Engine failure results in the loss of thrust, which is required for aircraft to maintain altitude or climb further. However, engine failure does not necessarily culminate into the complete loss of aircraft control. Aggressive use of flight controls, namely rudders and ailerons, can steer the flight to safety.
Aircraft compensate for a loss of thrust by losing altitude. They have a thrust-to-drag ratio of 10:1, which means they can fly 10 miles forward for every 1 mile lost in altitude. Cruising altitudes of 35,000 ft (~6 miles) give aircraft a distance of 60 miles to find a suitable place to conduct an emergency landing. Engine failure is easier to deal with at higher altitudes than at lower altitudes, such as when taking off.
Pilots faced with engine failure must conduct forced landings on the most favorable surface available to them. Here’s an interesting catch, this surface need not only be land. Airplanes can be ditched, i.e., landed on water or ice, without compromising passenger safety.
Similar to crumple zones in cars, aircraft have expendable parts in their structure to dissipate the force of landing in inclement terrain. These include the wings, landing gear, and even the bottom part of the fuselage.