Originally Posted by
tdracer
Some thread drift here, but having worked modern FADECs, that's not entirely true. Modern FADECs have surge detection/recovery logic that was completely lacking in the older hydro controls, so surges can be dealt with far more effectively. Further, the update rate varies dramatically depending on the particular FADEC function. We break the FADEC down into 'major frame' and 'minor frame'. Major frame means the FADEC has done pretty much everything it can do every major frame (there are sometimes a few engine monitoring functions that don't happen every major frame, but they are strictly things that don't in any way actually affect the actual engine control). Major frame update rates are typically around 200 milliseconds (e.g. 5 Hz). The more time sensitive tasks are done up to once per 'minor frame'. Depending on the task, it may happen once per minor frame, once every two or four minor frames, all the way up to once per major frame. For example, the fuel metering valve position command is updated every minor frame. Not familiar with the newest crop of Pratt FADECs, but on the modern GE FADECs the minor frame is 15 milliseconds (~66 Hz).
In short, modern FADECs can deal much faster and more effectively with a surge. However if the surge was caused by mechanic damage (e.g. FOD) - rather than a temporary airflow disruption, it may not matter.
Appreciate that. Thank you.