Claw, Sure, and sorry for not catching the "this is how you actually report a bug" thread. I'm using Windows (8.1, if it matters), KSP version 0.24.2 via Steam, although I don't actually play the game through the Steam client all that often (again, I don't know if that matters, so I'll just dump all of my info on you and you can choose what's helpful and what's not). According to my task manager, I'm playing the 32-bit version. Some amplifying information: Originally, I thought the error might be in my design, so I modified it in a couple of ways and tried to work around it that way. The problem remains. The craft are very simple, and aptly named Problem Child Mark 1 and Mark 2. In order to re-create the incident after the first time, I followed a rigid flight plan based on my original intent. Procedures as follows: From start position on runway, activate brakes, activate SAS, check stage sequencing. Release brakes, activate engine, 1/3 throttle on Mk. 1, 1/2 on Mk. 2. Take off as soon as airspeed allows, ~80 knots for Mk. 1, ~118 for Mk. 2. Proceed to shore on heading 090. Once over water, immediately bank 45 degrees right, come to heading 135 true and proceed until the Old Airfield is at bearing 300 relative. Bank left 45 degrees and throttle back two notches, come to bearing 090. Once on course, lower landing gear. Once over land and on satisfactory approach, cut engine to idle (X key) and land with a rate of descent no faster than 5 m/s. Apply brake and come to a stop. The error occurs shortly after settling into the long leg of the plan (bearing 135 outbound to the old airfield), ~6.7 km from the end of the runway where the craft starts, and well over the sea. Also, I discovered that the instability settles down somewhat if you're in "straight and level" flight after the loss of stability, however it goes bonkers again if you attempt even the smallest maneuver and there is only a narrow band of stable flight. If you pitch above or below that band, the aircraft will twist, spin, stall, and dive. I have attached to this message a folder containing the output log, my Dx diagnostic readout, persistent save file, craft files for both mk. 1 and mk. 2, and 16 screenshots. The cockpit view screenshots are only from Problem Child Mk. 2. https://www.dropbox.com/sh/z3mwi4o2pmsidgc/AACSPupeQDhay86A2R0LC9OUa?dl=0 Hope this helps! Soph