United Air Lines Boeing 247 bearing tail number NC13304 exploded midair while flying over Chesterton, Indiana. The flight — designated Trip 23 — had departed Newark, New Jersey, stopped in Cleveland, and was en route to Chicago, then onward toward Oakland, California. On board were three crew members and four passengers; none survived. Investigators concluded that the plane’s tail section had been blasted off by a nitroglycerin-based explosive device placed in the baggage compartment. The crash and explosion marked the first proven case of sabotage of a commercial aircraft in U.S. history.
Eyewitnesses on the ground reported hearing a powerful explosion shortly after 9:00 p.m. and seeing the plane aflame at an altitude near 1,000 feet. After the crash, a second explosion occurred. The wreckage lay across a wooded farm in Jackson Township about five miles southeast of Chesterton, adjacent to a gravel road on the Smiley farm. The tail section was found at some distance from the main wreckage. Forensic examination revealed outward bending and tearing of the fuselage edges near the tail, consistent with an internal blast. Investigators ruled out mechanical failure, fuel vapor ignition, or structural flutter. The Bureau of Investigation (precursor to the FBI) led a sweeping inquiry, involving agents such as Melvin Purvis, interviewing hundreds of people along the route from New York to California. Despite intensive efforts, no suspect was charged.
That crash carried profound historical significance. In the early 1930s, commercial aviation was still in a formative stage. The Boeing 247 itself was among the earliest modern airliners, with all-metal semi-monocoque construction, retractable landing gear, and the ability to carry ten passengers. It represented the direction of aviation toward speed, comfort, and technical sophistication. The bombing of NC13304 exposed vulnerabilities in commercial flight security before regulatory systems had matured.
The event forced aviation authorities, carriers, and government agencies to confront the possibility of deliberate attacks on civilian aircraft. Though aviation regulation primarily addressed mechanical safety and navigation until then, the Chesterton explosion demanded the incorporation of security considerations, such as baggage inspection and passenger oversight. It marked a turning point in public perception: air travel, once feared for its mechanical hazards, now faced the unseen threat of sabotage.
The investigation methods applied in the Flight 23 crash advanced forensic practices in aviation. The analysis of blast patterns, residue detection, and fragment dispersion became key tools in later accident and sabotage investigations. The case laid a precedent for future forensic aviation investigations by establishing that an internal explosion could be distinguished from external failure.
Over ensuing decades the crash remained a touchstone in discussions of airline security. Later bombing cases, such as United Air Lines Flight 629 in 1955, were often compared to NC13304 as a historical precursor. The Chesterton case remained unsolved and mysterious, but it engaged public attention and spurred awareness in aviation circles.
Because no criminal prosecution ever followed, much of the motive and method remain speculative; investigators raised theories including disgruntled employees, disputes over pay, and sabotage linked to life-insurance arrangements. None of these have been confirmed. Yet the fact that the case was officially deemed sabotage gives it enduring weight as the first proven bombing in U.S. commercial aviation.
The legacy of the 1933 Chesterton bombing lies in its role as a catalyst. It pushed aviation oversight to broaden from mechanical safety to threat mitigation. It pressed carriers and regulators to consider security in design, operations, and passenger handling. It also illustrated how aviation progress—faster, more capable aircraft—created new risks that had to be met. As the first confirmed act of airborne sabotage in U.S. history, the explosion of United Air Lines Flight 23 remains a milestone in American aviation—a dark event that reshaped how we think about safety in the skies.
References / More Knowledge:
“United Air Lines Flight 23.” Wikipedia. https://en.wikipedia.org/wiki/United_Air_Lines_Flight_23
“10 October 1933 | This Day in Aviation.” ThisDayInAviation.com. https://www.thisdayinaviation.com/10-october-1933/
“What Happened to UAL Flight 23?.” HistoryNet. https://www.historynet.com/what-happened-to-ual-flight-23/
“Crash Of A Boeing 247D In Chesterton: 7 Killed.” BAAA-ACRO. https://www.baaa-acro.com/crash/crash-boeing-247d-chesterton-7-killed
“First Aircraft Sabotage | Guinness World Records.” GuinnessWorldRecords.com. https://guinnessworldrecords.com/world-records/first-aircraft-sabotage