This is Opacity Zero, a show about challenging the unknown with curiosity. I am Melanie Heymans, welcome back to episode three – Errare Humanum Est.
This stall warning sounded 75 times before Air France Flight 447 crashed into the Atlantic Ocean killing all 216 passengers and 12 crew members in the early hours of June 1st 2009.
Air France Flight 447 was a scheduled international passenger flight from Rio de Janeiro to Paris, which crashed almost 4 hours after takeoff due to an aerodynamic stall. Simply put an aerodynamic stall happens when a plane doesn’t have enough forward speed for the wings to generate sufficient lift to keep the aircraft airborne leading to a quick, sometimes uncontrolled, descend.
For a wing to create lift it needs a certain speed and a certain angle of attack, that’s the angle between the wing and the air flowing towards it. The flight crew can change the angle of attack by pointing the nose of the aircraft up or down. Each aircraft has a critical angle of attack which describes the angle for maximum lift – for most aircraft this angle lies at around 15 – 20 degrees. Above the critical angle of attack it gets increasingly hard for the wings to create lift and the airplane starts to stall.
If you have ever held your hand out of the window of a driving car you have already played with this phenomenon. If you keep your hand parallel to the ground the air presses hard against the side of it and you need quite some strength to keep it that way. As soon as you tilt your hand a bit upwards and change the angle of attack, the airflow lifts your hand up. Now if you tilt it too much, beyond the critical angle of attack, you lose the lift and your hand is pushed back and down by the airflow and by gravity.
In a very simplified way that’s what happened to Air France Flight 447 – but what or better who put the aircraft in a stall?
On the night of May 31st 2009 three experienced pilots were at the controls of the Airbus A330 on its journey from Rio to Paris. About 3 and half hours into the flight the captain, in a standard procedure, handed over control to one of the two co-pilots, and went to take a nap. Shortly after the aircraft flew through some turbulence and the plane’s pitot tubes, which determine air speed, iced-over. In another standard procedure, the aircraft turned off the autopilot, due to the missing speed information, and handed control over to the pilots. As the pilot in charge took over he abruptly and unnecessarily raised the nose of the aircraft, increasing it’s angle of attack, and leading it into a climb to its maximum altitude of 38000 feet. As the pilot continued to raise the nose of the aircraft the angle of attack increased rapidly towards 30 degrees, causing the wings to lose lift and the aircraft to stall. Despite all persistent and quite clear symptoms over the next few minutes, the crew never understood that they were in a stall situation and never undertook any recovery maneuvers, which lead to the crash of a perfectly flyable aircraft and the death of 228 people on board.
Air France Flight 447 is a very tragic but by far not the only incident of a plane crash caused by human error. More than 50% of all aviation accidents are caused directly or indirectly by a human being.
Could human error have caused the disappearance of MH370?
Let’s start out by defining what human error means:
Human error describes any actions or the lack thereof that fail to physically or mentally recognize, change, prevent or mitigate a certain situation. While previous definitions called this type of error “pilot error” the term has been changed to “human error” to more realistically reflect that anybody who acts in a support capacity of a flight may contribute to the error chain, not just the pilots. Still for the scope of this Podcast we will mainly focus on human error within the cockpit.
According to the “Human Factors Analysis and Classification System”, which is used by official aviation and transportation organizations, human errors can be divided into four different levels:
- Organizational Influences
- Unsafe Supervision
- Preconditions for Unsafe Acts, and
- Unsafe Acts, further broken down into
- errors, and
While all four of these categories are dependent on each other and all of them are important, we are going focus on the last category, unsafe acts.
As mentioned before, unsafe acts are broken down into two categories:
- Errors, which describe mental or physical activities of a person that fail to achieve their intended outcome and are divided into three sub-categories:
- Decision Errors
- Skill-based errors, and
- Perceptual errors
- The second category of unsafe acts are violations
According to a long-term analysis of the Federal Aviation Administration, 79.2% of all aviation accidents due to human error are caused by skill-based errors, 29.7% by decision errors, 13.7 by violations and 5.7% by perceptual errors. You might have already thought to yourself, wait these numbers add up to more than 100%, and you are absolutely right. The reason for that is that many accidents are associated with multiple error categories, still nearly 61% of all accidents caused by human error begin with a skill-based error, about 19% with a decision error, 8 with a violation and 4% with a perceptual error.
Let’s take a look at these individual categories and explore how likely they are to have caused the disappearance of MH370.
Let’s start out with our biggest category, skill-based errors, which describe errors in basic flight skills that occur without much thought.
- If we are only looking at fatal aviation accidents the most common type of skill-based error to happen is “improper maintenance of airspeed”.
A quite tragic example of this type of skill based error is Asiana Airlines Flight 214, a scheduled transpacific passenger flight from Seoul to San Francisco, that crashed on final approach with 307 passengers and crew on board, due to inadequate monitoring of airspeed by the flight crew. During the already mismanaged initial approach the captain of Asiana Airlines Flight 214 selected an inappropriate autopilot mode which deactivated the automatic airspeed control. As a result the airspeed of the aircraft decreased, unnoticed by the flight crew, and the plane descended below its desired glide path. By the time the crew realized that they were flying too slow and too low it was already too late and the aircraft struck the seawall and crashed short of runway 28L at San Francisco International Airport.
- The second, most frequent, type of skill-based errors – again that’s errors in basic flight skills that occur without much thought – is “improper control or handling of the aircraft on the ground or in the air“.
American Airlines Flight 587, a scheduled passenger flight from New York City to Santo Domingo crashed into Queens shortly after take-off on November 12th 2001, killing all 260 people on board and 5 people on the ground, due to improper handling of the aircraft by the first officer. On the morning of November 12th 2001, American Airlines Flight 587, took-off runway 31L at John F. Kennedy International Airport in NYC, shortly after a Japan Airlines Boeing 747. About a minute after takeoff American Airlines Flight 587 encountered wake turbulences from the Boeing 747 in front of it. The first officer of Flight 587 attempted to stabilize the aircraft with continuous unnecessary and excessive rudder movements which stressed and eventually snapped off the aircraft’s vertical stabilizer – remember that’s the shark fin on the tail of a plane – causing the aircraft to lose control and crash. If the first officer would have stopped making additional inputs, the aircraft would have stabilized by itself and this horrible accident would have never happened.
- The third most common type of skill-based human errors is “the occurrence of a stall or a spin” like it happened in the case of Air France Flight 447.
The flight crew made inappropriate control inputs, destabilized the plane, failed to follow appropriate procedure and to recognize that the aircraft had stalled, and consequently did not make any inputs that would have made it possible to recover from the stall. To err is human and in this and many other cases skill-based human error paid the ultimate price, human life.
Did the flight crew of MH370 make a flight skill mistake? Was it a skill-based error that made the Boeing 777 and its 239 passengers on board disappear without a trace? Unlikely. Neither improper maintenance of airspeed, nor improper handling of the aircraft or a failed recovery from a stall make a lot of sense in the case of MH370. The simple fact that the aircraft diverted and vanished hundreds of miles from its actual flight path without ever establishing any contact with air traffic control basically rules out any scenario like the ones we just heard about. Even a skill-based error that might have incapacitated the passengers and crew doesn’t explain the huge diversion and the manual turns hours into the silent flight of MH370.
Let’s look on and explore our second category of human errors, decision errors.
Decision errors are defined as errors that represent conscious, goal-intended behavior that proves inadequate or inappropriate for the situation.
- The most frequent error type in this category is, “in-flight planning“, which refers to decision making or plan revisions performed after the aircraft has taken off.
A tragic example of this type of decision error is Thai Airways International Flight 261, a scheduled passenger flight from Bangkok to Surat Thani. Flight 261 crashed on its third attempt to land killing 101 of the 146 people on board. According to the official investigation the accident occurred due to the pilot’s attempt to approach the airport in lower than minimum visibility with rain. In addition to that the pilots suffered from the accumulation of stress, the final approach being their third attempt, and may have experienced spatial disorientation.
- The second most frequent type of decision errors is “planning or decision making on the ground“.
The deadliest accident in aviation history, the Tenerife airport disaster, is a tragic example of that type of human error.The Tenerife airport disaster was a fatal runway collision between KLM Flight 4805 and Pan Am Flight 1736 at Los Rodeos Airport in Tenerife on March 27th, 1977, killing 583 people.
For both flights, Tenerife was an unscheduled stop due to a bomb explosion at Gran Canaria Airport, their actual destination. Los Rodeos, a regional airport, had only one runway and struggled accommodating the extra traffic that was diverted to it due to the explosion. As Gran Canaria Airport reopened later that day, both flights, KLM 4805 and Pan Am 1736 got ready for takeoff. Soon after the KLM was cleared to taxi down the runway, make a 180 degree turn and get into takeoff position. A few moments later the Pan Am was instructed to follow the KLM down the same runway but to exit about halfway and use the parallel taxiway.
While the Pan Am made its way down the runway, the flight crew of the KLM misinterpreted several communications with Air Traffic Control as clearance to takeoff and started its takeoff roll down the runway. At the same time Pan Am’s Crew informed Air Traffic Control that they were still taxiing down the runway – due to dense fog, neither the crews nor the control tower were able to see that the planes were heading towards each other.
As the tower instructed the Pan Am to report back when they cleared the runway the KLM flight engineer asked “Is he not clear, that Pan American?” The captain of the KLM replied “Oh, yes” and continued with the takeoff. By the time the two crews saw each other it was already too late to aboard the takeoff – and while the Pan Am crew took a sharp left turn in an attempt to avoid the collision, the pilots of the KLM prematurely lifted the nose of the aircraft trying to take off before hitting the Pan Am.
At this point the KLM was within 300 feet of the other aircraft and while its nose cleared the Pan Am, the engines, lower fuselage and main landing gear struck the upper right side of it at about 160 miles per hour. After remaining airborne for a few seconds the KLM crashed into the ground 500 feet past the collision, killing all passengers and crew on board.
- The third most frequent type of decision based errors relates to “fuel management” and generally describes situations of in-flight fuel starvation.
Hapag-Lloyd Flight 3378, an international passenger flight from Crete to Hannover, Germany with 143 passengers and 8 crew on board crash-landed in Vienna after running out of fuel on July 12th 2000.Shortly after takeoff in Crete the flight crew realized that they were not able to fully retract the landing gear. After several attempts they decided to leave the gear fully extended and continued their flight towards Germany. To account for the extra drag produced by the landing gear the flight crew recalculated the aircraft’s fuel consumption and decided to shorten the flight to Munich instead of flying to Hannover. Unfortunately the crew didn’t realize that their fuel calculations were incorrect until their fuel reserves dropped rapidly while they were still in Greek airspace. Instead of diverting to the nearest airport, which would have been 10 minutes away, the captain of Flight 3378 decided to fly on to Vienna. About 150 miles from Vienna the low fuel warning went off and the captain finally decided to declare an emergency. Both engines flamed out 14 miles from Vienna leading to a crash landing 2000 feet short of the runway.
Did MH370 vanish due to a decision error in-flight? Did someone on the ground make a wrong decision and sealed MH370s fate? Did MH370 run out of fuel? Yes, most likely someone in the cockpit of MH370 made a wrong decision, yes, someone on the ground might have sealed the fate of 239 people, including their own. And yes, MH370 most likely eventually crashed due to fuel starvation BUT no, most likely none of this happened due to human error.
Similar like with skill-based error, a scenario like in the cases we just heard about is highly unlikely. If MH370 would have simply run out of fuel on its way from Kuala Lumpur to Beijing the flight crew should have declared an emergency, attempt an emergency landing, or we should at least have found evidence of an accident along the planned flight path, and not evidence of hours of flight after it diverted. The same argumentation holds for any “honest” errors during flight or on the ground, so let’s look on.
The third and final error category is perceptual errors, which describe situations in which sensory input is degraded. This type of error often happens when flying at night, in weather, or in other visually impoverished situations.
Air China Flight 129, an international passenger flight from Beijing, China to Busan, South Korea crashed into a hill near Busan killing 129 of 166 people on board on April 15th 2002. After a routine 2 hour flight from Beijing the crew of Flight 129 received clearance to land in Busan in light rain and mist. The flight crew aborted its first approach due to low visibility, lost situational awareness and went below the minimum safe altitude while circling the runway and crashed into a hill.
Yes, MH370 was flying at night but as we talked about in episode two, the weather was good and visibility was high. If the flight crew would have lost situational awareness they wouldn’t have flown on for several hours not contacting anyone, also for perceptual errors the likelihood is very low, so let’s take a look at our last category of unsafe acts, violations.
Violations, which describe willful disregard for the rules and regulations of safe flight, are much less common than errors.
A deeply tragic example of an aviation accident caused by a violation is Aeroflot Flight 593, an international passenger flight from Moscow to Hong Kong that crashed into a hillside killing all 75 people on board. During the flight one of the pilots of Aeroflot 593 brought his children into the cockpit while he was on duty and against regulations allowed them to sit at the controls. While in the pilot’s seat one of the children switched off parts of the autopilot unnoticed. Shortly after the aircraft started banking right causing confusion in the cockpit and leading to a loss of control by the pilots. When the flight crew managed regain control the altitude of the plane was too low to recover and the aircraft crashed into the ground.
Now the question remains, did someone on board MH370 or on the ground willfully disregard the rules and regulations of safe flight? Yes, probably, did they do it by mistake? Probably not.
Acts of sabotage, next time on Opacity Zero.