• March 3, 1991
── united airline flight 585
── 737-200 in Colorado Springs in 1991
── summary: loss of control due to rudder hardover
── Widefield Park, El Paso county near Colorado springs municipal airport, colorado springs, colorado
──
── rolled to the right and went into a vertical dive
──
── On March 3, 1991, United Airlines Flight 585, a Boeing 737-200, rolled to the right and went into a vertical dive while attempting to land in Colorado Springs, Colorado. The resulting crash killed all 25 people on board. The National Transportation Safety Board (NTSB) conducted a thorough investigation. A rudder problem was suspected. Because the aircraft's rudder components were severely damaged in the crash, the components could not be tested or fully evaluated. As a result, the NTSB was unable to conclusively identify the cause of the crash.[1]: 47 << from www.wikipedia.org entry on Eastwind airline flight 517 >>
──
── during the landing approach, the plane rolled to the right and pitched nose-down into a near-vertical dive.
──
── On March 3, 1991, United Airlines Flight 585, a Boeing 737-200, crashed while attempting to land in Colorado Springs, Colorado. During the airplane's landing approach, the plane rolled to the right and pitched nose-down into a near-vertical dive.[2]: ix The resulting crash destroyed the aircraft and killed all 25 people on board.[2]: ix << from www.wikipedia.org entry on Boeing 737 rudder issues >>
• April 11, 1994
── << from www.wikipedia.org entry on Boeing 737 rudder issues >>
──
── Boeing 737-300
── summary:
──
── rolled violently to the right and continued to pull to the right
──
── On April 11, 1994, a Continental Airlines pilot, Ray Miller, reported his aircraft rolled violently to the right and continued to pull to the right for another 18 minutes; the Boeing 737-300 landed safely. Continental removed the flight data recorder and rudder PCU from the incident aircraft and provided them to Boeing for investigation. Boeing concluded that the rudder had inadvertently moved due to an electrical malfunction, but only 2.5 degrees and for less than two minutes in total, a finding disputed by Ray Miller.[9]
── electrical malfunction, ([ what kind of electrical malfunction ])
• September 8, 1994
── USAir Flight 427
── 737-300 near Pittsburgh in 1994
── summary:
── Hopewell Township, Pennsylvania
──
── abruptly rolled to the left while on approach
──
── On September 8, 1994, USAir Flight 427, a Boeing 737-300, abruptly rolled to the left while on approach to Pittsburgh International Airport in an accident very similar to that of Flight 585. The resulting crash killed all 132 people on board.[1]: 1 The NTSB's subsequent investigation persisted throughout the late 1990s. << from www.wikipedia.org entry on Eastwind airline flight 517 >>
──
── suddenly rolled to the left. Although the pilots were briefly able to roll right and level the plane, it rolled left a second time and the pilots were unable to recover.
──
── On September 8, 1994, USAir Flight 427, a Boeing 737-300, crashed near Pittsburgh, Pennsylvania. While on approach to Pittsburgh International Airport, Flight 427 suddenly rolled to the left. Although the pilots were briefly able to roll right and level the plane, it rolled left a second time and the pilots were unable to recover.[3]: 4 The resulting crash killed all 132 people on board.[3]: 9 The NTSB realized early into its investigation that the crash of Flight 427 might have been caused by an unintended or uncommanded rudder movement, similar to the suspected (but not yet established) cause of the Flight 585 crash.[3]: 44 As a result, the NTSB conducted additional testing on United Flight 585's Parker-Hannifin PCU servo during its Flight 427 investigation.[2]: 73 << from www.wikipedia.org entry on Boeing 737 rudder issues >>
── the gap in the flight data recorder (FDR), during which no data was recorded, lead Boeing to suspect and insist that the pilot had responded incorrectly to a wake turbulence incident.[6] << from www.wikipedia.org entry on Boeing 737 rudder issues >>
── At the request of the NTSB, data from the Penny & Giles quick access recorder (QAR) of a British Airways (BA) Boeing 747-400 was supplied to the NTSB by BA. The data was from a London-Bangkok flight in which the aircraft suffered an uncommanded elevator movement and momentary elevator reversal on take-off, the aircraft then landed safely. Operating alongside the FDR system, the QAR on BA's 747-400s, in conjunction with a Data Management Unit, received and recorded more aircraft parametric data, including control input values at a higher rate.[7] This BA data led to renewed suspicion of the similar valve design used on the 737 rudder. As a result of this earlier BA incident, Boeing had, in fact, modified the design of the 747 elevator servo system, and the modified system had been retroactively fitted to all 747-400s in service.[6] << from www.wikipedia.org entry on Boeing 737 rudder issues >>
── renewed suspicion of the similar valve design used on the 737 rudder
──
• June 9, 1996
── Eastwind airline flight 517
── Boeing 737-200 (registration number N221US)
── Summary: Uncommanded rudder hardover[1]
loss of rudder control and the plane rolled sharply to the right
── As the plane continued to descend through 4,000 feet (1,200 m), the captain suddenly experienced a loss of rudder control and the plane rolled sharply to the right.[1]: 51
──
── rolled sharply to the right.
── The aircraft experienced two episodes of rudder reversal while on approach to land
──
── On June 9, 1996, while the NTSB's investigation of Flight 427 was still ongoing, the pilots of Eastwind Airlines Flight 517 briefly lost control of their aircraft, a 737-200, while flying from Trenton, New Jersey, to Richmond, Virginia.[2]: ix The aircraft experienced two episodes of rudder reversal while on approach to land in Richmond. Unlike the two prior incidents, the rudder issues on Flight 517 spontaneously resolved and the pilots were able to safely land the aircraft. One of the 53 people on board was injured.[3]: 51 << from www.wikipedia.org entry on Boeing 737 rudder issues >>
── On June 9, 1996, while operating a passenger flight from Trenton, New Jersey to Richmond, Virginia, the crew of Eastwind Airlines Flight 517 temporarily lost control of their Boeing 737-200 because of a rudder malfunction. The crew were able to regain control and land the aircraft successfully. One flight attendant was injured.
──<< from www.wikipedia.org entry on Eastwind airline flight 517 >>
── Thermal shock testing revealed that the uncommanded rudder movement could be replicated by injecting a cold PCU with hot hydraulic fluid. Thermal shock resulted in the servo's secondary slide becoming jammed against the servo housing, and that when the secondary slide was jammed the primary slide could move to a position that resulted in rudder movement opposite of the pilot's commands.[2]: 79 [3]: 294 The NTSB concluded that all three rudder incidents (United Flight 585, USAir Flight 427, and Eastwind Flight 517) were most likely due to the PCU secondary slide jamming and excessive travel of the primary slide, resulting in the rudder reversal.[3]: 294 << from www.wikipedia.org entry on Boeing 737 rudder issues >>
── Flight 517 was instrumental in resolving the cause of Boeing 737 rudder issues that had caused two previous fatal crashes because it was the first flight to experience such rudder issues and land safely, allowing investigators to interview the pilots about their experience and to study the aircraft.
──
── the captain felt a brief "kick" or "bump" on the right rudder pedal.
── the plane rolled sharply to the right.
──
── While on approach to Richmond International Airport, Richmond, Virginia, United States, at an altitude of about 5,000 feet (1,500 m) MSL, the captain felt a brief "kick" or "bump" on the right rudder pedal.[1]: 51 Around the same time, a flight attendant at the rear of the plane heard a thumping noise underneath her.[1]: 52 As the plane continued to descend through 4,000 feet (1,200 m), the captain suddenly experienced a loss of rudder control and the plane rolled sharply to the right.[1]: 51
──
[[ ]]
• December 19, 1997
<< look up silkair flight 185 >>
── SilkAir Flight 185
──
──
──
── On December 19, 1997, SilkAir Flight 185 crashed in Indonesia, killing 104 people. Because the crash involved a Boeing 737-300 rolling and diving toward the ground at a steep angle,
──
•
──
──
____________________________________
<< from www.wikipedia.org entry on Boeing 737 rudder issues >>
Rudder function[edit]
Unlike other twin-engine large transport aircraft in service at the time, the Boeing 737 was designed with a single rudder panel and single rudder actuator.[2]: 14 The single rudder panel is controlled by a single hydraulic Power Control Unit (PCU).[2]: 13 Inside the PCU is a dual servo valve that, based on input from the pilot's rudder pedals or the aircraft's yaw damper system, directs the flow of hydraulic fluid in order to move the rudder.[2]: 19 The PCU for affected Boeing 737 aircraft was designed by Boeing and manufactured by Parker Hannifin.[2]: 20
[[ ]]
Boeing 737 Rudder Design Study
<< look this up >>
http://www.airlinesafety.com/faq/B-737Rudder.htm
____________________________________
• Rudder function
── single rudder panel and single rudder actuator
── rudder actuator
── The single rudder panel is controlled by a single hydraulic Power Control Unit (PCU).
── hydraulic Power Control Unit (PCU)
── Inside the PCU is a dual servo valve that, based on input from the pilot's rudder pedals or the aircraft's yaw damper system, directs the flow of hydraulic fluid in order to move the rudder.
── servo valve, rudder pedals, yaw damper system, hydraulic fluid
── designed by Boeing
── manufactured by Park Hannifin.
____________________________________
wikipedia
March 3, 1991
united airline flight 585
loss of control due to rudder hardover
Widefield Park, El Paso county
near Colorado springs municipal airport, colorado springs, colorado
• April 11, 1994 (a Continental Airlines pilot, Ray Miller) (??)
September 8, 1994
USAir Flight 427,
Boeing 737-300
Thursday, September 8, 1994, the Boeing 737 flying this route crashed in Hopewell Township, Pennsylvania
On September 8, 1994, USAir Flight 427, a Boeing 737-300, abruptly rolled to the left while on approach to Pittsburgh International Airport in an accident very similar to that of Flight 585. The resulting crash killed all 132 people on board.[1]: 1 The NTSB's subsequent investigation persisted throughout the late 1990s.
June 9, 1996
Eastwind airline flight 517 had a similar problem
Summary: Loss of control due to rudder hardover[1]
Flight 517 was instrumental in resolving the cause of Boeing 737 rudder issues that had caused two previous fatal crashes because it was the first flight to experience such rudder issues and land safely, allowing investigators to interview the pilots about their experience and to study the aircraft.
____________________________________
<< www.wikipedia.org entry on Eastwind airline flight 517 >>
At the request of the NTSB, data from the Penny & Giles quick access recorder (QAR) of a British Airways (BA) Boeing 747-400 was supplied to the NTSB by BA. The data was from a London-Bangkok flight in which the aircraft suffered an uncommanded elevator movement and momentary elevator reversal on take-off, the aircraft then landed safely. Operating alongside the FDR system, the QAR on BA's 747-400s, in conjunction with a Data Management Unit, received and recorded more aircraft parametric data, including control input values at a higher rate.[7] This BA data led to renewed suspicion of the similar valve design used on the 737 rudder. As a result of this earlier BA incident, Boeing had, in fact, modified the design of the 747 elevator servo system, and the modified system had been retroactively fitted to all 747-400s in service.[6]
Unlike other twin-engine large transport aircraft in service at the time, the Boeing 737 was designed with a single rudder panel and single rudder actuator.[2]: 14 The single rudder panel is controlled by a single hydraulic Power Control Unit (PCU).[2]: 13 Inside the PCU is a dual servo valve that, based on input from the pilot's rudder pedals or the aircraft's yaw damper system, directs the flow of hydraulic fluid in order to move the rudder.[2]: 19 The PCU for affected Boeing 737 aircraft was designed by Boeing and manufactured by Parker Hannifin.[2]: 20
The single rudder panel is controlled by a single hydraulic Power Control Unit (PCU).[2]: 13
The NTSB and Boeing engineers conducted a series of tests on the PCUs from Flight 517 and Flight 427, as well as PCUs used in other aircraft and a brand-new PCU that had not yet been used in flight (the PCU from Flight 585, although it had been recovered, was too badly damaged to test in this manner).[3]: 71, 81–85 Testing revealed that under certain circumstances, the PCU's dual servo valve could jam and deflect the rudder in the opposite direction of the pilots' input.[3]: 81–85 Thermal shock testing revealed that the uncommanded rudder movement could be replicated by injecting a cold PCU with hot hydraulic fluid. Thermal shock resulted in the servo's secondary slide becoming jammed against the servo housing, and that when the secondary slide was jammed the primary slide could move to a position that resulted in rudder movement opposite of the pilot's commands.[2]: 79 [3]: 294 The NTSB concluded that all three rudder incidents (United Flight 585, USAir Flight 427, and Eastwind Flight 517) were most likely due to the PCU secondary slide jamming and excessive travel of the primary slide, resulting in the rudder reversal.[3]: 294
The following Boeing 737 aircraft incidents were also suspected of being caused by a rudder PCU malfunction:
• On June 6, 1992, Copa Airlines Flight 201, a 737-200 Advanced, flipped and crashed into the Darién Gap jungle, killing 47 people. Investigators initially believed that the airplane experienced a rudder malfunction, but after an exhaustive and extensive inquiry, they concluded that the crash was caused by faulty attitude indicator instrument readings.
• On March 8, 1994, a Sahara Airlines aircraft that had three trainees and one supervising pilot on board crashed after performing a "touch-and-go landing" at New Delhi Airport and slammed into a Russian jet. The four pilots and five ground workers (a total of nine) were killed. Although repairs were done to the PCU with unauthorized parts, the incident is still thought to be in part due to the plane's rudder reversing both right and left.[9][10][11]
• On April 11, 1994, a Continental Airlines pilot, Ray Miller, reported his aircraft rolled violently to the right and continued to pull to the right for another 18 minutes; the Boeing 737-300 landed safely. Continental removed the flight data recorder and rudder PCU from the incident aircraft and provided them to Boeing for investigation. Boeing concluded that the rudder had inadvertently moved due to an electrical malfunction, but only 2.5 degrees and for less than two minutes in total, a finding disputed by Miller.[9]
• On February 23, 1999, MetroJet Flight 2710, a 737-200, experienced a slow deflection of the rudder to its blowdown limit while flying at 33,000 feet above Salisbury, Maryland. While a rudder malfunction was suspected, the aircraft was an older 737 and its flight data recorder only recorded 11 flight parameters, compared to the hundreds of parameters recorded by newer aircraft. NTSB chairman Jim Hall said that the investigation was "hampered by the lack of basic aircraft data."[12][13] All 112 passengers and five crew members (117 total) survived the incident.
On December 19, 1997, SilkAir Flight 185 crashed in Indonesia, killing 104 people. Because the crash involved a Boeing 737-300 rolling and diving toward the ground at a steep angle,
____________________________________
737-200 in Colorado Springs in 1991
https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_commercial_aircraft#1991
March 3, 1991
https://en.wikipedia.org/wiki/Boeing_737_rudder_issues
Testing revealed that under certain circumstances, the PCU's dual servo valve could jam and deflect the rudder in the opposite direction of the pilots' input.[3]: 81–85 Thermal shock testing revealed that the uncommanded rudder movement could be replicated by injecting a cold PCU with hot hydraulic fluid. Thermal shock resulted in the servo's secondary slide becoming jammed against the servo housing, and that when the secondary slide was jammed the primary slide could move to a position that resulted in rudder movement opposite of the pilot's commands.[2]: 79 [3]: 294 The NTSB concluded that all three rudder incidents (United Flight 585, USAir Flight 427, and Eastwind Flight 517) were most likely due to the PCU secondary slide jamming and excessive travel of the primary slide, resulting in the rudder reversal.[3]: 294
As a result of the NTSB's findings, the Federal Aviation Administration ordered that the servo valves be replaced on all 737s by November 12, 2002.[8]
investigators considered the possibility of rudder hardover due to PCU servo malfunction.[14]
https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_commercial_aircraft#1994
https://en.wikipedia.org/wiki/Boeing_737_rudder_issues
On September 8, 1994, USAir Flight 427, a Boeing 737-300, crashed near Pittsburgh, Pennsylvania. While on approach to Pittsburgh International Airport, Flight 427 suddenly rolled to the left. Although the pilots were briefly able to roll right and level the plane, it rolled left a second time and the pilots were unable to recover.[3]: 4 The resulting crash killed all 132 people on board.[3]: 9
https://en.wikipedia.org/wiki/USAir_Flight_427
Thursday, September 8, 1994, the Boeing 737 flying this route crashed in Hopewell Township, Pennsylvania
Summary: Loss of control due to rudder hardover[1]
After the longest investigation in the history of the National Transportation Safety Board (NTSB), it was determined that the probable cause was that the aircraft's rudder malfunctioned and went hard over in a direction opposite to that commanded by the pilots, causing the plane to enter an aerodynamic stall from which the pilots were unable to recover. All 132 people on board were killed, making the crash the deadliest air disaster in Pennsylvania's history.
Several employees of the U.S. Department of Energy had tickets to take later flights, but used them to fly on Flight 427.
The NTSB remarked that no airline had ever trained a pilot to properly recover from the situation experienced by the Flight 427 pilots and that the pilots had just 10 seconds from the onset of the roll to troubleshoot before recovery of the aircraft was impossible.[11]: 153
Investigators later discovered that the recovered accident rudder power control unit was much more sensitive to bench tests than other new such units. The exact mechanism of the failure involved the servo valve, which remains dormant and cold for much of the flight at high altitude, seizing after being injected with hot hydraulic fluid that has been in continuous action throughout the plane. This specific condition occurred in fewer than 1% of the lab tests but explained the rudder malfunction that caused Flight 427 to crash. The jam left no trace of evidence after it occurred, and a Boeing engineer later found that a jam under this controlled condition could also lead to the slide moving in the opposite direction than that commanded. Boeing felt that the test results were unrealistic and inapplicable given the extremes under which the valve was tested.[13][11]
── The exact mechanism of the failure involved the servo valve, which remains dormant and cold for much of the flight at high altitude, seizing after being injected with hot hydraulic fluid that has been in continuous action throughout the plane.
── The jam left no trace of evidence after it occurred, and a Boeing engineer later found that a jam under this controlled condition could also lead to the slide moving in the opposite direction than that commanded.
The NTSB concluded that similar rudder problems had caused the previously mysterious March 3, 1991 crash of United Airlines Flight 585 and the June 9, 1996 incident involving Eastwind Airlines Flight 517, both Boeing 737s.[1]: 292–295 The final report also included detailed responses to Boeing's arguments about the causes of the three accidents.
However, the FAA changed its attitude after a special task force, the Engineering Test and Evaluation Board,[14] reported in July 2000 that it had detected 46 potential failures and jams in the 737 rudder system that could have catastrophic effects. In September 2000, the FAA announced that it wanted Boeing to redesign the rudder for all iterations of the 737, affecting more than 3,400 aircraft in the U.S. alone.[14]
Boeing agreed to redesign the rudder control system with a redundant backup and paid to retrofit the entire worldwide 737 fleet.[20] Following one of the NTSB's main recommendations, airlines were required to add four additional channels of information into flight data recorders in order to capture pilot rudder pedal commands, and the FAA set a deadline of August 2001 for airlines to comply.[21]
____________________________________
Peter Robinson, flying blind : the 737 max tragedy and the fall of boeing, 2021
p.39
two crashes
737-200 in Colorado Springs in 1991
737-300 near Pittsburgh in 1994
faulty rudder design
a single-paneled rudder
The crashes had been the result of a faulty rudder design.
[a single-paneled rudder design] lacked a device called a limiter, which made the plane more vulnerable to what's known as a hardover, an uncommanded deflection that appeared to happen only in extremely rare circumstances, such as when microscopic bits of grit got stuck in a valve.
p.181
In the wrangling over the Boeing rudder design blamed for two crashes back in the 1990s, litigation had eventually turned up a memo titled “We have a problem”, in which engineers acknowledged ── even before a second crash ── that a rudder valve had the potential to jam. Some pilots had seen the anguish it caused colleagues who were asked to explain themselves years later, and they became more careful about what they put in writing.
── “We have a problem”, in which engineers acknowledged that a rudder valve had the potential to jam.
(Flying blind : the 737 max tragedy and the fall of boeing / peter robinson.
new york : doubleday, 2021, bibliographical references and index., (ebook), (hardcover), (trade paperback), (ebook), boeing company──management.|boeing 737 (jet transport)──accidents.|aircraft industry──united states──management.|aircraft industry──united states──employees.|corporate culture., HD9711.U63 (ebook), 338.7/6291300973──dc23, 2021, )
____________________________________
• Rudder function
── single rudder panel and single rudder actuator
── rudder actuator
── The single rudder panel is controlled by a single hydraulic Power Control Unit (PCU).
── hydraulic Power Control Unit (PCU)
── Inside the PCU is a dual servo valve that, based on input from the pilot's rudder pedals or the aircraft's yaw damper system, directs the flow of hydraulic fluid in order to move the rudder.
── servo valve, rudder pedals, yaw damper system, hydraulic fluid
── designed by Boeing
── manufactured by Park Hannifin.
____________________________________
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