Radio Silence: The crash of Iberia flight 610

Admiral Cloudberg
28 min readNov 5, 2022


An infographic depicting flight 610’s impact with the TV antenna atop Monte Oiz in the Basque Country. (Mari Luz Alosso, J. A. Hermoso, and J. de Velasco)

On the 19th of February 1985, a Boeing 727 flying for Spain’s national airline clipped a mountaintop television antenna on approach to Bilbao, sending the plane plummeting into a ravine from which it would never emerge. The crash killed all 148 passengers and crew and plunged Basque Country into mourning. But to say that the crash was a surprise would be disingenuous — in fact, this was the third time in less than five years that an airliner in Spain flew into the ground while attempting to land. And yet, most of the public debate about the crash seemed to have little to do with improving Spain’s safety record, as various interest groups, from the airline to the media to the victims’ families, fought narrowly over whether the crash could be blamed on Captain José Luis Patiño. Why did he fly too low? Was he really as good a pilot as his colleagues claimed him to be?

The partisans of pilot error missed the point, but so did the other camp, which mainly sought to defend Patiño by claiming that Basque terrorists brought down the plane. In the end, it was obvious enough that Iberia flight 610 hit the TV tower by accident, and we know some of the basic reasons why — a misleading altitude alert system, an altimeter that was hard to read, a lack of altitude callouts by the crew. But the official inquiry bizarrely ignored several key questions, such as whether a ground proximity warning system could have prevented the crash, and why Captain Patiño was all but silent throughout the flight, seemingly refusing to talk about flying the aircraft — an area critical to understanding the accident, albeit one which forces us to descend into the minefield of speculation.


A 1973 advertisement for Iberia Airlines features a Boeing 727 and a vaguely fascist flight attendant uniform. (Vintage Italy)

Founded in 1927, Spain’s flag carrier Iberia Líneas Aéreas de España, better known just as “Iberia,” has acted since its inception as an arm of the Spanish state, whatever form that state happened to take. After initially folding in 1929, Iberia was brought back to life during the Spanish Civil War as the official airline of the Nationalists under Francisco Franco, and remained as such after the Nationalists swept Franco to power in 1939, becoming an international symbol of the dictatorship. Iberia remained the state airline after Franco’s death in 1975 and throughout the subsequent transition to democracy, and it is still the flag carrier today, where its common ownership with British Airways and Aer Lingus now reflects Spain’s membership in the pan-European project.

For an airline molded in the fires of dictatorship, Iberia’s safety record could have been worse. It has suffered four major disasters since the start of the jet age, but two of these were collisions in which the other plane was at fault. The other two were that most ubiquitous type of air crash, the once universal killer known as Controlled Flight Into Terrain. This is the story of the latter of those two, one which would turn out to be Iberia’s last fatal accident, and by far its most controversial.


EC-DDU “Alhambra de Granada,” the aircraft involved in the accident. (Reinhard Schmidt)

That story began at Madrid Barajas Airport on the morning of the 19th of February, 1985, aboard an Iberia Boeing 727 registered as EC-DDU and nicknamed “Alhambra de Granada.” Bound for Bilbao in Spain’s northern Basque Country, the flight promised to be a short one, but by some accounts its takeoff was delayed for almost as long as it was in the air. The stated reasons for this delay vary. Some versions purport that Iberia was subject to a bomb threat, forcing police to search the plane; others say the delay was because one of the passengers, former Francoist foreign minister Gregorio López-Bravo, was late to arrive. In any case, by the time Alhambra de Granada pushed back for flight 610 to Bilbao, 141 passengers and seven crew had boarded the plane, including López-Bravo, as well as the Bolivian Labor Minister, who was on his way to Bilbao to negotiate an electric rail project. Two opposition MPs were also said to have bought tickets aboard the flight, only to cancel at the last minute.

The crew of flight 610. Note that there are eight people listed here, not seven — I am unsure of the reason for the discrepancy. (El Correo Español)

In command of the flight was 51-year-old Captain José Luis Patiño Arróspide, who had been flying for Iberia for 19 years and had over 13,600 flight hours. He was joined by 38-year-old First Officer Emilio López Peña Ordóñez, and a Flight Engineer, 38-year-old Gregorio Arroba Martín Delgado.

Although some aspects of Captain Patiño’s background are subject to controversy, it is known that he had a complicated relationship with his employer. During the summer of 1984, a number of Iberia pilots went on strike, including Patiño. In a blatant retaliatory action, the airline fired some or all of the striking pilots, and Patiño was told on July 18th that his contract had been cancelled. He ended up being grounded for several months before Iberia reinstated him on November 29th, although it is unclear whether the airline did this voluntarily, or was ordered to give the strikers their jobs back. In any case, Patiño’s Boeing 727 type rating had lapsed during the intervening months, and he had to go back to training. By the time of flight 610, he had only just returned to regular line flying, and he had accumulated only 29 flight hours in the preceding six months.

The route of Iberia flight 610. (Google, annotations mine)

With First Officer López Peña at the controls, Iberia flight 610 departed Madrid at 8:47 a.m., expecting to arrive in Bilbao at 9:35. The flight climbed to its cruising altitude and proceeded uneventfully northward, the crew making all the expected radio calls along the way. The pilots are said to have engaged in a lengthy, off-topic conversation, although its subject has not been released. Regardless, all seemed normal as flight 610 departed its cruising altitude at 9:09, having been cleared by Madrid area control to descend to 10,000 feet and contact the Bilbao tower. In both English and Spanish, a flight attendant made a routine cabin announcement: “Ladies and Gentlemen, in fifteen minutes’ time we’ll land in Bilbao, which temperature is seven degrees centigrades [sic] and it’s foggy. Thank you.”

The weather in the Basque Country that day was indeed suboptimal, although not unusually so for that time of year. Weather observers were reporting broken cloud ceilings between 2,500 and 4,000 feet, with areas of denser fog, especially in the mountains. That meant that the pilots would need to land in Bilbao using the published instrument approach procedure for runway 30.

Runway 30 at Bilbao Airport was equipped with an Instrument Landing System, or ILS, to provide both lateral and vertical guidance to inbound aircraft. But before flight 610 could lock onto the ILS, it would need to reach the standard intercept point, known as the approach fix, while at the proper altitude. The period after the initial descent but before reaching the approach fix, referred to as the intermediate approach phase, is most important for understanding what happened to Iberia flight 610.

Breakdown of the intermediate phase of the approach to Bilbao runway 30. (CIAIAC, annotations mine)

At Bilbao, as at most airports, a standard procedure existed which was specifically designed to keep inbound aircraft away from terrain while also feeding them into the approach fix at the appropriate altitude. Because of high mountains surrounding the airport, planes were required to maintain an altitude of at least 7,000 feet unless they were following this procedure.

For runway 30, the intermediate approach procedure involved flying to the VOR beacon at the airport, known as BLV, at the sector minimum of 7,000 feet. Upon reaching BLV, the procedure called for a turn onto a southeast-bound heading reciprocal to runway 30, while descending to 5,000 feet. The inbound aircraft would then continue away from the airport on this heading until reaching the approach fix, located 13 nautical miles from BLV. The procedure called for flights to overfly the approach fix, then make a 180-degree loop to the right, which would bring the plane in line with the runway heading of 301˚ by the time it returned to the approach fix. During this turn, planes were allowed to descend from 5,000 feet to a new minimum safe altitude of 4,354 feet. After reaching the approach fix, the plane would then pick up the signal from the ILS, enabling further descent to the runway.

This route was rather indirect, since it forced inbound planes to fly 13 nautical miles past the airport and then turn around. As a result, controllers frequently invoked their right to clear inbound flights directly to the approach fix instead of flying to the VOR first. Although the tower did not have radar, this off-route shortcut was safe as long as traffic was light, and as long as planes maintained the sector minimum of 7,000 feet until joining the official procedure at the approach fix. Typically, flights would then descend to the minimum safe altitude of 4,354 feet while making the right-hand loop.

The differences between the standard intermediate approach procedure and the shortcut normally offered by controllers. (Google, annotations mine)

On board flight 610, the pilots presumably expected to receive clearance to perform this shortcut, as usual. But events on the flight deck were taking a strange turn. Even though he was also the one flying the plane, it was First Officer López Peña who said at 9:15, “Bilbao Tower, buenos dias, six one zero.”

“Iberia six one zero, buenos dias, go ahead,” the tower replied.

“We are leaving level one three for level one hundred, twenty-eight [miles] out,” said López Peña, explaining that they were passing through 13,000 feet on their way to 10,000.

“Roger, Iberia six one zero, stand by please,” said the tower. After a pause of ten or fifteen seconds, presumably to examine the traffic situation, the controller continued, “Iberia six one zero, you can continue descent for an ILS approach to Bilbao, runway three zero, wind is one hundred degrees at three knots.” Providing local air pressure information, the controller added, “QNH one zero two five, transition level seven zero.”

“Thank you,” López Peña replied. “Descending to sector minima, with one thousand and twenty-five?”

“Correct, one thousand and twenty-five,” said the tower. “And if you wish you can proceed direct to the fix.”

This was the usual shortcut that the pilots were probably expecting. But it seems that Captain Patiño made some sort of non-verbal gesture to First Officer López Peña indicating that he should reject the shortcut. Seconds later, López Peña said to the tower, “We are going to make the standard maneuver,” indicating his intention to perform the full procedure, as described earlier.

In the cockpit, First Officer López Peña turned to Captain Patiño and said, “Have they paid you? Have they given you your back pay?” Patiño must have given him a negative indication, because López Peña immediately added, “We’ll make the standard maneuver then.”

“Yes,” said Patiño.

“Alright,” López Peña said, laughing out loud.

The implication, of course, was that Patiño was going to reject any shortcuts, thereby using more time and more fuel, until Iberia paid him some portion of his salary which he felt he was owed.

“The other day, yesterday, the day before yesterday, I flew with Santiago de la Paz, it was the same,” said López Peña. “He’s another one of the accused… also in the same situation.”

This line suggested that López Peña was aware of the practice of costing the airline money by turning down shortcuts, and that Patiño was not the only one doing it.

López Peña continued to speak, without getting a reply from Patiño. “Well that’s what you…” A Morse signal sounded in the background. “Okay, then we will wait,” he said, followed by an ambiguous line, porque como nos vamos a dar, which could mean, “because they’re going to hit us,” or could imply an intention to get very drunk later, * depending on context which is missing.

Still receiving no response from Captain Patiño, First Officer López Peña and Flight Engineer Martín Delgado worked through the descent checklist, reviewing the minimum safe altitude of 4,354 feet, as well as fastening their seat belts, turning off anti-ice, setting their speed and altitude references, and other basic tasks.

(*According to a native Spanish speaker who I asked about it. Feel free to share other interpretations in the comments.)

Overview of the altitude alert and autopilot control panels. (CIAIAC, annotations mine)

Although he wasn’t speaking, it is thought that Patiño was staying on top of at least one cockpit task: setting the altitude alert system.

The altitude alert system is integrated with the autopilot in order to inform the pilots when the plane is approaching, or deviating from, a particular altitude selected by the crew. On the Boeing 727, during a step descent such as the approach to Bilbao, the autopilot would have been set to “altitude capture” mode, in which the autopilot automatically levels the plane at a specified altitude. During a normal descent, a pilot will use the altitude selector knob to select a desired altitude, which will appear in the altitude window. The pilot will then press the “ALT SEL” button on the autopilot panel, arming the autopilot’s altitude capture function. Then, when the plane approaches the selected altitude, the altitude capture mode will engage, causing the autopilot to level the plane.

Meanwhile, as the plane descends through 900 feet above the selected altitude, the altitude alert system will emit a two-second aural tone. At this point, a pair of “altitude alert” lights on the pilots’ control panels will also illuminate. The lights will remain illuminated until the plane reaches 300 feet above the selected altitude, at which point they will extinguish. If the plane levels off at the selected altitude, the altitude alert won’t sound again. However, should the plane continue to descend, the aural tone will sound again at 300 feet below the selected altitude, and the altitude alert light will begin flashing. This same process applies during climb, but in reverse. The diagram below provides a spatial representation of this alert sequence.

The full range of altitude alert sounds and lights, in both capture (acquisition) mode and deviation mode. (CIAIAC)

Initially, the altitude alert and the autopilot worked together as intended. Captain Patiño selected a target altitude of 7,000 feet, and the aural tone sounded at 7,900 feet. The autopilot then engaged in altitude capture mode and smoothly leveled the plane at 7,000 feet, just as it reached the VOR. In the background, Captain Patiño could be heard idly singing, “Hay que ver, porque hay que ver…”
To the tower, López Peña said, “Seven thousand feet over the VOR, Iberia six one zero, initiating the maneuver.”

“Roger, six one zero,” said the tower. This would be the last communication from flight 610.

As López Peña instructed the autopilot to begin a right turn onto the outbound leg from the VOR, Captain Patiño changed the selected altitude to 5,000 feet, in accordance with the standard procedure. The plane then began to descend at a rate of 1,000 feet per minute.

Just over one minute after leaving 7,000 feet, the plane reached 5,900 feet, and the altitude alert tone sounded again. Forty-seven seconds later, the autopilot successfully leveled the plane at 5,000 feet, the minimum altitude prior to overflying the approach fix.

Shortly thereafter, at 9:25, Captain Patiño again reduced the selected altitude, this time to 4,300 feet, approximately the minimum safe altitude at the approach fix. Strictly speaking, because the minimum was 4,354 feet and the altitude selector knob operated with 100-foot increments, he should have rounded up to 4,400, but either setting would have kept the plane well clear of terrain.

Differences in the minimum altitudes between the standard procedure and the shortcut. (CIAIAC, annotations mine)

Nine seconds after Captain Patiño selected 4,300 feet, First Officer López Peña used the vertical speed wheel to select a descent rate of 1,500 feet per minute. Considering that they only needed to lose 700 feet and had plenty of time in which to do it, this descent rate was plainly excessive. So why did he choose it?

The root of this decision seems to trace back to the moment eight minutes earlier when the controller cleared López Peña to fly directly to the approach fix, only for Captain Patiño to tell him to fly the standard procedure via the VOR instead.

As mentioned earlier, the sector minimum in that area was 7,000 feet, and this altitude had to be maintained unless one was following the standard approach procedure. Therefore, if one were to take the shortcut by skipping the VOR to begin the procedure at the approach fix, one would arrive over the fix at 7,000 feet, rather than 5,000 feet. This would in turn require one to lose 2,700 feet during the loop instead of 700 feet, necessitating a higher descent rate. This is what López Peña would have been used to, given that there was almost never any good reason to turn down the shortcut. As a result, it is thought that he had already planned to lose 2,700 feet after overflying the approach fix, and in a momentary lapse of attention, forgot that this was not the version of the approach that he was actually flying.

Thinking about the alerts generated in the accident scenario. (CIAIAC, annotations mine)

Compounding his mistake was the design of altitude alert system. When Captain Patiño selected a target altitude of 4,300 feet, the plane was only 700 feet above this altitude, so the aural tone which would normally be heard at 900 feet above the selected altitude never went off. Instead, the altitude alert light illuminated immediately, with no sound to draw attention to it.

Even with both of the above misunderstandings in place, the autopilot should still have kicked in to level the plane at 4,300 feet. But here came the third, fatal link in the sequence of events: the altitude capture mode never engaged. There are a number of possible reasons why this might have occurred, which will be discussed later. In any case, however, the result was that in less than 30 seconds, flight 610 sailed straight through its selected altitude with First Officer López Peña none the wiser.

A few moments later, the plane reached 4,000 feet, and the aural tone sounded to inform the pilots that they were 300 feet below the selected altitude. But López Peña probably thought this this was the tone for 900 feet above the selected altitude, which he would have expected to hear first. And so he let the plane keep descending, even as the little altitude alert light flashed away in the corner.

Shortly thereafter, at an altitude of approximately 3,800 feet, López Peña reduced their descent rate from 1,500 feet per minute to 750 feet per minute, as he would do if he expected the autopilot to capture the selected altitude soon. But the plane just kept descending, steadily dropping toward the ground, even as López Peña started the loop back to the approach fix.

“Five, please,” he said, asking the flight engineer to extend the flaps.

Two seconds after that, he said, “Minimum one six three,” indicating the minimum speed for flaps five, then added, “Four thousand three hundred [in the] curve,” reiterating the minimum safe altitude. Unfortunately, he would have no time to realize that he was actually 1,000 feet below it.

Flight 610 impacts the TV antenna. (Mari Luz Alosso, J. A. Hermoso, and J. de Velasco)

The word “curve” had scarcely left the First Officer’s lips when a massive television antenna materialized out of the fog. There was just enough time for someone to shout, “My god!’ And then, in a banking right turn, the plane clipped the antenna with the underside of its nose, followed a split second later by an almighty ripping sound as the tower sliced off the 727’s left wing at its root. As its wing spiraled away into the clouds, the plane rapidly rolled inverted, pitching over into a long, downward arc. The terrain beneath it fell away almost as fast, and for a few more seconds the cockpit voice recorder captured the pilots’ shouts of terror, followed by the sound of the plane hitting trees, and then silence. Almost fully upside down, the 727 streaked down the precipitous mountainside, mowing down an immense swath of pines, before it slammed hard into the ravine at the bottom, instantly killing all 148 people on board.


No other photo so vividly captures the long trail of destruction carved by the airplane as it plummeted down the mountainside. (Bureau of Aircraft Accidents Archives)

Although controllers sounded the alarm minutes later when the flight failed to respond to radio calls, no one was initially sure where or whether the 727 had gone down. Searchers were still en route to the plane’s last suspected position when the first emergency call came in nearly 40 minutes after the crash. The accident had in fact been discovered by a local farmer, who, having been alerted by the noise, made his way into the forest high on the slopes of Monte Oiz, where he encountered a nightmarish scene of destruction. Most of the plane had been piled into the bottom of a ravine like a great heap of rubbish, with a long, straight clear-cut path leading up into the fog from whence it came. And all around were strewn the grisly remnants of the passengers and crew. Fragments of bodies were scattered on the forest floor and mixed in with the burning wreckage: here and there a hand, a foot, a torso. Pieces of flesh could be seen hanging from trees. Already scarred for life, the farmer fled the horrific scene and called the police.

The left wing came to rest high on the slope of Monte Oiz. (Bureau of Aircraft Accidents Archives)

Before long, a vast throng of rescuers descended upon the crash site, located on the northeast slope of the 1,026-meter (3,366-foot) Monte Oiz, some 26 kilometers east of the runway. They found the remains of the 727 scattered across a distance of one kilometer, from the ravine all the way back up to the summit of the mountain, where a television antenna belonging to Basque-language TV station Euskal Telebista had been sliced in two at a height of 42 meters above its base. Several key portions of the plane were still lying near the antenna, including the left wing, while the fuselage was found more than 950 meters farther on, along with its occupants. But while rescuers quickly determined that there were no survivors, poor communication at the accident scene led to persistent reports for several hours that between 20 and 40 people may have survived, a rumor which sent the families of those on board scrambling to area hospitals in search of their loved ones, only for the ambulances to arrive empty.

The same poor emergency management also led to one of the most distasteful scandals surrounding the accident, as news crews were allowed direct access to the scene before the bodies of the victims had been removed. Photographers took countless photos and videos of the mutilated remains, many of which were then published, in full color no less, on the pages of some of Spain’s leading tabloids. It is unclear whether anyone was found responsible for letting the photographers in, but the fact that the photos were then plastered onto the front pages of newspapers was certainly an indictment of Spain’s prevailing media culture.

A Spanish newspaper displays a headline which reads, “24 hours before the disaster, the Madrid-Bilbao flight received a bomb threat.” (El Alcazar)

Meanwhile, investigators from Spain’s Civil Aviation Accident and Incident Investigation Commission, known by its Spanish acronym CIAIAC, gathered at the crash site to begin piecing together the cause. However, rumors were already circulating that the crash was no accident. In the 1980s, Spain was still battling frequent small- to medium-scale attacks by the Euskadi Ta Askatasuna, or ETA, an armed terrorist group seeking an independent Basque homeland. Allegedly, there had been threats to Iberia flights heading to Basque Country on the day of the accident, possibly including the accident flight, although official confirmation of this is sketchy at best. Some of these rumors suggested that the intended target was Gregorio López-Bravo, the former Foreign Minister under the Franco regime. These rumors only intensified when López-Bravo turned out to be among eight passengers whose bodies were never identified.

Despite the speculation, however, bringing down an airliner to kill one man was not the ETA’s modus operandi, as the group tended to prefer targeted assassinations and direct attacks on military personnel and police. Furthermore, for crash investigators, it was obvious that that the plane broke up only after it hit the television antenna. No parts of the plane were found before the tower, and the neat slice through the antenna indicated that the plane was in a shallow right bank at the time of the collision, exactly as it should have been during that part of the approach. The only thing amiss was that the plane was 1,000 feet too low. The question, necessarily, was why.


The TV antenna as it appeared after the crash, with its top 12 meters missing. (Bureau of Aircraft Accidents Archives)

Upon listening to the cockpit voice recording, investigators made a number of interesting observations. The first of these was that the minimum safe altitude of 4,354 feet was known to the pilots, and their descent below it must have been unintentional, as First Officer López Peña could be heard referencing the minimum just seconds before the crash. However, the recording also revealed that the crew’s altitude awareness may have been compromised, as there were no altitude callouts, which normally should have been made by the non-flying pilot every 1,000 feet.

This raised a corollary question: who was the one actually flying the plane? Normally, investigators can identify the non-flying pilot by the fact that this pilot should be the one making the radio calls. But while Captain Patiño handled the radio early in the flight, at some point he stopped doing so, and by the time of the descent, it was First Officer López Peña who could be heard on the radio, despite the fact that no transfer of control had taken place. Instead, López Peña continued to perform tasks, such as requesting flaps, which indicated that he was the flying pilot, even though he was now also talking to air traffic control.

In fact, Captain Patiño was almost totally absent from the recording. In addition to the early radio calls, he also participated in the off-topic conversation during cruise, but after this he never uttered a word related to the operation of the aircraft. During the entire period from the top of descent until impact, the only words attributed to Patiño were a single “yes” and a few lines from a song.

Most of the debris ended up in this narrow ravine. (Unknown author)

The CIAIAC’s official report did not even attempt to explain Patiño’s bizarre silence. However, it’s hard to imagine that this was anything other than deliberate. The fact that he performed radio calls before the off-topic conversation, but ceased doing so after, also raises some questions about what may have been said during this period. Unfortunately, the contents of the conversation have not been published, but it seems as though from that point onward, Patiño outright refused to do his job.

Whether it explains his silence is debatable, but there is plenty of evidence that Patiño had beef with his employer. As mentioned earlier, Patiño had recently been fired for striking. Furthermore, the First Officer’s comments suggest that Patiño felt that Iberia owed him money, and that he stuck to the published maneuver in order to increase costs for the airline. López Peña also mentioned another pilot who was “in the same situation,” suggesting the possibility that Patiño and other dissatisfied pilots might be engaged in a semi-coordinated work slowdown campaign. However, this line of inquiry can only be speculative, as the official report completely avoided the topic, and research for this article turned up no further information about labor relations within Iberia at the time of the accident.


Another view of the swath through the trees, this time in color. (Bureau of Aircraft Accidents Archives)

Although the decision to reject the controller’s proffered shortcut set the sequence of events in motion, it was not the cause of the accident. As was explained earlier, investigators believed, based on a number of items of evidence, that First Officer López Peña was caught off guard by the decision to use the standard approach procedure, and did not complete his mental transition to the new plan. Consequently, when he arrived over the approach fix at 5,000 feet instead of 7,000, he commenced a descent more suited to the latter than the former. This is not to say that López Peña was unaware in principle that he was at 5,000 feet and not 7,000, but rather that his actions were automatic.

Here it must be noted that investigators believed that Captain Patiño was the one making altitude selections, not First Officer López Peña. There were two main reasons for this: first, because other pilots who had flown with Patiño said it was normal for him to do this; and second, because some of these selections were made while López Peña was busy talking to ATC, and it would have been difficult to do both simultaneously. This created an awkward situation where Patiño was influencing the behavior of the autopilot, but was not calling out what he was doing. Had López Peña been doing this himself, he probably would not have suffered the aforementioned memory lapse.

Rescuers surround the wreckage of the plane, searching for human remains. (Bureau of Aircraft Accidents Archives)

Investigators were able to determine with a great deal of certainty that the last altitude selected by Patiño was 4,300 feet, because the altitude window was found in the wreckage with its rotating display stuck at this value. However, the flight data recorder clearly showed that the plane did not level off at this altitude, and continued descending until it struck the TV antenna at an altitude of approximately 3,300 feet.

By messing with the altitude selection system, investigators found a number of ways in which the autopilot could fail to level off at the selected altitude. For instance, if the selected altitude was too close to the present altitude, the plane would descend through the selected altitude before “altitude capture” mode could engage; furthermore, the autopilot would then allow the descent to continue indefinitely rather than climbing. The same thing would occur if one of the pilots moved the autopilot’s vertical speed selector wheel after altitude capture mode was engaged. Altitude capture mode could also fail to arm if the autopilot were disconnected and then reconnected, even though the selected altitude would remain in the altitude window. But none of these scenarios fit with the available evidence, and investigators preferred two more prosaic explanations: after using the altitude selector knob to enter 4,300 feet into the altitude window, Captain Patiño either forgot to press the “ALT SEL” button to arm the altitude capture function, or one of the pilots accidentally pressed the button a second time, causing it to disarm. The only indication of such a mistake would have been the absence of an amber “ARM” light under the “ALT SEL” button.

In addition to these two closely related scenarios, investigators also could not conclusively rule out that Patiño waited too long to press the “ALT SEL” button because the First Officer’s hand was in the way, or that the autopilot somehow malfunctioned, although this was considered unlikely, since the system was working correctly just moments earlier.

An engine and part of the outer fuselage skin were among several recognizable pieces of the airplane. (Bureau of Aircraft Accidents Archives)

In any case, because the altitude alert system was separate from the autopilot, the aural altitude alerts would have sounded as normal, even though altitude capture was not armed. Furthermore, because the selected altitude of 4,300 feet was less than 900 feet below the present altitude of 5,000 feet, the first aural alert to go off was not the one at 900 feet above, but the one at 300 feet below. If he thought he was descending to 4,300 feet from 7,000, then López Peña would not have been surprised that the plane did not level off, nor would he have been aware that there would be no “900 feet above” alert, or that the first alert he would hear would be “300 feet below.” Because these alerts sounded the same, he most likely assumed that the alert he heard was “900 feet above,” and that the autopilot would level the plane after descending a further 900 feet. Had they actually descended 900 more feet without leveling off, he eventually would have realized his mistake, but the plane struck the antenna before he could do so.

In fact, the only indication as to which alert had sounded was the altitude alert light on his display, which was steady after “900 feet above” but would begin flashing after “300 feet below.” However, most other indications were showing him what he expected to see, so confirmation bias could have caused him to overlook this minor discrepancy.

A newspaper headline reads, “The greatest tragedy in the history of the Basque Country.” (El Correo Español)

All of this having been said, López Peña could still have detected his error simply by reading his altimeter. In reality, however, this was easier said than done. The Boeing 727 involved in the accident was equipped with an antiquated “drum pointer” style altimeter, in which hundreds of feet were displayed on a circular dial, while thousands of feet were displayed on a rotating drum set into the dial, as shown below. Studies dating back to the 1950s had shown that drum pointer altimeters were easy to misread, because reading the instrument required two separate actions, and the thousands window was difficult to see, especially when the drum was halfway between two numbers. As a result, pilots sometimes glanced at the instrument, read the hundreds dial, and then subconsciously assumed the thousands digit to be whatever they wanted. In fact, one survey showed that nearly 80% of pilots who flew planes with drum pointer altimeters admitted to having misread them, and a similar percentage said they had seen others misread them. Many of these pilots heavily criticized the design, noting that it should be possible to derive the altitude of the airplane with one quick glance at the altimeter, rather than two.

Based on this evidence, investigators speculated that if First Officer López Peña glanced at his altimeter during the final descent, he could simply have misread it, coming away with a number that was 1,000 feet too high.

A drum pointer altimeter somewhat similar to the one in the Boeing 727. This one is from a fighter jet, but the principle is the same. (F4 Phantom Parts)

Needless to say, the shortcomings of these altimeters were well known to the industry, and some of the same studies referenced in the CIAIAC report were also cited by the NTSB in its reports on a series of 727 crashes clear back in 1965. Drum pointer altimeters were eradicated from the US fleet soon after, but by 1985, they could still be found on planes flying for Spain’s national airline.

This was not the only finding which called into question the state of Spain’s aviation infrastructure. Obviously there was the fact that the airport in a major, first-level city didn’t have any approach radar. It was also noted that Monte Oiz, despite being the highest peak in the area, was not marked on the official approach chart for Bilbao.

And then there was also the presence of the TV antenna itself. Records showed that the antenna was constructed in 1982 without notifying aviation authorities, even though the tower’s 54-meter height meant that this was required. Furthermore, the minimum safe altitude of 4,354 feet was determined based on a 300-meter vertical separation from the top of Monte Oiz, but the antenna exceeded the height of the mountaintop by 28 meters. The real minimum safe altitude therefore should have been approximately 4,446 feet. Had this been the minimum, then in theory, assuming the pilots would round the minimum safe altitude down as they did in the event, they would have selected an altitude of 4,400 feet instead of 4,300 feet, causing all the events of the final minutes to happen 100 feet higher. It is possible, although not provable, that this would have resulted in the plane missing the antenna.

A piece of the plane lies on the ground near the TV antenna. (El Correo Español)

The elephant in the room, however, was a deficiency never mentioned in the CIAIAC’s report: the plane’s lack of a ground proximity warning system, or GPWS. In 1985, ground proximity warning systems had been required in the United States for a decade, but it does not appear that “Alhambra de Granada” was equipped with one. Some readers may even have noticed the lack of any “pull up” warnings on the cockpit transcript.

The GPWS technology available in 1985 could only look below the plane, not ahead of it — that is, it measured dangerous closure rates with the ground directly below, and would be useless if terrain rose up very suddenly. However, it seems likely that if a GPWS had been installed, it would have activated as the plane traversed the relatively gentle south slope of Monte Oiz in the moments before the crash. Given that the plane hit the antenna only 12 meters below the top, it would only have taken a few seconds’ warning for the pilots to have pulled up enough to avoid the disaster.

Despite this glaring deficiency, however, GPWS technology was not discussed in the official report, even in the recommendations section. The CIAIAC did recommend a number of changes, including that drum pointer altimeters be replaced, and that the “300 feet below” alert should sound different from the “900 feet above” alert. But the seemingly obvious recommendation that Spanish airliners be equipped with ground proximity warning systems was nowhere to be found.


Another overview of the crash site, with the tree scar. (Bureau of Aircraft Accidents Archives)

These systemic deficiencies should have generated pressure on Iberia and the Spanish government to update their regulations, but in the aftermath of the crash public anger was often misdirected. Naturally, as it became clear that human error was the likely cause, media coverage began to focus on the pilots. Initial reports cited Captain Patiño’s family, friends, and coworkers, who universally proclaimed that he was an excellent pilot with extensive experience landing in Bilbao. Many people pre-emptively bristled at the suggestion that he may have committed an error, reflexively labeling any such speculation as somehow cheap or disingenuous, simply because the pilots were not alive to defend themselves. The backlash became particularly intense when Spanish newspaper El Pais published the contents of Patiño’s personnel file, which allegedly contained many negative comments from his instructors about what they perceived as his careless and detached attitude. Patiño’s family was so incensed by the article that they successfully sued El Pais for 10 million pesetas on the grounds that the newspaper had defamed his honor. Not all of the victims’ families agreed, however: several of them wrote an open letter to the newspaper thanking it for its in-depth coverage and criticizing Patiño’s family for seeking higher settlements than the passengers got, even though he may have caused the accident.

In any case, it was not until much later that investigators revealed that Patiño was not even the one flying the plane when it hit the antenna. Although his silence on the flight deck contributed to First Officer López Peña’s loss of situational awareness, no specific actions by Patiño were listed in the final probable cause statement.

A piece of a wing lies on a path near where the plane came to rest. (Bureau of Aircraft Accidents Archives)

Despite this, however, many accounts of the disaster continue to suggest that the pilots were scapegoated, or that Patiño was unfairly criticized. It has even been suggested that the decision to reject the shortcut had nothing to do with a work slowdown, and that Patiño simply wanted to avoid bad weather between their position and the approach fix. This argument ignores the fact that there were no storms in the area, and while there were areas of fog, the flight was operating under instrument flight rules and was nowhere near the part of the approach where seeing the ground was important, so there was no obvious reason for the pilots to have diverted around a mere cloud.

Others go even farther in their exculpation of the crew: to this day it is not uncommon to see third party commentators, especially family members of the victims, insisting that the crash really was an ETA terror attack all along. This lack of trust may have arisen because neither the airline nor the CIAIAC appears to have given much thought to communicating with the families after the crash, as many of them were simply told that their loved ones had died, then never heard from any officials again.


Firefighters extinguish the flames after the crash. (El Correo Español)

Despite all these administrative blunders, investigative blind spots, and unanswered questions, something did fundamentally change in the wake of the accident. Between 1982 and 1985, there were four airline accidents in Spain with over 50 fatalities, but after Iberia flight 610, no Spanish airline suffered a major disaster for 23 years. During that time, drum pointer altimeters disappeared, ground proximity warning systems were eventually installed, and new generations of planes with better pilot interfaces took over the airways of Europe. Today, such an accident would be all but unimaginable, and not only because GPWS exists as a last line of defense. Modern flight displays contain far more information than the basic analog instruments on the 727, providing pilots with a comprehensive picture of where their plane is and what it’s doing. Long gone are the days when a crew could fly into a mountain because of an ambiguous alert and a button left unpressed. Looking back now at Iberia flight 610 and the environment in which it took place, it’s hard to imagine why anyone ever doubted the cause. Forty years ago, we thought flying was safe, but in hindsight, so thin at times was the line between life and death!


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Admiral Cloudberg

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