Highest death toll from an aircraft ground collision

The deadliest accident in the history of commercial aviation was the Tenerife Airport Disaster, which took place on 27 March 1977. Two heavily loaded Boeing 747s collided on the runway at Los Rodeos Airport in Tenerife, Spain, killing 583 people.

The two aircraft involved were Pan Am flight 1736 from Los Angeles via New York JFK, which was carrying 380 passengers and 16 crew, and KLM flight 4805 from Amsterdam Schiphol Airport, carrying, 14 crew and 235 passengers. Both were well-maintained modern aircraft with experienced flight crews, the KLM aircraft was even captained by Louis Veldhuyzen van Zanten, head of the airline's 747 pilot training program.

Neither plane was scheduled to land at Los Rodeos; their destination was the larger and better equipped Gran Canaria Airport, located on the island of the same name some 90 km to the east. At around 1 p.m. that day, Gran Canaria Airport was closed following a bomb threat. The only viable alternate destination for many of the aircraft was the small, single-runway airport on Tenerife.

At 2:30 p.m., the Gran Canaria Airport was reopened, but by then around a dozen airliners, including everything from small prop planes to four-engined 747s, were stacked up on the tarmac at Los Rodeos. Many had been forced to let their passengers disembark, and were now struggling to round them back up to leave. The KLM pilots decided to refuel their plane during the wait, but in the process blocked the taxiway, preventing the Pan Am flight from leaving either.

As the afternoon wore on, the weather at Los Rodeos got progressively worse, with a heavy fog descending on the airport. By the time the pair of 747s were cleared to depart at 4:51 p.m. it had lowered visibility down to around 100 m.

What followed was a series of tragic miscommunications involving an overworked and flustered group of fairly inexperienced air-traffic controllers and two airline crews who were both trying to navigate an unfamiliar airport almost blind. The situation was made worse by the fact the airport was not set up for aircraft as large as the 747, meaning that the controllers were having to guide them around the taxiways using non-standard routes, and also that the pilots were having to concentrate hard on turning manoeuvres to avoid running onto the grass or striking ground structures.

The direct causes of the crash were two fatal misunderstandings. The first involved the crew of the Pan Am flight, who couldn't make sense of the ambiguous directions they'd been given by their controller, leaving them taxiing down the runway from the west. The second involved the captain of the KLM flight at the eastern end of the runway, who misinterpreted the order to wait for takeoff clearance as takeoff clearance itself.

The KLM flight was accelerating down the runway when the Pan Am 747 loomed into view, turned almost at a right angle across the runway as it turned onto one of the side taxiways. Captain van Zanten tried to take off early, pulling back hard on the yoke, but didn't manage to get clear. The KLM plane lifted about two metres off the runway before bellying into the upper half of the Pan Am plane's fuselage, tearing both planes apart.

Everyone on the KLM flight was killed within a few seconds as the aircraft tumbled down the runway in flames. The only survivor was a local tour guide, whose final destination was on Tenerife anyway, and who had snuck out of the airport during the hold. Surprisingly, many on the Pan Am flight survived the initial impact, but the speed with which the fire spread, combined with the relatively advanced age of the passengers – most were retirees traveling for a cruise – meant that only 61 people managed to get out from the 395 on board.

In the aftermath of the disaster, airports and airlines around the world worked to standardize the phrasing and terminology used in crucially important instructions. They most notable changes being a shift to controllers never saying the word "takeoff" except in the context of explicit final clearance to depart, and not using filler phrases (such as "OK..." or "right...") that can be interpreted as positive response.