When dealing with physical systems it is impossible to have no bugs. To give an extreme example, there is a not a small chance that the cosmic rays can change a bit in a system's memory - https://stackoverflow.com/questions/2580933/cosmic-rays-what...

The issue here is overflow due to time. The time is saved in a variable (don't know how much bits), which overflows after the gives period. Now there are two options 1. Upgrade circuits of every plane. These planes were designed/built a long time back. Bigger registers were not practical due to costs. 2. Document it and have a process for it.