While a Boeing 747 is designed as a four-engine aircraft, it is technically capable of maintaining level flight on only two engines under specific conditions, though it is considered an emergency situation rather than a standard "cruise." If two engines on the same side fail, the aircraft faces significant aerodynamic challenges due to asymmetrical thrust; however, if one engine fails on each side, the plane is much more balanced. In a two-engine scenario, the 747 cannot maintain its optimal high-altitude cruise or its maximum weight capacity. The pilot would be forced to descend to a "driftdown" altitude, which is a lower, denser airspace where the remaining two engines can provide enough thrust to keep the plane airborne. This maneuver is part of standard pilot training. While the aircraft won't fall out of the sky immediately, the reduction in power means it can no longer clear high mountain ranges or maintain high speeds. The goal in such a scenario is always to divert to the nearest suitable airport as quickly as possible. Modern twin-engine planes like the 777 are designed specifically for long-haul "two-engine" flight, but for the 747, losing half its power is a critical event.