The hidden danger. Accident 1991.
The hidden danger. Accident 1991.

The hidden danger. Accident 1991.


            Morning. 3 March 1991 of the year. After a short 17 minute flight from Denver, the company's 585 flightUnited Airlines"Landing in Colorado Springs. It was a great day, but meteorologists reported that Colorado Springs expected strong turbulence and wind gusts. Commander Boeing 737 was 52 year old Harold Green. He was a pilot with 20 years of experience and impeccable reputation. All information about the series: The hidden danger. Accident 1991. read below ...


            At Colorado Springs Municipal Airport, an air traffic controller was preparing to take flight 585. Soon the aircraft pilots saw the airport. They received a go-ahead for landing and began to decline towards the 39 strip. As the speed decreases, the 585 flight becomes more sensitive to turbulence. Therefore, the co-pilot requested details of the landing of other aircraft. They were informed that due to wind gusts a short-term drop in speed was observed at an altitude of 150 meters.


            Decreasing, the pilots experienced some difficulties due to the strong wind. However, they coped with it. From the windows of the airport tower, the dispatcher watched the final stage of the landing approach of flight 585. The closer the airport was, the more it began to shake the plane. Suddenly, unexpectedly Boeing 737 began to go out of control. He began to spin and he went into an uncontrollable tailspin. The pilots could do nothing. The controller watched as the Boeing 737 crashed into the ground. Rescue services arrived at the crash site almost immediately, but almost nothing remained of the plane. A pile of wreckage from a 38-ton passenger plane was buried in a fire-blackened impact crater. 


Eyewitness: The plane did not slide and bouncing like a normal landing. He just hit his nose on the ground. That's all.


            No man survived. All 20 passengers and 5 crew members were killed by hitting the ground. Colorado Springs has become the site of one of the most mysterious plane crashes in history. Before nightfall, investigators from the National Transport Safety Committee (NTSB) arrived at the crash site. They had a very difficult investigation, because from the plane almost nothing was left.


Investigator: Police cordoned off the area. One of the doctors gave me a cup of tea. We were all shocked by what he saw.


shoal            The answer to the fate of the 585 flight lay fragmented in a deep hole. The fuselage of the strike formed by an accordion. Other parts of the aircraft were scattered around. Much damage was caused by fire. Everything happened in a relatively small area and many details were burned. It was certain that before the collision with the ground, the plane was intact. There was no explosion in the air. The investigators tried as best they could, but they still did not know that their investigation would be the longest in the history of aviation.


            The engine turbine, hydraulic pressure gauge, voice recorder in the cockpit were carefully removed from the accident site, photographed and sent to the laboratory for analysis. First, investigators began to investigate the "black boxes" of the aircraft. 70% of all air crashes happen because of pilot errors, and the investigators wanted to find out what the crew did before the accident.


Investigator: I immediately realized that this crew was one of the most exciting, with whom I had to deal with. By appointment only create a sense of a great crew, rarely makes a mistake. I thought it wiser to seek the cause of the crash in the mechanics of the aircraft.


            The more experts examined the 585 flight, the more suspicion fell on some kind of mechanical failure. The researchers suspected a malfunction steering wheel, which is located at the end of the tail of the aircraft.


Investigator: We focused on what could cause a reversal of the aircraft.


            The study of the rudder very difficult damage. Fortunately, the control unit survived. This unit is constantly used in flight. It performs functions similar to the steering amplifier in the car. When the pilot presses the pedal, the track guidance systems deliver hydraulic fluid to the control unit. It turns the pilot's movements into pressure, which is necessary for the movement of the rudder Boeing 737. The heart of the control unit is a valve with two hydraulic boosters. It is shaped like a soda can. It has two moving mechanisms that slide past each other, directing the flow of compressed hydraulic fluid that drives the steering wheel.


Expert: This valve is very unique. In essence, this two valves in one. He has a complex structure.


            When the technician opened the control unit, he found metal fragments floating in the hydraulic fluid. It was an alarming discovery. These particles could cause valve sticking. In such a case, rudder steering would be impossible. Yet the experts were not in a hurry with the conclusions.


Investigator: The aircraft crashed and burned. It was severely damaged control devices that we have tested. The badly damaged item, the harder we were to conclude that it is working.


            The control unit was sent to the laboratory of the manufacturer. There the interference version due to strange pieces of metal was rejected. The investigators were told that the filter does not allow them into the sensitive valve, which directs the fluid and drives the steering wheel. Investigators could no longer detect anything that would explain the strange movement of the rudder.


Investigator: We have had no clear information as to say that the crash was to blame for the faulty control unit.


            The investigation has reached a dead end. But there was one more suspect - bad weather conditions. Meteorological experts tried to establish whether strong wind was a factor that contributed to the accident. They listened to eyewitness testimony that on the day of the crash, strange weather was observed in the mountains. The moment Flight 585 landed, one man's car was nearly blown off the road by a strong gust of wind. But over time it became clear that the downdrafts could not shoot down the plane and put it into a tailspin.


            21 has passed a month since the start of the investigation. Investigators studied all the evidence available to them, but were left with nothing. Only the fourth time in its history, NTSB issued a report before reaching conclusions. The reason for the crash of Flight 585 has not been established.


            After 2, after the publication of the report, another accident happened. On a clear, windless day, the American 427 flight approached Pittsburgh. Captain Peter Germano and co-pilot Chuck Emmett were preparing for the approach. Approaching the airport, the pilots watched another flight that flew 10 kilometers above them. No signs of trouble. However, after passing through the turbulent zone formed after another plane, the Boeing 737 suddenly and dangerously began to turn left. No action of the pilots helped. He also, having entered a corkscrew, crashed into the ground. Although the rescuers arrived quickly, there was no hope for the 132 passengers.


            When experts from the NTSB arrived at the crash site, they realized that the search for clues would be long and exhausting. Soon, thanks to eyewitness accounts and data from the black boxes, investigators began to realize that there were striking similarities between the 427 case and the 585 flight. In essence, they were a mirror image of each other. On approach, the 585 flight turned right, and “US Air»427 - left. Both crews were caught by surprise, and after a few seconds both aircraft dived into the ground.


Investigators: We all know about the accident in Colorado Springs. We tried not to get hung up, and re-examine the situation.


            The work of the investigators continued, and the list of similar elements grew. The flight 427 engines also worked properly. But there was one significant difference. When the 427 flight approached Pittsburgh, there was complete calm.


Judge: After examining the flight data recorder, it became clear that the evening was quite calm. There was no turbulence. Pilots were calm and spoke about the landing.


            As with the 585 flight, the investigators focused on the mechanical causes of the crash. Almost immediately, they made an encouraging discovery. Miraculously, most of the aircraft’s tail and rudder have survived. The hydraulic devices inside the tail are also well preserved. These details were immediately sent for examination, because the pressure on the NTSB from the public was increasing. In both accidents, the Boeing 737 plane crashed. In this regard, the question of their safety was raised.


Investigator: As the chief investigator, I have never allowed the thought that this investigation remains unresolved. We went ahead and tried until we had to learn.


            Investigators studied all versions, but the main suspect remained a hydraulic ventilator - part of the aircraft control unit. As last time, experts found that there were metal particles in the hydraulic fluid. However, research has shown that they did not affect the performance of the system.


Expert: This unit has passed all performance tests. There was no indication of his failure. He worked on the set parameters, as it should.


            Investigators returned to the study of the actions of the pilots. They knew that the rudder had completely turned in one direction. Also, the investigators saw that the co-pilot, who was piloting the plane at the time of the accident, actually pressed the steering pedal strongly and held it. It was very unusual.


Investigator: I thought about it, because I'm a pilot myself. It was not like a rational behavior.


Accident 1991


            Also, the flight data recorder data showed that problems with the 427 flight started at the moment of passing through the associated air flow. The recorder even recorded a dull thumping sound of flow turbulence when the 427 flight flew through that zone. These data showed that something happened that caught the pilots by surprise. They reacted very quickly, but it turned out that nothing helped.


            It's been almost 2 years since the crash, and the investigation has stalled. The fall of both aircraft was strikingly the same, but the investigators did not know the reason.


Investigator: We started to give up. Months began to grow in the years to come. Boeing 737 - excellent aircraft. We can not find a flaw in it. It does not go out of our heads.


            9 June 1996, the long awaited clearance finally appeared. Another Boeing 737 landed in Richmond, Virginia. Suddenly, the plane began to spin right.


Captain: We realized that we had some problems with the rudder. I turned the control knob in the opposite direction and push the pedal, but it did not budge.


            For more than 30 seconds, the plane flew dangerously tilting to the right. The pilots did everything possible to prevent the aircraft from turning over. Then just as suddenly, the mysterious force that held the plane released him, returning the wings to a horizontal position. No sooner had the pilots and passengers recovered, as the plane turned on its side again. 30 seconds Boeing 737 lived his life. Then he leveled off.


Captain: After the second time I looked at the co-pilot and said, 'Declare a state of emergency. Tell the dispatcher that we have a problem. "


            Fortunately, the third turn did not happen and the plane was able to land safely.


Captain: When I zarulivaet plane, then felt my legs shaking. I took a speaker to explain to the passengers what had happened. But I realized that he knew nothing. I just could not find the words.


            The next day, a team of investigators arrived in Richmond. Finally, they had access to a Boeing 737 with a rudder defect that survived. The crew also survived and they could tell a lot. It immediately became clear that an incident with an 517 board is very similar to the two previous cases. The pilots told investigators that the steering pedal had jammed and they could not move it. The control unit is removed, examined and checked again and again. To everyone's disappointment, he functioned perfectly. Even with a whole plane and live pilots, the investigators could not solve the case.


            Soon, the experts decided to put more pressure on what they already researched. They have been subjected to temperature shock control unit. Superheated hydraulic fluid was applied to the cold block.


Expert: We stood and watched the blocks move the steering wheel right and left. Suddenly he stopped. It just stuck. Completely ceased to function.


            Investigators experimentally proved that the valve is controlled rudder could get stuck. It was an ominous discovery, as the Boeing 737 was the most popular passenger aircraft. However, another discovery awaited them.


Investigator: The most important discovery happened when a mechanic Boeing, studying the results of the test data set, which indicated that the gate reverses direction.


            It became clear that the valve could not only get stuck, but also work in the opposite direction. This meant that every time the pilot tried to correct the inversion, the pilot only aggravated the situation. The pilots were faced with a very unusual situation and did not understand what was happening.


            After the investigation, extensive changes were made in the aircraft to enhance the safety of the Boeing 737 and the entire aviation industry. New training protocols have also been developed to teach pilots how to respond in case of unusual situations in flight. The double hydraulic valve was redesigned to eliminate the possibility of malfunction. And Boeing spent hundreds of millions of dollars to replace valves in thousands of aircraft around the world. After their replacement, similar incidents no longer happened.


            It took 10 years for investigators to uncover this complex matter. 


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