The Universal Acceleration portion of FE theory supposes a constant acceleration over time.
Some look at that see a fault in reaching the speed of light in a short time. Some counter with an argument regarding relativity.
1) What is the issue with accelerating past the speed of light?
2) Why is it necessary to rely on an unobservable effect to counter this?
So actually you can't accelerate past the speed of light. The problem is that there is universal acceleration of 9.8m/s^2 on Earth. This is where the Flat Earth Flipper Theory comes into play.
The Flat Earth Flipper Theory is such that the Earth accelerates relatively "up" at 9.8m/s^2 until it
almost hits light speed, at which point it flips around 180 degrees and starts the cycle over again, this time going "down", but flipped. This cycle explains a lot actually, especially things traditional FE theory cannot.
When the Earth flips, it creates
a lot of friction and heat, and this heat remains in the planet for a very long time. Over time, however, the planet starts to cool, and it keeps doing so until the next flip. Coincidentally, the same time it flips is usually around the time of an Ice Age. We are currently somewhere in between these two stages, so no need to be worried.
One can even say the dinosaurs were made extinct due to a great flip, and only smaller animals survived. As well, Pangaea split due to a great flip as well.
If you are interested in the Flat Earth Flipper Theory, there was a general thread made a few months ago where this and a lot more (seasons, sun/moon physically staying up in the sky, solar & lunar eclipses, etc.) explained in greater detail. Hope this helped!