There have been many cornerstones in the history of civil aviation leading to major changes and new regulations. These include the first balloon flight in 1783, the Wright Brothers’ first successful flight in 1903, the first intercity flight by henry Farman in 1908, the first non-stop passenger flight from London to Paris in 1911, the first solo transatlantic flight in 1927, the first supersonic flight in 1947, and so on. Yet, none of them has been more important than safety and the latter has always been the game changer in aviation.

To set an example, in 1972, Eastern Air Lines flight 401 from New York to Miami with 163 passengers, 10 flight attendants, and a flight crew of 3 pilots crashed into the Florida Everglades causing the death of 101 people. The final report of the NTSB (National Transportation Safety Board) revealed that the cause of Lockheed Tristar’s crash was due to pilot error in failing to “monitor the flight instruments during the final four minutes of flight, and to detect an unexpected descent soon enough to prevent impact with the ground” and one of the first changes to regulations in the aftermath of this accident was that many airlines started to implement crew resource management (CRM) training to enable their pilots to find more efficient ways of problem solving in the cockpit. 

This was, of course, not the first and last accident that necessitated the implementation of new regulations either for aviation professionals or other components of this ever-growing industry. In another instance in 1978, a Boeing commercial airliner 727 of Pacific Southwest Airlines collided with a private Cessna 172. This mid-air collision over San Diego was reported by the NTSB to have probably resulted from PSA crew’s loss of visuals with the Cessna and it resulted in two immediate new regulations by the FAA: implementation of TRSA (Terminal Radar Service Area) and the implementation of Class B Airspace for the safe separation of aircraft. 

Last but not least, in 1983, an electrical fire on an Air Canada flight from Dallas Forth Worth to Montreal caused toxic smoke in the fuselage caused the death of 23 passengers which resulted in the installation of smoke detectors in lavatories and lighting on the floor level to lead onboard passengers to the nearest exit in case of emergency. Although these accidents are only some examples of more than 11,000 thousand accidents in total that have been recorded since 1970, it clearly shows how significant they are in the history of civil aviation and the evolution of safety management. 

All in all, it can be said that two historic events have challenged the safety measures and resulted in more significant regulations to be implemented for safer airspace: The Zagreb mid-air collision and the so-called Tenerife disaster in two consecutive years. What differentiates these two accidents from the others is that non-standard and even no use of phraseology and communication problems resulting from a lack of English language proficiency were reported to be contributing factors to these accidents.  For this very reason pilots’ and air traffic controllers’ (ATCOs) English language proficiency has started to be taken into consideration much more seriously thanbefore. Yet, it took more than a decade for the ICAO to implement new regulations regarding this matter. For this reason, it is of great importance for the aviation industry to get a better understanding of a series of events that ended up in miscommunication so that more can be done, if necessary, to ensure safety in the air and on the ground.

Background of the disaster

Famous American poet Robert Frost said, “Two roads diverged in a wood / and I— I took the one less traveled by / And that has made all the difference”. On March 27, 1977, two different routes were supposed to diverge in the second most populous island of the Canary Islands. However, both the KLM flight and the Pan Am flight took the less traveled by route and that made all the difference as it resulted in 583 fatalities and 61 injuries.

What started asjoyful air travel from Amsterdam Schiphol Airport to Gran Canaria Airport for 234 passengers of KLM flight 4805 was about to turn into the deadliest disaster in aviation history at around 13:15 local time in the Canary Islands when a bomb exploded in the Gran Canaria International Airport and the airport was closed for air traffic operations. That’s why KLM flight 4805 had to divert to Los Rodeos International Airport in Tenerife. Similarly, the Pan Am flight 1736 operating from Los Angeles to Canary Islands with a stopover in New York was told by the ATC to divert to Los Rodeos although the Clipper 1736 (Pan Am) had enough fuel to circle in a holding pattern for 2 more hours. After landing, both 747s were parked on the only taxiway parallel to runway 12-30 as there was not enough space to accommodate both super jumbos at the same time on the apron. When Gran Canaria Airport was reopened for air traffic operations, both KLM and Pan Am were ready to take-off from runway 30 for their original destination. However, the only way to get to the take-off position on the foggy runway 30 was to taxi all the way down and to backtrack at the end of runway 12. What’s more the Pan Am pilots realized that it was not possible to maneuver due to a lack of safe clearance between them and KLM’s super jumbo which was refueling at that time. After all, there existed only one option for the air traffic controller to safely guide these two super jumbos to the take-off position on runway 30. First, the KLM plane would taxi down to the end of runway 12, backtrack, and then hold at take-off position; then the Clipper would taxi on runway 12 and take the third exit to clear the runway for KLM. However, nobody could have imagined how all these plans would lead to a chain of misunderstandings and end up in the deadliest air traffic accident in history. English language proficiency was what really mattered throughout this series of events and it is most certainly worth further analysis here once again. 

The misunderstandings

Two non-native speakers of English, Spanish Air Traffic Controller and Dutch pilot, communicate over radio for the clearance (Cockpit Voice Recorder):

KLM 4805: The K.L.M. four eight zero five is now ready for take-off and we are waiting for our ATC clearance. (17:05)

Tenerife APP: K.L.M. eight seven zero five you are cleared to the Papa Beacon, climb and maintain flight level nine zero, right turn after take-off, proceed with heading four zero until intercepting the three two five radial from Las Palmas VOR. (17:05)

KLM 4805: Ah – Roger Sir, we are cleared to the Papa Beacon, flight level nine- zero until intercepting the three two five. We are now at take-off. (17:06)

Tenerife APP: O.K. Stand by for take-off, I will call you. (17:06)

For many people, this exchange of messages seemed routine at first. However, there was a slight difference which caused the disaster. First, at the time the clearance was requested by the KLM crew, the super jumbo had already completed its taxi down to the end of runway 12 and had backtracked. It resulted in the very first misunderstanding between air traffic controller and the KLM crew because when the controller gives the KLM clearance, the crew misunderstood the clearance as a further leave to take off. That’s why, the KLM crew ended the readback with the following statement: “We are now at take-off”. Furthermore, the controller responded, “O.K. Stand by for take-off, I will call you”, which made the whole communication even more complicated. Such misunderstandings occurring between two non-native speakers of English or between a native speaker and non-native speaker are quite common. In one attempt to identify these issues, the US Federal Aviation Administration found out that “non-native English-speaking pilots are at a disadvantage flying into countries where their primary or native language is not spoken”. Similarly, it is as challenging for native English-speaking pilots to communicate with air traffic controllers whose mother-tongue is not English. The main problem with the Tenerife disaster was closely related to this issue. Although the KLM captain Jacob Louis Veidhuyzen van Zanten with 11,700 flight hours and the first officer Klass Meurs with 9,200 flight hours were quite experienced in their profession, it was clear in this disaster that they were not competent enough in terms of English language proficiency to clear everything up with the controller. Having a non-native English-speaking background, the statement “We are at take-off” was clear enough for the KLM crew to mean that they were, in actuality, rolling on the runway. Yet, the same statement meant something totally different to the other person, the air traffic controller. Oxford Learners’ Dictionary states that the preposition “at” is “used to say where something/somewhere is or where something happens”. So, what the air traffic controller, as a non-native speaker of English, comprehended from the KLM crew’s statement was that the KLM super jumbo was physically located on runway 30 and not on the go yet. Having a heavier workload than that of a usual workday and giving air traffic control service under low visibility on the day of the disaster, there was no chance for the controller to verify the KLM aircraft visually. The lack of English language proficiency to fully comprehend the intended message was clearly unfolded in this disaster and it was also reported by the Dutch investigators as the number 1 factor contributing to the accident: “Inadequate language”.

Ambigious words

Another interesting fact regarding the contributory role of English language proficiency in Tenerife Disaster was the ambiguous words. The use of standardized phraseology is a must in all air traffic operations to avoid ambiguity and the standard phraseology is well-established in several documents such as ICAO Annex 10 Volume II Chapter 5, ICAO Doc 4444 Chapter 12 and in ICAO Doc 9432 - Manual of Radiotelephony. Furthermore, many national civil aviation authorities publish manuals on radiotelephony for same purpose. Although, majority of these publications date back to the aftermath of the disaster, it was known that Spanish air traffic controllers and the Dutch pilots were not unfamiliar with the phraseology.

The underlying factor causing ambiguity also resulted from the nature of radiotelephony communication between pilots and air traffic controllers. The investigation of the Air Line Pilots Association (ALPA) pointed out this issue. The utterances of the KLM crew were not only out of standard phraseology but also ambiguous. The report of ALPA stated that the radio message “We are now at take-off” were analyzed by experts and there was no common ground to meet on. While some of the experts comprehended the message as “We are now at take-off”, the others claimed that it could have also been comprehended as “We are now uh taking off”. Taking the unusual situation in Tenerife on that day and the pressure on the KLM first officer after the diversion because of the terrorist attacks on Canary Island into account, it was possible to conclude for the investigators that his pronunciation of certain words was undoubtedly hurried and his voice was tremulous. Yet, the ambiguity was also identified on the other end of the line.

The official report of ALPA clearly showed that “air traffic control was provided by a ground controller and an approach controller” and that “the tower controller was not manned because of a lack of personnel”. Also, “the tower control frequency (118.7 MHz) was used by both the approach controller and ground controller”. As a result, the Pan Am was cleared onto the taxiway by the ground controller whereas the same clearance for KLM was provided by the approach controller. This, in fact, made a huge impact on the series of events that took place later on. Due to unclear accent of the ground controller who cleared Pan Am onto the runway 12, there was an ambiguity for the Pan Am crew regarding their taxi clearance, which was as follows:

Tenerife GRD: Seven one two stand by. Break, Clipper one seven three six leave the runway (dah) three one (dah) on to (our) left. (17:01)

Pan Am 1736: I am sorry, say again please. (17:01)

Tenerife GRD: Leave the runway the third one (your) left. (17:01)

Pan Am 1736: Okay, ah, taxi down the runway at the first intersection on the left, is that correct? (17:01)

Tenerife GRD: Negative the third one, the third one and change on one nine point seven (17:01)

Pan Am 1736: Okay, the first one and one nineteen seven changing. (17:01)

The conversation between the ground controller and Pan Am crew started with ambiguous words by the controller which resulted from his unclear English accent influenced by Spanish. So, the Pan Am crew cannot make sure whether the intended message was “our” left or “your” left and whether the “first” or “third” left. Even when the Pan Am crew changed the frequency, there was still no clear comprehension of the taxi instruction. The following conversation was recorded between the Pan Am pilot and Spanish approach controller:

Pan Am 1736: Tenerife, the Clipper one seven three six. (17:02)

Tenerife APP: Clipper one seven three six, Tenerife. (17:02)

Pan Am 1736: Ah- We are instructed to contact you and, also taxi down the runway, is that correct? (17:02)

Tenerife APP: Affirmative, taxi into the runway and -ah- leave the runway third, third to your left. (17:02)

Once again, English language proficiency and the variation in the accents of the pilot and air traffic controller were reported to be contributory factors in official reports of the Tenerife disaster. Apart from other causes of the accident, things could have been different if both sides had been clear enough on (1) whether they were on the go or not, and (2) whether the requested exit on the runway was the first or third exit. In that case, the two super jumbos might have not been on Runway 30 at 17:06 GMT in Tenerife, Spain. The deadliest air traffic accident in history was just about to happen after the final words of the KLM crew were heard on the radio, “We are at take-off”. While the readback was being read at 17:06 GMT by the KLM crew, the super jumbo also started its take-off roll. Unfortunately, the other super-jumbo Clipper 1736 had already passed the “third” exit and was trying to clear the runway for KLM. In just five seconds after the V1 callout, KLM’s super jumbo collided with Clipper 1736 causing 583 fatalities, which was later officially reported to have primarily resulted from language difficulties including accent and idiomatic usage.

Implications for aviation professionals

The passion of flying has always been an indispensable part of our lives as aviation professionals and enthusiasts. No matter what motivated us, we have always worked hard to be a part of this never-ending passion. While doing so, the first and foremost principle we were taught was safety first, both on the ground and in the air. What’s more, the very well-known expression “Flying is not dangerous; crashing is dangerous” was heard over and over on various occasions. It is very probable that the justification for putting such great emphasis on safety is based on two facts: first, the human factor is always a part of all flights and air traffic operations no matter how “smart” the latest aircraft instruments are. Second, globalization has required aviation professionals to be more effective communicators as there are more non-native speakers of English as lingua franca than native speakers. Hence, the role of pilots, air traffic controllers, aircraft mechanics, ground handling staff, and others has evolved over time. Moreover, it has gone beyond the borders of being a passive receiver of a message or instruction. It is time for us to be the facilitator in these exchanges of messages firstly by recognizing the differences of English-speaking aviation professionals and then by making use of the full mental capacity to maintain effective communication. What the ICAO has implemented so far to ensure that pilots and air traffic controllers have the required English language competency for safer operations is to be considered within this context. Yet, this seems to be quite a challenge for the ICAO as there are many other factors affecting the radiotelephony communication between pilots and air traffic controllers. It means that a proficient (Level 6) English-speaking pilot may even end up badly when things really got out of hand in cases like Tenerife Disaster. For this reason, insisting on the use of standard phraseology, avoiding the use of local languages, asking for clarification, making your pronunciation as free from the influence of the mother tongue as possible, these are all must-have aviation communication skills in the 21st century.  Consequently, communication breakdowns happen in our daily lives all the time, you could say they’re a dime a dozen, we might not even realize them most of the time but there is no chance for error or cutting corners in official aviation communication where safety unequivocally comes first