Have you ever noticed those little white spirals in the center of airplane engines and wondered what they are? They aren’t just there to look cool, they actually have a very important purpose. Do you know what that purpose is? Wonder no more: I’m about to solve the mystery of jet engine spirals for you.
The spirals I’m referring to can be seen on the aerodynamically shaped cones which cover fan blade mounts in jet engines. Many of the biggest plane engine manufacturers have been painting spirals on them for decades, and the practice actually dates all the way back to World War Two when spirals were often painted on the propeller cones of fighter jets.
The benefits of the spirals are actually two-fold. The primary reason is for the safety of the ground crew, to give the maintenance team a visual sign that the engines are running. Even when engines are only running at idle power their pull is still extremely strong so the danger zone of a Boeing 737 is nine feet around each engine.
When the engines are running above idle power this area increases to 14 feet, and for larger airplanes with larger engines workers need to stay even further away. Any person that enters this danger zone risks the horrifying fate of ending up inside the engine. So, it’s extremely important that maintenance people know whether or not one is running.
You might think that the noise made by these mammoth engines would alert the ground crew that they’re running, but they’ll usually be wearing ear defenders. And, there’ll often be multiple aircraft in close proximity to the one they’re working on, so it can also be difficult determining where the engine noise is coming from.
Visually identifying a running engine is equally as difficult, even in broad daylight. The spinning blades become translucent when in operation, which makes them very difficult to see. These spirals make it much easier to identify a running engine as the white paint is still visible even when they’re running at full power.
Similarly, propeller planes also undergo paint jobs to reduce the number of accidents while the plane is on the ground. The tips of the propellers have bright painting colors so that they’re more visible to the naked eye, which helps reduce the risk of walking face-first into the deadly spinning blades.
The second benefit is that these spirals keep planes out of danger when they’re up in the air. Although there are debates around this theory, the spirals may scare away birds that otherwise might fly into plane engines.
The theory is that birds like to hide away in caves and dark spaces. So, the dark hole that the spinning turbines create confuses and attracts them.
The most credible proof of the spirals working to reduce bird strikes comes from Japan’s All Nippon Airways. They completed a year-long study on the theory back in 1986 where they painted a ‘wobbly ball’ onto the cone on the engines of 26 of their Boeing 747’s and 767’s.
At the end of the year-long experiment, an average of only one bird had hit each of the painted planes, whereas an average of nine had hit the non-painted planes.
This saved the company almost $200,000 which equates to almost $500,000 today. Obviously, they subsequently decided to paint the design onto all of their large-body aircraft.
Rolls-Royce is also quoted as being pro-spirals, stating that, “in-flight these swirls flicker as the engine rotates at high speeds, scaring birds and allowing them to fly clear of the engine”.
Their spiral design is a longer and thinner version of the one on General Electric’s engines, and they’re not the only two styles out there. There’s also the apostrophe, the typhoon, and a couple of other designs that are pretty rare.
But, some sources say that the markings don’t make a difference to bird strikes, including Boeing themselves. In Aero, their safety newsletter, they state that it’s a common misconception that spirals deter birds from flying into aircraft engines.
But in my opinion, a paint job is worthwhile if it can save lives and a $10 million engine replacement.
Perhaps you’re thinking, “are bird strikes even that common?” The answer is yes, bird strikes happen much more frequently than you might think, and in 2003 alone there were an incredible 5,900 incidents listed by US civil aircraft. The engines suffer the brunt of the damage, with 44% of all bird strikes affecting that part of the plane.
And, it seems as though there are several wildlife factors which point to an increase in bird strikes. The population of greater snow geese in North America rose from 50,000 to 1 million between 1966 and 2009, for example, and the nesting population of bald eagles in the United States rose from less than 400 pairs in 1970 to more than 13,000 in 2010.
This is a pricey problem for the aviation industry, and the FAA estimates the cost for the US aviation industry to be $400 million annually. And that’s just the US! The Central Science Laboratory estimates that the total worldwide figure is $1.2 billion annually, because of repairs and lost revenue.
There’s also sadly a cost in terms of human lives, as 200 people have died worldwide by being sucked into an engine since 1988. Imagine how high that number could potentially be without those spirals!
One of the worst plane accidents caused by a bird strike to its engines was the 1988 crash of Ethiopian Airlines flight 604. The plane was less than a year old. On that day, it took off for its second leg of a domestic flight with 104 people on board.
During takeoff, both engines of the aircraft ingested a flock of pigeons. Both engines lost thrust, and the pilots had to land the plane without the landing gear in position. The plane burst into flames when it hit the tarmac and 35 passengers lost their lives in the resulting blaze.
Perhaps the most famous bird strike thankfully wasn’t fatal, but it was dramatic enough to make a movie out of.
In 2009 US Airways flight 1549 was climbing to an altitude above New York when it hit a flock of Canada geese and lost all engine power. The pilots knew it was impossible to reach an airport so they landed the plane in the Hudson River. Everyone survived and the pilot’s heroic handling of the incident inspired the 2016 film, Sully.
These spirals seem to do a pretty good job of keeping plane engines free of birds, but pilots and air traffic controllers have training to take steps to further reduce the chance of an avian incident occurring. Less than 8% of bird strikes occur at over 3,000 feet, so pilots get their planes above this altitude as quickly as possible.
The use of avian radar at civilian and military airfields also helps to reduce the number of collisions. It tracks thousands of birds in real-time to ensure they are far enough when a plane is taking off.
Now, back to the primary purpose of the spirals: to keep the maintenance crew safe. You might be wondering what happens if a person gets sucked into a plane’s engine and well, I’ve seen some photos and I can tell you it’s not pretty, so I definitely won’t be showing you them, but you can always google at your own risk.
I can also tell you that it’s impossible to survive after going inside these giant turbines. The metal blades at the front of the engine suck a huge amount of air into the engine, mixing it with fuel to make the hot gas that creates thrust. They’ll chop up anything that touches them. Further into the engine is a row of spinning zigzag blades that further compress the air. This causes further mincing of anything that’s unlucky enough to get in their path.
Then, the gooey remains of the unlucky person would go into the air-fuel mixing combustion chamber. The force in the chamber would gasify the remains and shot them out of the engine’s nozzle. Gross, huh.
Sadly, despite safety measures sometimes accidents happen and people get a little too close to jet engines. In 2006 Continental Airlines flight 1515 was preparing to depart from El Paso airport. But a suspected oil leak required an inspection from mechanics. During the maintenance procedure on the running engine, one of the mechanics stepped too close to it and was immediately sucked in, to the horror of the maintenance crew and passengers onboard.
And in India in 2015 a similar incident occurred which also resulted in the death of a maintenance person. The worker, who worked for Air India, was standing next to the plane. The aircraft was moving away from an airport gate at Mumbai airport. The pilot misinterpreted a signal and switched on the engines, sucking up the maintenance man in front of more than 100 horrified passengers.
The only way to survive a brush with a jet engine is if you somehow get snagged in the inlet and don’t actually get sucked into the turbine’s blades.
But, these spirals aren’t the only life-saving features on planes. Have you ever noticed the metal rods that stick out of the back of a plane’s wings? Well, they’re called static wicks and they’re there to prevent lightning strikes from having an effect on the aircraft. Every aircraft is struck by lightning an average of once per year, and without those metal rods fires could break out from sparks caused by electrical storms.
And what about those tiny holes in aircraft windows? Well, they’re there to stop you dying, too. As a plane ascends to higher altitudes air pressure drops outside the plane. But there should be a steady air pressure inside the plane’s cabin to stop us from passing out. The tiny hole, or “bleed hole”, helps to balance the pressure between the cabin and the air outside to relieve stress on the outer window pane and keep us safe.
Still, It’s not just planes that have design quirks to keep us safe. Have you notices that pen caps have holes in them? Believe it or not, that’s a safety feature for stopping a person suffocating should they accidentally swallow the pen lid. So as you’ve seen, some minor details in everyday life have huge life-saving consequences.
Will you feel safer the next time you fly, knowing that there are so many safety measures in place? Or will you spend the entire journey panicking about deadly bird strikes? Let me know in the comments whether this article has helped your fear of flying or if it simply made it worse.
One thing’s for sure, I bet you won’t ever risk getting too close to those jet engine spirals!