Two jumbo jets came frighteningly close to each other over Scotland this summer after misunderstanding air traffic control commands, according to a recent report.
The incident was explained in the latest release from the UK Airprox Board, which studies near-miss situations.
On June 23, a Lufthansa 747-830 flying to Washington, D.C. and a British Airways 747-436 en route to Vancouver were flying on converging routes when air traffic control had them climb to the same altitude.
When the planes were 9.8 nautical miles apart, a Short Term Conflict Alert (STCA) was triggered, and a controller ordered one plane to turn to the left and the other to the right.
If they had followed those instructions, according to the report, there would have been no problem. But each crew followed instructions meant for the other. Instead of diverging, they flew closer together.
With 100 feet of vertical separation (effectively nothing on planes that are 60 feet tall), they ended up just 2.8 nautical miles (3.2 miles) apart. The minimum safe separation is 5 nm.
It’s not clear what caused the confusion, according to the report:
“The Board was surprised that all four pilots [two in each plane] had misheard or misinterpreted the avoiding action instructions despite at least one of the crews reading them back correctly. One airline pilot Member wondered if there could have been callsign confusion; this was discounted because they were not similar.”
The Board concluded that the role of air traffic control — putting the planes at the same altitude — was “contributory,” because “his subsequent recovery actions” would “have resolved the confliction.”
The pilots, however, “by flying each other’s avoiding action ATC instructions,” caused the near miss. Nonetheless, there “was no risk of a collision.”
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