The crash Aeroperú Flight 603 is the story of another aircraft which was in good flying order except for a blocked Pitot-static system which led to onboard systems giving the pilots unreliable and conflicting information about their air speed and altitude. Again, the pilots were overwhelmed with inconsistent information.
As in the crashes of the Airbus AF 447 and the Birgenair Flight 301, the pilots of Aeroperú were flying over water.
Flight 603 was a scheduled flight from Lima, Peru to Santiago, Chile. It originated at Miami International Airport. It crashed on 2 October 1996, killing nine crew and 61 passengers. The aircraft was a Boeing 757-23A, one of what was then a new a new generation of computer-controlled aircraft in which pilots were trained to rely on a flight data system which was designed to reduce errors, both mechanical and human.
Problems began within two minutes of take-off. The altimeter read zero but the plane was clearly airborne. The 757 had three altimeters, one for the pilot, one for the co-pilot and one for back-up. All three seemed to be dead.
"The altimeters are stuck," said the co-pilot. The landing gear had only just been raised.
The pilot replied: "This is really new."
As in the Birgenair Flight 301, the pilots faced a "Rudder ratio" alarm which warned them to avoid large or abrupt rudder movements. It's a warning that the plane is flying too fast.
Then the air speed indicators seemed faulty. Confused with bewildering number of warnings the Captain decided to land. He was flying at night, over water, with no visual reference points and not able to trust his instrument readings.
With various alarms in the cockpit the co-pilot told air traffic control: "We declare emergency. We have no basic instruments. No altimeter. No [air speed indicator]. We declare an emergency."
There was confusion between the pilot and co-pilot as to whether the auto-pilot was engaged or not. At one point the pilot notes with concern that the auto-pilot had switched off.
Having warned the pilots that the aircraft was going too fast, the systems gave a warning that it was in danger of hitting the ground. An electronically-activated voice sounded a "too low terrain" warning.
Within six minutes of take-off the pilot said: "We don't have control, not even the basics."
The co-pilot saw that the speed was shown as zero. But air traffic control told the pilot that the plane was going up. This was wrong. Onboard systems were relaying faulty height readings to air traffic control.
Actual radio communication between the plane and airbase
A ground proximity alarm warned the pilots they were dangerously low. But air traffic control told them they were at nearly 10,000 feet.
As on the Birgenair Flight, the pilot's controls were shaking to give the pilots an unmistakable warning of an imminent stall, though there was a high indicated air speed. Another over-speed warning sounded.
The pilot said: "We are not stalling. It's fictitious. It's fictitious."
The last recorded words of pilot: "I have it. I have it we are going to invert!"
The aircraft bounced on the water, fell back and sank.
Tape was later found to have covered the 757's static port, which is part of the Pitot-static system. This caused the instruments to go haywire. Maintenance workers had cleaned the jet, covered the ports with tape and forgotten to remove it.
Unnoticed by the pilots or air traffic control, the plane had been slowly descending.
National Geographic's documentary on the Aeroperú crash concluded that it was a "deadly lesson in how reliant pilots have become on their automated flight systems and how helpless they can be when the systems are crippled".
- US Coast Guard software aids search for ill-fated Air France wreckage
- Opinion: Could the Air France crash have been related to on-board computer systems?
- Air France crash thought to be caused by system failure
- Air France Airbus part recovered by merchant ship.
Image taken from Wikimedia Commons.