Disaster in Lima, Peru

"flying blind"

CG render of Flight 603 reflected in the water just below and before it ditched

Aeroperú Flight 603

On October 2, 1996, shortly after take off just past midnight, the Boeing 757 airliner crew discovered that their basic flight Instruments were behaving erratically and reported reiciving contradictory serial emergency messages from the onboard computer, such as rudder ratio, overspeed, underspeed and flying too low. The crew declared an emergency and requested an immediate return to the airport. Faced with the lack of reliable basic flight instruments, constantly receiving contradictory warnings from the aircraft's flight computer (some of which were valid and some of which were not), and continuously believing that they were at a safe altitude, pilot Eric Schreiber and copilot David Fernández decided to cautiously begin the descent for the approach to the airport. Since the flight was at night over water, no visual references could be made to convey to the pilots their true altitude or aid the pilots in the descent. Also, as a consequence of the pilot's inability to precisely monitor the aircraft's airspeed or vertical speed they experienced multiple stalls resulting in rapid loss of altitude with no corresponding change on the altimeter. While the altimeter indicated an altitude of approximately 9,700 feet, the aircraft's true altitude was in fact much lower. It struck the water approximately twenty-five minutes after emergency declaration. All nine crew members and sixty-one passengers died.

The peruvian accident investigator, Guido Fernández, was the uncle of the co-pilot, David Fernández, but, despite originally holding some reservations about the potential conflict of interest, the National Transportation Safety Board appointed investigator - Richard Rodriguez - determined that he could properly investigate the accident. The US Navy provided equipment to locate the wreckage of the Boeing 757. The later investigation of the accident revealed that a piece of masking tape accidentally left over the static ports (on the bottom side of the fuselage) after cleaning the aircraft led to the crash. Employee Eleuterio Chacaliaza left the tape on by accident.

The static ports are critical to the operation of virtually all of those flight instruments that provide basic aerodynamic data such as airspeed, altitude and vertical speed, not only to the pilots but also to the aircraft's computers, which provide additional functions such as warnings when flight characteristics approach dangerous levels. The blockage of all of the static ports is one of the few common-failure modes resulting in total failure of multiple basic flight instruments and as such is regarded as one of the most serious faults that can occur within the avionics systems.

The design of the aircraft did not incorporate a system of maintenance covers for the static ports. Such covers are commonly employed in aviation for blocking access to critical components when the aircraft is not in operation and are generally a bright color and carry flags (which may have "remove before flight" markings). Instead, the design of the aircraft and the relevant maintenance procedure called for the use of adhesive tape to cover the ports.

As a result of the blocked static ports the basic flight instruments relayed false airspeed, altitude and vertical speed data. Because the failure was not in any of the instruments but rather in a common supporting system, thereby defeating redundancy, the altimeter also relayed the false altitude information to the Air Traffic Controller, who was attempting to provide the pilots with basic flight data. This led to extreme confusion in the cockpit as the pilots were provided with some data (altitude) which seemed to correlate correctly with instrument data (altimeter) while the other data provided by ATC (approximate airspeed) did not agree. Although the pilots were quite cognizant of the possibility that all of the flight instruments were providing inaccurate data, the correlation between the altitude data given by ATC and that on the altimeter likely further compounded the confusion. Also contributing to their difficulty were the numerous cockpit alarms that the computer system generated, which conflicted both with each other and with the instruments. This lack of situational awareness can be seen in the CVR transcript. The fact that the flight took place at night and over water thus not giving the pilots any visual references was also a major factor.

At first, the investigation put the responsibility for the accident on the flight deck crew.

Rumors abounded that the crash was caused by sabotage because the Peruvian mafia supposedly wanted one of the passengers (a prisoner who was being extradited to argentina) dead. These rumors were never confirmed.