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The Impact of Mechanical Failure in Aviation Accidents

Updated: Dec 11, 2023

Bangalore, India

Ever wondered how even the most advanced planes, flown by skilled pilots, can tragically crash due to mechanical failures? Every part of a safe flight conceals potential risks. In heartbreaking instances, these failures result in devastating outcomes and claim numerous lives. Today, let's delve into a detailed case involving three planes: two facing the same fate and one miraculously escaping, revealing the hidden threats within aviation technology.


The Crash and Investigation of United Airlines Flight 585

On March 3, 1991, United Flight 585's final approach to Colorado Springs turned tragic. Despite clear skies, the flight faced gusty winds and severe turbulence, causing the plane to sharply bank to the right. Within moments, the aircraft spiraled out of control, resulting in a devastating crash upon impact. Regrettably, all 25 individuals on board lost their lives in this incident, leaving a profound impact on the aviation community.


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control panel in an airplane cockpit

Following the Flight 585 crash, the National Transportation Safety Board (NTSB) swiftly launched an investigation. Initial findings at the site revealed an unusual debris pattern, ruling out mid-air collisions or parts falling off mid-flight, as the wreckage was confined to a smaller area. This led investigators to believe the plane crashed at high speed, nose down.

Crucial components, including engine

turbines, hydraulic gauges, in-flight data, and the cockpit voice recorder (FDR and CVR), were recovered and sent for analysis. These pieces provided crucial insights, helping investigators understand cockpit dynamics and the plane's behavior, essential for piecing together the crash sequence.


In the aftermath of the Flight 585 crash, investigators meticulously analyzed the cockpit voice recorder (CVR) to grasp the pilots' decisions and perceptions that fateful day. The CVR analysis portrayed the Flight 585 pilots as highly skilled, adopting essential safety measures like increasing speed to mitigate turbulence. This led investigators to question the likelihood of pilot error. Mechanical issues, especially engine failure, were explored next. However, after thorough examinations of engines and pressure gauges, no irregularities were found; the engines were functioning normally before the impact.


Following the Flight 585 tragedy, investigators honed in on potential flight control damage, particularly the rudder. Despite the challenges posed by the post-crash fire and impact, the

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functions of airplane parts

intact Power Control Unit (PCU) in the tail was scrutinized. Examination of the PCU, housing the vital dual servo valve for rudder movement, revealed microscopic metal chips in the hydraulic fluid. However, this concern was dismissed, given the fluid's filtration process before entering the valve. Despite exhaustive efforts, the NTSB couldn't definitively identify the crash's origin, resulting in the case being classified as undetermined.



The Crash of US Air 427 and the similarities to United Airlines 585

On September 8th, 1994, US Air 427, en route from Chicago to Pittsburgh, faced a tragic end as it neared its destination. Pilots were alerted to another plane at a similar altitude, shifting their focus to avoiding turbulence and wake vortex caused by the nearby aircraft. Following slight turbulence, US Air 427 suddenly sharply banked to the left and uncontrollably rolled towards the ground. Despite the crew's desperate efforts, the aircraft couldn't be stabilized. The crash claimed the lives of all 132 passengers and crew members onboard.


At the crash site, investigators meticulously combed through the wreckage for any clues. Despite the extensive damage, eyewitness accounts and data from the CVR and FDR revealed significant parallels between the crashes of US Air 427 and United Airlines 585. Both involved Boeing 737s, with Flight 585 rolling right and Flight 427 rolling left, showcasing a recurring trend. Engine failure was ruled out in both cases. However, differences emerged in the weather conditions during Flight 427.



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plane crash debris with an intact tail

Upon examination, US Air 427's surprisingly intact tail was sent for analysis. Comparable metal chips in hydraulic fluid were dismissed as they wouldn't have entered the valve. NTSB investigators reexamined the valve, finding no faults, circling back to the possibility of pilot error. FDR data revealed a full rudder deployment, pointing to rudder hardover caused by mechanical failure or pilot input. Despite in-depth analysis, the cause of both crashes remained undetermined, leaving investigators perplexed.



The Miracle of Eastwind 517

On June 9th, 1996, Flight 517, en route from Trenton to Richmond, faced a crisis during its final approach to Richmond International Airport. Suddenly, the plane rolled sharply to the right, indicating a rudder malfunction. Despite the pilot's efforts, the rudder pedal remained stuck. After a momentary stabilization, the plane banked right once more before straightening out. Recognizing a serious flight control problem, the pilot skillfully managed an emergency landing, ensuring the safety of all passengers and crew onboard.


Eastwind Flight 517 faced a scenario similar to the challenges faced by United Airlines Flight 585 and USAir Flight 427. This pivotal moment gave NTSB investigators an opportunity to delve deeper. With a living pilot and a functional aircraft, they conducted thorough research, gathering essential data. The PCU chamber underwent rigorous lab tests, passing each examination successfully.



Conclusion: The root cause of the problems

NTSB investigators performed a thermal shock test on the PCU, simulating flight conditions with extreme temperatures. Unexpectedly, the valve jammed, uncovering a shared problem in all three flights: the rudder. This revealed that Boeing 737's rudder, PCU, and dual servo

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the thermal shock test

valve could jam under certain conditions, raising serious concerns about Boeing component manufacturing. With thousands of Boeing 737s in operation, this issue sent shockwaves through the aviation industry.


Upon revisiting the unresolved United Airlines 585 crash, investigators found parallel circumstances. When the pilot applied force to the rudder pedal, the reversal caused the rudder to move opposite to commands, aligning with patterns observed in the other cases.


Boeing and airlines implemented vital upgrades to the rudder system, emphasizing safety as a top priority. Pilots received specialized training to manage unexpected cockpit situations, including rudder reversals. These measures successfully averted future incidents, highlighting the industry's dedication to enhancing flight safety through comprehensive training and advanced technology.



In the realm of modern aviation, every incident serves as a valuable lesson. Through delving into the causes and implementing preventive measures, the industry not only resolves immediate issues but also strengthens the entire aviation system. This continuous process of learning, adapting, and training highlights a shared commitment: ensuring every flight is as secure as possible.


 
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