Aeroperú Flight 603

Investigation

The Commission of Accident Investigations (CAI) of the Director General of Air Transport (DGAT) of Peru wrote the final accident report.

The chief Peruvian accident investigator, Guido Fernández Lañas, was the uncle of the co-pilot, David Fernández. There were some reservations about the potential conflict of interest, but the National Transportation Safety Board-appointed investigator, Richard Rodriguez, determined that Fernández Lañas could properly investigate the accident.

The Peruvian Navy collected the floating wreckage. After the Peruvian authorities asked for assistance, the United States Navy provided equipment to locate the underwater wreckage of the Boeing 757 and retrieve its flight data recorder and cockpit voice recorder.

Later investigation into the accident revealed that adhesive tape had been accidentally left over some or all of the static ports (on the underside of the fuselage) after the aircraft was cleaned and polished, eventually leading to the crash. Employee Eleuterio Chacaliaza had left the tape on by mistake.

The static ports are vital 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 in avionics systems.

Boeing's design of the 757-200 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, Boeing designed the 757-200 to rely on a maintenance procedure that 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 erroneous altimeter data was also broadcast to air traffic control, which 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 design flaw resulted in a correlation between the altitude data given by ATC and that on the altimeter, which 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 destruction of the flight crew's ability to maintain situational awareness was revealed by the cockpit voice recorder transcript. That the flight took place at night and over water, thus not giving the pilots any visual references, was also identified as a major factor. The official accident report concluded that the flight crew, distracted by the conflicting warnings, did not heed the GPWS alarm activated by the radar altimeter reading after descending through 2,500 ft. Paradoxically, the radar altimeter was working correctly since it is independent of the other systems, even the blocked sensors that confused the on-board computer and, of course, the pressure altimeter as well.