This question is specific to the iFly, not FSCrew. I hope it's not minded that I post this thread here, as I saw no other suitable place for it. 

 

I did a second flight today with the iFly, this time for KATL to KDCA. I had an issue during takeoff. I advanced throttles to roughly 40% N1, then engaged TOGA, and began to hold the center line, all the while keeping an eye on my V-speeds. At somewhere around 100-120 knots, the plane began to pull hard to the right and despite my strong pressure on the left rudder pedal, it still continued to pull right. My acceleration rate rapidly fell and upon rotation, found myself falling. I then feverishly glanced at the MCP and saw that VNAV had been disengaged. Upon reenabling VNAV the plane then recovered, although just barely. I was then able to stabilize and engage AP. 

 

Any ideas as to what could cause this? I don't recall moving either my yoke or throttle, and outside of holding the center line, I wasn't making any severe adjustments to my rudders. 

Maybe you had an engine failure?

Maybe you had an engine failure?

 

That immediately came to mind, but based on the fact that the plane was able to recover and fly the remainder of the route with no issues, I managed to rule that out. 

 

I attempted the same takeoff from the same runway (27R @ KATL) and had no issues. Going to assume it was a quirk related to AT/TOGA and VNAV disengaging. I may have bumped a piece of my hardware without realizing it. Not totally sure what the issue was, but given that it was fine on try #2 I'm not going to worry about it for the time being.