Photo: Thomas Hengge/Anadolu via Getty Images
On Friday night, northeast Philadelphia was rocked by the high-speed impact of a medevac jet that nose-dived into a busy avenue shortly after takeoff from North Philadelphia Airport. Having climbed to an altitude of 1650 feet, the plane plummeted nearly vertically at more than 200 mph. Heavily loaded with fuel for a planned 1000-mile flight to Springfield, Missouri, the plane exploded with the power of a cruise missile, incinerating cars and rattling neighborhood windows as it send a fireball into the night sky. All six people aboard the plane were killed, as was at least one person on the ground, and several other people were injured. It was the second horrific plane crash in the U.S. in as many days, following the collision between a American Airlines passenger jet and a military helicopter in Washington, D.C. on Wednesday night.
Dashcam footage of the Jet Rescue Air Ambulance crash in Philadephia tonight.
The Learjet appears to have impacted the ground at a nearly vertical angle. The last transponder signal, sent seconds before the crash, showed a descent rate of more than 11,000 feet per minute. pic.twitter.com/27hGq2xcny
— OSINTtechnical (@Osinttechnical) February 1, 2025
At time of writing, details of the Philadelphia accident are scarce. The plane was a Mexican-registered Learjet 55, a plane last produced in the 1980s. It was operated by a company called Jet Rescue Air Ambulance and was reportedly returning a young patient and her mother to Mexico after receiving treatment for a life-threatening condition at Shriners Children’s Hospital in Philadelphia. In addition to the pilot and co-pilot two medical personnel were also aboard the plane. In recent days the plane had traveled frequently between Haiti, Mexico, and the United States. The company had suffered an earlier fatal crash in Morelos, Mexico in 2023.
In the weeks ahead, accident investigators from the National Transport Safety Board will interview witnesses, collect and examine the wreckage, study maintenance records, and, if it is available, review data from the plane’s flight data recorder to understand what caused the crash and issue safety recommendations to prevent similar tragedies from recurring. As they assemble the evidence, investigators will be thinking about similar accidents that have happened in the past, looking for patterns to guide them in their search for the causal factors.
Here is a far-from-exhaustive list of some possibly relevant antecedents to Friday’s crash, regarding why aircraft can go into nose-dives.
Pilot Disorientation
At the time of the crash the weather in Philadelphia was overcast, with a cloud ceiling of 400 feet. That means that mere seconds after takeoff the pilot flying the plane lost all visual reference to the ground, seeing out the window only shades of gray and black. Under so-called “instrument conditions” the human brain is easily tricked into perceiving turns or acceleration as vertical motion and can easily become badly disoriented.
When Kobe Bryant’s pilot ascended into a layer of clouds while traversing a mountain pass in Los Angeles, the helicopter entered a bank that the pilot didn’t perceive and was soon spiraling towards the ground.
A more insidious form of disorientation is caused by the somatogravic illusion, in which linear acceleration caused by an increase in engine thrust is perceived as a climb. In 2019, a Boeing 767 carrying cargo for the US Postal Service was coming in to land at Houston amid stormy, cloudy weather and was maneuvering to avoid a patch of precipitation when they hit rough air. Perhaps trying to escape a sudden downdraft, the flight crew pushed the throttle to full, and then, possibily perceiving the resulting acceleration as a sharp climp, pushed the control yoke aggressively forward. The plane plummeted from 6000 feet to impact with the ground in 18 seconds.
Navigation Equipment Failure
In order to avoid disorientation, pilots are taught to ignore the sensations of their inner ear when flying in instrument conditions and instead focus exclusively on their navigational instruments, such as the traditional “attitude indicator” which tells pilots at a glance whether they are climbing, diving, or turning. Modern aircraft also include a system called a flight director that superimposes an arrow on their primary flight display that tells them where they should steer in order to remain on course. The display is calculated using information from an ADIRU (Air Data Inertial Reference Unit), a type of computer that integrates information from air sensors and accelerometers to figure out where the aircraft is located and how it is oriented. Because the system is of life-or-death importance, it is triply redundant, with a separate ADIRU for the pilot and the copilot as well as an extra backup. All the same, things can go wrong.
In 2016 a Swedish cargo jet was flying to Tromso, Norway in the middle of the night when a faulty ADIRU led the plane’s flight computer to erroneously conclude that the plane was flying too nose-high. The flight director instructed the flight crew to push the nose down, which they did. The plane entered a negative-g dive that left the two pilots hanging in their seat straps and impacted the snowy tundra at 585 m.p.h.
Mechanical Failure
A modern high-speed aircraft is a miracle of performance that results from large forces balanced with remarkable precision. This is achieved by means of complex machinery, of which the failure of any component can result in a sudden, irreversably catastrophic disruption of that balance. A particularly critical compenent of this dynamic is the tail, particularly the horizntal stabilizer and elevator, which provide a counterforce to balance the weight of the aircraft and the lift of the wing. If a plane loses its tail, there is nothing to prevent the plane’s center of gravity from pulling the nose directly towards the earth.
In 1991 a Continental Express turboprop was flying from Laredo, Texas to Houston when part of the left horizontal stabilizer came flying off. The plane, an Embraer 120 Brasilia, had had a history of mechanical issues and had been sent for unscheduled repair work 33 times prior to the accident. Just before the flight maintenance workers had replaced de-icing boots on the horizontal stabilizer but had failed to replace all of the screws. When the part broke off the plane entered a negative-g dive that partially tore off one of the wings, spilling fuel that then ignited in a fireball. All 14 aboard were killed. The slipshod maintenance procedures that led to the crash helped spur a significant change in FAA rules.
Suicide
Tightening operational procedures can help eliminate mechanical and control failures, but there is one component of the aviation system that is fundamentally prone to errors of a kind that are unpredictable and hence impossible to eliminate completely: the human mind.
Sometimes people snap, and sometimes they do that while at the controls of an airplane. In October 2023 an off-duty pilot named Joseph Emerson was deadheading on an Alaska Airlines flight from Everett, Washington to San Francisco when he tried to crash the plane by reaching forward and pulling the levers that deploy the engines’ fire-suppression system. Wrestled into submission by the flight crew, Emerson later told police that he’d been hallucinating and had told himself, “This is real, I need to wake up.” Though his attempt was foiled, others have not been. In 1997 the pilot of a 737 flying from Jakarta, Indonesia got up from his seat and pulled the circuit breakers that powered the black boxes. Back at the controls, he put the aircraft into a vertical dive that took the plane from 35,000 feet to impact with Sumatra’s Musi River in less than a minute. Accident investigators later surmised that the plane had broken the sound barrier during its descent. All 104 people aboard the airliner were killed and pieces of wreckage were found embedded as deep as 15 feet into the riverbed.
Hopefully in the coming weeks, investigators will be able to determine what caused Friday’s medevac jet crash in Philadelphia and with what they learn prevent a similar tragedy from ever happening again.
