Why Planes Nosedive [video]

Understanding sudden, catastrophic descents

Of all disasters that can befall a plane, probably none is more terrifying than a sudden, near vertical dive at full speed into the ground. In today’s episode, will look at some of the reasons that this kind of accident can occur. The context, of course, is the crash last Friday, January 31, 2025, by a Learjet 55 less than a minute after takeoff from North Philadelphia airport.

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.

In today’s episode we run through a far-from-exhaustive list of some possibly relevant antecedents to Friday’s crash.

1. 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 percieved 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.

2. 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 the Inertial Reference System, a computer that integrates information from GPS and accelerometers to generate a robust model of 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 IRS 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 mph.

3. 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 horiontal 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 signficant change in FAA rules.

4. 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 were killed. The plane and its occupants were so thoroughly shredded that not a single body was left intact and pieces of wreckage were found embeded as deep as 15 feet into the riverbed.

Which type was the Philadelphia crash?

At the time I made the video, I was thinking that the first scenario, pilot disorientation, was most likely. But in thinking about it since then, I’m wonding if the closest antecedent might be the crash of Korean Air Cargo Flight 8509, a 747 which crashed shortly after taking off from London Stanstead Airport in 1999. As in the Philadelphia crash, the plane took off at night and ascended into a low cloud layer at 400 feet of altitude. Like the Swedish cargo jet, the inertial navigation unit feeding information to the captain’s attitude indicator was broken. The captain put the plane into a bank, but his attitude indicator did not reveal this. The first officer and flight engineer could both see properly working attitude indicators and tried to tell the captain what was happening, but due to poor cockpit resource management the captain ignored them, and the plane crashed into a nearby village just 55 seconds after takeoff — a timeframe eerily similar to the Philadelphia crash. All four crewmembers aboard the plane were killed. Fortunately, there were no casualties on the ground.

Another way I’ve changed my thinking since I recorded the video is that I’ve become more optimistic. Originally it was unknown whether the Learjet was equipped with a flight data recorder and cockpit voice recorder, as these were not originally included when the plane was built and were not required by federal regulations. But it turns out that fortunately the aircraft was equipped with both forms of black box, and they’ve been recovered. I think investigators will be particularly interested to hear what the flight crew were saying to one another after they entered the clouds, and whether their attitude indicators were all in agreement with one another.