Here's Why Airplane Engines Have White Spiral Marks on Them

Are you a frequent flyer? If yes, then you've probably noticed the swirls on aircraft engines. Let's find out what those marks are for!
Interesting Engineering

Are you a frequent flyer? If yes, then you've probably noticed that most aircraft have swirls painted on their engines. And just in case you are wondering what they are for, this article will attempt to enlighten you on that matter. As cute and as comical as they look, those spirals on the spinner cones are more than just aesthetics - they are an important safety measure for ground crew and even for birds.

Ground crew warning

We all know that aircraft engines produce deafening noises when they are running and surely that's enough warning for the ground crew to be aware of the dynamic engine. KLM's Renee Penris has posted out a blog to explain the importance of painting the engines with spirals and it makes sense what they had to say about it.


"The spiral has a fairly straightforward function, alerting ground staff to a running engine and ensuring that no one comes too close to it. If an engine is running, you see a white blur or a hypnotizing swirl, depending on the rotation speed of the engine. This visual cue is extremely clear and warns everyone on the apron to stay away from the huge jet engines".

A follow-up question was asked: "can’t ground staff hear the deafening roar of a running jet engine"?

Penris explained the ground crew's perspective of things saying "Well, there could be several engines running at once near ground crew, plus they wear hearing protection. If five engines are singing in your ears, it isn’t always obvious which is running and which isn’t".

A random squiggle seems like a small price to pay for protecting the crew that works around an aircraft. Just take a look at this video which shows a technical crew being sucked into a running engine. It just shows how unaware people could be when working on aircraft engines.

Most Popular

The spirals perform for extended purposes too. In older days, the ground crew or maintenance technicians can also communicate to the flight crew which direction the fan is rotating as they are able to tell from the spin of the spirals. This gave the flight crew the go ahead if it's safe to start their flight procedure. However, this procedure is no longer needed as engines nowadays are automatically started and do it by themselves.

Spirals come in different shapes and sizes. The above engine is determined to be a General Electric engine as it is designed in a 'g' shape spiral. Rolls-Royce, however, has a longer spiral design which you can see from this video. The design and size don't actually matter as they all serve the same purpose which is to warn ground crew if the engine is running.

Do the spirals actually warn birds too?

As early as the 1980s, aviation companies have started investing in these nosecone spirals as the bird-strike accidents were costing them steep fines. Rolls-Royce has explained in their centenary press release one of the purposes of the spirals in their spinners.

"In-flight these swirls flicker as the engine rotates at high speed, scaring birds and allowing them to fly clear of the engine".

This article from Boeing's Aero Magazine, which was co-written by a researcher and pilot, begs to disagree as they debunk the 'Common Misconceptions About Bird Strikes'. Essentially, the birds tend to steer clear from airplanes because of aerodynamic and engine noise. So, they avoid planes in general before even seeing the 'flickering' spirals on the engines.

KLM's Penris concluded in the aviation company's blog that the spirals purpose to repel birds from being struck by the engine is not scientifically proven.

"Boeing and Rolls-Royce, for example, say the spiral does not prevent birds from flying into the engine, as the rotation would be too fast for the birds to see the spiral. Other studies have suggested painting spiral shapes on the spinner cones do help prevent bird strikes. I guess the answer to this question can only be “maybe”, at this point. If only we could ask a bird".

Sources: KLM, Rolls-Royce, Boeing's Aero Magazine

message circleSHOW COMMENT (1)chevron