About planes, defense, statistics and unconventional thinking

Avraham Wald discovered a phenomenon called "survivorship bias". He knew that when examining the reasons why people, animals, plants, machines or any other population survived certain events or processes, if only those who survived and not those who perished are examined. This will lead to the reasons for non-survival not being taken into account"

Lieutenant-Colonel Kim Nicole Campbell, seen in the attached photos next to her plane, is an A-10 Thunderbolt pilot in the US Air Force. In April 2003, during the war against Saddam Hussein's army in Iraq, Campbell (then a captain) and another A-10 pilot were sent on a close assistance mission to US Army ground forces near Baghdad.
After they made a sniping flight and began to soar to circle the target area to assess the vulnerability, her plane was hit by a strong explosion, apparently from an air-to-ground missile or a shell fired from an anti-aircraft gun.

Campbell immediately felt that control of the steering systems was lost, and the plane began to dive; She estimated that the hydraulic steering system had stopped functioning, and activated the bypass switch for the mechanical steering system, which operates through cables and rods connected to the stick and pedals. To her delight, the system responded and the plane was back under control. Although A-10 pilots had only tried to land using the manual system three times before, of which two attempts ended in a crash, one of them in a fatal accident, Campbell decided to try to land the plane at the American Air Force base in Kuwait. According to her, the plane was difficult to steer, but controlled nonetheless. She managed to land the plane safely, and when she got out of it she was amazed to see hundreds of punctures and holes caused by the fragments of the exploded missile. She herself was not hurt, and a day later she went on another mission. For landing the damaged plane, she received the Distinguished Flying Cross of the Air Force.
However, the story that led to the high survivability of the A-10 began about 60 years earlier, in the early 40s.

After the US entered World War II, in the middle of 1942, American Air Force bombers began to carry out attacks on German soil; Shortly thereafter, the American and British Air Force Command decided to add protection to bombers and attack aircraft. Since the ability to protect the planes with steel plates was limited due to the weight the plane could carry, it was decided to protect the most vulnerable areas of each plane, in a way that would best contribute to their survivability.

Ground crews at UK airports were required to inspect aircraft returning from bombing missions and assisting the ground forces, and to map the areas that had received the most hits. They counted the amount of bullets and shrapnel that hit each area of ​​the planes that returned, and found that most of the hits were in the wings and body, and a small number in the cockpit and engines. The obvious and logical conclusion in the eyes of all those involved was, of course, to protect the areas where the greatest amount of vulnerability was counted. Fortunately (as it turned out later), one person thought otherwise.

Avraham Wald (1902-1950), who was born this week 112 years ago, was a Jewish mathematician, born in Hungary. During the 20s and early 30s, he acquired his education at the university in his hometown of Cluj (now in Romania) and later at the University of Vienna, where he received his doctorate in mathematics. He specialized in the use of mathematics in economics, advanced geometry and statistical research methods, and published dozens of articles describing his research. With the annexation of Austria by Nazi Germany in 1938 and the increased persecution of the Jews, he left with his family for the USA. Fortunately for him, due to the reputation he acquired due to his work, he had an open invitation from the Coles Research Institute for Economic Research in the USA, and thus he could get an immigration visa to the USA. He was accepted to the faculty of Columbia University in New York as a lecturer and researcher, and joined a team called the "Statistical Research Group".

With the USA's entry into World War II, the team began to assist the US Army in various studies. At the beginning of 1943, Wald was asked to summarize the collection of data and reports made on the topic of attack statistics and bombers and to submit recommendations for implementation by the aircraft manufacturers.
Wald didn't know much about fighter planes, bombers, dogfights and anti-aircraft fire; But he did know well, from statistical studies he conducted in the past, a phenomenon called "survivorship bias". He knew that when examining the reasons why people, animals, plants, machines or any other population survived certain events or processes, if only those who survived and not those who were lost are examined, it would lead to the reasons for not surviving being counted. He immediately realized that planes that were damaged in the cockpit area and in the engines were not taken into account in the statistics that were made, simply because they did not return from the mission. As a result, he recommended to the Air Force exactly the opposite of what others recommended - to protect the cockpit and engine areas, contrary to many other opinions.
It is not obvious that Wald convinced the senior officials of the Air Force and the US Department of Defense with his claim; He was not a military man, nor an expert in the field of aviation or armaments, nor an American citizen, but a Jewish immigrant who lived in the USA for only a few years, at a time when immigrants were not particularly welcome there (Jewish-Hungarian physicist Leo Szilard, who wanted to warn the American government about The Germans intended to develop an atomic bomb about three years earlier, he was reluctant to do it alone for similar reasons, and enlisted his famous friend and media favorite Albert Einstein to help him. But Wald's ability to explain to the Air Force officers the error in their premise proved him right, and the development requirements given to all aircraft manufacturers were updated accordingly.
One of the planners who strictly applied Wald's recommendation was Alexander Kartovli (1896 - 1974), the chief engineer of the airplane manufacturer "Republic". Kartavli was also an immigrant, born in Georgia (then in the territory of Tsarist Russia) who left for France after World War I, where he studied aeronautical engineering, and began his career as a test pilot; After an accident and an injury he had to retire from this position, he worked for a short time as an engineer at the Bellario company in France and then immigrated to the USA, and in 1931 he joined the Seversky Aircraft Corporation as chief engineer. A few years later the company changed its name to "Republic Aircraft Corporation".
Kartavli received the updated protection requirements at a time when he was in the final stages of development of the P-47 Thunderbolt aircraft, which was intended to be a combat aircraft and close assistance to the ground forces. During the war, the P-47 was the largest and heaviest fighter plane powered by a single Pratt & Whitney R2800 engine; It was equipped with eight 0.5 machine guns, and could carry bombs or rockets weighing more than a ton, at a range of about half that of the B-17 bomber. In accordance with the protection requirements, his cockpit was surrounded by a steel "bathtub" and the engines were also protected accordingly. More than 15,000 such planes were produced, and the P-47 acquired a name for itself as a particularly resistant plane, one that could withstand many hits and bring the pilot back safely, while accompanying bombers and helping the ground forces closely.

After the war, Kartavli continued to develop other aircraft, the most well-known of which are the F-84 Thunderjet/streak (which had two incarnations, as a straight-wing aircraft and a swept-wing aircraft, and was the first jet fighter aircraft capable of refueling in the air) and the F-105 Thunderchief bomber. In 1960, he began to design the A-10, according to the Air Force's requirement for a close support aircraft for ground forces and anti-armor warfare. Based on his experience from the development and service of the P-47, and since the A-10 is required to perform a similar mission, Kartavli protects it similarly to the P-47: a cockpit surrounded by titanium walls, engine housing envelopes are protected and in addition a manual backup system for the hydraulic steering system, At a time when it seemed that hydraulic steering systems would be the only ones in use, due to their much greater convenience in operation. About 700 aircraft of this model were produced, took part in the two wars in Iraq and are still in use today.

Some argue that Kartavli's work was downplayed over the years (especially during the Cold War years), compared to that of his colleagues from other companies, because the US was not comfortable admitting that one of its most important aircraft designers was born in the Soviet Union of that time, and we may even be suspected of dual loyalty. However, his work methods spoke in his favor, and today he is considered one of the pioneers in the field of aeronautical planning.

Avraham Vald and Alexander Kartovli, who were both unconventional in their way of thinking, contributed greatly to the victory of the Allies in World War II and to saving the lives of many pilots and aircrews to this day, each in his own special way.

• About the life and work of Avraham Vald
• A site dedicated to Alexander Kartovli, and films and photos of the planes he designed
• About Kim Nicole Campbell's flight and story in April 2003