral lines can reduce the number of the accidents caused by the birds. According to this theory, it is much easier for the birds to notice the white colour of the spiral, which gets a shape of a blurry circle while the engine is on, and therefore birds are more likely to avoid the aircraft engine. But, this theory was very popular back in the 80's, and we can only say that there are not enough evidences to prove if this theory is correct, so we won't keep on writing about it.
Finally, take a look on the picture below that contains really interesting designs of these safety, white lines painted inside the aircraft engine.
Definitely, our favourite design is the hurricane that Philippine Airlines has on their Airbus A330, and what's your favourite one?