Tenerife 1977 - Part 1
Collision between KLM Boeing 747 and Pan American Boeing 747
Image: Tenerife North Airport
On Sunday 27 March 1977 at time 17:06:50 GMT there was a collision on the runway at Los Rodeos Airport, Tenerife, Canary Islands.
The collision was between a Pan American World Airways Boeing 747-121 aircraft (Registration N736PA - callsign Clipper 1736) and a KLM Royal Dutch Airlines Boeing 747-206B (Registration PHBUF - Callsign KLM 4805). 583 lives were lost.
On the one hand, the situation (“the what happened”) can be described quite simply. On the other hand, deeper analysis is required to obtain an understanding of the reasons WHY this accident occurred.
The simplistic version is that, in conditions of low visibility, both aircraft taxied via the single runway at Los Rodeos. The KLM 747 entered the runway first, backtracked the full length, turned round 180 degrees, received an Air Traffic Control Clearance (but not a take-off clearance), and then commenced its take-off. The Pan Am 747 was also backtracking the runway and had not vacated the runway when the KLM commenced take-off. Due to weather, the runway was not visible from the control tower. The airport was not equipped with surface movement radar. Runway centreline lighting was out of service. The two aircraft were not visible to eachother until moments before the collision.
To delve further, even 46 years later, is not an easy exercise even though there is voluminous commentary about the accident. My analysis is based on the official reports issued by the Spanish and Dutch authorities. There is also a valuable human factor report published by the USA Air Line Pilots Association. When considering the reports, I have tried to apply my own professional knowledge of the situation in civil aviation and air traffic control in the 1970s. Where something is just my opinion, I say so.
Part 1 of this viewpoint looks at the general civil aviation situation in those, increasingly distant, days. Part 1 also notes some basic points.
Part 2 considers the detailed reports, the conclusions, and look at key developments resulting from the accident.
The 1970s in civil aviation:
The 1950s and 60s saw nations emerging from World War 2. The political scene was changing in Europe with the emergence of the European Communities. Also, the dominance of certain political “strongmen” was weakening but even they were not slow to recognise that tourism was one way of improving their beleaguered economies.1 (In Spain, Franco died in 1975 and, in Yugoslavia, the time of Tito was approaching its end. He died in 1980).
Across the world there were numerous airports with poor infrastructure resulting from under-investment. Inadequate air traffic control facilities were commonplace. Some notable airports were not equipped with air traffic control radar even thought they were expected to handle significant numbers of passenger-carrying aircraft. As demand for holidays with almost guaranteed sunshine grew, the airports serving such destinations lagged behind. Even where new airports were constructed ( or improved), alternate airfields were generally neglected.
Airport development was also slow to catch-up with new aircraft types. The jet-age had begun in the 1950s with the De Havilland Comet and, by the early 1960s, jet travel was well-established. Other aircraft types of the period included the Boeing 707 (in airline operation from 1958), the Douglas DC8 (from 1959), the Douglas DC10 (1971), and the Lockheed Tristar from 1972. In 1970, the “wide-body” Boeing 747 entered service with Pan American.2 The introduction of new aircraft types sometimes required appropriate developments at airports - e.g. widening of taxiways etc - but these did not always take place.
On 10 June 1975, at London (Heathrow), a Trident aircraft was the first civil airliner in scheduled passenger service to perform an automatic landing. This pioneered reductions in aircraft operating minima but suitable instrument landing systems, airport approach lighting, runway lighting and taxiway lighting were also required for such “low visibility” operations. The required improvements at airports came gradually during the 1970s and later.
Up to the late 1960s, many airline pilots and air traffic controllers were recruited from the military.3 Such recruits were were already well-versed in the basics of aviation and that made their conversion to civilian work easier. As this source dwindled, various training schemes were established such as the Hamble scheme for trainee pilots and the UK’s Air Traffic Control Cadet scheme (from 1962).
Civil aviation of the 1960s and 1970s certainly had ex-military personnel who were used to acting in a command position. Sometimes, this resulted in human factor problems in their dealings with others though it did not always do so.
During the earlier days of aviation, “the authority gradient” on a flight deck could be pronounced.4 Some senior captains were noted for being particularly authoritarian. The extent, if any, to which “authority gradient” played a part in the Tenerife disaster will be considered in Part 2.
Aircraft navigation methods developed markedly during World War 2.5 By the 1970s, en-route navigation was usually by ground-based aids such as the Non-Directional Beacon (NDB) or the Very High Frequency Omnidirectional Radio Range (VOR). Instrument Landing Systems (ILS) were the norm for final approach to the landing runway. Navigation aids such as Global Positioning Systems (GPS) lay well into the future as did airborne technology such as Airborne Collision Avoidance (ACAS) and Ground Proxmity Warning Systems (GPWS).
That is some of the background to the developing civil aviation scene of the 1970s. I now turn to some basic points which will assist in reading my analysis of the Tenerife accident.
Visibility from aeroplanes:
In May 1927, Charles Lindbergh flew his “Spirit of St Louis” from Roosevelt Field, Long Island to Paris Le Bourget. The flight took over 33 hours. On arrival in Paris, he was greeted by a crowd of around 150,000 people. A remarkable feature of Lindbergh’s aeroplane was that he had installed a periscope so that he could see forwards!
The Spirit of St Louis is far from being the only aeroplane design to give pilots problems with visibility. Many modern cockpits (flight decks) also present problems to aircrew. Let’s look briefly at the Boeing 747.
The typically large dimensions of the B747 are shown in this diagram - (Note: dimensions were altered as variants of the aeroplane were manufactured).
The side-view shows that the pilot is sat around 40 feet (12.2 metres) above ground with the aircraft’s nose ahead of him. A typical semi-detached home is a similar height. The result is that there is a visibility “cut-off” for about 100 feet (30.5 metres) ahead of the aircraft.
Bear this in mind when we come, in Part 2, to the aeroplane taxiing along a runway in low visibility and looking for an exit to the pilot’s left.
Turning circles for large aeroplanes on the ground:
Another issue with large aeroplanes is the turning circle when on the ground. Take a look at the B747 undercarriage -
There is a considerable distance between the main wheels (16 tyres) and the nose wheel. It is obvious - (though the obvious is not always noticed) - that the more space available to make a turn the better. A comfortable turning circle diameter is in the region of 50 metres) but the 747 could achieve it in 45 metres by use of its body gear steering.
Radio:
A quite common problem with radio voice communications arises if two (or more) stations transmit simultaneously. This can result in a “squeal” which either makes the messages unreadable or, sometimes, only part of a message is heard.
Radio communications require discipline including the use of standard phrases and the avoidance of words/terms (such as OK) often used in everyday language. It is also vital that complete transmissions have to be heard by both air traffic control and other pilots. Where overlapping or garbled communications occur there is an immediate need to ensure that messages are properly received by the intended recipients.
The UK’s Radiotelephony Manual (CAP413) notes at para 2.80
Direct communications between pilots and ATSUs can be adversely affected by simultaneous transmissions which, effectively, block all or part of intended messages. Moreover, whilst the situation may be apparent to the controller or another pilot, the individuals who inadvertently make such transmissions may be unaware. On hearing a simultaneous transmission it can be helpful for the controller (or another pilot if it is the controller’s transmission which has been blocked) to draw attention to the situation using the word ‘blocked’
ATC Clearances:
The Manual of Air Traffic Services Part 1 has a great deal to say about “ATC clearances.” (I have linked to the latest edition of the Manual but procedures relating to clearances are very long-standing).
The primary purpose of an ATC Clearance is to separate the aircraft from other known flights.
An ATC clearance authorises an aircraft to proceed under conditions specified by an ATC unit. Clearances are based solely on known traffic conditions and are required for any flight, or portion of a flight, which is provided with an air traffic control service.
ATC clearances have to include - (1) Aircraft identification as shown in the flight plan; (2) Clearance limit; (3) Route - (if specified in the controller’s local instructions); (4) Levels of flight for the entire route or part thereof and changes of levels if required; (5) Any necessary instructions or information on other matters such as approach or departure manoeuvres, communications and the time of expiry of the clearance.
3.1 A clearance limit is the point to which an aircraft is granted an ATC clearance and shall be specified by naming: (1) an aerodrome; (2) a reporting point; or (3) a controlled or advisory airspace boundary.
A simple example of a clearance would be -
The pilot will write this down and read it back to ATC.
At present-day busy airports, Standard Instrument Departures (SID) are likely to be in use. The details of these are published in aeronautical documentation available to pilots. As an example -
The UK’s Radiotelephony Manual (CAP413) dates from September 1978 and its text embodies lessons learned from the Tenerife tragedy. The Manual notes that -
Generally, controllers will avoid passing a clearance to a pilot engaged in complicated taxiing manoeuvres and on no occasion when the pilot is engaged in line up or take-off manoeuvres.
An ATC route clearance is NOT an instruction to take-off or enter an active runway. The words ‘TAKE-OFF’ are used only when an aircraft is cleared for take-off (or if the take-off clearance is cancelled. At all other times the word ‘DEPARTURE’ is used.
Pilots are to readback certain matters including Clearance to Enter, Land On, Take-Off On, Backtrack, Cross, or Hold Short of any Active Runway.
Flight time limitations:
It was recognised in the 1950s that a contributory factor in some aircraft accidents may have been aircrew fatigue but legal regulation was a long-time coming. In the UK, a committee was set up in 1973 under the chairmanship of Group Captain Douglas Bader (1910 - 82) and this led to the UK introducing legal limitations. Other nations (e.g. Holland) also introduced limitations.
The KLM Captain at Tenerife had a concern about how the Dutch rules applied to his flight. The Dutch rules had been recently amended and a Captain’s discretion to extend the limits was removed.
Flight time limitation rules have become a complicated topic. It will suffice here to note that the UK’s Air Navigation Order 2016 requires operators of aircraft to establish a scheme for the regulation of flight times for aircrew and the scheme has to be approved by the Civil Aviation Authority.6
A Scheme for the Regulation of Air Traffic Control Officer hours was introduced in the UK but this was withdrawn on 7 March 2022. The UK now complies with rules established by the European Union and retained within the UK following Brexit.7
Language:
There are three ways that language can be a contributing factor in accidents and incidents: a) incorrect use of standardized phraseologies; b) lack of plain language proficiency; and c) the use of more than one language in the same airspace.
In November 1996 there was a mid-air collision over India between a Saudia Boeing 747 and a Kazakhstan Ilyushin 76 in which 349 people were killed with no survivors. One of the Inquiry’s recommendation concerned Language Proficiency.8
It was not until 1998 that the International Civil Aviation Organization (ICAO) introduced language proficiency requirements - see Language proficiency (icao.int). ICAO Document 9835 is a Manual on the Implementation of ICAO Language Proficiency Requirements.
Part 2 of this Viewpoint looks at WHY the Tenerife accident occurred, the official conclusions, and key developments resulting from the accident.
Pan American ordered 25 Boeing 747-100 in 1966. The commercial aim was to carry more passengers in a single flight and reduce prices.
To some extent the military is still a source of airline pilots - e.g. British Airways - Pilots (ba.com) and British Airways - Future Pilots (ba.com)
See World War II Advances Air Navigation | Time and Navigation (si.edu)
Authority Gradients | SKYbrary Aviation Safety
World War II Advances Air Navigation | Time and Navigation (si.edu)
The European Union Aviation Safety Agency brought about standardisation across EU member States.
See European Union - Regulation 2018/1139 - retained in UK under provisions in the European Union (Withdrawal) Act 2018. Article 50 requires rules and procedures for air traffic controllers in regard to duty time limitations and rest requirements.
The Inquiry report is 1996 Charkhi Dadric accident upload (dgca.gov.in)