Does anyone have any insights on the Transformer Rectifier Unit (TRU) in the ATR and what the conditions/requirements are for activating it? I had assumed that once I had both engines running in AUTO and the presence of DC power, that the TRU would be available but it took some time between when I flipped the condition levers to AUTO and when I reached the runway before I could uncage and get that button to take. In this vid, you can see at 12:08 it won’t engage, so I set the levers to AUTO and at 12:28 I hit the TRU again and it doesn’t register. With nothing configuration-wise changing significantly after that, just before departure at 16:17, I hit it and it takes. What is the critical requirement for it becoming available or is it just that the DC gen needs to be active for a bit?
