Airplane crashes and accidents are horrific things, involving exploded and smashed things that would make Michael Bay blush, as well as high body counts. Usually, there is a chain of events that have to occur before any sort of disaster, but especially aircraft accidents. If anything in the chain is done differently, the accident doesn’t happen. In most cases, the circumstances of the accident are beyond that which anyone could have foreseen or stopped.

And then there’s the accidents that if someone hadn’t been asleep at the wheel, wouldn’t have gone down at all.

5. Tuninter Flight 1153

Every pilot’s worst nightmare is having to ditch into water. Certain Sullenberger piloted aircraft notwithstanding, aircraft are not designed to be flown into water. But that’s the situation the flight crew of Tuninter Flight 1153 found themselves faced with. For some reason, both engines of their ATR-72 aircraft had failed, and it soon became obvious they weren’t going to make it to the nearest airport on Sicily. Their only other option? To land on the Mediterranean Sea.

Despite the best efforts of the two pilots, the aircraft came apart on impact, killing 16 out of the 35 on board. Investigators at first suspected mechanical failure. After all, why else would two engines stop working mid flight? But when they pulled out the wreckage of the engines from the sea bed, nothing was wrong with them at all. They came to a horrifying conclusion: Flight 1153 must have run out of fuel. But that didn’t make sense. The pilots later told investigators that the fuel gauge read 1800 kilograms of fuel. What they had no idea about (and what investigators later discovered) was that the aircraft had the wrong fuel gauge installed on it. The ATR has two different aircraft types: the 42 and the 72. The 42 is much smaller than the 72, so you aren’t supposed to use a 42 gauge in a 72 aircraft, because it will tell you the plane has more fuel than it really does: 1800 kilograms more, to be exact.

And while the two fuel gauges do look the same:

There are different registration numbers on each one, and there is no reason why a maintenance man shouldn’t have been able to read the damn thing and tell the difference. What’s worse, the pilots went under the assumption that they had enough fuel before they took off, and didn’t get a refueling slip, required before taking off. And to top it all off, the pilots hadn’t handled the situation as they should have, feathering the props and adjusting their speed to that of prime gliding velocity. They should have been able to make it to Palermo. Several people went to jail for this accident, including the two pilots.

4. Aeroperu Flight 603

On October 2, 1996, Aeroperu Flight 603 took off from Chavez International Airport in Lima, Peru. The aircraft was a brand new Boeing 757, but something was wrong. The airspeed indicators, altimeters, and vertical speed indicators seemed to not be working. They had no idea how fast they were going, how high they were, or how fast they were ascending or descending. Compounding this problem was flying at night, over the ocean, so there was no visual reference points. The pilots kept getting confusing and contradictory warnings from the aircraft: some said they were flying too fast, some said too slow, some said too low to the ground, and then the autopilot stopped working. The best comparison that can be made to this situation is driving in a car down a country road at night, with no headlights, your speedometer is telling you you’re driving faster, then slower than you really are, and having the horn honking constantly and being unable to turn it off.

The aircraft crashed into the water, killing all 70 people on board. No one could figure out what went wrong with the aircraft’s instrumentation. Perhaps the onboard computer had suffered a critical malfunction? The actual answer was much more simplistic. Airplanes measure airspeed and altitude using instruments called pitot tubes, which take in air that moves fluid around inside the instrument to determine changes in air pressure which is then relayed to the flight computer and the pilots. In order to work, the pitot tubes need to have a constant flow of air into them; if the tube is blocked, the instruments won’t read properly.

On this aircraft, the pitot tubes are located inside what is known as a static port, to prevent clogging. When the aircraft is worked on or cleaned, proper procedure is to cover these ports up. This had been done on Flight 603. The only problem was, the maintenance man had forgotten to remove the tape after the work was finished. There were no flags or brightly colored warnings to inform anyone involved with the plane to remove the tape, as there are on other aircraft, it was just plain tape. Pulling the wreckage of the plane from the bottom of the ocean, the evidence was damning:

70 people had died because of a piece of duct tape.

3. Helios Airways Flight 522

On August 14, 2005, The Greek Air Force scrambled two F-16s to intercept a 737 that was circling Athens International Airport. The plane was not answering Air Traffic Controller calls, and wasn’t communicating at all with the ground. The jet caught up with the jumbo jet, ready to shoot it down if it proved to be a terrorist attack. The fighter pilots reported that the oxygen masks were deployed in the passenger area, and that no one was moving anywhere in the plane, including the cockpit. Then, one man appeared in the captain’s chair, apparently trying to regain control of the aircraft. Both engines flamed out, and the airliner crashed in Marathon, Greece. All 121 passengers and crew were killed. Autopsies were performed, and all the people were alive at the time of impact, so why weren’t they moving around when the fighters flew next to it? What had happened to the pilots? Hypoxia had happened. For those of you who failed basic anatomy, hypoxia is what happens when a person is starved of oxygen, after about 5 minutes without breathable air, you pass out.

At 20,000 feet, there isn’t enough oxygen in the atmosphere to breathe, that’s why planes are pressurized with ground level air so that people can fly at that height without dying of oxygen starvation. But, Helios 522 had never pressurized, and the entire plane was incapacitated, save for one flight attendant who had gotten to bottled oxygen stored in the kitchen (as opposed to passenger oxygen mask, which contain only about 10 minutes of emergency air.) A certified pilot himself, he had tried to save the airplane before it ran out of fuel, but was unable to: he simply wasn’t experienced enough.

As for why the plane didn’t pressurize in the first place, that’s tragically simple to understand. A suspected air leak had led to a pressurization test the day before Flight 522 took off. Part of this test is switching the plane’s pressurization switch from automatic to manual, allowing the workers to pressurize the plane while on the ground. No significant air leak was found, but the workers forgot to switch the pressurization switch back to auto. When Flight 522 took off the next day, it didn’t pressurize, and the flight crew mistook the warning sound as another problem, never dreaming they could have a pressurization problem on a modern aircraft. The engineers on the ground trying to help the pilots fix the problem even asked them if the pressurization switch was set to auto, but the pilots either never heard, or disregarded this, and succumbed to hypoxia seconds later. Flight 522 was now doomed.

2. Aeroflot Flight 593

On March 23, 1994, a brand new Airbus A310 operated by Aeroflot traveling from Moscow to Hong Kong suddenly crashed in Siberia, killing all 75 on board. There was nothing mechanically wrong with the aircraft, why would it suddenly smash into the ground? The answer could be found on the Cockpit Voice Recorder, in one of the strangest accidents in the history of aviation. Yaroslav Kudrinsky was taking his two children Yana and Eldar on their first international flight, and in the middle of the night, with Kudrinsky as relief pilot in command, the two teenagers were brought into the cockpit to visit their father.

Inexplicably, and against airline regulations and common sense, the proud father allowed his children to sit in the captain’s chair, and even operate the controls. He didn’t think there would be a problem, because the autopilot was in command and the co pilot was still at the other set of controls in case of something going wrong. When Eldar pushed the control column hard enough for 30 seconds, long enough to contradict the autopilot, it partially disengaged, switching control of the ailerons to the pilot. The ailerons control the plane’s pitch, and without the flight computer or the pilots controlling them, the airplane began to bank to the right, imperceptibly at first.

No one in the cockpit noticed the change, because Russian planes normally gave an audible warning when a switch from autopilot to manual was made, and no such warning sounded. The bank continued getting steeper and steeper. Eldar noticed first, but the pilots were two slow to react, until the plane was banked at almost a 45 degree angle, the g forces pressed everyone to their seats or to the back of the cockpit. The only one with both hands on the controls was Eldar, and he didn’t have experience or strength enough to turn the stick back left without help.

Then the aircraft began to dive towards the ground as it stalled. Finally, Eldar was able to get out of the captain’s chair, and both captain and co-pilot were able to take control together. But by then, it was too late, there wasn’t enough altitude to recover, and the plane smashed into the mountains. It has been the only major aircraft accident attributed to having a kid at the controls, but it should never have happened at all.

1. Air Canada Flight 143

Air Canada Flight 143 was a Boeing 767 traveling from Montreal to Edmonton on July 23, 1983. While cruising along at 41,000 feet, first one, then both engines flamed out. Inexplicably, they had run of fuel. Despite not having a checklist for what to do if both engines stop working, the captain was able to force the jumbo jet to transform into a giant glider.

Recognizing the plane would hit the ground before reaching any active airport, they diverted to Gimli Industrial Park Airport, a former Canadian Air Force base that had since gone private, and in fact was playing host to a sports car race in which part of the decommissioned runway was being used. The stage was seemingly set for disaster.

The pilots muscled the plane down to the runway, blowing out 2 tires and the forward landing gear collapsed, causing the nose to scrape the ground and smash the guardrail installed after the runway was decommissioned (it had been turned into a drag racing strip.) There were some minor injuries to the passengers, but incredibly, no one was killed.

Why had the aircraft run out of gas midflight? By all accounts, the plane should have had enough to get to Edmonton plus a half hour of emergency reserve, but the tanks were completely dry. The answer, believe it or not, was the wrong answer. To a math problem, that is.

In 1983, Air Canada and Canadian aviation in general was in the process of converting from Imperial units (pounds and gallons)to the metric system (liters and kilograms.) Because the fuel quantity indicator on the aircraft was malfunctioning, it had to be calculated by hand. Instead of using the conversion factor for Kg to L (0.803) the ground crew used the conversion factor for Lb to L (1.77) So, instead of having 22,300 kilograms of fuel on board, they had 22,300 pounds, or a little over 10,000 kg, which gave them enough fuel to run out exactly where they did.

The two pilots were given the Sullenberger treatment, receiving airmanship awards and (possibly) math tutoring. As for the Gimli Glider, as the plane became known, it was repaired and flown by Air Canada for another 25 years before being retired and flown to the Mojave Desert to take its place in aviation history.

By Ben Adelman