> why airplanes have to dump fuel when emergency/unplanned (e.g. due to medical emergency) landing
Though perhaps that's not the best example - for a really urgent medical emergency where every minute matters, an overweight landing would certainly be considered ahead of wasting precious time dumping fuel. Equally, there are a few more other types of emergencies where you'd want to get back onto the ground ASAP even if that means exceeding the maximum landing weight.
> While the passengers may survive a full weight landing, the plane will incur heavy damage.
At least these days, all aircraft certified under Part 25 must be able to land at maximum take-off weight with a descent rate of 6 ft/s (360 ft/min), which is already at the border towards what would be considered a hard landing (at maximum landing weight, planes need to allow a landing with 10 ft/s / 600 ft/min without structural damage).
So of course you still need to consider whether the changed performance characteristics (approach speed, required runway length, climb gradient for go-arounds, etc.) at MTOW will still allow you to land safely in that specific situation, but fear of "heavy damage" is not something you need to consider.
You might want to bring the plane down a little even more careful than usual, the brakes certainly have to work harder and maybe the plane needs to be inspected afterwards just to be sure, but otherwise you should be fine.
Though perhaps that's not the best example - for a really urgent medical emergency where every minute matters, an overweight landing would certainly be considered ahead of wasting precious time dumping fuel. Equally, there are a few more other types of emergencies where you'd want to get back onto the ground ASAP even if that means exceeding the maximum landing weight.
> While the passengers may survive a full weight landing, the plane will incur heavy damage.
At least these days, all aircraft certified under Part 25 must be able to land at maximum take-off weight with a descent rate of 6 ft/s (360 ft/min), which is already at the border towards what would be considered a hard landing (at maximum landing weight, planes need to allow a landing with 10 ft/s / 600 ft/min without structural damage).
So of course you still need to consider whether the changed performance characteristics (approach speed, required runway length, climb gradient for go-arounds, etc.) at MTOW will still allow you to land safely in that specific situation, but fear of "heavy damage" is not something you need to consider. You might want to bring the plane down a little even more careful than usual, the brakes certainly have to work harder and maybe the plane needs to be inspected afterwards just to be sure, but otherwise you should be fine.