Comprehensive testing is at the core of any airframe development, and that means modeling and measuring the worst case scenario. Though likely to never happen in practice, engineers need to know how components will perform in an emergency situation — so they test them to their limits.
The aborted takeoff is one such test that Boeing uses to gauge the performance of a vehicle’s braking system and condition thereafter. At full load and under full take off power, a system is tested by suddenly slamming on the brakes with no reverse thrust. How quickly the aircraft stops and the condition of the landing gear is a reflection of how successful the test is.
In the above video you can see the results of a recent test at Boeing on their upcoming 747-8 freighter. In coming to a stop the brakes glow red hot and the landing gear begins to smoke, but that result is actually good — the fully loaded aircraft stops 700 feet short of the target distance, which means safer, more effective breaking.
Whether or not the passengers onboard have wet their pants is another question. You can read more about the test over at Boeing’s website.