[RealityVoid]

My take was initially similar to yours but I have just updated it considering the affected units did not in fact have EDAC on them. With ECC, I would say the odds of having such an error decrease dramatically. But without it... yeah, I can believe it.

[trebligdivad]

Where did you see that it didn't have ECC?

[RealityVoid]

"As noted in section 3.5.2, the CPU module on units 4167 and 4122 did not incorporate EDAC, nor was it required by the aircraft manufacturer’s specification"

It was apparently added in a later HW revision

"The LTN-101 ADIRU’s CPU module was later redesigned to reduce costs and to include error detection and correction (EDAC). EDAC is used for detecting and correcting single-bit errors in RAM chips to give protection from single event effects (SEEs, see section 3.6.6). This change was a significant redesign and resulted in a new CPU module part number (466871-01). The EDAC was performed by a new ASIC, and all of the RAM chips used on the CPU module were replaced with a different chip.13"

https://www.atsb.gov.au/sites/default/files/media/3532398/ao...

[trebligdivad]

Thanks; hmm but that means the version with EDAC has been in use since 2002, so is less likely related to todays update? (hth did they design stuff without protection back upto that point?)

[RealityVoid]

It's not _only_ that, it's also the fact that the failure mitigation was not catching it, so even if they "fix" the random spikes issue, they still need to consider the "what if" issue if the thing _still_ happens. My money is that they will mitigate this:

"There was a limitation in the algorithm used by the A330/A340 flight control primary computers for processing angle of attack (AOA) data. This limitation meant that, in a very specific situation, multiple AOA spikes from only one of the three air data inertial reference units could result in a nose-down elevator command. [Significant safety issue]"

It's the only one marked "Significant safety issue" so my money is on that.

[berti]

That's applicable for one specific model of ADIRU (basically determines where the aircraft is in 3d space in terms of position, rotation, velocities, and accelerations) from a single manufacturer (Litton). These aircraft have dozens of computers for different functions, many of them with multiple manufacturer options. There are at least 4 different ADIRU makers that airlines have been able to specify at different times including the Litton.

The ELACs (controlling the elevator and aileron actuators according to the demands computed by other functions) are made by Thales specifically for this aircraft type and probably have a quite different design.