Lima air traffic control

Between 0102 and 0104, Low terrain alarms, wind-shear alarms, and ground proximity warning alarms all sounded. At 0105 52, they were 50 miles from Lima, heading west. Lima Air Traffic Control said they were at 10,000 feet, but that was based on the faulty data from the aircraft s communication link. They were actually below 4000 feet. 

At 0107 h they were at 4000 feet (although they believed they were much higher) and they held this altitude for one minute, before beginning a slow descent. At 0109 36, Lima Air Traffic Control said Altitude is 9700 and speed is 240 knots, 51 miles from Lima. Again, their altitude was actually much lower. They continued descending but tlieir actual height was now below 1000 feet... 

At 0110 17, low terrain audible alarms started and sounded twenty-two times for the remainder of the flight, but Lima Air Traffic Control again advised at 0110 18 that their altitude was 9700 feet. 

Their confusion was compounded by Lima Air Traffic Control sending altitude information that the pilots believed was being sourced completely independently using the air traffic control radar, when it was actually just data from the plane s own... 

The recycling of bad altitude information by Lima Air Traffic Control was a further layer of confusion in this accident. Improved training for Lima air traffic controllers was recommended. 

Aeroperu 603 asked the air traffic control tower at Lima to provide altitude readings from their ground radar, which had recently been returned to service after a major service. The tower responded by providing altitude data from its screens, which the air traffic controller believed were generated from the radar systems, but which were actually data provided by the aircraft s own communications data link with the ground i.e., the tower was simply reading back to Aeroperu 603 its own faulty altitude data. 

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