How A Blocked Static Port and Human Error Brought Down Aeroperu Flight 603
Shortly after midnight on October 2, 1996, Aeroperú Flight 603 crashes into the ocean. Join Shelly as she tells the story of a cockpit in chaos and an investigation that uncovered how a simple human error set off a deadly and shocking chain of events that led to a catastrophic outcome.
Please note the following sources were heavily referenced to create the script for this episode, including the episode “Flying Blind” for the Seconds from Disaster television show, an article on Fear of Landing.com, an article on Computerweekly.com, and an article found on the New York Times.
Pilots Get Faulty Instrument Readings Right After Takeoff
Aeroperu Flight 603 has just arrived in Lima, Peru, from Miami International Airport in Miami, Florida, and is now on its way to Santiago, Chile. The plane is carrying 70 people, including 61 passengers, most of which are Peruvian or Chilean citizens, as well as 9 crew members.
The captain is 58-year-old Eric Schreiber Ladrón de Guevara, who has logged almost 22,000 flight hours (including 1,520 hours on the Boeing 757), and the first officer is 42-year-old David Fernández Revoredo, who has logged almost 8,000 flight hours, with 719 of them on the Boeing 757.
Flight 603 is a Boeing 757, which at the time in 1996, is a state-of-the-art aircraft with a sophisticated, computer-aided design. It also featured a highly automated glass cockpit with shared instrumentation, avionics, and flight management systems. Color displays replaced conventional electromechanical instruments with increased automation. All these features were, of course, designed to streamline the cockpit and make for a highly stabilized ride for passengers.
The flight crew performs the customary checklists and then prepares for takeoff. At just 12:42 AM on the morning of October 2nd, Flight 603, flown on this leg by First Officer Fernández, glides easily and smoothly into the starry, early morning sky.
Shortly after they have left the ground, the pilots receive a highly unusual reading on their instrument panel: the onboard altimeters (which measure the height of the aircraft off the ground) say their altitude is zero. Captain Schreiber knows this is incorrect and concludes that the instrument must be stuck because they clearly were not on the ground – they were in a climb. And to make matters worse, not only does the Captain’s altimeter say zero, but so does the First Officer’s as well as the backup altimeter. All three altimeters say “zero”.
But before Captain Schreiber has time to fully troubleshoot the altimeter issue, he is interrupted by a wind shear alarm, which sounded three times, and warns the flight crew of a sudden change in wind speed or direction, for example a microburst. Effectively, it means that you are heading through an unpredictable set of fast winds. This too is puzzling.
And then another very important instrument also malfunctions. The airspeed indicator, which tells them how fast the aircraft is going, has failed. The pilots now have no idea how fast they are going nor how high they are flying.
The captain attempts to notify Lima air traffic control (ATC) but is interrupted by yet another alarm: this time, the rudder ratio alarm, which indicates that the pilots need to avoid any abrupt rudder inputs.
All these warnings are coming from the aircraft’s onboard computer system, but there is no clear reason WHY this is all happening. And then suddenly, the altimeter readings spring back to life and the pilots have a glimpse of their altitude. But now the captain’s and first officer’s altitude readings are different – one says they are going up, and one says they are going down.
Because all the critical instruments seem to be going haywire, Captain Schreiber attempts to engage the autopilot as a means by which to give them time to troubleshoot all the alarms and warnings blaring at them in the moment. But the autopilot requires identical data from two out of three of the plane’s flight control computers, and the instrument readings on Captain Schreiber’s panel versus First Officer Fernández’s do not match. This causes the autopilot to disengage. It simply cannot function without the aligned data.
Multiple Alarms Sound Inside the Cockpit, Creating Confusion
Then, if these warnings and issues were not already enough, the mach trim warning starts to sound, which means that the plane is not flying at a level position and the airspeed is too high and the stabilizer has stopped functioning. Oh yeah, and the other alarms were still sounding. Picture blinking red and yellow lights that are beeping over and over. Yet, to the pilots, the plane seems to be flying normally.
The captain calls for them to go to basic instruments, and tells First Officer Fernández, “we are in an emergency.” First Officer Fernández officially declares an emergency by contacting ATC. And now they must try at an emergency landing.
Here is what is interesting about the dialog between the captain and first officer: they are basically wondering if maintenance screwed up something, causing the plane to go into this chaotic breakdown. First Officer Fernández exclaims, “these assholes from maintenance move everything.” And Captain Schreiber seems to agree with the first officer when he asks, “what shit have they done?”
As is customary during an emergency, Captain Schreiber takes back control of the aircraft. Meanwhile, the pilots contact ATC and request vectors for ILS, or the instrument landing system, which will help guide them to the runway. This system provides information on their course while altitude information comes from the plane’s transponder.
The first officer asks the air traffic controller for the aircraft’s flight level and speed. The radar controller confirmed that they are at 4,000 feet. This must have been a great relief to the flight crew, as it corresponded to what the altimeter in the cockpit is showing. They focus again on the rudder ratio and their airspeed, which still appear to be low.
They continued to climb. The first officer then asks the controller again to confirm their airspeed and their altitude, which are the two parameters needed for safe flight. The controller responds that they were currently climbing through 6,000 feet. The first officer said that their altimeter showed 7,000 feet and the controller confirmed that was correct: “Now reading seven zero.”
Now, just 5 minutes into this flight, the pilots try to troubleshoot the big picture: what explanation could possibly exist for all the warnings. First Officer Fernández reviews the flight manual for answers.
Tensions Run High in the Cockpit as Pilots Try to Identify Altitude and Airspeed
Tensions are also running high as the Captain communicates back and forth with ATC, relying on ground control for airspeed and altitude information at every step of the way. The pilots are very, very confused at what is happening overall with the plane. In the cockpit, they work through what seem to be the relevant checklists while climbing to 12,000 feet out to sea. And, again, they have all these alarms blaring at them. It is clear to both pilots their instruments couldn’t be trusted.
Air Traffic Control gives them a new heading to turn them back towards the airport just in case they lost radio communications. The controller tells them that next they would turn right to intercept the localizer with an initial descent to 4,000 feet. The flight crew follow the vectors from ATC and attempt to set up for a landing with no key indicators available to them.
As Aeroperú 603 begins its descent, the displayed airspeed starts to increase rapidly. The overspeed warning now sounds. This is another warning which needs immediate attention and action. It means that the speed of the plane is exceeding the structural and engine tolerance limits: basically, the warning meant the aircraft was going faster than Boeing deemed safe for a 757.
The pilots know they cannot trust their instruments, so they had a decision to make: do they speed up or do they slow down? One must be true while the other one must be false.
They are now 15 minutes into the flight. It is critical to remember that all this confusion, these contradictory alarms, are all happening within minutes.
ATC confirms that the aircraft is 31 miles west of the airport at just over 10,000 feet with a speed of 270 knots. Meanwhile, the cockpit display showed an airspeed of 350 knots. Again, from the pilots’ perspective, which was one is right?
Reassured by the radar controller that they are indeed flying at 10,000 feet, they continue their descent. The overspeed alarm sounds again and continues to sound, even though they’d reduced the thrust and activated the air brakes.
Then things go from bad to worse. The stick shaker activates, the control columns vibrating violently. The stall warning means that the aircraft is in danger of stalling. Remember, an overspeed warning means you are going too fast; a stall means you are going too slow. The captain must prioritize which one they tackle first, but the million-dollar question remains, which one is right?
The flight crew are desperate now. They are beginning to realize that a safe landing is nearly impossible. First Officer Fernández asks ATC, is there another aircraft to help them understand the situation? Maybe if someone could fly alongside the plane, that would help them determine whether their airspeed was dangerously high or critically low. It would also confirm their altitude. Maybe they could follow that aircraft down toward the runway. And amazingly, the controller tells them that they had another aircraft almost ready for take-off that would come and fly with them as a guide plane, but it would take another 15 minutes. This, by the way, is called formation flying, when one aircraft guides another.
Captain Schreiber Does Not Believe Aeroperu Flight 603 is in a Stall
But Captain Schreiber is angry at the First Officer for asking ATC about formation flying. The captain believes the overspeed warning is accurate while the first officer is convinced that they are stalling. Both believe their altitude was at 9,500 feet since ATC was able to confirm that for them.
Captain Schreiber tells the first officer, “we are not in a stall. It’s fictitious, it’s fictitious.” First Officer Fernández argued back, “no! If we have shaker, how would it be not…” They argue back and forth a little bit at this moment. They refer to checklists repeatedly, even though there was clearly nothing there that can help them. The situation in the cockpit is quickly devolving and the pilots have ceased to work together as a team. And to add to the confusion, ATC keeps confirming with them that Flight 603 is indeed at around 10,000 feet.
And then the most terrifying thing is about to happen. The next alarm to sound is the Ground Proximity Warning System, calling out TOO LOW, TERRAIN, TOO LOW, TERRAIN. If this indicator is correct, this means a collision with the ground is imminent. The warning sounds twenty-two times over 45 seconds. The captain believes they must have inadvertently overflown the coastline and are heading into the Andes mountains, where he knows the terrain swiftly rises to ten thousand feet. The first officer calls ATC who says that radar shows Flight 603 out to sea and flying at 10,000 feet.
Captain Schreiber turns the plane back out across the sea, hoping to avoid a collision with the mountains that he thinks they must be flying toward. Desperate to get the aircraft onto the ground, they descend again, ignoring the Ground Proximity Warning System.
And then it must have been terrifying to finally see… the dark waves of the ocean light up in front of their eyes.
First Officer Fernández shouts to the Captain, “We are impacting water!” The controller, equally frantic at hearing that sentence come over the channel, shouts, “Go up, go up if it indicates pull up!” On the cockpit voice recorder (if you are brave enough to listen) you can hear the first impact with the water. The aircraft hits the ocean surface at a 10-degree angle and at 260 knots for the first time with left wing and engine.
For the next 20 seconds, the pilots struggle to gain altitude. But it is too late; with idle thrust and already dangerously slow, the speed slowed to nothing. The captain realized he’d lost control of the aircraft, saying, “We are going to invert…” as the wing dropped, and the Boeing banked left. That’s when the CVR abruptly ends.
As they crash into the water, the captain’s instruments showed that their airspeed was 450 knots, but the altimeter still read 9,700 feet above sea level, which also matched the controller’s radar, was obviously inaccurate.
What Aeroperu Flight 603 Passengers Experienced
Only in the last seconds would the passengers have known what was happening, as the previous climbs and descent were too gentle to be felt, even in the cockpit. The passengers, like the flight crew, could see nothing out of the windows other than the black night and the lights of the wings reflecting off the cloud. The cabin crew, unprepared for the emergency, could not offer any help. There were no life jackets nor life rafts for the passengers.
The aircraft plunged into the Pacific Ocean and sank. This was October and the winter water temperatures were likely near to freezing; anyone who survived the impact and escaped the cabin would have had less than 15 minutes to survive before falling unconscious or collapsing with exhaustion. However, it’s unlikely that anyone made it out of the aircraft at all.
In all, there are no survivors on Aeroperú 603 – all 70 people have perished. The harrowing flight lasts just about 30 minutes. Nine bodies eventually float to the surface – the rest sink with the plane to the sea floor.
First Officer’s Uncle Appointed as Lead Accident Investigator
Aviation accident investigator Guido Fernández is appointed as lead investigator for the crash of Aeroperu Flight 603. And he unknowingly has a personal connection to this crash. At 4:30 in the morning, just a couple hours after the crash, Fernández received the call that a plane had crashed, and his nephew, First Officer David Fernández, had been lost. Investigator Fernández said despite the personal loss related to the crash, he had a duty and a mission to fulfill in finding out what happened onboard, despite his personal feelings.
The investigation begins first by trying to locate both recorders (which they do find). The National Transportation Safety Board (NTSB) in the US is also asked to participate in the investigation. One of the first things the NTSB recommends to Peruvian investigators is to consider having Captain Fernández step down as lead investigator due to concerns that he may be too personally motivated in this investigation. But within a short period of time, it becomes very clear to the NTSB that Fernández is able to be objective. One of the NTSB team members later commended Fernández for his professionalism and said he was an excellent investigator and did an outstanding job.
Aeroperu Flight 603 Investigation Zeroes in on Static Port Blocked by Tape
Investigators next listen to the cockpit voice recorder for clues as to what happened and immediately it is clear that there were problems with the pilots being able to identify the plane’s altitude and speed, which created a scene of total chaos in the cockpit. And these two data points (altitude and speed) are a function of the pitot static system.
Let’s talk about the pitot static system, which is found on all aircraft. External ports on the outside of the plane’s fuselage measure air pressure to provide data on altitude and speed. The pitot measures the dynamic air pressure, and the static ports measure the static air pressure: between them, they feed the altitude and the airspeed to the flight crew. It is vital that they are protected from contamination. If these ports are blocked, then the data becomes faulty. So, if the plane was otherwise operating normally, which it was, how and why did the ports become blocked?
Investigators soon find the startling answer at the bottom of the sea. When they examine the exterior of the fuselage, they find that every single port was blocked. By TAPE. And the investigation uncovers a terrifying sequence of events caused by a seemingly simple human error.
Mechanic Forgets to Remove Tape from Static Port, Leaving it Blocked
While Aeroperu Flight 603 waited at the airport in Lima to takeoff, the maintenance team replaced two turbine blades and repaired the hydraulic pump. The last stage was to clean and polish the lower front part of the fuselage. This was done by a line mechanic, who started his work by covering the static ports with silver masking tape to make sure that none of the polish or other foreign material would interfere with the air intake. The mechanic was supposed to use brightly colored tape, bit he did not, and he has never been able to explain why he chose the silver duct tape.
The mechanic should have removed the tape when he finished but somehow, he forgot. The standard procedure is that a Quality Control staff member is supposed to check the line mechanic’s work – but he did not do that. And then a supervisor who was also supposed to check the work was out sick that night and a different line mechanic was filling in for the supervisor. He did not see the tape, most likely, because the tape was a dull silver color, and the static ports are high off the ground; none of the people who should have been involved in the handover noticed that the tape had not been removed. Responsibility for the aircraft then goes to the line chief.
The line chief then hands it over to the pilot responsible for the flight, in this case Captain Schreiber. Finally, the pre-flight checks included the specific task of checking that the static ports were clear; however, when the captain did his walk-around, he never noticed the tape.
As Fernández, the lead investigator, said in the Mayday episode for this crash, “A little piece of paper with glue caused an accident. But the paper and the glue are not to blame. Humans are to blame because humans used that tape in the wrong place and for the wrong purpose.”
Not only was there a negligent error on the part of maintenance, but the pilots were also relying on ATC for their altitude information throughout the flight. Why was this information inaccurate? The controller was using secondary radar, which means that he was picking up the airspeed and altitude information from the aircraft’s transponder. Rather than confirming their height, he simply repeated the same altitude information that their instruments were showing them. The partially blocked static ports were not able to measure their altitude correctly and so the information displayed on his radar was just as wrong as it was in the cockpit. It was essentially the blind leading the blind. The pilots had no idea and were making decisions based on this faulty data.
Blocked Static Port Also Found as Contributor to Birgenair Air Crash
And Aeroperu Flight 603 is not the first instance where investigators have encountered issues with a blocked port. Just eight months earlier, a Birgenair Boeing 757, carrying charter passengers to Germany, crashed into the sea at nighttime soon after take-off from the Dominican Republic, killing all 189 on board. A fault in the air-speed indicator and pilot error was blamed for the accident. And in that wreckage, one of the static ports had been found to be blocked. Take to the Sky will cover this crash on a future episode.
What both crashes highlighted is that a crew will get confused by the many erroneous indicators in the cockpit and not be able to identify the underlying problem – the flight computer or the inputs that the flight system relies upon, such as the pitot tube or the static port. Three months after the Birgenair crash, bulletins had been issued to all airline carriers about the pitot static problems, but Aeroperú had not yet implemented the changes. They recommended that the 757 aircraft flight manual include the information that if the rudder ratio and the mach trim alarms go off at the same time, it’s a symptom of an airspeed discrepancy and likely a failure of the air data.
However, as it had only happened once, this information was not disseminated with a sense of urgency and the Aeroperú flight crew had no idea.
But investigators believe that even if Captain Schreiber and First Officer Fernández knew about the bulletins it still may not have been enough to prevent the crash. The intensity of the situation in the cockpit was one in which no one was doing their best thinking. So many pilots and even several investigators have been quoted in various articles about this crash saying that it is so easy to say after the fact what they should have done when you are in the light of day and do not have a multitude of screaming alarms beeping at you and a plane full of people whose lives you have in your hands. Basically, the general perspective is, solving the mystery of the blocked ports was not impossible but it was not as easy as some may think it could have been.
Rumors also abounded that the crash was caused by sabotage because supposedly the Peruvian Mafia wanted one of the passengers (a prisoner who was being extradited to Argentina) dead. No evidence ever emerged to support this unofficial theory.
Victims’ Families of Aeroperu Flight 603 Receive Then Highest-Ever Cash Award in Settlement
The crash of Aeroperú 603 caused 70 people to lose their lives and their families sought justice. In November 1996, 41 families sued Boeing. The premise of the suits was that Boeing had to reasonably foresee the misuse of their product (in this case, the static port being covered up) and was responsible for all the things that went wrong because of the covered port. To clean the airplane, one must cover the static port. If the covering does not come off, the plane can crash. Simple and true. Boeing argued that Aeroperú was at fault since it was their mechanic that covered the port, and they blamed the captain for not catching it in his preflight check. But one of the NTSB investigators for the crash said they understood why the captain missed it – it had been at night when he did his check, and the ports are about 15 feet high. They were easy to miss if the tape is the same color as the fuselage.
In 1999, the law firm representing more than two-thirds of the victims’ families confirmed that the family members of the passengers aboard Aeroperú flight 603 received one of the largest cash awards ever from an airplane crash outside the United States aboard a non-U.S. carrier. The awards were so high because of the terror that the passengers and crew likely experienced, including the fact that most probably survived the crash only to drown. As one attorney said point blank, “They were awake; they were horrified; they knew what was happening.”
Meanwhile, the mechanic who physically covered the ports was sentenced to jail for negligence. Many saw this as an unfair repercussion given the mechanic’s understanding of the situation and many more felt that the supervisors, who were not blamed, were the ones responsible if anyone were.
Hindsight is 20/20 When It Comes to What Happened on Aeroperu Flight 603
Lastly, as part of the investigation, the pilots’ performance was analyzed. One of the conclusions investigators reach is, that the pilots were both very focused on ground speed. However, if they had used other data such as the speed and direction of the wind as well as the aircraft’s ground speed, one could manually work out something close to the current airspeed. Unfortunately, the flight crew were so overloaded by the pressure of the situation, they did not factor in this additional information.
Aeroperú Files for Bankruptcy Following the Crash of Flight 603
The Flight 603 incident contributed to the eventual demise of Aeroperú, which was already plagued with financial and management difficulties. As a result of the crash of Flight 603 and the large amount of money paid for the settlements (which had aggravated the already existing financial issues even further), Aeroperú declared bankruptcy and ceased all operations in March 1999.
And THAT is the unsettling and tragic story of Aeroperu Flight 603.