In 2008 a Qantas Airlines flight suddenly dipped downwards in the middle of a flight, passengers experienced -0.8g’s of force and there were a few injuries so the flight had to make an emergency landing. Why?

Before I go into why, I would like to explain Cosmic rays. Cosmic rays are high-speed and highly-energised rays that zip through the universe. These rays usually come from Supernovae. When these rays enter the Earth’s atmosphere, a wondrous spectacle occurs that no one can see. When a particle from the Cosmic ray comes into contact with a particle from the Earth’s atmosphere it gives rise to a cascade of particles. First pions are created but these decay quickly and become Muons, Protons, Electrons, Positrons etc. All of this happens above our heads whilst we, below, are trying to submit our Physics assignment 1 minute before the deadline hoping that our internet doesn’t suddenly stop but unbeknownst to you an army of these particles are trying to ruin your day.

When one of these charged particles enter a micro electronic device such as a transistor, if it contains enough charge, it can flip a bit from 0 to 1 or vice versa. This leads to a corruption of memory in the device. This is called a Single Event Upset. This usually leads to your device freezing or “glitching”.  Imagine trying to explain to your professor that you couldn’t submit your essay because Cosmic rays flipped bits in your computer. The professor would go, “Now that’s a “bit” much”. Especially if you were doing an Arts degree.

What happened on that Quantas flight? Well, the plane has an ADIRU(Air Data Inertial Reference Unit) system. ADIRU tells us the Air Speed, Angle of Attack and Altitude of the plane. What happened was a Cosmic ray flipped a bit, which then in turn changed the byte. The byte was associated with the label and it switched the labels from Angle of Attack to Altitude. The airplane was a bit confused and tried to correct this mistake by tilting upwards at a ridiculous angle which caused the planes stall warning system to go off. To correct this the plane dipped downwards to stop this “stall”.

Are you afraid of flying now?


Don’t worry. Nowadays there are more than one ADIRU system so if one is affected then the others can override this.

And to all electronic devices, these are usually radiation hardened and have ECCs (Error Correction Code) This adds an additional bit to the device to ensure that the total number of bits with a value of 1 is always even or odd. Some can only detect errors but not correct them but there are more advanced versions of ECCs which can both detect and correct. These are called Reed Solomon codes. They use an advanced mathematical algorithm to, basically, add a safety net to the data. It’s like when you are shipping off something valuable and you use bubble wrap. Think of the Reed Solomon codes as that. The bigger the error the more bubble wrap you need.

And that is all for now, so basically, SEUs are like cosmic sneezes that cause our electronics to catch a glitchy cold.


“The most beautiful thing we can experience is the mysterious. It is the source of all true art and science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed.” – Albert Einstein


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