Lost Souls of Grammatiko: The crash of Helios Airways flight 522
Note: this accident was previously featured in episode 32 of the plane crash series on April 14th, 2018, prior to the series’ arrival on Medium. This article is written without reference to and supersedes the original.
“Helios 522, do you read?”
These immortal words, spoken again and again in futile expectation of a reply, have since come to embody one of history’s most haunting air disasters, one which played out in the sunny skies over Greece on the 14th of August, 2005. It was a catastrophe unlike almost any other: a Boeing 737 full of passengers, circling on autopilot off the coast of Athens, in complete radio silence with no one at the controls. In the windows, people lay slumped over, unmoving; the captain’s seat sat empty; and yet the engines continued to run, propelling the plane around and around until it ran out of fuel. Fighter jets followed it down, watching as it glided to its doom, when, to their amazement, a person appeared in the cockpit — a mysterious figure, not one of the pilots, who sat in the left seat and whispered desperate “mayday” calls until the end, unable to stop the plane from crashing. Who was this lonely soul still clinging to life aboard a ghost plane? What horrible fate had befallen the passengers and crew? These questions would haunt both Greece and the world, as investigators pieced together a sad tale of errors and missed opportunities which sent the 737 and its unconscious occupants gliding silently into the golden crown of Grammatiko Hill.
In the placid waters of the eastern Mediterranean, some one hundred kilometers from the coasts of Turkey and Syria, lies the island nation of Cyprus, the European Union’s most isolated member, and one of its smallest. Once an Ottoman territory, then a British colony, now an independent nation, Cyprus’s modern history has been marked by a tragic conflict between its Greek-speaking south and its Turkish-speaking north, leaving the island divided and quashing local dreams of being annexed by Greece or Turkey. Independent initially against its will, Cyprus has made do, becoming an alternative holiday destination despite the UN-demarcated no-man’s land which still snakes across the island and through the streets of its capital.
If one wants to fly to Nicosia, the capital and largest city of Cyprus — (the unrecognized state of Turkish North Cyprus, as the other half is known, also claims Nicosia as its capital, but controls very little of it) — then one must first fly to another city, then drive the rest of the way. Nicosia’s international airport, which lies inside the demilitarized zone, has been largely abandoned since the war which divided the island in 1974, its run-down and dust-covered terminal buildings still decked out in early ’70s interior décor. Most international flights to Cyprus land in Larnaca, the country’s third largest city and home to its most developed airport. It was no surprise, then, that this was the place where, in 1998, a local businessman decided to found Cyprus’s first independent and first low-cost airline, christened Helios Airways, after the ancient Greek god of the sun.
Helios Airways began as a scrappy startup, and never really stopped being one. It claimed to offer tickets for half the price of those sold by Cyprus’s state-owned flag carrier, making it an attractive option for budget-minded European travelers looking for a cheap summer getaway. Its fleet initially consisted of two third-generation Boeing 737–800s, as well as a leased Airbus A319 belonging to another airline. Later, in 2004, the airline added a third Boeing 737, a second-generation -300 model built in 1998 and registered in Cyprus as 5B-DBY.
By all accounts, the introduction of 5B-DBY was rushed and disorganized. The United Kingdom Civil Aviation Authority, which had been contracted by the Cyprus Department of Civil Aviation to perform a number of regulatory functions, expressed repeated concerns that paperwork was not in order and that the timeline for the plane’s introduction was unrealistic, as company executives insisted on having it ready by the summer travel rush. Despite the warnings, however, 5B-DBY indeed carried passengers in the summer of 2004, although not without its fair share of issues.
In fact, the 737–300 was plagued by gremlins from the very beginning. Mechanics were unable to identify the root cause of many of the problems, which finally culminated in an incident serious enough to warrant outside investigation. In December 2004, 5B-DBY was moments away from beginning its descent into Larnaca after a flight from Warsaw when a loud bang was heard. Within seconds, the air rushed out of the cabin and the passenger oxygen masks automatically deployed. Recognizing that an explosive decompression had occurred, the pilots donned their own oxygen masks and initiated an emergency descent. As the plane lined up for landing, the aft flight attendants reported a concerning discovery: a hole had opened up in the seal around the right rear (R2) passenger door, big enough to stick a hand through (not that anyone was fool enough to try). The flight subsequently landed safely, and three passengers were treated for minor injuries.
An investigation by the Air Accident and Incident Investigation Board of Cyprus was unable to determine the reason for the explosive decompression, but regardless of the cause, the airplane required major repairs. However, after the incident, 5B-DBY’s chronic difficulties only got worse. Pilots reported constant problems with the equipment cooling system. At the same time, air was still leaking out somewhere, and the automated pressurization system kept throwing out errors. Mechanics probably never saw the error messages, which were buried in an electronic menu that they didn’t normally open. But from time to time, the issue surfaced in a manner which was visible to the crew, and then the plane would find itself back in for yet another round of unscheduled maintenance.
Early on the 14th of August 2005, the problems struck again. On a red-eye flight from London early that morning, the aft cabin crew heard banging sounds coming from the R2 door and observed ice forming around the door seal. After the flight landed in Larnaca at 3:25 a.m. local time, the problems were recorded in the technical log, and the plane was handed off to Helios Airways maintenance personnel for servicing. In charge of that effort would be British ground engineer Alan Irwin, a highly experienced mechanic who had previously worked for several large European carriers.
Given the door’s history, it was clear to Irwin that the sounds and presence of ice probably had something to do with a leak in the door seal. But when he inspected the door, he couldn’t find anything obviously wrong with it. To locate the leak, he would have to scale up the search by conducting a pressurization test.
Like all airliners, the Boeing 737’s cabin is pressurized in order to ensure that the occupants can breathe at high altitudes, where the outside air is less dense. Contrary to popular belief, however, no airliner is a perfect pressure vessel; in fact, if they were, the passengers would use up all the oxygen and succumb to carbon dioxide poisoning. The air in the cabin is in fact in constant motion, entering the fuselage through the bleed air intakes in the engines and exiting through outflow valves in the front and rear. Some air also escapes through various seals, through the toilets, and through other minor vents, cracks, and openings. Although the passengers don’t normally notice, the air in an airplane cabin is completely replaced via this cycle every few minutes.
During a normal flight, the pressurization process is handled automatically by the plane’s electronic pressure control system. Prior to takeoff, pilots simply enter the planned cruising altitude and the altitude of the destination, and the system calculates exactly how much and for how long it will need to open the main outflow valve in order to maintain a comfortable cabin pressure throughout the flight. It will even automatically regulate the rate of depressurization during the descent based on the height of the destination airport, ensuring that uncomfortable ear-popping is kept to a minimum.
However, if something is wrong with the automatic system, or if maintenance personnel want to test the integrity of the pressure vessel, it is also possible to control pressurization manually. This is accomplished by moving the pressurization mode selector switch on the P5 pressurization panel from “AUTO” to “MAN,” allowing a pilot or mechanic to directly control the position of the outflow valve. This was what the engineer intended to do aboard 5B-DBY.
Having gathered two other mechanics, one to watch the door from the inside and another to watch from the outside, Irwin moved the pressurization switch to “MAN,” closed the outflow valve, and turned on the auxiliary power unit, the plane’s backup generator. He then used the APU to start the air conditioning packs in order to draw air into the cabin. Within minutes, the pressure inside the plane began to increase, rising toward the nominal in-flight differential pressure 8.25 psi. Nevertheless, neither engineer was able to hear any sounds of air escaping near the R2 door, and the system was able to hold the pressure just fine. Writing off the test as inconclusive, he let the pressure differential return to zero, although not without accidentally hurting the assistant engineer’s ears in the process.
After the test, Irwin wrote in the technical log, “Door and local area inspected. NIL defects. Pressure run carried out to max diff…. No leaks or abnormal noises,” along with information about the pressure values used and the procedures followed. The problem hadn’t been solved, but he had done all he could. After releasing the plane for service, he went back to the office, believing that he had restored the airplane to its original configuration. But, as it turned out, he hadn’t.
Sometime before 8:00 that morning, two pilots and four cabin crew arrived at the aircraft to prepare for flight 522 to Prague, with a stopover in Athens. In command was 58-year-old Captain Hans-Jürgen Merten, an experienced pilot who had built his career in East Germany flying the Tupolev Tu-134, before finding himself bouncing around various small airlines in Europe after that type was removed from service. He had since built up a respectable number of hours on the Boeing 737, and although his reserved attitude sometimes went over poorly with Cypriot flight crews, there had been no serious complaints about his performance since he started at Helios Airways earlier in 2005.
His copilot that day would be 51-year-old First Officer Pampos Charalambous, a citizen of Cyprus, who was also experienced on the 737 and had been flying for Helios Airways since shortly after its founding.
In this case, it’s also worth going into a little bit more detail about the cabin crew. One of the flight attendants was Haris Charalambous — no relation to the First Officer — who is believed to have been assigned to the forward position alongside cabin supervisor Louisa Vouteri. One of the two flight attendants assigned to the rear of the airplane was Charalambous’s boyfriend, 25-year-old Andreas Prodromou, who had joined flight 522 at the last moment to spend time with his partner after a spot unexpectedly opened up. Prodromou was also an aspiring pilot with a private pilot’s license and a small amount of experience on light aircraft, and was working as a flight attendant to pay his way through training. A man of many talents, Prodromou was also a trained scuba diver.
As 115 passengers, mostly Cypriots and Greeks, boarded for the first leg to Athens, the pilots were finishing up their pre-flight preparations, entering route and approach information into the flight management system, tuning instruments to pick up relevant navigational aids, and, of course, entering the cruise altitude and destination altitude into the pressurization panel. In total, the pre-flight procedure included some 80 items, eight of which involved switches on the pressurization panel. One of these read, “Pressurization mode selector — AUTO.”
It would later be proven that the pressurization mode selector was actually set to manual, presumably having been left there after the pressure test earlier that morning. A green light labeled “MANUAL” would also have illuminated next to this switch. But despite these indications, and the requirement to check them, neither pilot noticed.
Having completed their pre-flight, the pilots would then have launched into the before start checklist, verifying once more that various aircraft systems were properly configured for flight. As Captain Merten read off each item, First Officer Charalambous replied with the appropriate callback, traversing his way from panel to panel through the cockpit. Step 12 on the 25-step checklist stated, “AIR COND & PRESS … PACK(S), BLEEDS ON, SET.” But once again, seemingly no one noticed that the pressurization mode selector switch was set to manual.
Still unaware that the automatic pressurization system was not turned on, the pilots started up the engines, pushed back from the gate, and taxied to the runway. After an uneventful takeoff roll, flight 522 became airborne at 8:07 a.m., climbing initially toward 10,000 feet, with further clearances expected to follow. They had no idea that the cabin outflow valve was almost all the way open, right where the mechanics had left it, and with the pressurization system set to “MAN,” it wouldn’t close unless they told it to.
For the next five minutes, there was no indication of a problem. With the plane climbing steadily at about 2,500 feet per minute, the cabin pressure equalized with the outside air pressure almost as fast. Below 10,000 feet, the passengers and crew were unlikely to have noticed any ill-effects, although perhaps their ears would have begun to feel strange. Radio communications remained normal, and the controller cleared flight 522 to ascend to its cruising altitude of 34,000 feet.
Then, at 8:12, as the plane climbed through 12,500 feet, the air pressure inside the cabin reached the equivalent of 10,000 feet, automatically triggering a cabin altitude warning horn. At pressure altitudes greater than 10,000 feet, passengers can begin to experience adverse health effects, and in fact if the cabin altitude rises higher than this, something must be wrong by definition, and proper procedure calls for the pilots to don their oxygen masks and descend immediately. But for some reason, that didn’t happen.
Instead, flight data indicates that Captain Merten, who was the pilot flying, disconnected the autopilot, reconnected it, disconnected the autothrottle, reduced engine thrust for several seconds, then turned the autothrottle back on. This response would have been quite mystifying had he not shortly thereafter contacted Helios Airways dispatch for help, revealing in the process that he had made a basic error which observers would only pick up on much later.
The conversations between flight 522 and Helios dispatch were not recorded, but according to the dispatcher’s recollection, Merten explained that he had a takeoff configuration warning horn, and some kind of problem with the equipment cooling system. This was beyond the dispatcher’s area of expertise, so he called in outside help — namely, Alan Irwin, the same maintenance engineer who had run the pressure test just a few hours earlier.
As its name implies, the takeoff configuration warning horn is only supposed to sound on the ground, when the pilots advance the thrust levers without correctly configuring the aircraft for flight — for example, if they haven’t extended the flaps, or if the stabilizer is set incorrectly. It cannot sound while in the air, because the warning is only armed when there is weight on the wheels. However, on the Boeing 737, the sound of the takeoff configuration warning horn was the same as that of the cabin altitude warning. Because the cabin altitude warning could only sound in the air, and the takeoff configuration warning could only sound on the ground, the likelihood of confusion between them was thought to be minimal. But Captain Merten had confused them anyway, as evidenced not only by his statement to dispatch, but by his instinctive rollback of the throttles, which would be the normal reaction to a configuration warning on the ground.
Not realizing that he had completely misidentified the warning, Merten was unsure what the problem was, and the only lead he had was another indication that had caught his attention: the equipment cooling lights.
The equipment cooling system draws in cabin air to cool the avionics bay beneath the cockpit. The system is on by default, but if it detects low airflow or low air density, the two equipment cooling lights, each labeled “OFF,” will illuminate to inform the pilots that the cooling system is not functioning.
When Merten first called dispatch, the plane was climbing through 16,000 feet, and the cabin altitude was about 12,000 feet and rising. Shortly after this, the air density in the equipment cooling system dropped low enough to activate the equipment cooling lights. This in turn caused the master caution light to illuminate, drawing the pilots’ attention to the cooling issue.
Over the radio, Merten told Irwin that “both my equipment cooling lights are off.” Unfortunately, Merten’s relatively limited knowledge of English had tied his tongue: he probably meant to say “both my equipment cooling ‘OFF’ lights are on,” but what came out was something altogether different. Unsure why Merten was concerned about a warning light being off, Irwin replied, “This is normal,” then asked Merten to confirm the problem. The Captain’s reply, however, was not very illuminating: “They are not switched off,” he said, according to Irwin’s recollection.
Sometime during this conversation, the cabin altitude rose through 14,000 feet, triggering the automatic deployment of the passenger oxygen masks. A “PASS OXY ON” indication illuminated on the overhead panel, but nobody noticed. This indication would normally have been accompanied by the illumination of the master caution light to gain the crew’s attention, but that light was already on, so it didn’t. Instead, even as the passengers and flight attendants began to put on their masks, Captain Merten remained focused on the equipment cooling system.
At this point, the contours of the conversation become slightly less clear. According to the version of events Irwin later gave to the police, he became suspicious that Merten might actually be looking at the green “MANUAL” light on the pressurization panel, which was next to the equipment cooling panel, so he asked, “[Can you] confirm that the pressurization panel [is] selected to AUTO?” On the other hand, an account of events which Irwin wrote on the day of the flight made no mention of any such question. Whether the question was in fact asked is therefore up for debate.
Whatever was said, Irwin’s various accounts agree that Merten then asked where to find the equipment cooling circuit breakers, to which Irwin replied that they were behind the captain’s seat. After that, no one ever heard from the flight again.
By the time the conversation with dispatch ended, flight 522 was approaching 29,000 feet above sea level, approximately the height of Mount Everest. The cabin altitude was somewhere between 24,000 and 26,000 feet. Mountaineers refer to anything above 26,000 feet as the “death zone,” because at those altitudes the human body will use up more oxygen than it can take in, resulting in deterioration of physical and mental faculties, followed eventually by death. Some of the world’s best mountaineers have spent as long as 21 hours in the death zone without supplemental oxygen and lived to tell the tale. The average airline passenger, on the other hand, who possesses neither superhuman fitness nor weeks of prior acclimatization to high altitudes, will lose consciousness in a matter of minutes. Unless oxygen intake increases, irreversible brain damage will eventually occur. Indeed, although mountaineers routinely spend days above 20,000 feet, a person suddenly transported from sea level to this altitude is likely to die quickly if left there.
Unfortunately, Captain Merten and First Officer Charalambous never donned their oxygen masks, and never realized that their airplane had not pressurized. The cabin altitude was approaching the death zone when Merten apparently got out of his chair to find the circuit breakers, collapsed from lack of oxygen, and never woke up. Charalambous fell unconscious at around the same time, still strapped into his seat. Those passengers and flight attendants who put on their oxygen masks would have stayed awake longer, but the passenger masks only provided about 12 minutes of oxygen, under the assumption that the pilots would descend to a lower altitude. Instead, flight 522 climbed on autopilot to 34,000 feet, the altitude which had been set by the crew, and leveled off. No doubt with increasing concern, the passengers would have waited for some announcement from the cockpit, but none ever came, and one by one they began to lose consciousness, swallowed up by a dizzying, euphoric blackness.
Back in Larnaca, Helios Airways dispatchers tried to call the flight, but got no response. Dispatch then called the area control center in Nicosia to see if air traffic control could contact the plane, but their calls also went unanswered, even when passed via relay planes near flight 522. And yet their radar screens clearly showed that the plane was still at its assigned altitude, proceeding on course to the next waypoint. In their opinion, this showed all the hallmarks of some kind of radio failure. The Nicosia controller asked flight 522 to change its transponder code, attempting to ascertain whether the flight might still be receiving messages even if it could not transmit. But the transponder code didn’t change.
For some time after this, the plane continued to fly along the course the pilots had programmed before takeoff. Entering Greek airspace, it flew directly to the VOR radio beacon on the island of Rhodes, then turned a couple of degrees to the right in the direction of waypoints RIPLI and VARIX. Greek controllers now tried to contact the flight, also without success. Over and over they asked, “Helios 522, do you read?” And in the wake of each message, only silence followed.
By 9:12, 52 minutes after the last transmission from Captain Merten, the plane was nearing reporting point RIPLI, where it would normally be expected to begin its descent into Athens. The controller issued a descent clearance, on the off chance that the pilots might somehow hear it, but no reply ever came, nor did the plane begin to descend. The flight computers had been programmed with the entire route all the way to Athens International Airport, but the autopilot would not initiate a descent unless instructed to do so.
Still at 34,000 feet, the plane overflew the VARIX reporting point, followed by the KEA VOR on the island of Kea, before making a slight left turn to intercept what appeared to be the standard instrument approach to Athens. To see the plane make such a maneuver while still at cruising altitude must have sent chills down the spines of the air traffic controllers. Concluding that this was no ordinary radio failure, they decided to call in the Air Force.
As the Hellenic Air Force prepared to scramble fighter jets to intercept the plane, flight 522 made a sharp right turn and lined up with runway 30L. Like some kind of zombie, it flew the approach which had been selected by the crew before takeoff, dutifully tracking toward the airport. Minutes later it overflew Athens International Aiport at cruise altitude, then initiated a right turn back to the KEA VOR, perfectly following the standard missed approach procedure for runway 30L, as it had been programmed to do if it did not land at the airport. After a few short minutes, it reached the VOR, at which point, having exhausted the programmed flight plan, the flight management computer instructed the autopilot to enter the published holding pattern around the VOR. From then on, flight 522 began to circle over the island of Kea, some 65 kilometers southeast of Athens.
Five times it circled, traveling southeast at first, then turning back to the northwest, then to the southeast again, over and over, as air traffic controllers watched in helpless bewilderment. It was not until 10:23, when flight 522 was on its sixth circle, that two F-16s of the Hellenic Air Force finally managed to catch up with it. It is doubtful that the F-16 pilots had any idea what to expect. The situation was already extremely weird, unlike anything they or the controllers had seen before — but things were about to get much, much weirder.
Approaching the airplane, the F-16 pilots attempted to signal their presence to the crew, but the 737 did not react. They checked the exterior for damage, but saw none. One of the F-16s now drew in for a closer look, and there the pilot came upon a scene straight out of a horror movie. The cabin lights were off, and the silhouettes of oxygen masks could be seen dangling in the aisles, backlit by the light streaming through from the opposite windows. Several passengers wearing oxygen masks lay slumped against the windows, utterly motionless. Positioning his jet alongside the cockpit, the pilot saw a person lying limp in the First Officer’s seat, showing no signs of life. The left seat was empty, and there was no sign of the captain. Shocked by what he had seen, the F-16 pilot could only conclude that flight 522 was a ghost plane, flying in a state of suspended animation with its passengers and crew either unconscious or dead.
When air traffic controllers received the pilot’s report at 10:32, they immediately declared an emergency, and first responders throughout the region began to prepare for an imminent disaster. No one knew where the plane would come down or what might happen when it did. Only one thing was clear: with no one at the controls, the plane was eventually going to run out of fuel and crash.
For another 14 minutes, the 737 continued to fly in circles, shadowed by the two F-16s, whose pilots seemed condemned to wait for the inevitable. And then, as yet unknown to the fighter pilots, something unbelievable happened: an “access requested” chime sounded in the cockpit, first once, then again. Incredibly, someone was at the door.
The chime sounded several more times, then rose to a continuous alarm which lasted for 20 seconds before the door unlocked with a click. The door opened, and a man in a light blue uniform walked into the cockpit, armed with one of the plane’s four portable oxygen bottles. With the mask over his face and the bottle beside him, he sat down in the captain’s seat and put his hands on the controls. The F-16 pilots could only watch in astonishment, relaying their observations back to air traffic control, even as their now-frantic attempts to get the man’s attention were met with failure.
By now flight 522 was in its tenth holding pattern, and its fuel reserves were nearly exhausted. The mystery pilot would have had little time to familiarize himself with the 737 cockpit, because less than one minute after he entered the flight deck, the left engine ran out of fuel and flamed out. Propelled by the asymmetric thrust from its remaining engine, the plane turned sharply to the left before rolling out on a northwesterly heading. Unable to remain at 34,000 feet on one engine, it then began to descend.
As it dropped, the flight data recorder captured unexpected variations in speed, pitch, and heading. These variations could only mean that the man was making inputs to the controls in an attempt to fly the airplane. And yet the fighter pilots still could not get his attention, and in fact they were forced to back off to reduce the risk of a midair collision.
Within minutes, the 737 crossed over the island of Euboea, descending rapidly. One of the F-16s drew close again and saw the First Officer sitting upright, as though the man had tried to wake him, but he remained motionless. The cockpit voice recorder, however, captured something else: a weak, exhausted voice, calling out, “Mayday, mayday, mayday, Helios Airways flight 522, Athens… mayday, mayday.” But no one could hear the transmission — the radio was still tuned to the frequency for Nicosia, which was out of range.
Shortly thereafter, the plane turned sharply to the left, crossing back over Euboea a second time. Approaching 7,000 feet and descending at several thousand feet per minute, flight 522 was already moments away from disaster when its right engine also ran out of fuel and flamed out. The F-16 pilots watched with bated breath: was the mysterious person in the cockpit going to try to land the powerless plane on the water? Did he have any control at all?
At that moment the man acknowledged the fighter for the first time, responding in kind to a hand signal. The fighter pilot then signaled that the mystery pilot should follow him to the airport, but the man replied by simply pointing down, as if to say, “The plane is going down, and there’s nothing I can do.”
Crossing back onto mainland Greece, the plane turned sharply to the left again, descending toward the hills which lined the coast northeast of Athens. Recognizing that a crash was imminent, the F-16s pulled away at the last moment. The man at the controls attempted to pull up just before impact, perhaps hoping to ease the plane into the ground, but his efforts were fruitless. Helios flight 522 impacted hard, digging three parallel furrows in the earth as it careened up the steeply sloping hillside, throwing up a great plume of dust. The tail section broke off as it slid upward, and then the plane crested the top of a ridge, becoming momentarily airborne again as it crossed a deep ravine, spewing pieces of the airframe through the air behind it. A split second later, the fuselage slammed into the side of a second ridge and burst into flames, catapulting huge masses of debris up and over the ridgeline and down the other side, until its momentum was at last exhausted. Seconds later, the F-16 pilots radioed it in: Helios flight 522 was down.
Fire crews and ambulances, already alerted to the ongoing emergency, immediately rushed to the scene of the crash on Grammatiko Hill, just outside the village of Grammatiko, some 35 kilometers northeast of Athens. Arriving within minutes, they were confronted with a tragic tableau of devastation. The remains of the 737 and its occupants lay strewn for some 650 meters across two hills and two ravines, leaving little that was recognizable, save for the tail, where the inverted face of the sun god Helios still stared out over the burning ridgeline.
Fire crews put out the fire almost immediately, but it erupted again after they thought they had finished, spreading to nearby chaparral and taking on wildfire characteristics before an air tanker sortie managed to bring it under control some 30 minutes later. By then, however, it was clear that none of the 121 people on board had survived, making Helios Airways flight 522 the deadliest crash in the history of both Greece and Cyprus.
The shock of the disaster was compounded by the bizarre details of the flight, which leaked to the press almost immediately. Somehow, a plane had flown for nearly three hours without radio contact, with both pilots and all the passengers unconscious or dead, except for one man, who seemingly tried but failed to save the plane only at the very end of the flight. Were the passengers dead before impact? Who was the man at the controls, and how did he remain alive and conscious? And most importantly, what had incapacitated the occupants — was it a toxic gas, like carbon monoxide, or a simple lack of oxygen? Faced with an accident unlike almost any other in history, Greek investigators would be hard pressed to piece everything together in time to ward off the rumors. Indeed, so intense was the public interest in the accident that a number of hoaxes appeared in the first days, including a man who faked text messages from a person on board the plane, as well as a fake image purportedly taken from one of the F-16s, which circulated widely on the internet despite the fact that it showed the wrong type of 737.
One by one, however, investigators began to pull back the curtain from the flight’s many mysteries. Autopsies showed that all 121 passengers and crew were alive on impact, proving that the lack of motion observed by the F-16 pilots was because the occupants were unconscious, not dead. Toxicological tests further proved that none of the occupants were exposed to any type of poison gas. With this information in hand, the only reasonable conclusion was that the plane either lost pressurization, or never pressurized in the first place.
A number of items strongly pointed to the latter of these two explanations. The loss of contact occurred while the plane was still climbing, right at the point where one would expect the pilots to lose consciousness if the aircraft did not pressurize after takeoff. The fighter pilots observed no damage to the exterior which could have pointed to an explosive decompression. And perhaps most interestingly, the P-5 pressurization panel was found in the wreckage with the pressurization mode selector switch set to “MAN” instead of “AUTO.” Already aware of the pressure test which was conducted on the morning of the flight, investigators wondered: had the engineer simply forgotten to return the switch to its proper position?
There was initially some doubt about this finding, due to the fact that the switch was found turned past the “manual” position entirely, indicating that it may have been wrenched sharply in that direction on impact. In order to be certain what position the switch was in during the flight, Greek investigators decided to try to extract data from the non-volatile memory of the electronic pressure control system, which recorded a number of values, including the position of the main outflow valve, as well as the cabin altitude. This endeavor proved successful, and the data proved a central thesis of the inquiry: that the outflow valve was in the fully open position from the moment the plane took off, preventing the cabin from pressurizing.
The data also revealed that there were problems with the pressurization system on all of the last 74 flights which remained in the system’s memory. During many of these flights, the system generated an error message which read “30 inflow/leakage,” which occurs when the automatic pressurization system has to keep the outflow valve closer to the closed position than expected in order to maintain cabin pressure. This normally indicates that excessive leakage is occurring somewhere else, which was consistent with cabin crew reports of continued problems with the R2 door ever since it explosively decompressed in December 2004. Notably, however, the system did not throw out any errors on the accident flight which would indicate a total failure of the automatic pressurization system. This strongly suggested that the reason the outflow valve remained open throughout the flight was because the system was in manual mode, and no one ever closed it.
Because the pilots normally never touch the pressurization mode selector switch, investigators were forced to conclude that the engineer had almost certainly left it in manual after the pressure test, despite his heartfelt denials. To this day, however, Alan Irwin insists that he moved the switch back to AUTO before he left the airplane.
In fact, Irwin’s story is rather tragic, and serves as an unfortunate example of the consequences of using investigative findings to assert individual blame. Days after the crash, Irwin was interviewed by Cypriot police, who accused him of failing to move the switch back to “AUTO,” and more or less implied that he was going to be held responsible regardless of his answer. Irwin fervently denied the charges, and indeed, by all accounts he genuinely believed he had put the switch back where it belonged. Evidence indicates that he was mistaken, but that doesn’t mean he was insincere. Nevertheless, a Greek court subsequently charged Irwin and five others with 121 counts of manslaughter in connection with the crash, sending his life into a tailspin. He lost his job, his marriage fell apart, and his wife drank herself to death in 2012. After an ordeal lasting several years, he was finally acquitted on appeal, but the damage had been done. The simple truth, which the court eventually acknowledged, was that the crash wasn’t his fault, even if he did forget to move the switch back to “AUTO.” It was probably an innocent mistake, and maybe if it had been treated as such, there would be a lot less bitterness surrounding the crash. Partly out of personal necessity, Irwin continues to stand by his belief that the system itself must have failed in some way that investigators did not detect, and sympathetic media can and do take his side from time to time, as a long-form Guardian piece did in 2020. That explanation probably can’t be entirely ruled out, but given the lack of evidence of any failure, the simpler answer is that Irwin was mistaken, and that was the position quietly adopted by the Greek investigators.
Part of the reason why the crash was not Irwin’s fault even if he did leave the switch in “MAN” is because plenty of other checks and balances existed to ensure that such an error would not lead to disaster, and these also failed.
Several opportunities to prevent the crash were presented to the pilots in the form of routine checks of the pressurization setting. The pre-flight procedure included eight items on the pressurization panel, including the position of the pressurization mode selector, and the pilots were supposed to check these settings again before engine start and a third time after takeoff. Because the cockpit voice recorder only captured the final 30 minutes of the flight, it was impossible to prove that the pilots correctly carried out these checks. Nevertheless, a number of factors may have caused them not to notice the incorrect setting even if the checks were accomplished. One of the most insidious of these was the fact that the switch almost never moved, and after checking it three times on every single flight and never finding it in the wrong position, the act of checking could have become purely automatic. Research has shown that people can and do miss seemingly obvious discrepancies while running through deeply ingrained routines, because they simply see what they’re expecting to see, without processing what is actually in front of their eyes. It was therefore entirely possible that First Officer Charalambous looked at the pressurization panel and instinctively called out “set,” without ever realizing that the switch was set to manual instead of automatic.
In addition to this fundamental shortcoming of human psychology, investigators noted a number of other factors as well. One of these was that the “manual” light on the pressurization panel illuminated in green, a color which typically indicates normal functioning and would therefore have failed to draw the pilots’ attention. Had this light illuminated in red, the probability that Charalambous would have noticed it may have been much greater. Furthermore, with each successive check, Charalambous would have been less likely to look closely, due to the expectation that any discrepancy would have been detected by previous checks. And finally, investigators could not help but note that comments on Charalambous’s training record indicated that he struggled with checklist discipline, making him relatively more predisposed to the types of errors described above.
Even after flight 522 took off, opportunities remained to avert disaster. The most significant last line of defense was the cabin altitude warning horn, which began to blare when the pressure inside the cabin reached the equivalent of 10,000 feet. The warning was surely working, since it was still going off when the cockpit voice recording began more than two hours later. But the fact that it sounded the same as the takeoff configuration warning ultimately proved fatal.
As explained earlier, the cabin altitude warning and the takeoff configuration warning used the same alert tone, which was considered justifiable because there was no overlap between the flight regimes during which they could activate. This choice was prompted by the fact that when the 737 was designed in 1967, the capacity available for storage of various aural tones was of much greater concern than it is today. Unfortunately, by 2005 this warning configuration still hadn’t been updated despite growing evidence that it was causing confusion. The basic problem was that pilots could spend an entire career flying 737s and never hear a cabin altitude alert in line operations, but due to the design of the before start procedures, takeoff configuration warnings were heard rather frequently. The configuration warnings on most aircraft arm themselves when the thrust levers are moved to the takeoff position, regardless of whether the engines actually produce takeoff thrust. As a result, the warning would often sound while the pilots were checking the full range of thrust lever motion prior to starting the engines, because the alarm thought they were taking off without having extended the flaps. Over time, this conditioned pilots on the 737 to associate that particular sound more closely with the takeoff configuration warning than with the cabin altitude warning.
This fact had led to a number of incidents in the early 2000s involving 737 crews who mistook a cabin altitude warning for a takeoff configuration warning. In one of the most serious of these near-misses, in 2002 a Ryanair 737 failed to pressurize after takeoff, and the crew misidentified the cabin altitude warning. A flight attendant attempted to draw the pilots’ attention to growing discomfort in the cabin, but she was told to stand by. While troubleshooting what they thought to be a takeoff configuration warning, the pilots let the cabin altitude reach 14,000 feet before the captain suddenly noticed that the air conditioning packs hadn’t been turned on. He immediately switched them on, causing the cabin to pressurize and avoiding an accident. Nevertheless, Irish investigators wrote that “the potential for a full-scale accident is self-evident,” words which would prove tragically accurate.
In another similar incident at an undisclosed carrier in the United States, the pilots of a 737 cruising at 37,000 feet were troubleshooting what they thought was a sensor problem when the cabin altitude alert unexpectedly sounded. They both initially misidentified the alert as a takeoff configuration warning, which they thought might be related to the sensor problem they were experiencing. However, after some time the first officer suddenly recalled that the cabin altitude warning and the takeoff configuration warning sounded the same, at which point they noticed that the cabin was slowly losing pressurization. After making an emergency descent followed by a safe landing, the captain was concerned enough to file an anonymous report with the NASA Aviation Safety Reporting System, which stated in part: “A safety issue I would like to raise awareness about based on my experience is the lack of wisdom in having the TKOF warning horn double as the ALT warning horn. Because the cabin was losing pressure slowly, we did not feel any pressure changes in our ears that would have normally served to alert us to a pressurization problem. If the FO had not happened to remember that the horn also serves as a cabin ALT warning horn, we may have continued trying to troubleshoot the air/ground problem, until passing out from lack of oxygen.”
These two cases were merely the most dramatic of at least half a dozen known incidents involving this particular point of confusion. The reports had in fact made it to Boeing, which by 2004 appeared to be aware of the problem. However, the company was reluctant to redesign the warning system, and opted instead to add language to the Flight Crew Training Manual informing pilots of the potential to confuse the two warnings. But even this palliative measure couldn’t save flight 522, because the revision was scheduled to go into effect in October 2005, and the crash took place in August.
Returning to the sequence of events, it was now apparent to investigators that the misidentification of the warning was one of the final links in the chain leading to the crash of flight 522. Nevertheless, a few observations remained. For one, the activation of the equipment cooling “OFF” lights could have distracted the crew from other indications, such as the “PASS OXY ON” light, that would have more obviously pointed to a pressurization problem. This distraction might have been especially potent if the pilots were aware of this airplane’s history of equipment cooling problems, which were unrelated to the events of flight 522, but could have drawn their minds away from cabin pressure as a possible reason for the illumination of the cooling lights. Furthermore, if the equipment cooling lights came on before the passenger oxygen masks dropped, then the accompanying illumination of the master caution light would have drawn their attention to the first indication, but not the second, because it was already on.
Because the beginning of the flight was not recorded on the CVR, it is unknown what exactly the pilots were doing as the plane climbed toward its cruising altitude. Most of what we know concerns Captain Merten, who was on the radio with dispatch, while virtually nothing is known about the actions of First Officer Charalambous. All we know for sure is that they must have remained distracted until they passed out from lack of oxygen, without ever recognizing what was happening. That’s the insidious thing about hypoxia: the worse it gets, the harder it becomes to realize that one is hypoxic. Mental faculties slowly slip away until one is no longer capable of identifying that a problem exists. By remaining distracted through the phase of mild hypoxia, where they might otherwise have recognized the problem, the crew allowed themselves to reach a state in which they could not save themselves, at which point the fate of flight 522 was sealed.
Although the Greek Air Accident Investigation and Safety Board had much to say about the thought processes of individuals, it also spent considerable time examining the safety culture at Helios Airways and in Cyprus as a whole, noting that both could have played an indirect role in the accident.
In fact, the simplest description of the safety culture at Helios Airways would be that there was none. The airline was a mess from top to bottom, driven by a CEO who, subordinates claimed, was only interested in profit. The COO, who had been hired just two weeks before the crash, told investigators that he arrived to find an airline in a concerning state of disarray, driven by a “culture of fear” which encouraged people to “stretch the rules to the limits.” He stated that “aircraft utilization was extremely high with insufficient downtime,” that schedules were “extremely tight” and there was “some evidence that flight times were manipulated to bring them [within] limits,” that some employees had not been granted leave in over 2 years, and that the company lacked a formal budget and a system for distributing resources.
His assessment was not far off the mark. Key management positions were empty, and the company had trouble recruiting and retaining qualified people to fill them. At lower rungs of the airline, turnover was out of control, to the point that no mechanic had ever stayed at the company for more than 21 months, and the situation among the pilots was almost as bad. In such an environment, no one would have felt particularly invested in the company’s long-term safety culture. After all, if no one intended to stay for very long, then systemic safety issues were nobody’s problem.
As it turned out, Helios Airways had already come under scrutiny by the United Kingdom Civil Aviation Authority, which carried out several audits of the company and its UK-based maintenance contractor, ATC Lasham. These audits found so many paperwork issues that it was hard to even know where to begin correcting them. Numerous manuals were out of date or had unclear provenance. In fact, Helios Airways did not have a contract with Boeing to receive updates to manuals for the accident aircraft, opting instead to get them from the airplane’s previous owner. Investigators were astonished to discover that Helios had a policy of screening these updates and only applying the ones it considered “important,” a shockingly negligent policy which was something of a microcosm of the broader company culture. It would later be noted that one of the updates which was not implemented was a change to the wording of the before start checklist which would have explicitly asked the crew to check the status of the pressurization mode selector switch, rather than simply stating “PRESS … SET.”
In another equally concerning discovery, investigators were told that planned flight times were listed as being shorter than they actually were in order to avoid the appearance of scheduling crews beyond their duty time limits. This could have led to chronic fatigue among the flight crews, potentially influencing the failure of the accident crew to detect the position of the mode selector switch.
The issues definitely didn’t end there. The UK CAA repeatedly found that the airline lacked a quality control system, and that emergency equipment was missing, including emergency exit instructions, first aid kits, and flashlight batteries. On the ground, management was absent and employees were left to fend for themselves. One report warned that the lack of operational control was actively compromising flight safety. And despite all of these findings, Helios Airways made little effort to correct the problems, and the same issues came up in successive audits, over and over again. Events finally came to a head in November 2004, when the CAA auditor informed Helios Airways that if it didn’t correct these chronic discrepancies by December 17th, its air operator certificate would be revoked. Helios Airways narrowly avoided being grounded by correcting all the specific listed deficiencies by December 9th, but at the core of the company, nothing had fundamentally changed.
Helios Airways kept getting away with this kind of behavior in part because the Cyprus Department of Civil Aviation was effectively absent. The agency seemed to have informally delegated virtually all of its oversight activities to the UK CAA, which had no direct authority and was supposed to be playing only an advisory role. According to Cypriot officials, the Safety Regulation Unit of the DCA only really existed on paper up until 1998, because before that date there were only two airlines in Cyprus, both state-owned, which had their own independent oversight arrangements. The arrival of Helios Airways and other private carriers forced the Safety Regulation Unit to become more than just an idea, but by 2005, not much progress had been made. The unit had few employees — the number appears to have been in the single digits — and several key positions were unfilled. When questioned about its oversight of Helios Airways after the accident, the members of the unit descended into “accusations and finger-pointing,” including allegations that the SRU had engaged in favoritism toward Helios Airways and that inspections of the airline had been conducted only on paper. Indeed, the only audits of the airline were those conducted by the UK CAA, and despite content in the audit reports which was clearly intended to be reviewed by the Cyprus DCA, most of the reports didn’t even have so much as a DCA employee’s signature on them, let alone a formal reply. Considering this regulatory environment, it was apparent how Helios Airways could have descended into such internal anarchy.
Of course, even with the direct and indirect causes having been established, the story of flight 522 contained one final, completely unexpected twist: the eventual appearance of a person in the cockpit who attempted unsuccessfully to fly the plane. Although the identity of this person was initially mysterious, an answer was reached within days, thanks to surviving Helios Airways cabin crew members and a little bit of basic deduction. The F-16 pilot had described what looked like a flight attendant uniform, and the person was definitely male, not female. That ended the search all by itself, because there was only one male flight attendant on board: Andreas Prodromou, the 25-year-old aspiring pilot who joined the crew roster just a couple hours before the flight. Prodromou’s coworkers also confirmed that it was his voice which made the mayday call captured by the cockpit voice recorder near the end of the flight. The question, then, was how he had survived so long, and what he was trying to do.
For the cabin crew, the first sign of trouble might have been a growing sense of physical discomfort, followed by the deployment of the oxygen masks. The forward flight attendants would have been able to hear the cabin altitude warning emanating from the cockpit, but it was unlikely that they knew its meaning.
In some previous cases in which planes failed to pressurize, flight attendants had called the problem to the pilots’ attention in the nick of time. In one such incident in 2000 involving Aer Lingus, a flight attendant’s persistence in informing the crew of events in the passenger cabin was credited with averting a very similar accident. But as far as we know, none of the cabin crew members on flight 522 attempted to warn the pilots of a problem. This may have been due in part to a lack of clarity about what to do if the oxygen masks dropped and the pilots did not initiate an emergency descent. Believing that guidance from the crew would come at any moment, the flight attendants might have simply hesitated to act until it was too late.
Nevertheless, when his oxygen mask ran out, Andreas Prodromou still had the presence of mind to grab one of the plane’s four large, portable oxygen bottles, two of which were stored in the aft galley, near his seat. He may have been facilitated in this effort by his scuba training, which had no doubt increased both his ability to breathe conservatively and his familiarity with supplemental oxygen systems.
One of the enduring mysteries of flight 522 is why, having presumably acquired a portable oxygen bottle early in the sequence of events, Prodromou didn’t enter the cockpit until the very end of the flight. One possible reason is that he simply didn’t know how to get in. The door would have been locked before takeoff, according to standard practice since the 9/11 attacks, and according to other Helios employees, only the cabin supervisor was given the emergency override codes. Cabin supervisor Louisa Vouteri is thought to have fallen unconscious along with the rest of the passengers and crew, meaning that Prodromou would have had to find where she kept the codes before he could get into the cockpit. This could have taken quite some time — not just to physically locate the codes, but also to think of looking for them in the first place. Despite his use of supplemental oxygen, Prodromou was likely partially hypoxic and may not have been thinking clearly during most of the flight, hindering his ability to quickly develop and execute a plan. In addition, it has been speculated, albeit without evidence, that Prodromou might have spent time trying unsuccessfully to revive his fellow flight attendant and girlfriend Haris Charalambous, who was seated next to the cabin supervisor in the forward galley. (Some early news reports claimed that the F-16 pilots saw her in the cockpit trying to help Prodromou fly the plane, and these reports are still sometimes quoted today, but they appear to have been false.) Examination of the wreckage later showed that three of the four portable oxygen bottles were used during the flight, but it was not clear whether Prodromou drained all three of them himself, or whether he might have used one to try to rouse additional crewmembers.
Unfortunately, if he waited more than a few minutes to do this, he would have been out of luck. The final cabin altitude was determined to be around 28,000 feet equivalent, which would have been sufficient to cause irreversible brain damage in all unconscious occupants well before the crash.
By the time Prodromou managed to apply the emergency override code and enter the cockpit, it was too late for him to do much to save the plane. Both pilots were beyond recovery, and less than one minute of fuel remained in the left wing tanks. Prodromou did possess a private pilot’s license, but he had only a few hours in a Cessna, which was not very helpful when trying to fly a 737, especially with a failed engine. To make matters worse, the combination of hypoxia and extreme stress would have impeded his ability to make rational decisions. Despite this, flight recorder data showed that he did attempt to control the plane, even though the aim of his attempts was unclear. He also tried to broadcast a mayday call, but did not appear to be aware that the radio was still tuned to the Nicosia frequency, which was out of range. There was some evidence that he then tried to wake the First Officer, but in any case he was too far gone. At that point all Prodromou could do was ride the plane down, and, perhaps, steer it away from populated areas — although it is not known whether he thought about this. What we do know is that he pulled up at the last moment to reduce the angle of impact with Grammatiko Hill, presumably hoping that this would improve his chances of survival. Unfortunately, he was unsuccessful, because the plane’s airspeed and rate of descent were so great that a fatal impact was all but assured.
As hauntingly strange as the crash of flight 522 proved to be, it was a wakeup call to the industry about a type of accident that was, in hindsight, almost bound to happen. Despite a large number of near misses involving pressurization, Greek investigators felt that European and American authorities had not taken the danger seriously enough, with tragic consequences. In their final report, they issued a number of recommendations intended to reduce the risk of such an accident ever happening again, many of which, they were pleased to note, were quickly implemented. Among other actions, Boeing updated its 737 maintenance manual to explicitly state that the pressurization mode selector must be returned to “AUTO” after a pressure test, and the FAA issued an airworthiness directive mandating that the takeoff configuration warning and the cabin altitude warning on the Boeing 737 be accompanied by separate warning lights which would clearly indicate which alarm is sounding. Numerous changes were also made to both normal checklists and emergency procedures. And lastly, the Cyprus DCA underwent a major restructuring and hired more personnel, beginning a closely supervised process intended to bring it up to European Union standards.
As for Helios Airways, the crash was the beginning of the end. Despite an attempt to rebrand as “αjet,” the tour operators who represented a large part of the airline’s customer base weren’t fooled by the name change, and bookings dropped precipitously. By the end of 2006, the airline was in such dire financial condition that the government of Cyprus abruptly seized its assets to cover $2 million in unpaid back-taxes. The airline formerly known as Helios Airways was thus grounded effective immediately. Airline executives denounced the move as “illegal” and accused the government of corporate raiding, but they had few sympathizers. As far as most people were concerned, Cyprus was better off without them. Many in fact thought the crackdown on the airline should have gone much farther — anger remains over the fact that the airline’s corrupt executives never went to prison.
Seventeen years after flight 522 fell to earth in Grammatiko, the tragic story of the ghost plane continues to captivate. The sequence of events reads like a movie script, from the undeniably bizarre premise, to the dramatic incapacitation of the crew, to the unprepared young man who tried to rise to the occasion. There was even a romantic subplot, or at least we think there was. But Helios Airways flight 522 was not a movie. Andreas Prodromou couldn’t save the plane, and even if he somehow had, he would have been the only survivor. Real life sometimes gives us Hollywood premises, but it rarely gives us a Hollywood ending. Instead, we find ourselves wondering what Prodromou saw and felt as he wandered around a ship of lost souls, like a living crewman on the Flying Dutchman. He was alone, not just physically, but spiritually, experiencing a unique form of nightmare shared by no one, before or since. And yet, despite the odds being stacked against him, he tried his best, perhaps believing that he held in his hands not just his own life, but 120 others — even though we now know that they were too far gone to save. There can be no doubt, then, that he was a hero. After all, not all heroes succeed — sometimes heroism just means fighting until the end.
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