Why Boeing Did Not Include Manual Reversion in the 777 and 787

Manual reversion, a feature that allowed pilots to revert to rudimentary flight controls in the event of a complete hydraulic failure, was not included in the Boeing 777 and 787 models. This article explores the reasons behind this decision, examining the evolution of aircraft systems, the potential risks, and the alternatives Boeing implemented for critical flight operations.

The Evolution of Aircraft Hydraulics

Manual reversion was a common feature in earlier aircraft, such as the Boeing 707, 727, 737, and Douglas DC8. These aircraft typically had simple hydraulic systems with off-spring tabs that would compensate for a complete hydraulic failure. However, with the advancement in technology, newer aircraft models began to incorporate more sophisticated systems.

Boeing 747 and Its Hydraulic Systems

The 747, a larger aircraft, utilized a more complex hydraulic system with four engine-driven and one air-driven hydraulic systems. With the removal of engines, the 747 could still operate under emergency conditions. Unfortunately, a tragic incident involving Japan Airlines highlighted the limitations of this system when a bad pressure bulkhead failure cut all four hydraulic systems, leading to a crash.

The DC10 and Its Hydraulics

Another significant accident involving the DC10 due to an engine explosion further emphasized the challenges of relying on hydraulics for safe operation. The DC10, like the 747, also had a complex hydraulic system with multiple sources of power. However, the inherent risks of potential failure and the need for a fail-safe mechanism influenced Boeing's development team.

Risks and Challenges of Manual Reversion

While manual reversion provided a backup in cases of hydraulics failure, it also came with its own set of risks. Manual reversion typically required a crosswind limitation, usually around 12 knots, to prevent aircraft control issues. The potential for reduced performance and control under certain weather conditions made manual reversion a less ideal solution for modern, larger aircraft like the 777 and 787.

The Role of Electrically Driven Systems

Boeing adopted electrically driven standby rudder pumps and auxiliary pumps as a safer alternative to manual reversion. The 777 and 787 models incorporate these features, ensuring that if the hydraulic system fails, the aircraft can still manage essential flight control functions through electrical systems.

Modern Flight Control Systems

The 757 and 767 models introduced three hydraulic systems, with 2 plus rudder standby. These designs also included a Ram Air Turbine (RAT) for hydraulics, which could be used by the aircraft to generate emergency power in the event of an electrical failure. The 777 and 787 largely advanced this concept, with more reliable and efficient backup systems.

Management of Manuals and Aircraft Systems

Despite the complex nature of modern aircraft, Boeing still provides comprehensive manuals for each model. These manuals include detailed instructions on various aspects of the aircraft's operation, maintenance, and emergency procedures. However, with the increasing use of computerized systems, the manuals are often digital, making them more accessible and easier to update.

Role of Engineers and Pilots

The primary responsibility of engineers and pilots is to ensure that the aircraft operates safely and efficiently. Modern aircraft like the 777 and 787 are designed with multiple layers of safety, including emergency power systems, backup controls, and automated systems. These systems are continuously monitored and tested to ensure they function correctly.

Conclusion

In conclusion, while manual reversion was a common feature in earlier aircraft, it was not included in the Boeing 777 and 787 due to the inherent risks and the availability of modern, more reliable backup systems. The evolution of aircraft technology has led to more sophisticated and safe solutions, ensuring that the latest Boeing models can handle emergencies with greater reliability and safety.