Fateful Assumptions: The 1972 Chicago-O’Hare Runway Collision

Admiral Cloudberg
25 min readApr 22, 2023
The burnt remains of North Central Airlines flight 575 lie on the runway at Chicago O’Hare International Airport after it collided with a Convair 880. (Bureau of Aircraft Accidents Archives)

On the 20th of December 1972, a North Central Airlines DC-9 taking off from Chicago O’Hare International Airport clipped the tail of a taxiing Delta Air Lines flight amid dense fog, sending the plane crashing back to the runway in flames. Aboard the Delta Convair 880, 93 passengers and crew escaped serious injury, but on the burning DC-9, a raging fire and heavy smoke claimed the lives of 10 passengers during the mad rush to evacuate.

The collision shut down the world’s busiest airport for several hours, but it had been closed before the crash, too, due to fog — the very same fog which prevented the two crews from seeing each other as North Central Airlines flight 575 sped down the runway and Delta flight 954 wandered into its path. However, the reason the two planes came into contact at all hinged on a series of misunderstandings, ambiguous clearances, and complacency on the part of the Delta crew and the ground controller handling them, as they attempted to reach a holding point in low visibility. The fact that a few words put the planes on a collision course, and the fact that 10 people died in a fire following a survivable crash, illustrated the relative lack of safeguards in place in 1972 — and led NTSB investigators to issue several recommendations that would foreshadow future improvements in aviation safety.

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O’Hare International Airport as seen from space in 2019. (NASA)

For an impressive 35-year period between 1963 and 1998, Chicago’s O’Hare International Airport was the busiest in the world, and as of 2019 it still ranked number one in total aircraft served. Multiple aircraft take off or land at O’Hare every single minute, and hardly anything ever goes wrong: other than occasional drama, like hard landings and accidents with ground equipment, there hasn’t been a major crash at the airport since 1979. An underappreciated aspect of this safety record is the absence of collisions, despite the airport’s numerous intersecting runways, busy airspace, and complicated taxiway networks, which make on-ground navigation a challenge for the inexperienced. It is perhaps ironic, then, that O’Hare’s worst ever collision occurred not during peak operations, but on a foggy night in 1972, when hardly any planes were arriving or departing.

N954N, the North Central DC-9 involved in the accident. Not to be confused with Delta flight 954, the flight with which it collided. (Bob Garrard)

The 20th of December 1972 had been difficult for travelers and staff alike at O’Hare International Airport, thanks to dense fog and drizzle which blanketed the region for most of the day. For several hours, O’Hare was closed to all arrivals and departures due to insufficient visibility, causing escalating delays throughout the network. Among the affected flights was North Central Airlines flight 575, a regularly scheduled service to Madison, Wisconsin and Duluth, Minnesota. Based in Minneapolis, with destinations throughout the upper Midwest and neighboring regions, North Central Airlines was a major regional carrier between 1952 and 1979, when it merged with Southern Airways to create Republic Airlines. The company operated a fleet consisting mainly of twin rear-engine McDonnell Douglas DC-9 short range jets, and it was one such plane, registration N954N, which found itself stuck at O’Hare that day, waiting for conditions to enable its departure for Madison.

In command was a veteran airman, 49-year-old Captain Ordell Nordseth, who had over 20,000 flight hours; and a less experienced First Officer, 32-year-old Gerald Adamson. Also on board were two flight attendants to tend to what promised to be a light passenger load: in total, 41 passengers had boarded by the time the flight finally left the gate, well below the plane’s capacity. Many of them arrived only at the last moment, seeking any available flight to Madison or Duluth after hours of delays and cancellations.

N8807E, the Delta Convair 880 involved in the accident. (Bob Garrard)

Sometime after 17:00, conditions improved just enough to allow takeoffs and landings to resume. That was a major relief for the crew of Delta Air Lines flight 954, a four-engine Convair 880 passenger jet inbound from Tampa, Florida. The Convair crew consisted of three pilots: 36-year-old Captain Robert McDowell, 31-year-old First Officer Harry Greenberg, and 29-year-old Flight Engineer Claude Fletcher, none of whom had more than 5,500 total flying hours. Rounding out the crew were four flight attendants, who were responsible for the well-being of 86 passengers.

As flight 954 neared Chicago at 17:23, the pilots tuned in to the latest broadcast from the Automatic Terminal Information System, or ATIS, which informed them that landings were being conducted on runway 14 Right, with takeoffs on runways 14 Right and 14 Left, amid visibility of ¼ mile (400 m) with a cloud ceiling of 200 feet (60 m) above ground level. The conditions were extremely marginal, but still above the minimums for an Instrument Landing System Approach.

At 17:39, however, there was a slight change of plans, as the approach controller announced that landings would now be conducted on both parallel runways 14R and 14L. Flight 954 was cleared to approach 14L, and the crew contacted the tower at 17:46 to seek landing clearance. The tower finally cleared them to land at 17:52, and despite the low visibility, the pilots set their plane down on the runway without incident about three minutes later.

A map of locations at O’Hare mentioned in this article. (Own work, map by Google)

As flight 954 was on final approach, the crew of North Central Airlines flight 575 received permission to taxi away from the gate, a full 90 minutes behind schedule. The pilots were informed that runway 27 Left was being used for takeoffs, and the ground controller cleared them to proceed to the head of the runway.

Meanwhile, at 17:55, as Delta flight 954 rolled out on runway 14L, the tower controller asked the flight to report clear of the runway, which First Officer Greenberg did about one minute later. With Captain McDowell still at the controls, flight 954 taxied down to the south end of runway 14L, crossed the runup pad for runway 32 Right, and entered a taxiway known as the Bridge, so named because it crossed a bridge over the airport’s entrance highway.

The runup pad, or simply the “pad,” is a wide, paved area near the head of a runway, which planes use to wait in line and spool up their engines before taking off. Because runway 32R was simply runway 14L in the opposite direction, the runup pad for runway 32R was located at the departure end of runway 14L, where flight 954 taxied across it en route to the Bridge.

After First Officer Greenberg reported clear of the runway, the tower controller instructed the crew to contact ground control. Greenburg acknowledged, but before anyone followed up, Flight Engineer Fletcher needed to figure out where they were going. Calling the Delta ramp control agent on his own radio, Fletcher learned that their gate was unavailable, and that they would need to hold at a point west of the terminal, known as the “penalty box.” This was the default place to wait in the event that an arriving flight’s assigned gate was occupied, which was the case that night, as numerous flights were behind schedule and had yet to depart, including one which was blocking flight 954. In response, Fletcher asked how long they would have to wait at the Penalty Box, and the ramp agent replied that he would call them back.

Moments later, at 17:57, First Officer Greenberg called ground control and reported, “Delta nine five four is with you inside the Bridge and we gotta go to the box.”

On duty in the tower that evening was a single ground controller, Patrick O’Brien, who was responsible for all surface movements at O’Hare. At that moment, he was unable to see the taxiing aircraft due to the darkness and dense fog, so he tracked their locations by recording each aircraft’s position reports on a scratch pad. In this case, since flight 954 was contacting him for the first time, he believed it to have just landed on runway 14L, and so he provided a preliminary clearance: “Okay,” he said, “if you can just pull over to the thirty two pad.”

“Okay, we’ll do it,” First Officer Greenberg replied.

In the tower, O’Brien wrote down a note indicating that flight 954 was headed for the 32R runup pad. He expected the flight crew to ask for further clearance only upon reaching it.

In reality, however, he had missed a crucial detail: namely, that flight 954 had already passed the 32R pad and was “inside the Bridge.” To reach the 32R pad from this position, they would have to turn around and taxi against the normal flow of traffic back to the head of the runway, which made no sense to the Delta crew. In their view, when O’Brien mentioned the “32 pad,” he could only have meant the runup pad for runway 32 Left, which lay ahead of them and was closer to the penalty box.

What the pilots of flight 954 were thinking when they accepted the taxi clearance. (Own work, map by Google)

Believing that the controller could only have cleared them to the 32L pad, the crew of flight 954 proceeded down the Bridge, passed around the south side of the terminal, and made a 90-degree left turn onto the North-South taxiway, which led directly to the 32L runup pad. The crew did not find it especially noteworthy that reaching this pad required crossing runway 27 Left — after all, last they heard, that runway was not being used for departures or arrivals.

In fact, however, when the controllers decided to use both runways 14L and 14R for arrivals, they opened runway 27L for departures. Among the first flights to use it would be North Central Airlines flight 575, which had just left the gate a few minutes earlier, and was cleared to assume the takeoff position at 17:58. Twenty-six seconds later, the tower controller cleared it for takeoff, informing the pilots that the visibility was ¼ mile. From their position, it looked like the visibility might be even less than this, but it was hard to tell.

The final movements of the two aircraft before the collision. (Own work, map by Google)

After finishing a few final checks, the pilots advanced the thrust levers together, and Captain Nordseth called the tower to report, “Rolling.” Within moments, the DC-9 was away, accelerating down runway 27L into the impenetrable fog. With First Officer Adamson at the controls, Captain Nordseth made routine airspeed callouts, verifying that acceleration was normal. The plane passed V1, the maximum speed at which the takeoff could be aborted, and approached rotation speed. Nordseth called out, “Rotate,” and Adamson started to pull back on the controls to lift the nose off the runway.

It was at that moment that the fog at last revealed a terrifying obstacle: another plane, its taxi lights illuminated, standing directly in their path. It was Delta Air Lines flight 954, the four-engine Convair 880, making its way across runway 27L en route to the 32L pad — and there was no time to avoid it.

Amid shouts of alarm, First Officer Adamson pulled back on his control column as hard as he could, and Captain Nordseth jumped on the controls to assist. They had no chance of stopping before reaching the Convair, but they could at least try to climb over it. The DC-9 pitched up steeply, its tail dragging along the runway in a shower of sparks, as passengers held on for dear life. “Pull ‘er up!” Nordseth shouted, hauling back on the controls — but it was too late.

Aboard Delta Air Lines flight 954, a flight attendant had come up to the cockpit to ask how long they would have to wait, given that passengers were becoming worried about missing connections. Captain McDowell started to respond, uttering the words, “Ah, we can’t even — ” And then, out of the corner of his eye, he spotted the DC-9 barreling toward them, landing lights glaring, its nose high in the air as it struggled to become airborne. He barely had time to let out an exclamation of surprise before the planes collided.

An adapted NTSB diagram showing the routes of the planes before the collision, and where they ended up afterward. (NTSB)

At the last second, North Central flight 575 managed to lift off the runway, but the collision could not be avoided. Traveling at takeoff speed, flight 575’s lower fuselage clipped the tip of the Convair’s left wing, severing it in the process, while the nose gear struck a glancing blow to the top of the passenger cabin. Simultaneously, the right wing and right main landing gear impacted the Convair’s vertical stabilizer, which separated, taking with it the DC-9’s landing gear and at least one of its flaps. The left main gear also struck the top of the fuselage. And then, in the blink of an eye, the collision was over, and flight 575 was airborne.

On board the DC-9, however, it was immediately obvious that continued flight would be impossible. The collision had caused severe damage to the landing gear, right wing flaps, and lower fuselage, and structural elements from the Convair’s tail had been ingested into the right engine. Unable to produce enough power and lift to stay airborne, the DC-9 immediately stalled, triggering the stick shaker stall warning. Recognizing the severity of the damage, Captain Nordseth flew the plane through the stall and back onto the ground, impacting runway 27L a mere 547 feet (167 m) beyond the site of the collision. On touchdown, the remaining landing gear immediately collapsed, and the plane entered an uncontrolled skid, slewing off the right side of the runway at over 100 miles per hour (160 km/h). Fuel lines in the lower fuselage ripped open and sparks ignited the escaping fuel vapors, sending flames streaming behind the plane as it crossed a grass verge, skidded over a taxiway, and finally came to rest on runway 32L, after sliding half a mile (880 m) across the airport surface.

Delta flight 954 sits on the taxiway after the accident, missing its tail and with escape slides deployed. (Bureau of Aircraft Accidents Archives)

On the Delta Convair, meanwhile, the passengers and crew heard and felt a heavy lurch, and people seated along the right side caught sight of North Central flight 575 slamming back onto the runway, trailing fire. First Officer Greenberg spotted the crippled DC-9 disappearing into the night and exclaimed, “That guy crashed!” Seconds later, someone mentioned something about a fire, and someone else ordered, “Shut ’em down,” referring to the engines. Captain McDowell ordered an evacuation, and the flight attendants deployed the emergency slides, shepherding the 86 passengers off the plane and onto the runway. Although the plane was severely damaged, they were relieved to discover that only two passengers had suffered minor injuries, having apparently struck their heads against the wall during the impact. The aft galley behind the last row of passenger seats had been crushed down to 38 inches (96 cm) above the floor, but thankfully, no one was standing there at the time.

After the crash, the DC-9 burned over rapidly. (Todd Overgard)

The evacuation aboard the North Central DC-9 was by far the more harrowing of the two. Almost immediately, flames erupted through the damaged floor and into the back of the passenger cabin, sending passengers fleeing for their lives as soon as the plane came to a stop. The forward flight attendant opened the left main entry door, jumped outside, and urged the passengers toward it, while the other flight attendant, seated in seat 15B, opened the nearby left forward overwing exit and stepped out onto the left wing, also shouting for passengers to follow. Another passenger opened the right forward overwing exit and escaped through it, but the rest of the exits — the right main entry door, the two aft overwing exits, and the removable tailcone — were never opened, and in fact the latter probably could not have been opened, due to the collapse of the landing gear, which would have impeded the deployment of the tailcone exit’s built-in air stairs.

The evacuation was swift, but in the end, not swift enough. While those in the front of the plane and near the left overwing exit escaped without injury, black smoke began to fill the cabin within 30 seconds after the plane came to a stop. Floor-to-ceiling flames were visible in the last rows before the smoke blocked all light, plunging the cabin into darkness. People struggled forward, coughing and choking, until they spilled out the exits and into the waiting arms of the crew. The pilots swiftly evacuated as well, with First Officer Adamson escaping through the cockpit window, while Captain Nordseth left via the main door; he later returned in search of more passengers, but was quickly beaten back by the intense smoke. By then, they were out of time — within a minute of the start of the evacuation, the entire cabin was engulfed in flames. To those who had escaped, their own diminished numbers made it clear that not all had been so lucky.

Another view of the DC-9’s badly damaged cockpit. (Todd Overgard)

At the control tower, the dense fog prevented the controllers from immediately realizing that a crash had occurred, and neither crew managed to make a mayday call before shutting down their engines. As a result, it was not until the tower controller noticed that North Central flight 575 had not appeared on his radar scope and could not be raised by radio that he realized anything was amiss. The crash alarm was finally activated around two minutes after the collision, when another pilot reported seeing flames on runway 32L, and fire trucks arrived within a minute to find the DC-9 fully involved in a raging fire. Firefighters and rescuers were initially so preoccupied with knocking down the blaze and tending to the survivors that no one realized another plane was involved, and in fact 28 minutes passed before anyone stumbled upon Delta Air Lines flight 954. The passengers and crew were rather cold after having stood on the runway amid fog and drizzle for almost half an hour, but no one on that plane was seriously injured, much to the relief of everyone involved.

The toll on the DC-9, unfortunately, was heavier. Between 15 and 17 people had been injured, some seriously, and nine passengers were missing. After the fire was put out, rescuers eventually found their bodies still inside the aircraft, having perished in the smoke and flames during the rush to escape. Five of the victims never left their seats, apparently having been engulfed where they sat; one of these was disabled and could not have left the plane without assistance. Survivors recalled a flight attendant shouting for someone to help a lady who couldn’t walk, but tragically, no one did.

In contrast, four of the victims did attempt to escape, but never made it. Two were found in the very back of the plane, having apparently tried to reach the tailcone exit, but were overcome before they could try to open it. The remaining two had traveled forward, past the main entry door and into the cockpit, where they succumbed to toxic fumes. It was clear from the positions of their bodies that they must have walked right past the exit, unable to see it amid the smoke-filled darkness.

Most of the DC-9’s fuselage was consumed by fire. (Bureau of Aircraft Accidents Archives)

In the end, a 68-year-old man who initially survived with severe burns also died in hospital several days later, bringing the final death toll to 10. Even so, the collision was not the worst crash in Chicago that month — in fact, the accident came just 12 days after United Airlines flight 553 crashed on approach to Midway Airport, killing 45. Furthermore, just 9 days later, Eastern Air Lines flight 401 crashed in the Everglades, killing another 101 people and permanently wiping both earlier crashes from the news cycle.

Nevertheless, a team of investigators from the National Transportation Safety Board immediately set to work analyzing the circumstances that led to the collision, as well as the survival factors that determined who lived and who died. Their analysis would ultimately place blame on a number of missteps and assumptions in the minutes leading up to the crash.

Regarding the fatalities, however, the NTSB could not help but note that all 10 victims survived the initial crash, only to die in the fire, making their deaths inherently preventable. It would have been difficult if not impossible to save the five who never left their seats, but the four victims who attempted to escape but failed to find the exits could in theory have made it. The NTSB noted that the emergency lighting in the cabin should have come on, given that it was armed and there were no major disruptions to the cabin structure before the fire, but the passengers were likely unable to see the lighting through the smoke for two reasons: first, it was too dim to begin with; and second, it was located near the ceiling, which is also where smoke tends to gather. In practice, these factors made the emergency lighting almost useless, because no one could see it — especially not the two passengers who missed the main entry door and ended up in the cockpit. If the emergency lighting around this door had been visible, they might have survived.

Additionally, the NTSB felt that some of North Central’s rules could have made the evacuation less efficient. According to company policy, in the event of an emergency evacuation, the flight attendants were to exit immediately and call to passengers from outside the plane, which could result in confusion inside the cabin due to their absence. Such a policy is certainly counter to modern practices, which normally ask flight attendants to stand inside the doors in order to shout commands and push hesitant passengers down the escape slides. This wasn’t simply a case of time revealing the best practices — in the NTSB’s opinion, the inadequacy of North Central Airlines’ procedures was perfectly apparent, even by the standards of 1972.

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The fire burned for only 16 minutes, but by the time it was out, little of the passenger cabin was recognizable. (Todd Overgard)

As for the collision itself, the NTSB traced the seeds of disaster back to a moment 37 minutes before the crash, when the crew of Delta flight 954 listened to the ATIS broadcast and learned that runways 14L and 14R were being used for departures. Although controllers later opened runway 27L for departing aircraft and switched 14L to arrivals, the Delta pilots were only informed of the change in status to 14L, not 27L. Since runway 14R was being used for both arrivals and departures, they probably assumed that the same was now true of runway 14L, giving them no reason to believe that additional runways may have been opened for departures. This assumption would later influence their decision-making as they approached the site of the collision.

The next misunderstanding, however, occurred as flight 954 exited runway 14L after landing. Normally, flights switched to the ground control frequency as soon as they left the runway, but in this case First Officer Greenberg didn’t call ground control until after Flight Engineer Fletcher had contacted the company ramp to confirm their delay. As a result, ground controller Patrick O’Brien’s first call to flight 954 was not answered, and Greenberg didn’t call him back until about a minute later, when they were already on the Bridge taxiway. At that point, Greenberg reported that they were “inside the Bridge” — which should have cleared everything up immediately, but for whatever reason, it did not. At an NTSB hearing, O’Brien testified that he didn’t hear the words “inside the Bridge,” and investigators believed he was telling the truth. How he could have missed such an important part of the transmission is uncertain, but according to a book by crash survivor Todd Overgard, rumors held that he had suffered a recent personal tragedy and may have been distracted.

A close-up of the DC-9’s charred right engine and tail section. (Todd Overgard)

In any case, the NTSB noted that if he did not hear the words “inside the Bridge,” then First Officer Greenberg’s transmission would not have contained a position report, which should have prompted O’Brien to ask where the plane was. But instead, he assumed that flight 954 was in the same place as most planes that contacted him — that is, leaving runway 14L. He then issued a clearance to the “32 pad,” and wrote in his notebook that flight 954 was at the runway 32R runup pad. This confirmed that he indeed had not heard flight 954 report “inside the Bridge,” because if he had, an instruction to taxi to the 32R pad would have made no sense, for the reasons that were discussed earlier.

In response to this instruction, First Officer Greenberg simply replied, “Okay, will do,” which did not clarify what, exactly, he believed he was doing. At that time there was no requirement for crews to read back taxi clearances, so this wasn’t a breach of procedure, and O’Brien did not ask for further confirmation. Therefore, both the controller and the flight crew now believed that the other was aware of their intentions, even though they were actually headed for different runup pads.

Here the NTSB also faulted the crew of flight 954 for assuming that a clearance to the “32 pad” meant the 32L pad, without asking for clarification. Although a clearance to the 32R pad didn’t make sense, the 32L pad was itself quite far away, and investigators felt that the pilots should have asked for confirmation before proceeding to taxi half way across the airport. One certainly has to wonder whether the relatively low-time crew of flight 954 was too hesitant to question a controller at the busiest airport in the world.

Officials examine the wreckage of the DC-9’s aft passenger cabin. (Todd Overgard)

This misunderstanding would have been inconsequential had the taxi route to the 32L pad not crossed the active runway 27L. Today, crossing a runway requires explicit permission from ground control, but this was not the case in 1972, nor was there any type of system which could signal whether a runway was occupied. The pilots could, and perhaps should, have stopped to ask whether it was safe to cross runway 27L before entering it, especially given the conditions, but they were not required to do so. If they knew 27L was an active runway, they might have asked for confirmation that they were cleared to cross, but here’s where their very first misunderstanding made all the difference — because they were never informed that runway 27L had been opened, they probably thought departures and arrivals were still confined to runways 14L and 14R. Although the lights on 27L were illuminated, which is usually a sign that a runway is active, this observation apparently failed to stir them from their pre-existing belief that the runway was not being used. Thus it never occurred to them that the fog might conceal a speeding DC-9, and they taxied blithely into its path.

Once the Convair 880 entered the runway, the collision was inevitable. Investigators calculated that under the prevailing visibility, the Convair would not have become visible to the DC-9 pilots until the two planes were less than 1600 feet (500 m) apart, at which point it would have been both too late to abort and too early to climb. In the end, the NTSB praised Captain Nordseth and First Officer Adamson for their handling of the collision, writing that they did all they could to avoid the Convair and successfully minimized the consequences of the subsequent ground impact.

The DC-9’s tail section eventually lost structural integrity and collapsed to the ground. (Bureau of Aircraft Accidents Archives)

While there was nothing the pilots could have done to avoid the crash, the NTSB pointed out that the same could not be said of the air traffic controllers. In the NTSB’s public hearing, the tower controller on duty that day, who was responsible for takeoffs and landings, testified that he had observed a visibility of only 1/8 mile (200 m) before the crash, but was overruled by his supervisor, who determined the official visibility to be ¼ mile (400 m). This was significant because the minimum visibility for takeoff on runway 27L was ¼ mile, meaning that if the tower controller’s observation had been allowed to stand, North Central flight 575 probably would not have been allowed to take off. In hindsight, it seems possible that the lengthy closures which had already taken place that day were putting pressure on the tower supervisor to avoid further delays, even if it meant overestimating the prevailing visibility.

Additionally, the NTSB found that O’Hare was one of the few airports in the United States that was equipped with ground radar, which can detect airplanes moving on the airport surface and display their positions to controllers. And yet, although three minutes passed between ground controller Patrick O’Brien’s first contact with flight 954 and the collision, he never once looked at the ground radar display to verify whether flight 954 was following his instructions.

The ground radar at O’Hare, officially known as ASDE, short for Airport Surface Detection Equipment, used primary radar to display only blank targets; it could not interrogate an aircraft’s transponder to determine its identity, nor could it distinguish between airplanes and ground vehicles. Furthermore, in the areas near the terminal, objects and buildings generated clutter on the display, and controllers complained of persistent blind spots. Nevertheless, the NTSB found that except for one blind spot along the Bridge taxiway, airplanes away from the terminal could be readily identified, especially when moving. In fact, flight 954 would have been easily visible both at the moment it contacted ground control, and at the point where the collision occurred, along with many points in between. Therefore, if O’Brien had looked at the ASDE display before contacting flight 954, he could probably have detected that it was not actually leaving runway 14L, and was in fact already inside the Bridge.

A radar display of the general type which would have been in use at O’Hare in 1972. This particular display is showing the situation in the air, not the ground, but the general appearance would have been similar. (Glenn Chatfield)

The NTSB noted that on top of its perceived unreliability, the usefulness of the ASDE was further compromised by tower procedures which did not mandate its use, and a lack of specific training for controllers regarding its capabilities and limitations. These deficiencies had led to a culture where earlier practices predating the installation of the radar persisted, and ground controllers rarely looked at it, even in conditions of low visibility. Tower controllers explained that they often used it to determine whether an aircraft had landed or executed a missed approach, but ground controllers, including O’Brien, didn’t use it at all. These habits had developed despite the O’Hare tower operating procedures, which specified that ground controllers must use the ASDE — although they didn’t explain how, exactly, or when.

Additionally, the crash could have been prevented at various points if controllers had used standard terminology. For instance, “32 pad” is not standard terminology, because it could refer to multiple locations, and while controllers might have believed that the intention behind such an instruction would normally be obvious, it only takes one edge case for such ambiguity to cause problems. In general, controllers at major airports resist insinuations that they should always use standard terminology because it can make transmissions substantially longer, a major liability at busy airfields with frequent traffic movements. But in conditions of low visibility, where the positions of airplanes are not being directly verified, removing ambiguity is not a luxury, but a necessity. In this case, for instance, no adverse impact on traffic turnover would have occurred if O’Brien asked flight 954 for its position and/or specified exactly where he wanted it to taxi, but 10 lives would have been saved.

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The Convair 880 involved in the accident was stripped of salvageable parts before being scrapped. (Jon Proctor)

In response to these findings, the NTSB issued a number of recommendations, several of which led to substantive changes. In the field of air traffic control, the NTSB recommended that controllers be required to read back a flight’s position report if its position is not being verified visually or by radar, ensuring that controllers are less likely to miss a position report without following up. This recommendation was adopted by the FAA in 1974 and became standard practice. The FAA rejected a similar recommendation suggesting that pilots be required to read back taxi clearances when visibility is less than ½ mile, but reading back taxi clearances did eventually become standard practice anyway. Efforts were undertaken to improve the reliability of the ground radar at major airports, and today the unreliable systems that existed in 1972 have long since been replaced by more advanced displays which filter out clutter and provide information about an aircraft’s identity (although this new technology would not appear until long after the accident). But perhaps the most interesting NTSB recommendation was that pilots be required to request permission from air traffic control before crossing a lighted runway in low visibility, regardless of whether they have received clearance to taxi to a point on the other side. This recommendation seems like common sense, and yet the FAA rejected it, writing that a pilot is free to request affirmation of a clearance if conditions call for it, but that a requirement to do so every time they approach a runway would be unreasonable. This situation persisted until the development of lighted runway stop bars, which are now used at major airports to indicate whether a runway can safely be crossed or not. If the stop bar is red, a pilot must request permission before crossing it, regardless of what other clearances may have already been issued.

The NTSB also published several recommendations related to passenger survival, including that flight attendants receive more realistic evacuation training; that North Central improve its evacuation procedures; that emergency lights be made more powerful; and that tactile and visual exit location indicators be made easier to see in conditions of smoke and darkness. The content of this final recommendation would eventually be implemented in the form of emergency track lighting in aircraft floors, but not until after a 1983 tragedy involving Air Canada flight 797 underscored the need.

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A basic breakdown of the 2023 incident at JFK. (New York Post)

In the end, the collision at O’Hare served not as a direct catalyst for change, but rather as another example in a long chain of disasters, until future accidents finally forced authorities to take action. Safeguards were eventually implemented which would prevent this accident from occurring today. And yet, the problem of ground collisions has not disappeared. In 2022, two firefighters at Lima Airport in Peru were killed and dozens of passengers were injured when a fire truck pulled out in front of an Airbus which was accelerating for takeoff. And in the first quarter of 2023, multiple near misses occurred on runways in the United States, including an incident at JFK in January which bears some resemblance to the 1972 collision. In that event, an American Airlines crew taxied across the wrong runway ahead of a departing Delta Air Lines flight, forcing it to abort; any direct danger was thankfully avoided because the controller was keeping close watch and saw the conflict coming.

These incidents show that while measures like stop bars and mandatory readbacks can do a lot to decrease the risk of ground collisions, the maintenance of our current safety record still relies to some degree on the vigilance of pilots and controllers. With that in mind, and with more than 50 years having passed, the best lesson to be drawn from the O’Hare collision might be a timeless one: that assumptions are dangerous. If we assume that modern safety measures obviate the need for clear communication and faithful cross-checking, then someone, somewhere, will eventually manage to line up the holes in the Swiss cheese. And if recent near misses are anything to go by, there are some pilots and controllers out there right now who are lucky that that person wasn’t them.

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Admiral Cloudberg

Kyra Dempsey, analyzer of plane crashes. @Admiral_Cloudberg on Reddit, @KyraCloudy on Twitter and Bluesky. Email inquires -> kyracloudy97@gmail.com.