So-called human factors and a series of small technical snags in the Indonesian air traffic control system led to the crash of Sukhoi Superjet 100 S/N 95004 on May 9 outside Jakarta, in which 45 people died, according to a final accident report released Tuesday by Indonesia’s National Transportation Safety Committee. Investigators have concluded that the cockpit crew of the ill-fated demonstration flight, unaware of the mountainous area surrounding their flight path, disregarded an alert from the airplane’s Terrain Awareness and Warning System (TAWS).
The report also noted that the Jakarta radar service had not established the minimum vectoring altitudes and lacked a functioning minimum safe altitude warning (MSAW) for the particular area surrounding the crash site on Mount Salak. Finally, said the report, distraction to the flight crew from prolonged conversation not related to the progress of the flight resulted in the pilot inadvertently exiting a right orbit he requested and for which he received ATC approval.
A contingent of Russian officials held a special briefing on the matter in Moscow on Tuesday. The participants—Pavel Vlasov, head of Mikhail Gromov’s Flight Test Institute; Yuri Slyusar, deputy minister for industry and trade; Igor Vinogradov, SCAC vice president; and Alexander Donchenko, head of the CIS’s ARMAC aviation authority—attempted to explain why a technically flawless airplane outfitted with the most modern Western avionics systems flew into a cliff face. Vlasov, a highly decorated test pilot and former MiG deputy director general, concluded that the Superjet flight crew—consisting of two Sukhoi test pilots and an Indonesian pilot representing a customer—simply lost orientation when making the aforementioned orbit (an incomplete 360-degree turn) in poor visibility. It appears that both Russians knew nothing of the mountain chain in western Java and their Indonesian counterpart in the jump seat insisted that the area down the airplane’s flight path lay “flat.” As a result, the commander ignored TAWS audio warnings.
In a period of 38 seconds the system sounded a “terrain ahead, pull up” and six “avoid terrain” audio warnings. Finally, seven seconds before impact, it signaled “landing gear not down” after the radio altimeter detected ground less than 800 feet below. Although the navigation display (ND) automatically went into TAWS mode and pictured terrain ahead in red, the commander switched the display onto weather radar mode out of concern for thunderstorms more than high ground, according to Vlasov.
During the briefing in Moscow, Vlasov and Vinogradov noted that apart from digital maps downloaded into the Thales-made TAWS computer, the Russian crews carried with them a complete set of paper maps made in their home country depicting Mount Salak and other mountains in the region. However, the report by the Indonesian authorities indicated that the available charts on board the aircraft did not contain information relating to the area in question and the nearby terrain.
Investigators confirmed that the flight plan called for instrument flight rules (IFR) and a cruising altitude of 10,000 feet. When the crew asked to descend to 6,000 feet, the air traffic controller gave his permission, in the belief the pilots wanted to start descending in preparation for landing. Some six and a half minutes later the airplane hit a ridge of Mount Salak, killing two Sukhoi test pilots, a navigator, a flight test engineer, and 41 passengers including a Snecma representative, four SCAC employees and 36 invitees (34 Indonesian passport holders, a U.S. national and a French citizen).