The wreckage of a plane ended its exceptional 20-plus years of service last year.
On July 17, 1996, TWA flight TWA800 took off from JFK International Airport in New York. Soon, the bottom of the Boeing 747 bound for Paris suddenly exploded, and the wreckage was scattered on the sea off Long Island, New York, killing all 230 people on board.
To investigate the cause of the accident, investigators salvaged tens of thousands of pieces of the plane's wreckage from the sea and carefully pieced it together over the years to come to a conclusion.
The survey also became one of the longest, most complex and expensive in aviation history, taking more than four years and costing more than $40 million.
After an agreement was reached with the families of the victims, the wreckage was moved into a warehouse at the National Transportation Safety Board (NTSB) training center in Virginia.
By agreement, the wreckage will not be displayed, but only used for training, and has been studied by thousands of air crash investigators and transportation experts from around the world for more than 20 years.
Although the wreckage of the plane is not open to the public, the families of the victims can pay their respects at any time.
In the years following the crash, some people would come and leave mementos on their family's seats.
The wreck of TWA800 was finally decommissioned and destroyed as the lease for the nearly 3,000-square-meter warehouse expired.
"Advances in investigative techniques, such as 3D scanning and drone imagery, have reduced the importance of large-scale reconstruction of investigative techniques," the NTSB said in a statement.
"The investigation of almost every accident starts from restoring the scene. The investigation agency looks for black boxes, searches for all wreckage from the crash site, and finds all the physical evidence at the scene, all in order to restore the original appearance at the time of the accident." In an interview with China Youth Daily · In an interview with a reporter from China Youth Daily, Wang Yanan, the editor-in-chief of Aviation Knowledge magazine and an aviation expert at Beihang University, said that the investigation process of the air crash was both like archaeology and case-solving.
"Restore a plane from debris like an archaeologist"
At 8 p.m. local time on July 17, 1996, in the apron of JFK International Airport in New York, USA, TWA flight TWA800 took off one hour late.
The Boeing 747, carrying 212 passengers and 18 crew members, was hot in July and passengers in the cabin waited restlessly.
The flight was delayed because an unclaimed checked bag was loaded onto the plane.
Since the death of Air India Flight 182 in 1985 when a checked bag containing a bomb was put on a plane, airlines around the world have required that all luggage and passengers must be matched one-to-one before the plane can take off.
At 8:19 that night, the airport notified that the owner of the luggage had been found, which was a false alarm.
Flight TWA800 was finally cleared to take off.
Shortly after takeoff, during the climb, there was a sudden loud noise and white smoke from the bottom of the aircraft, the aircraft disintegrated, and a large amount of fuel ignited a raging fire on the sea.
After an overnight search, rescuers confirmed that all 230 people on board were killed.
The National Transportation Safety Board (NTSB) immediately established an air crash investigation team.
According to the relevant provisions of the "Convention on International Civil Aviation" and its annexes, the country where the air accident occurred is usually responsible for the investigation, and the country to which the aircraft operator, manufacturer and passenger belong can send representatives to participate in the investigation.
Wang Yanan, who is familiar with aviation history, introduced that air crash investigations are generally carried out in parallel from three aspects. On the one hand, it is to find the black box, because it is a reliable data basis. "Any evidence is not as direct and powerful as the black box." The investigation, the collection and arrangement of all the wreckage at the crash site and the basic restoration of the relative orientation of the aircraft, aims to "reproduce the state of the accident at the moment"; on the other hand, it is the peripheral investigation of the accident, such as the investigation of all personnel involved in the accident , to retrieve all relevant information, archives, etc.
On the seventh day after the wreckage was recovered, the marine search and rescue team found the black box of the aircraft. However, the black box data did not help the investigation. The conversation content of the cockpit call recorder was normal. After a loud noise, the recording stopped, and the flight data recorder also Nothing out of the ordinary.
Investigators examined all the wreckage, hoping to find signs that the plane had been bombed or hit by a missile, but there were no clues.
When the plane disintegrated in the air, the first part that fell off may be the source of the problem. Investigators found that the wreckage closest to the airport basically came from the central fuel tank, with obvious burn marks on it.
In the 1990s, the United States suffered a series of terrorist attacks. The FBI also launched a criminal investigation into the air crash. They said that trace amounts of explosive residues of unknown origin were found in the wreckage of the plane. They believed that this was an attack against the American people. Terrorist attacks.
Witnesses also said they saw objects with suspected missiles flying into the sky.
This puts the direction of the NTSB's investigation into question.
The NTSB decided that stitching together all the wreckage was probably the only direct way to prove that the plane wasn't blown up by a missile, but it was destined to be a long and hard job.
While splicing the wreckage of the plane, investigators are also looking for what caused the fuel tank to burst into flames. They need to prove that the plane's fuel is flammable and the force of the explosion can blow up the fuel tank, in addition to finding the spark that ignited the fuel tank.
Although the temperature at Kennedy Airport on the day of the incident did not reach the flammable temperature of the oil and gas mixture in the aircraft's fuel tank, investigators found through the aircraft's drawings that the air-conditioning system was just below the central fuel tank, and it would continue to heat itself during operation. Later, the air-conditioning system had been on for several hours in order to cool the passengers.
Investigators found a Boeing 747 of the same model and turned on the air conditioning hours earlier.
In the same field with the same temperature and the same fuel, the investigators also flew to the same altitude and found that the flammable temperature was exceeded by a full 16 degrees Celsius.
Another experiment showed that heated to the same temperature, the fuel tank would explode with more than double the strength of the fuel tank.
Where did the spark that ignited the fuel tank come from?
When the investigator repeatedly listened to the cockpit voice recorder, they found that someone in the conversation said, "Why is the fuel gauge of the No. 4 engine going crazy?" Then there were two short-lived sound loss in the recording, which the investigator believed must be certain. It's a short circuit in the plane's wiring.
The wiring of a Boeing 747 is 290 kilometers long, covering the entire fuselage. After careful investigation, investigators found that some of the wires' insulation was damaged and fell off.
In the wiring layout of the aircraft, the fuel indicator system has a large number of wires directly routed in the fuel tank.
On the other hand, the huge project of splicing the wreckage of the aircraft has also been completed, and the fuselage after splicing can not see any traces of being hit by missiles.
The final version of the investigative report was released on August 23, 2000. The NTSB believed that the crash of the airliner may have been caused by damage to the insulating rubber of multiple bundled wires in the aircraft, and high-voltage power was transmitted to the wires connected to the fuel level sensor in the fuel tank. The high-temperature fuel aerosol was ignited by sparks generated by high-voltage electricity and caused an explosion, which eventually led to the disintegration of the aircraft.
The FBI also agreed with the fuel tank explosion inference.
The report recommends inspections and repairs to the electronic circuits on all Boeing 747s, while also recommending major changes to the plane's design, including adding an extra layer of insulation between the air conditioning system and fuel tanks.
The FAA subsequently required that large aircraft need to add inert gas to the central fuel tank, and add thermal insulation materials between the central fuel tank and the air conditioning equipment to prevent the fuel from being heated.
"The more complete the structure of the aircraft is, the better it is for accident investigation, because the more complete the structure is, the more technical information before the impact can be preserved." Wang Yanan said, "Once the aircraft disintegrates into a large number of small fragments, it becomes very dangerous. It's difficult, and the investigation is like archaeology at this time."
"The archaeological team got a lot of fragments from the soil, and to put it together into a complete object, it may take decades to get results, because some fragments have been lost in the soil layer." Wang Yanan said, " The same is true for air crash investigations. It is conceivable that it is quite difficult to splicing out the original plane with a large number of fragments, and it is not just to complete the task by splicing the appearance, but also to use the aircraft restored from these debris fragments to find it. crux of the matter.”
"Black boxes are often conclusive evidence"
Wang Yanan introduced that after the air crash, the search, decoding and reading of the black box, the verification and extraction of the wreckage at the scene, including the remains of the plane and the victims, and the peripheral investigation will be carried out at the same time.
But data from the plane's black boxes is considered key evidence.
"Just like solving a case, there is some peripheral evidence and some key evidence, and these key evidence may be in the information in the black box." In many cases, the information in the black box may directly give important investigations direction, other work pressure can be significantly reduced.
The official name of the airliner's "black box" is "Flight Information Recording System".
They are responsible for receiving the information collected by various sensors in flight in time, and automatically convert them into corresponding digital signals for continuous recording.
In order to facilitate the search, the black box is painted with a striking orange-red and marked "Do Not Open", but in the early days of its use, because the data recorded is mainly used for aviation accident investigation, maintenance or flight test, it has It has a strong sense of mystery, so it is called "black box", and this name is still used today.
The International Civil Aviation Organization (ICAO) requires large commercial aircraft to carry two flight recorders: the flight data recorder (FDR) and the cockpit voice recorder (CVR).
The former records at least more than 1,000 flight parameters of the last 25 hours of operation, while the latter records flight crew communications and cockpit ambient sounds during the last 2 hours of operation.
While only recording sounds, the onboard voice recorder has the potential to contain critical information.
"Often, when the plane is in an abnormal situation, the pilot's conversation will include this information." Wang Yanan gave an example. For example, how is the state of the plane, is it abnormal compared to the previous state?
Or when some technical situation emerges, the pilots may give some operational instructions to each other.
For example, the captain will ask the first officer to operate some systems, and these conversations can reflect the pilot's operational intent, including a discussion of the technical state of the aircraft, and a record of the pilot's operational intent.
This background sound can also include audible system noises in the cabin, or alarms from important systems on the plane.
"These sounds help investigators to use their ears to feel the state of the cockpit in the last period before the accident." Wang Yanan explained, "For example, the black box of the 'Germanwings' back then, after listening to the cockpit call recorder, the investigator would Understand that the crash was definitely not caused by a technical problem, and a few key speeches revealed the root cause of the accident."
On March 24, 2015 local time, a Germanwings Airbus A320 aircraft numbered 4U9525 crashed in southern France.
The plane was flying from Barcelona, Spain to the western German city of Dusseldorf, carrying 144 passengers and six crew members.
The wreckage of the plane was scattered on the mountain, and it has completely disintegrated. No one survived at the scene.
Based on the analysis and research of the data and radio communication records in the two "black boxes" of the crashed passenger plane, the investigators pointed out that the crashed passenger plane had turned on the autopilot mode during the climb phase, and the captain left the pilot after the plane entered the cruise phase at an altitude of 11,600 meters. cabin.
After that, the co-pilot Lubitz, who was left alone in the cockpit, "deliberately" adjusted the cruising altitude of the aircraft from 11,600 meters above sea level to 30 meters above sea level, causing the plane to continue to descend until it crashed.
This was confirmed in an investigation report released by the French National Bureau of Investigation and Analysis of Civil Aviation Safety (BEA), which is responsible for investigating the crash of the Germanwings airliner.
The cabin call recorder showed that Lubitz repeatedly told Captain Sondheimer, "You can go to the toilet."
After Sondheimer replied, "You can take over the flight," there were the sounds of seats being pushed back and doors closing.
In the next 2 minutes, the plane descended more than 600 meters.
Air traffic controllers tried to contact the plane, but received no response, and the "descent rate" automatic alarm signal in the cabin sounded almost simultaneously.
Soon there was a loud thud, like someone trying to get into the cockpit.
Sondheimer yelled, "For God's sake, open the door," as passengers screamed.
Two minutes later, the sound of Sondheimer hitting the door with an axe was heard in the voice record, and the plane was only more than 2,000 meters above the ground.
About 90 seconds later, a new siren sounded from the plane: "Ground, pull up! Pull up!" Sondheimer shouted: "Open the damn door!"
Lubitz could be heard breathing for the last two minutes before the plane hit the mountain, but he didn't say a word.
The investigation revealed that Lubitz had suffered from depression but was later allowed to return to his pilot duties.
Just a few months before the crash, he suffered from insomnia and fears he was going blind.
But he did not report these matters to the airline as required.
Several European airlines have introduced new regulations for this. Since then, during the flight, there must be two crew members in the cockpit of the passenger plane at the same time to prevent unforeseen events.
If one of the pilots needed to use the toilet, a flight attendant temporarily entered the cockpit instead.
The black box is crucial to solving the mystery of the air disaster, so it is also one of the strongest parts on the plane.
Its storage unit can withstand high-speed impacts of more than 400 km/h, and can also withstand high temperatures of 1,000 degrees Celsius for more than 1 hour.
In many air accidents, the fuselage has long been broken into pieces, but the black box is still intact.
"Like MH370, if neither the black box nor the wreckage can be found, we can only rely on external investigations. The possibility of obtaining key clues is too low, and it has become an unsolved case without a convincing investigation report." Wang Yanan Say.
In October 2018, a Boeing 737 MAX aircraft of Indonesia's Lion Air flew from Jakarta to Pangkapang Port and plunged into the sea within 13 minutes of takeoff, killing 189 people.
The black box on the plane was finally salvaged from the Java Sea by the Indonesian Navy.
The flight data recorder recorded the source of the accident - a newly installed Maneuvering Characteristics Augmentation (MCAS) system on the aircraft.
This is a system that automatically adjusts the aircraft's inclination. An angle-of-attack sensor of the aircraft makes the flight control system think that the aircraft's elevation angle is too large, and the horizontal tail is continuously lowered to lower the nose. Automatically repeats lowering the machine head.
The pilot pulled the stick 26 times, but ultimately failed to save the plane.
Half a year later, in March 2019, the same type and the same tragic incident also befallen an Ethiopian Airlines plane, which crashed about six minutes after takeoff, killing 157 people on board.
EgyptAir's cabin voice recorder showed the desperate pilot shouting, "Pull up! Pull up!" in the final moments before the crash.
After the incident, the aircraft was grounded worldwide, and the investigation that lasted for many years finally determined that a major defect in the trim system caused the air crash.
"Some technical glitches that weren't fatal, were not handled effectively enough, and the situation worsened."
Sometimes, the foreshadowing of an air disaster is buried in the ground.
On August 14, 2005, the pilots of the Greek Air Force were tasked with flying a fighter jet to track a civil airliner.
According to the report, after entering the flight information region of Athens, the capital of Greece, the passenger plane never communicated with air traffic control and circled over Athens without any response.
The Air Force pilot flew the fighter jet to the vicinity of the passenger plane and saw that in the cockpit of the passenger plane, the co-pilot seemed to be sleeping with his head down, and the captain's seat was empty.
In the cabin, all passengers wore oxygen masks and leaned back in their seats with their eyes closed.
The people on the entire plane seemed to be sleeping, and the plane was later dubbed the "ghost flight".
Soon after, the Boeing 737-300, carrying 115 passengers and six crew members, began a steep descent and eventually crashed in the mountains northeast of Athens after running out of fuel, with no survivors.
The autopsy reports of the passengers confirmed that all passengers died not from inhalation of toxic substances or explosions, but from impacts.
Air crash investigators found that engineers had used the plane's backup power equipment to manually pressurize the cabin before the accident to determine whether there was a leak in the door.
During the inspection, engineers changed the P-5 booster plate responsible for boosting to "manual mode" in order not to use the aircraft's engine and to use the backup power booster.
The P-5 booster panel found in the wreckage showed that the plane was still in "manual mode" when it crashed.
When the plane climbed to an altitude of 5,000 meters, the cabin began to lose pressure, the cabin oxygen mask fell off, and the system issued an alarm.
In the cabin, passengers put on oxygen masks in panic, while in the cockpit, the captain and co-pilot were unconscious due to lack of oxygen.
In autopilot mode, the aircraft climbed to an altitude of 10,000 meters and started level flight.
The oxygen masks, which passengers depend on for a living, are only enough for 12 minutes.
Four months later, the accident investigation team took the same type of Boeing 737 aircraft of Greek Olympic Airlines and conducted a test with the same flight time and flight route of Helios 522 flight four months ago.
Shortly after takeoff, investigators asked the captain to change the P-5 pressurizer to "manual mode," and it didn't take long for an alarm bell to sound in the cockpit as the plane climbed.
When the aircraft climbed to an altitude of 5,000 meters, the main warning light came on.
At this point, the investigators in the cabin began to feel the symptoms of hypoxia: the eardrums swelled, the dizziness, almost like drinking, the thinking began to blur.
Similarly, the windshield falling off accident on British Airways Flight 5390 in 1990 started when the aircraft was overhauled. The on-duty maintenance technician did not refer to the aircraft overhaul manual and the recommendations of the warehouse management, and chose screws smaller than the original by the naked eye in the dark. 1/200 of the screw.
Fortunately, after the captain was sucked out of the cabin, the co-pilot made a successful forced landing.
According to statistics, most air crashes occur in the take-off and landing phases, and the 3 minutes of the take-off phase and the 7 minutes of the landing phase are even collectively referred to as the "black 10 minutes".
Wang Yanan explained that because the speed and altitude of the aircraft changed greatly at this time, the movement of the atmosphere was also the most violent when crossing the troposphere.
During take-off and landing, the configuration of the aircraft itself is also undergoing great changes, and the throttle of the engine and the attitude of the flaperons are changing, so the possibility of problems with the aircraft at this stage is high.
He roughly divided flight accidents into several categories, one is technical failure, and the other is human-caused.
The latter are often operational reasons or various human factors, and there are other external reasons caused by environmental changes such as weather.
These factors are also intertwined.
He analyzed: "Generally speaking, technical failures and human problems generally account for the vast majority, and the two often occur at the same time. Often a technical failure occurs first. This technical failure is not fatal, but the pilot's The disposal was not effective enough or not timely enough and not accurate enough at the time, which caused the state of the aircraft to deteriorate rapidly and eventually turned into a very bad situation.”
The most typical case is the accident of Air France flight AF447 disappearing over the Atlantic Ocean in June 2009.
After a two-year search and salvage costing nearly 30 million euros, the plane's black box was recovered in May 2011.
By restoring the cockpit voice recorder data in the black box, investigators learned what happened to flight AF447 some time before its disappearance.
The report shows that before the crash, the plane may have encountered a large ice crystal cloud over the Atlantic Ocean. At high altitude and low temperature, the ice crystal blocked the pitot tube and made it malfunction, resulting in the inability to read the speed data. sounded.
At this time, the captain was resting in the rest cabin, and the co-pilot Bonan instinctively pulled up the joystick and pulled up the nose, but the wings lost aerodynamic force and the fuselage dropped rapidly; another co-pilot Robert realized that the plane was in the In the stalled state, the "recovery" process was performed and the joystick was pushed down, but since the two did not cooperate and fought each other, the two diametrically opposed operations canceled each other out.
When the captain returned to the cockpit, the passenger plane was out of control, and the three were unable to return to the sky. The plane "shot" horizontally into the Atlantic Ocean, killing all 238 people on board.
In Wang Yanan's view, the investigation of an air crash is not only to find out how the accident occurred, but also to check whether the same situation will occur on other aircraft to prevent the same accident.
As the documentary "Havoc in the Sky" elaborates: "It's not difficult to do any investigation and point the finger at a person, but we have to find out why the accident happened and how to prevent it from happening again."
(Partial source documentary "Aerial Cataclysm")
China Youth Daily, China Youth Daily reporter Liu Yan Source: China Youth Daily