Transcription
Imagine you're a passenger on a routine flight. It's a busy morning at the airport, and after a long wait behind a queue of other aircraft, the pilots finally line up on the runway and begin taking off. You're pushed into your seat as the plane accelerates. But when the nose lifts into the air, the rest of the plane doesn't follow it. Thumps and bangs rock the aircraft as its tail scrapes along the ground and the engines backfire. Now you have just seconds to live.
This is the horrifying story of Delta Flight 1141. An accident that never had to happen.
It was just after 8:00 in the morning on August 31st, 1988, at Dallas Fort Worth Airport in Texas. 101 passengers began settling into their seats on board a Delta Airlines Boeing 727. Their destination was Salt Lake City in Utah, about 2 and 1/2 hours away. The aircraft had arrived in from Jackson, Mississippi, earlier that morning, and some of the passengers were still on board to continue their trip to Utah. A number of them were families returning from holidays, while others were traveling to Salt Lake City on business. Also on board were four cabin crew members. The aircraft was 14 years old, and save for a fuel gauge which wasn't working, the plane appeared to be in good working order. Unbeknownst to anyone, though, the aircraft was carrying one more fault, one which would have dire consequences as the plane began its takeoff roll.
In the cockpit were three flight crew. The captain was 48-year-old Larry Davis. Davis was a highly experienced pilot who had been with the airline for over 20 years. In this time, he had built up over 17,000 hours of flying experience in many different aircraft, including the Douglas DC9 and the Lockheed L-1011. He was well used to the 727 at this point, having accumulated more than 7,000 hours in it. Davis would be the pilot flying on this flight, while his first officer monitored the aircraft. That first officer was 37-year-old Carrie Wilson Kirkland, known to his friends and colleagues as Wilson. He had been with Delta for 9 years and had built up about 6,500 hours total flying time, 4,000 of which were on the 727. He had been a flight engineer on the aircraft up until 8 months ago. The two pilots knew each other very well and were quite comfortable flying together. The third member of the flight crew was the flight engineer Steven Jud, aged 30. A former naval aviator, he was new to Delta Airlines, having just joined the company 7 months previously. He had 3,000 total hours, 600 of which were on the 727. All three pilots were well rested for the flight and had clean flying records.
While on the ground, the pilots reviewed the weather information all the way to Salt Lake City. The weather at Dallas was clear, and the winds were calm. By all appearances, this would be a perfect day for flying. The only point of note the pilots were aware of was that there were birds in the vicinity of the airport.
Once everyone and everything was on board, the doors were closed, and the jet bridge was removed from the aircraft. At just before 8 that morning, Delta Flight 1141 was pushed back from the gate. As the plane was being pushed back, Captain Davis told his colleagues that he had not received his paycheck yet and asked them if they had got theirs. They said that they had. The pilots continued discussing pay and savings as the pushback was completed and as they began starting the plane's three engines.
Following a slew of catastrophic accidents in the 1970s, a new rule was introduced into airline cockpits around the world known as the sterile cockpit rule. This prohibits pilots from talking about anything not related to the flight from the moment the engines are started until the aircraft has climbed through 10,000 ft. The purpose of this rule is to ensure that during these busy moments in the flight, all conversations are related to flying the aircraft. This allows important tasks like checklists to be performed in a distraction-free environment. Right from the outset of this flight, the crew of Flight 1141 was violating this rule.
Once all three engines were started, First Officer Kirkland requested taxi clearance from the ground controller. On this morning, Flight 1141 would be sticking to the inner taxi route until it had reached the threshold of runway 18 left, one of the airport's two southerly facing runways. It was a busy morning at Dallas, and the pilots knew that it could easily be half an hour before they were first in line for takeoff. There would be no need for rushing on this morning. The atmosphere in the cockpit was relaxed as the crew taxied out. Despite the fact that they had now come to a stop and were being ignored by air traffic control, spirits remained high. "How about looking down here at Delta's now and then?" joked the captain, pretending to address air traffic control. "While we're still young," added the first officer. "How about looking down here while we still have teeth in our mouths?" The three of them laughed.
Strangely, for both of the checklists that had been pulled out so far, it wasn't the captain who had called for them, but the other two crew members. As pilot flying on this leg, this was the captain's job. This hinted at an atmosphere in the cockpit, which went further than mere calmness. Recently, Delta Airlines had been audited by the Federal Aviation Administration after a series of widely publicized incidents involving pilot error. In their audit, the inspectors noted breakdowns in communication, a lack of coordination, and a lack of cockpit discipline amongst flight crews. The FAA blamed improper training programs and crew manuals, and they noted that the airline did not have a standardized approach towards cockpit management. Captains were more or less free to run things as they wished. Although Delta had taken steps towards rectifying some of these deficiencies since the audit, these problems ran deep in the airline and were not of the sort that could easily be trained away. What this meant for Flight 1141 was that the responsibility to keep the flight running smoothly had been diffused by the captain across all three members of the flight crew. The problem with that is that when everybody is in charge, nobody's in charge. We'll see how this dynamic played out shortly.
Seeing how long a taxi this was likely to become, Captain Davis decided to save some fuel by shutting down engine number three, the plane's right-hand engine. He would start it up again when it was almost his turn for takeoff. This was standard procedure at Delta, and nowadays, keeping one engine off during taxiing is even more commonplace. As they continued out on two engines, the flight engineer called for the taxi checklist to be resumed, with the pilots setting the air speeds for takeoff, making sure the altimeters had the correct pressure setting, ensuring that the flight instruments were working, and checking that the plane's horizontal stabilizer was set for takeoff. This was quite a long checklist, but it would take even longer than normal to finish because, as the pilots were carrying it out, a cabin crew member came into the cockpit for a chat. She was curious about the delays and she wanted to know if the pilots had any idea about when they might be taking off. Even with an extended taxi time, entering the cockpit was forbidden because slow or not, taxiing is still a critical phase of flight subject to the sterile cockpit rule. However, much like pilots who are well accustomed to the era before the sterile cockpit, cabin crew were also used to entering cockpits and talking to flight crews that they knew well during ground delays. This particular cabin crew member had been with Delta for 30 years.
As the aircraft crawled along the busy taxiway meter by meter, the first officer and cabin crew member began chatting. The discussion ranged from preferences in food and drink to the upcoming presidential election between George H.W. Bush and Michael Dukakis. All three flight crew members took part in the discussion, but it went on primarily between the first officer and the cabin crew who had entered. Captain Davis was of the belief that because they were moving so slowly on the taxiway, this did not count as a critical phase of flight, and so he allowed the distraction to continue. Mostly staying out of the conversation, Flight Engineer Jud continued to monitor the plane's surroundings and his own instrument panel. In what would soon prove to be a haunting aside, First Officer Kirkland joked that they should discuss the dating habits of the cabin crew so that the media would have something to talk about if the plane crashed and the cockpit voice recorder was recovered. "We got to leave something for our wife and children to listen to," he said. The captain then went on to discuss the crashes of American Airlines Flight 191 in Chicago and Delta Flight 1288 in Dallas 3 years back. The crew could not have known that on this day, Delta 1141 would soon be joining this dubious list of air crashes in what would turn out to be one of the worst decades for aviation in U.S. history.
At this point, almost 10 minutes had passed since the flight attendant had entered the cockpit. The captain realized that they had forgotten to switch over to the next ground controller for final taxi instructions to the runway. "Don't we have to change to ground here?" he asked. "Yeah, sorry. I'm sitting here talking to the flight attendant," replied Kirkland. Kirkland then switched over to the right frequency and contacted the controller. At this point, the conversation moved onto the birds, which the crew could spot at the window. It was just before 9:00 in the morning now, and the flight was now fourth in line for takeoff. The flight engineer took the initiative to give the cabin announcement, telling the passengers that they were number four for departure and telling the cabin crew to prepare the cabin. Essentially, he was performing the job of the captain in prompting the cabin crew member to leave the cockpit and getting the aircraft ready for departure. The pilots switched over to the tower frequency and then started up the number three engine. The flight engineer then resumed the taxi checklist, which should have been completed long ago. "Engine instruments check normal," replied First Officer Kirkland. "Engine anti-ice, it's closed." In the minds of the crew, it would probably be another 5 to 10 minutes before it was their turn for takeoff. Plenty of time to finish this checklist and the before takeoff checklist. But after half an hour of waiting, things were now about to happen very quickly for Flight 1141.
At that moment, the tower controller saw an opportunity to bring the flight to the front of the queue. He told them to line up on the runway. This caught the flight crew off guard. Now they would have to finish up both the taxi checklist and the before takeoff checklist all by the time they had lined up on the runway. This would have been a good time for the captain to tell the controller that they needed a few more minutes. As strange as that would sound, given that they'd been taxiing for nearly half an hour at this point, but instead, the pilots accepted the controller's instruction to line up. Under pressure, the flight engineer quickly ran through the final items of the taxi checklist with the first officer. "Shoulder harness, they're on. Flaps 15, 15, 15 green light. Flight controls tops and bottoms are checked. Nav instruments, they're set." Then Jud flipped to the before takeoff checklist, and he and Kirkland hastily went through that as well. "Takeoff briefing is complete." The takeoff briefing had not been done, at least not in the previous 30 minutes. This was the captain's job, and its purpose is to ensure that the crew knows how the departure is to be flown, whether it includes any noise abatement procedures, hazards, or any other unusual aspects. Regardless, the pilots had taken off from Dallas so many times that on this occasion, they could let it slide.
But the brief wasn't the only thing that had been left out. Part of the checklist involved confirming the position of both the flap lever and the flap indicator to check that the flaps were set for takeoff. The first officer had responded to these items in the normal way, saying that the flaps had been set to 15°. But this had not been done. In the rush to get the plane ready, the first officer responded to the checklist not by visually confirming the position of the relevant switches and indications, but by just reciting what he knew to be the correct responses after so many repetitions of the same checklist. He simply responded by memory.
Unfortunately, recent changes to company procedures had made this mistake even easier to make. Up until 5 months previously, the procedure dictated that flaps were to be extended immediately after the plane's engines had been started. This was a clear rule, and there was little room for pilots to improvise. But then the procedure was changed, allowing pilots to extend the flaps any time after leaving the ramp. This created a gray area; after departing the ramp could mean anything all the way until lining up on the runway. With no set point marking when the flaps should be extended, a distracted crew like this one could simply forget this crucial part of the before takeoff setup. What's more, it was not clearly stated which pilot was responsible for checking the flap position. In this gray sea of vagary, Flight 1141 swung into position on runway 18 left of Dallas. Now, there was just one thing standing between them and a doomed takeoff.
Before we get to that, we need to ask why it's so important that the flaps are extended before takeoff in the first place. After all, it's almost unreasonable that one misplaced lever could have such a devastating impact on the safety of the flight. The reason that flaps are so important has to do with the way that the wings generate lift, the force that causes the plane to climb. Engines are not what get the plane into the air. All they do is speed the plane up. As the plane gets faster, it is the wings that enable the plane to fly. They do this in a few ways. Part of it is the force of the air pushing against the underside of the wing. Part of it is the downwash of the air at the trailing edge after it has passed over the top of the wing. And part of it is the thinning of the air as it speeds up over the top of the wing, creating suction, which pulls the wing up. The faster the aircraft is traveling, the better the wings are at generating this upward force called lift. But this is where a problem comes in. Wings are designed for the phase of flight where planes spend most of their time: in the cruise. And because airliners like the 727 cruise high and fast, their wings are thin and flat. This is a perfect shape for cutting through the air for hours on end. But this thin, flat shape presents a problem at takeoff when the plane is traveling slowly. If encountering lots of air in a short period of time is what makes a plane fly, how could this be achieved when the plane is traveling slowly like on takeoff? The answer is that if you can't make the plane travel faster, you can make the wing bigger. The bigger a wing, the more air it can meet every second and therefore the better it will be at being a wing. The devices which achieve this are known as flaps and slats. They extend from the leading and trailing edges of the wing, increasing its size and giving it more curvature. With the flaps and slats extended, an aircraft can get into the air while traveling at a much slower speed.
A minute before 9:00 a.m., Flight 1141 was cleared for takeoff. Its wings were streamlined for high-speed flight, not at all shaped to deal with the slow air they would encounter at takeoff. But there was one last thing which stood between the pilots and their fatal mistake. The 727 is equipped with what's known as a takeoff warning system. This is a safety feature which sounds an alarm whenever the engines are pushed to takeoff power without the plane being ready for takeoff. If pilots try to take off with the speed brakes deployed, or the stabilizer trim not set properly, or the parking brake set, or with the flaps not set for takeoff, this warning provides an unmistakable sign that something is not right. But on this morning, when Captain Davis pushed the aircraft's three jet engines to takeoff power, this warning didn't sound. The 727 blindly accelerated down the runway with the three flight crew oblivious both to their own failure and to that of the aircraft.
As the aircraft picked up speed, the pilots made the callouts as usual. "Power set and estimates look good. Air speed coming up both sides, 80 knots." During the takeoff roll, the flight engineer noticed something odd. Like on most passenger aircraft, on the 727, the air conditioning for the cabin comes from the engines. This is air that could have been used to make thrust, but instead is siphoned off to provide air to the cabin. As such, when the air conditioning is on, the engines produce slightly less power. This normally doesn't matter, as jet engines produce much more power than they need to. But sometimes during takeoff, say when the temperature is high and the air is thin, the plane needs all the power it can get. It can't afford to have any air wastefully directed into the cabin when it could have been used for combustion. So for these situations, the 727 is equipped with a system which automatically stops air from coming into the cabin. This system arms during takeoff in case it's needed, and a light illuminates in the cockpit showing that it's armed. But on this morning, Flight Engineer Jud noticed that this indicator had not lit up. This was odd because the system should have armed when the captain applied takeoff thrust, as this is one of the three conditions required for the system to arm. Normally, it's the only condition which still needs to be satisfied at takeoff. In the moment, the flight engineer dismissed it as a mere curiosity. But the real reason the system hadn't armed was that one of the conditions for it to arm had not been met. That this system hadn't armed was unusual, but it wasn't a big enough deal for the flight engineer to bring it to the pilot's attention while they were focused on taking off. After all, this was a normal takeoff, and the system wouldn't be needed anyway.
"V1." At takeoff speed, known as V1, the captain began pulling back on his control column, and the nose of the plane rose, but the rest of the plane didn't follow it. Captain Davis continued raising the nose, but the main wheels stayed on the ground. Without flaps, it would need to be traveling a lot faster to get airborne. The air speed continued building as the plane powered along the runway. Finally, traveling at 158 knots, just short of 300 km/h, the main wheels left the ground, but only just. With the nose pointed 10° above the horizon, the tail struck the runway, sending up a shower of sparks. The banging noise startled the passengers and pilots alike. Neither had any idea what was going on. The stick shakers activated, shaking the pilot's control columns violently, warning them that they were approaching an aerodynamic stall. If they didn't lower the nose, the plane would come crashing back down to earth. Then, as the right-hand wing momentarily produced less lift than the left, the plane lurched to the right. The right wing tip struck the runway, producing another trail of sparks before Captain Davis managed to pull the wing back up. Panicked, he then raised the nose even more. With the air now coming into the engines from such an awkward angle, they were no longer able to process it correctly, and they began backfiring.
Kirkland had seen the engine thrust dropping and he concluded that an engine failure was responsible for the plane's unusual behavior. It seemed to explain everything: the aircraft's inability to climb, its near stall, its lurching to one side. But the truth was that this had nothing to do with the engines. They had been working perfectly well up until this point. The only problem was that all along the flaps had been tucked neatly into the wing. But in the heat of the moment, the pilots reflexively made up their minds. What they had on their hands was some kind of engine problem. Now convinced of this, there was no way the crew would realize what was actually wrong with the plane. But still, the flight could be saved. All the captain needed to do was to lower the nose, allow the air speed to build up, and continue the takeoff. But Davis simply held the nose up, only aggravating the situation. The wings rocked from side to side, and the captain held the control column with both hands, desperately trying to level the wings. The plane was howling along barely 20 ft above the runway surface, and it was running out of space. To their horror, the flight crew saw that they were headed straight for the antennas 1,000 ft beyond the end of the runway. It was now clear that there was no way out of this. First Officer Kirkland keyed his mic to alert the controller of the desperate situation, but there was nothing he could say. Before the throttles could be pushed forward, the engine's right wing struck the ILS antenna, rupturing it at the fuel tank. The right wing burst into flames, and the aircraft began rolling to the right, crashing down to earth just 24 seconds after first becoming airborne. When it hit the ground, it tumbled and rolled, breaking apart as it did. All 108 people on board survived the initial impact, but the post-crash fire claimed 14 lives: 12 passengers and two cabin crew.
It didn't take long for investigators to determine that the flaps had not been set for takeoff. The cockpit voice recorder and flight data recorder made that very clear. But a question remained as to why the takeoff warning system didn't sound. It should have given the pilots a clear sign when they advanced the throttles for takeoff that the aircraft was not properly set up to fly. As it happened on this particular aircraft, some of the electrical contacts on the part of the system which was connected to the throttle had corroded. What this meant was that the takeoff warning system only worked some of the time. Following the accident, the Federal Aviation Administration ordered that inspections be carried out on all of the nearly 1200 Boeing 727s in service. These inspections found 35 anomalies, 12 of which were of a similar type to that found on Delta 1141. To address this, the FAA recommended that the takeoff warning system take its information about the plane's throttle setting, not from the throttle levers themselves, but directly from the power output registered by the engines. They also recommended that these systems undergo more regular checking, every 200 flight hours, to ensure that they're working properly.
But the failure of this system was far from the only thing that led to the crash of Flight 1141. After all, systems like this are only a last resort for when every other safeguard has failed. The biggest changes resulting from this accident were in how airlines dealt with the human factors which led up to it. After the accident, the FAA implemented more rigorous measures to ensure that the sterile cockpit rule was being abided by. Airlines also began updating their crew resource management training to include the delegation of tasks by each flight crew member. No longer would it be unclear whose job it was to do what. Specific training on the dangers of distraction has also been introduced. And in the years since, the whole culture around the importance of having a sterile cockpit has changed.
There have also been significant technological innovations in the years since. On newer aircraft like the Boeing 787, checklists are now electronic. They appear on a screen in the cockpit, and items cannot be ticked off unless the corresponding system is configured correctly. These changes have completely transformed flight safety, and because they affect every aspect of a flight rather than just the setting of the flaps, they've gone on to prevent not only similar accidents but different kinds of accidents entirely. This has been the legacy of Delta Flight 1141, but it's a legacy which hasn't been without some problems. A strikingly similar accident happened in Madrid in 2008. You can check out the video I did on that incident here.