Here is a graphic of the computers that control aircraft flight control mechanisms as commanded by pilots using side-sticks in the cabin and by autopilot.
The 2 ELAC computers each control one of a pair of ailerons and elevators. They do not seem to back each other up.
https://coconote.app/notes/68dba254-9486-42ad-b454-6f15b3243bf3 states that "each computer is split into 2 physical units, programmed in different software languages, with separate power supplies and signaling paths."
Not 3x redundant 🤔
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https://www.aviationhunt.com/airbus-a320-ata-27/
4/n
The term SEU is often used when describing such issues. A Single Event Upset is the effect of a high energy ionizing particle (e.g., electron or proton) striking a computer or memory chip. It typically causes a single bit to flip from 0 to 1 or 1 to 0, without permanent damage.
There are other effects of particles striking chips such as bits latching up that require a power cycle or permanent damage to affected areas.
https://nepp.nasa.gov/docs/presentations/2020-Xapsos-Presentation-TAMU-Bootcamp-SEE-Environment-of-Space-20205011676.pdf
https://en.wikipedia.org/wiki/Single-event_upset
5/n
Energetic particles abound in the regions around earth in the form of cosmic rays, particles trapped in the radiation belts and particles in the solar wind/flares.
Most are deflected by earth’s magnetic field or absorbed by the atmosphere.
SEUs can affect microprocessor registers and on-chip memory, external memory and FPGAs.
An SEU's effect on a spacecraft or aircraft can vary from negligible to devastating, depending on which program or data bit gets clobbered.
https://en.wikipedia.org/wiki/Cosmic_ray
6/n
Space and aviation electronics use various techniques to handle SEUs, such as:
Shielding
Rad-hardened chips
Use of PROM, MRAM, Flash and SRAM over SDRAM
Error correction, typically used for memory access
Periodic reading and correction of memory/logic blocks, aka scrubbing, typically used with FPGAs
Triplicate logic elements or entire computer systems, with majority voting and repair of corrupted sections.
Software techniques to detect and reject corrupted data.
https://en.wikipedia.org/wiki/Triple_modular_redundancy
7/n
We all know that solar flares and CMEs, that produce beautiful auroras, are also capable of causing havoc with power and electronic systems. Most systems vulnerable to SEUs are designed to mitigate their effects. But as we know, software is often the Achilles heel. Kudos to Airbus for recognizing the problem early and taking action.
This is not the first such incident. The most famous case is Qantas Flight 72 in Oct 2008 with an A330.
https://www.atsb.gov.au/media/2008/release/2008_43
https://www.flyingpenguin.com/?p=74567
8/n
Pics of a Portable Data Loader (PDL) units and heavy cable used to upload software to the A320 ELAC computers.
9/n
AkaSci 🛰
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