Let's dive deep into the tragic story of United Airlines Flight 585. This wasn't just another aviation incident; it was a puzzle that took years to solve, shaking the confidence of pilots and engineers alike. Understanding what happened on that fateful day helps us appreciate the complexities of air travel and the importance of ongoing safety improvements. So, buckle up as we explore the details, investigations, and lasting impact of this event.

Background of United Airlines Flight 585

United Airlines Flight 585 was a regularly scheduled passenger flight from Peoria, Illinois, to Colorado Springs, Colorado, with a stopover in Denver. On March 3, 1991, the Boeing 737-200, registration number N999UA, was carrying 20 passengers and 5 crew members. The aircraft had accumulated approximately 45,000 flight hours and had a solid maintenance record. The crew consisted of Captain Harold Green, First Officer Patricia Eidson, and three experienced flight attendants. The weather conditions were generally good, with some reports of wind shear in the vicinity of the Colorado Springs airport. Everything seemed normal as the flight approached its destination. However, as the aircraft neared the runway, disaster struck, turning a routine flight into a catastrophic event.

The flight crew, led by Captain Harold Green, was highly experienced. Captain Green had logged over 12,000 flight hours, and First Officer Patricia Eidson had more than 4,000 hours. The three flight attendants were seasoned professionals, well-versed in safety procedures and emergency protocols. Before departure, the aircraft underwent a standard pre-flight inspection, and no significant issues were reported. The Boeing 737-200 was a workhorse of the airline industry, known for its reliability and performance. Yet, despite all these factors, the flight was destined for tragedy. The approach to Colorado Springs was uneventful until the final moments, when the pilots encountered a sudden and unexplainable loss of control.

As the aircraft descended towards the runway, it experienced an unexpected and severe deviation. Instead of maintaining a stable approach, the plane rolled sharply to the right and pitched nose-down. The pilots struggled to regain control, applying opposite rudder and aileron inputs, but their efforts were in vain. The aircraft continued its uncontrolled descent, and within seconds, it slammed into the ground. The impact was devastating, and the aircraft was instantly destroyed. There were no survivors. The crash sent shockwaves through the aviation community, prompting immediate investigations and raising serious questions about the safety of the Boeing 737 and the possible causes of the accident. The initial focus was on potential factors such as weather conditions, mechanical failure, and pilot error. However, as the investigation progressed, it became clear that the cause was far more complex and elusive than initially anticipated.

The Tragic Events of March 3, 1991

The events leading to the crash of United Airlines Flight 585 unfolded rapidly and without warning. As the Boeing 737-200 approached Colorado Springs Airport, the pilots prepared for a routine landing. The weather was relatively calm, with light winds and clear visibility. The aircraft was configured for landing, with flaps extended and landing gear deployed. Everything appeared normal as the flight crew communicated with air traffic control and made their final descent checklist. Suddenly, without any apparent reason, the aircraft experienced a sharp and uncommanded roll to the right. This initial roll was followed by a steep nose-down pitch, sending the plane into a rapid and uncontrollable descent.

The pilots, caught completely off guard, reacted swiftly to try and correct the situation. They applied full opposite rudder and aileron inputs in an attempt to level the wings and pull the nose up. Despite their best efforts, the aircraft did not respond as expected. The control surfaces seemed ineffective, and the plane continued to plummet towards the ground. The flight crew struggled to understand what was happening, their confusion and desperation evident in their final transmissions to air traffic control. The suddenness and severity of the event left them with virtually no time to troubleshoot the problem or execute any effective recovery maneuvers.

The final moments of Flight 585 were chaotic and terrifying. The aircraft was in a completely unrecoverable state, hurtling towards the ground at an alarming speed. The impact was catastrophic. The Boeing 737-200 struck the ground with tremendous force, disintegrating upon impact. The wreckage was scattered over a wide area, and there was no chance of survival for anyone on board. The crash site was a scene of devastation, with debris, personal belongings, and aircraft parts strewn across the landscape. Emergency responders arrived quickly, but it was immediately clear that their efforts would be focused on recovery rather than rescue. The tragedy of Flight 585 left an indelible mark on the community of Colorado Springs and the aviation industry as a whole, sparking an intensive investigation into the cause of the crash.

Initial Investigation and Findings

The immediate aftermath of the United Airlines Flight 585 crash saw a flurry of activity as investigators from the National Transportation Safety Board (NTSB) descended upon the crash site. The primary goal was to gather as much evidence as possible to determine the cause of the accident. The NTSB team included experts in aircraft structures, flight operations, meteorology, and human factors. They meticulously examined the wreckage, interviewed witnesses, and reviewed flight data records in an effort to piece together what had happened in the final moments of the flight.

The initial focus of the investigation centered on several potential factors. These included weather conditions, mechanical failure, pilot error, and the possibility of external factors such as a bomb or missile strike. Weather conditions were carefully scrutinized, with investigators examining wind patterns, temperature gradients, and the potential for wind shear. The aircraft's maintenance records were reviewed to identify any known mechanical issues or recurring problems. The pilots' training and experience were also examined, along with their performance during the flight, based on available data. The flight data recorder (black box) and cockpit voice recorder were crucial sources of information, providing valuable insights into the aircraft's performance and the crew's actions in the cockpit.

Despite the thoroughness of the initial investigation, the cause of the Flight 585 crash remained elusive. The flight data recorder showed that the aircraft experienced an uncommanded rudder deflection, but the reason for this deflection was not immediately clear. There was no evidence of mechanical failure, and the pilots appeared to have reacted appropriately to the situation. The weather conditions, while not ideal, did not seem severe enough to cause such a catastrophic loss of control. After months of investigation, the NTSB issued an initial report that was inconclusive. The report cited the uncommanded rudder deflection as a contributing factor but could not determine the root cause of the deflection. This lack of a definitive explanation led to widespread speculation and concern within the aviation industry, raising questions about the safety of the Boeing 737 and the potential for similar accidents in the future.

The Mystery of the Rudder Reversal

One of the most perplexing aspects of the United Airlines Flight 585 investigation was the mystery of the rudder reversal. The flight data recorder revealed that the aircraft's rudder, a control surface located on the tail that is used to control the plane's yaw (side-to-side movement), had moved in the opposite direction of what the pilots intended. In other words, when the pilots applied rudder to correct the roll, the rudder actually moved in a way that exacerbated the problem, causing the plane to roll even more sharply. This phenomenon, known as rudder reversal, was virtually unheard of in commercial aviation, and it defied conventional understanding of how aircraft control systems were supposed to function.

Investigators struggled to understand how such a malfunction could occur. The rudder control system on the Boeing 737 was a complex mechanical system with multiple components, including cables, pulleys, and hydraulic actuators. Any failure within this system could potentially lead to a rudder malfunction, but the exact mechanism that caused the rudder reversal remained a mystery. Engineers conducted extensive tests and simulations to try and replicate the conditions that might have led to the malfunction. They examined the rudder control system for any signs of wear, damage, or manufacturing defects. They also explored the possibility of aerodynamic factors, such as unusual wind conditions or turbulence, that might have contributed to the problem. However, despite their best efforts, they were unable to pinpoint the precise cause of the rudder reversal.

The inability to explain the rudder reversal created a significant challenge for the NTSB. Without a clear understanding of what caused the malfunction, it was difficult to recommend effective safety improvements to prevent similar accidents in the future. The mystery also fueled public anxiety and eroded confidence in the safety of air travel. Passengers began to question whether the Boeing 737 was inherently unsafe, and pilots expressed concerns about the reliability of the rudder control system. The NTSB faced intense pressure to solve the mystery and provide a definitive explanation for the Flight 585 crash. The investigation stretched on for years, becoming one of the longest and most complex in the history of aviation accident investigation.

The Discovery of the Servo Valve Issue

Years after the initial investigation into United Airlines Flight 585, a breakthrough finally occurred. The focus shifted to the power control unit (PCU) servo valve within the rudder mechanism. It was discovered that under certain extreme temperature conditions, this valve could jam and cause the rudder to deflect in the opposite direction of the pilot's input. This phenomenon, known as a "servo valve hardover," was extremely rare but could potentially lead to a catastrophic loss of control.

Further investigations and simulations revealed the exact mechanism by which the servo valve hardover could occur. It was found that when the aircraft experienced rapid temperature changes, the different materials within the servo valve could expand and contract at different rates. This differential expansion could cause the valve to bind, preventing it from moving freely. If the valve became stuck in a position that commanded the rudder to move in the opposite direction, the pilots would be unable to override the malfunction. The severity of the hardover depended on several factors, including the temperature gradient, the aircraft's airspeed, and the pilot's reaction time.

The discovery of the servo valve issue provided a plausible explanation for the rudder reversal that had occurred on Flight 585. It also helped to explain why the pilots were unable to regain control of the aircraft. The servo valve hardover was a sudden and unexpected event that left the pilots with virtually no time to react. The malfunction occurred at a critical phase of flight, during the final approach to landing, when the aircraft was particularly vulnerable. The combination of these factors created a perfect storm that led to the tragic crash. The NTSB immediately issued recommendations for airlines to inspect and replace the servo valves in their Boeing 737 fleets. These recommendations were implemented worldwide, significantly improving the safety of the aircraft.

Impact on Aviation Safety and Regulations

The crash of United Airlines Flight 585 had a profound and lasting impact on aviation safety and regulations. The discovery of the servo valve issue led to a series of significant changes in the design, maintenance, and operation of the Boeing 737. One of the most important changes was the replacement of the servo valves in all Boeing 737 aircraft. The new servo valves were designed to be more resistant to temperature changes and less likely to experience hardovers. In addition, airlines were required to implement more rigorous inspection and maintenance procedures for the rudder control system.

The Flight 585 accident also led to improvements in pilot training. Pilots were given additional training on how to recognize and respond to rudder malfunctions. They were taught to use differential thrust and other techniques to maintain control of the aircraft in the event of a rudder reversal. The accident also highlighted the importance of cockpit resource management (CRM), which emphasizes the importance of effective communication and teamwork in the cockpit. CRM training was enhanced to ensure that pilots and flight attendants were better prepared to handle emergencies.

Furthermore, the Flight 585 crash prompted a review of aircraft certification standards. The FAA (Federal Aviation Administration) conducted a comprehensive review of the regulations governing the design and testing of aircraft control systems. The goal was to identify any potential vulnerabilities and to strengthen the certification process to prevent similar accidents in the future. The FAA also worked with aircraft manufacturers to develop new technologies and procedures for detecting and preventing rudder malfunctions. These efforts have led to significant improvements in aviation safety, making air travel safer for passengers and crew alike. The legacy of Flight 585 serves as a reminder of the importance of continuous vigilance and the need to learn from past mistakes.

Lessons Learned from Flight 585

The investigation into United Airlines Flight 585 provided invaluable lessons that continue to shape aviation safety practices. The primary takeaway is the critical importance of understanding complex system interactions within aircraft. The servo valve issue demonstrated how seemingly minor component failures could have catastrophic consequences when combined with other factors. This underscored the need for thorough testing and analysis of aircraft systems under a wide range of conditions.

Another key lesson was the significance of data analysis and anomaly detection. The flight data recorder provided crucial clues about the rudder reversal, but it took years to fully understand the implications of this data. This highlighted the need for more sophisticated data analysis techniques and the importance of identifying even subtle anomalies that could indicate potential problems. Airlines and manufacturers have since invested heavily in data analytics to monitor aircraft performance and detect potential issues before they lead to accidents.

Finally, the Flight 585 accident emphasized the importance of collaboration and communication within the aviation industry. The investigation involved experts from various fields, including engineering, meteorology, and human factors. The success of the investigation depended on the ability of these experts to work together and share information effectively. This collaboration has continued in the years since the accident, with airlines, manufacturers, and regulatory agencies working together to improve aviation safety worldwide. The tragic loss of Flight 585 serves as a constant reminder of the need for vigilance, innovation, and cooperation to ensure the safety of air travel.