Circle of Confusion

The flight crew’s lack of familiarity with nearby mountainous terrain, prolonged nonpertinent conversations that distracted them from monitoring the aircraft’s flight path and the pilots’ disregard of several terrain awareness and warning system (TAWS) warnings were factors that contributed to a controlled-flight-into-terrain (CFIT) accident that destroyed a Sukhoi RRJ-95B (Superjet) and killed all 45 occupants the afternoon of May 9, 2012, according to the National Transportation Safety Committee of Indonesia (NTSC).

The NTSC’s final report on the accident also cited the absence of minimum vectoring altitudes and a minimum safe altitude warning (MSAW) system for air traffic controllers handling flights in the area of West Java where the accident occurred. “The objective of the MSAW function is to assist in the prevention of CFIT accidents by generating, in a timely manner, a warning of the possible infringement of a minimum safe altitude,” the report said.

Demonstration Flight

The crew of the newly introduced regional jet was conducting a demonstration tour and making its second flight of the day from Jakarta’s Halim Perdanakusuma International Airport.

The pilot-in-command (PIC), the pilot flying, had 10,347 flight hours, including 1,347 hours in type. The 57-year-old pilot had experience in several military fighters and civilian cargo and passenger aircraft. The report noted that he had served as lead test pilot during the certification of the Superjet’s terrain and traffic collision avoidance system (T²CAS), which includes both terrain- and traffic-avoidance equipment.

The second-in-command (SIC), 44, had 3,318 flight hours, including 625 hours in type. He, too, had experience in several military and civilian aircraft.

The Superjet departed from Jakarta for the second 30-minute demonstration flight at 1420 local time. Aboard the aircraft were 40 passengers, the two pilots, a navigator, a test flight engineer and a steward. One of the passengers, representing a potential customer for the aircraft, was in the cockpit jump seat.

The crew conducted the takeoff from Runway 06, made a right turn at 2,000 ft and, per the flight plan, established the aircraft on the 200-degree radial of the VOR/DME (VHF omnidirectional radio/distance measuring equipment) located on the airport. The report noted that the radial was not a published airway.

The demonstration flight was planned to be conducted under instrument flight rules (IFR) at 10,000 ft southwest of Jakarta and within 50 nm (93 km) of the airport.

Unplanned Descent

The aircraft was southwest-bound at 10,000 ft when the SIC requested clearance from Jakarta Approach to descend to 6,000 ft. The controller asked the SIC to repeat the request. “The SIC repeated the request for descent to 6,000 feet,” the report said. “Subsequently, the Jakarta Approach controller responded and acknowledged the request by replying, ‘6,000 copied.’ The SIC then said, ‘Descending to 6,000 feet.’”

The course flown was different from that of the demonstration flight conducted earlier that day. The aircraft was at 20 nm DME on the 200-degree VOR radial when the crew began the descent; at this point on the previous flight, they had turned left at 10,000 ft to return to the airport and land on Runway 24, the runway on which they had departed.

The cockpit voice recording indicated that a passenger, a Sukhoi employee, apparently came to the cockpit and asked the PIC why he had decided to descend. The PIC explained that they were descending in preparation to land on Runway 06, rather than on Runway 24, as during the earlier demonstration flight. He said that the descent was necessary because, otherwise, “the altitude would be too high.”

The SIC requested and received clearance from the Jakarta Approach controller to conduct a “right orbit,” or circling right turn, at 6,000 ft. This was the last radio communication between the crew and air traffic control (ATC).

Tagged as a Fighter

The Jakarta Approach controller’s radar display showed that the aircraft was descending toward a restricted military training area that extends from the ground to 6,000 ft. The training area was not depicted on the navigation chart that the crew was using.

The report noted that although the Superjet was in radar contact, ATC authorities had not established minimum vectoring altitudes for the area; the minimum sector altitude was 6,900 ft.

Moreover, because the approach facility’s database did not contain the identification code for the new aircraft, the Superjet had been entered manually as a Sukhoi Su-30. Thus, the approach controller believed that he was handling a fighter. “The controller assumed that a military aircraft was eligible to fly in this area [and] approved the aircraft to descend to 6,000 feet,” the report said.

The controller’s workload was high; he was handling 13 other aircraft and his “communications were performed continuously, one after another, practically without pause,” the report said.

Cloud-Covered Terrain

Comments captured by the cockpit voice recorder during the descent indicated that the ground in the area was mostly covered by low cloud. The SIC said, “Dark cloud ahead,” and later remarked that he could occasionally see the ground through the clouds.

The crew was using an area navigation chart that included limited terrain information, according to the report. A different instrument chart with pronounced terrain contours and an even more terrain-descriptive visual flight rules navigation chart were available but were not carried aboard the aircraft.

The PIC used the autopilot’s heading mode to initiate and continue the turn. He initially selected a heading of 333 degrees and then made three more adjustments before selecting a heading of 150 degrees as the aircraft began tracking northbound.

The PIC began discussing features of the aircraft with the jump-seat passenger. He was demonstrating the terrain display provided by the electronic flight information system (EFIS) when he remarked, “But no problem with terrain at this moment.” The passenger said, “Ya, it’s flat.”

The report said that these comments likely were based on the EFIS terrain display that appeared during the PIC’s demonstration. At the time, the aircraft was headed northeast, toward the Java Sea, and the display likely did “not indicate any terrain information due to the flat area ahead,” the report said, noting that this might have “affected the PIC’s perception that the whole area surrounding the flight path was flat,” a perception that was reinforced by the passenger’s comment about the flat terrain.

Out of Orbit

The PIC and the jump-seat passenger were discussing the aircraft’s fuel consumption when the Superjet rolled out on the selected 150-degree heading. The aircraft then continued tracking southeast while the pilots discussed the heading required to return to Jakarta.

The aircraft was nearing the point at which it had begun the circling maneuver when the PIC selected a heading of 174 degrees. As the Superjet rolled out on this heading, the PIC told the SIC to request clearance from ATC for a right turn.

The SIC asked the PIC if he intended to make another orbit or to return to the airport. The PIC did not reply. The SIC repeated the question twice before the PIC said, “We will make approach.”

Both pilots then were distracted from monitoring the aircraft’s flight path. The PIC became engaged in another nonpertinent conversation with the jump-seat passenger, and the SIC was concentrating on determining the course to return to the airport. “The pilots may not have noticed that the aircraft had exited the orbit and assumed that it was still continuing to turn,” the report said.

The pilots then continued their discussion of the heading required to return to the airport and agreed on 020 degrees. The PIC told the SIC to ask Jakarta Approach for clearance to turn to 020 degrees and to descend to 1,600 ft for the VOR/DME approach to the airport. “The PIC’s intention to descend indicated that he was not aware of the mountainous area surrounding the flight path,” the report said.

The SIC did not respond to the PIC’s instructions to request clearance to return to the airport. The PIC repeated the instruction: “Just request quickly.” The SIC replied, “OK.”

‘Terrain Ahead, Pull Up’

The PIC then selected a heading of 325 degrees, and the autopilot commanded a right, 20-­degree-banked turn. Four seconds later, the TAWS generated a “TERRAIN AHEAD, PULL UP” warning, followed by six “AVOID TERRAIN” warnings. (The report noted that the latter warning is generated when a climb, alone, is not sufficient to avoid terrain and a turn also might be necessary.)

The TAWS warnings caused the pilots’ navigation displays to change to the terrain mode. During post-accident simulations conducted by investigators, the displays showed “a solid red cell with black cross-hatches … at a distance of 1 to 3 nm [1.9 km to 5.6 km]” and a flashing red “TERR AHEAD” message, the report said.

The SIC apparently was surprised by the terrain warnings. “What is that?” he asked. This question also indicated that he, too, “was not aware of the mountainous area surrounding the flight path,” the report said.

The PIC deactivated the TAWS, causing the EFIS terrain displays to vanish, and replied, “May be … database.” This statement indicated that the PIC believed that the TAWS warnings had been triggered by a database problem, the report said. There was no communication between the pilots for the next 20 seconds.

Shortly after the TAWS was disengaged, the aircraft’s crew alerting system generated an aural “GEAR NOT DOWN” warning. Although this warning is designed as a landing advisory when the landing gear is not extended below 800 ft above ground level, it would have provided an additional indication of the aircraft’s proximity to terrain, the report said.

Recorded flight data indicated that the PIC made a brief sidestick input corresponding to a 5-degree nose-up change in the aircraft’s pitch attitude. This caused the autopilot to disengage and the associated chime to sound.

The SIC again asked, “What’s that?” The PIC replied, “Autopilot off.”

Investigators were not able to determine why the PIC made the sidestick input. “The action of the PIC to manually fly by operating the sidestick to pitch up at 5 degrees could not be an indication of an attempted escape action,” the report said. “The investigation could not determine the reason of the PIC’s action.” The report also noted that at this point, the accident could not have been avoided.

Radar Contact Lost

The MSAW system at Jakarta Approach provided no terrain conflict alerts before radar contact with the aircraft was lost. Likely due to his heavy workload, the controller did not notice the disappearance of the aircraft’s radar target until 24 minutes later, the report said. The controller attempted to hail the crew, but there was no reply.

The Superjet struck a nearly vertical ridge near the top of Mount Salak at 6,000 ft and 28 nm (52 km) southwest of the airport. “The terrain information surrounding Mount Salak had not been inserted into the [MSAW] system,” the report said. Investigators also found that although the system was functioning properly, its aural warning mode had been disabled.

The antenna on the aircraft’s emergency locator beacon had detached on impact, and no distress signal was transmitted. The search for the aircraft was hampered by bad weather. Using recorded radar data, a search-and-rescue helicopter pilot located the wreckage the next day.

“The wreckage was spread over a wide area,” the report said. “Most of the wreckage —such as the landing gear, engines and vertical stabilizer — was found at the bottom of the valley at approximately 500 m [1,640 ft] below the impact point.”

The accident occurred at 1432, or 12 minutes after takeoff from Jakarta and 38 seconds after the first TAWS warning was generated. Analysis of recorded flight data showed no evidence of a pre-impact aircraft malfunction.

Training Recommended

The report said that post-accident flight simulations indicated that the TAWS aboard the Superjet was functioning properly and that the CFIT accident might have been avoided up to 24 seconds after the first terrain warning if the crew had taken appropriate action in response to the warning.

The NTSC issued several recommendations based on the findings of the accident investigation. Among the recommendations to Indonesian and Russian aviation authorities were to provide adequate training of pilots to respond properly to aircraft systems warnings and to ensure that all IFR flights are conducted in accordance with published minimum safe flight altitudes.

The committee also recommended that Russian authorities “review the current procedures for the preparation and conduct of demonstration flights and, if needed, introduce appropriate amendments.”

This article is based on NTSC Aircraft Accident Investigation Report KNKT.12.05.09.04, “Sukhoi Civil Aircraft Company Sukhoi RRJ-95B, 97004; Mount Salak, West Java, Republic of Indonesia; 9 May 2012.”