Hey guys! Ever heard of United Airlines Flight 585? It's one of those aviation mysteries that still sends shivers down the spines of even the most seasoned pilots and aviation enthusiasts. Buckle up, because we're diving deep into the story of this ill-fated flight, exploring the details, the investigation, and the ultimate conclusions. Let's get started!

The Fateful Flight: A Routine Trip Gone Wrong

On March 3, 1991, United Airlines Flight 585 was a scheduled flight from Peoria, Illinois, to Colorado Springs, Colorado, with a stopover in Denver. It was operated by a Boeing 737-200, a workhorse of the skies known for its reliability. The flight crew was experienced, and the weather conditions were normal for a late winter day in the Rockies. Nothing seemed out of the ordinary as the plane approached Colorado Springs Airport. As the Boeing 737-200, registration N999UA, began its descent into Colorado Springs, everything appeared normal. The pilots initiated their approach, and the aircraft was configured for landing. Suddenly, and without warning, the aircraft rolled violently to the right. The pilots fought to regain control, but the plane continued to descend rapidly. Despite their best efforts, they couldn't recover, and the aircraft crashed into Widefield Park, just east of the runway. All 25 people on board, including 20 passengers and 5 crew members, perished in the crash. The impact was devastating, and the wreckage was scattered across the park. It was a horrific scene, and the local community was immediately plunged into mourning. This section provides a detailed account of the events leading up to the crash, emphasizing the sudden and unexpected nature of the tragedy. The loss of life was immense, and the impact on the families and the community was profound. The initial response involved search and rescue operations, followed by the beginning of the investigation to determine the cause of the crash. This event marked the beginning of a long and complex journey to understand what went wrong on that fateful day.

The Initial Investigation: Unraveling the Mystery

The immediate aftermath of the crash saw a flurry of activity as investigators from the National Transportation Safety Board (NTSB) descended upon the scene. The initial investigation focused on several potential causes, including weather, mechanical failure, and pilot error. The weather was quickly ruled out as a significant factor, as conditions were relatively mild at the time of the accident. Attention then turned to the aircraft itself. The flight data recorder (FDR) and cockpit voice recorder (CVR) were recovered and sent to the NTSB laboratory for analysis. However, the data from the FDR was incomplete, and the CVR provided limited information about the crucial moments leading up to the crash. The investigators meticulously examined the wreckage, searching for any signs of mechanical failure. They scrutinized the engines, control surfaces, and hydraulic systems, but initially found nothing conclusive. With the available evidence, the NTSB was unable to determine a probable cause for the crash. The investigation was closed in 1994 with the conclusion that the cause was undetermined. This was a highly unusual outcome, as the NTSB typically strives to identify a specific cause or combination of factors that led to an accident. The inability to pinpoint a reason for the crash only deepened the mystery and added to the frustration of the victims' families and the aviation community. The initial investigation was thorough, but the lack of definitive evidence left many questions unanswered. The investigators faced significant challenges in their quest to understand what had happened to Flight 585. The mystery surrounding the crash persisted for several years, fueling speculation and debate among aviation experts. The closure of the investigation without a clear cause only added to the sense of unease and uncertainty.

The Colorado Springs Effect: A Pattern Emerges

In the years following the Flight 585 crash, two similar incidents occurred involving Boeing 737s. In 1994, USAir Flight 427 crashed near Pittsburgh, Pennsylvania, under almost identical circumstances. Then, in 1996, Eastwind Airlines Flight 517 experienced a similar, though non-fatal, incident while landing in Richmond, Virginia. These incidents raised concerns about a potential design flaw in the Boeing 737's rudder control system. Investigators began to suspect that the crashes were not isolated events but rather part of a larger pattern. The similarities between the Flight 585 crash and the USAir Flight 427 crash were particularly striking. In both cases, the aircraft experienced a sudden and uncommanded rudder movement, leading to a loss of control. The term "Colorado Springs Effect" was coined to describe this phenomenon, referring to the unexplained and potentially catastrophic rudder movements experienced by Boeing 737s. The emergence of this pattern prompted the NTSB to reopen the investigation into the Flight 585 crash. The investigators realized that they needed to re-examine the evidence in light of the new information from the other incidents. The focus shifted to the rudder control system and the possibility of a hidden defect that could cause the rudder to deflect unexpectedly. The discovery of these similar incidents was a turning point in the investigation. It suggested that there was a systemic issue affecting the Boeing 737, rather than just isolated mechanical failures or pilot errors. The "Colorado Springs Effect" became a central focus of the renewed investigation, and the NTSB dedicated significant resources to understanding the underlying cause of the phenomenon.

The Rediscovery: Unraveling the Technical Puzzle

The reopened investigation focused on the Boeing 737's rudder control system. Investigators discovered that under certain conditions, the rudder could reverse, meaning it would move in the opposite direction of what the pilots intended. This phenomenon, known as a rudder hardover, could occur due to a malfunction in the power control unit (PCU), which controls the movement of the rudder. The PCU was manufactured by Parker Hannifin. Further investigation revealed that thermal shock, caused by rapid temperature changes, could cause the PCU's slide valve to stick. This could lead to the rudder moving in the opposite direction of the pilot's input. Sophisticated simulations and laboratory tests were conducted to replicate the conditions that could lead to a rudder hardover. The tests confirmed that a thermal shock could indeed cause the PCU's slide valve to stick, resulting in a rudder reversal. This breakthrough provided a plausible explanation for the sudden and uncommanded rudder movements experienced in the Flight 585 crash and the other similar incidents. The rediscovery of this critical vulnerability in the rudder control system was a major step forward in understanding the cause of the crash. It provided a technical explanation for the "Colorado Springs Effect" and helped to unravel the mystery that had plagued investigators for years. The findings of the reopened investigation had significant implications for the aviation industry, leading to changes in the design and maintenance of the Boeing 737's rudder control system.

The Final Report: A Resolution, But Not Closure

In 2001, the NTSB issued its final report on the United Airlines Flight 585 crash. The report concluded that the probable cause of the accident was a loss of control of the aircraft resulting from a sudden, uncommanded rudder deflection. The NTSB determined that the rudder deflection was likely caused by a malfunction of the PCU, which resulted in a rudder hardover. The report also noted that the pilots' efforts to recover from the sudden rudder deflection were hampered by the aircraft's design and the speed at which the event occurred. The NTSB made several recommendations to the Federal Aviation Administration (FAA) and Boeing to improve the safety of the Boeing 737's rudder control system. These recommendations included redesigning the PCU to prevent thermal shock from causing a rudder hardover, improving pilot training to address the possibility of a sudden rudder deflection, and enhancing the aircraft's flight control system to provide better feedback to the pilots. The final report provided a resolution to the mystery surrounding the Flight 585 crash, but it did not bring complete closure to the victims' families. The knowledge that the crash was likely caused by a preventable mechanical failure was difficult to accept. The NTSB's final report was a culmination of years of investigation and analysis. It provided a comprehensive explanation of the events leading up to the crash and offered recommendations to prevent similar accidents from happening in the future. While the report brought a sense of resolution, it also served as a reminder of the lives lost and the importance of aviation safety.

Lessons Learned: Enhancing Aviation Safety

The United Airlines Flight 585 crash had a profound impact on the aviation industry. The investigation into the crash led to significant improvements in the design, maintenance, and operation of the Boeing 737 and other aircraft. The redesign of the PCU to prevent thermal shock was a crucial step in enhancing the safety of the Boeing 737's rudder control system. Improved pilot training to address the possibility of a sudden rudder deflection has also helped to prevent similar accidents. The crash also highlighted the importance of thorough and persistent investigation in the aftermath of an aviation accident. The NTSB's decision to reopen the investigation and pursue new leads ultimately led to the discovery of the underlying cause of the crash. The lessons learned from the Flight 585 crash have had a lasting impact on aviation safety. They have led to improvements in aircraft design, maintenance procedures, and pilot training, all of which have contributed to making air travel safer. The crash serves as a reminder of the importance of vigilance and continuous improvement in the aviation industry. The legacy of Flight 585 is one of enhanced safety and a commitment to preventing similar tragedies from occurring in the future.

So there you have it, the story of United Airlines Flight 585. It's a complex tale of investigation, technical challenges, and ultimately, a resolution that has made air travel safer for all of us. Thanks for sticking around, and until next time, fly safe!