Flight-data recorder traces from the Azerbaijan Airlines Embraer 190 illustrate the extent of damage with which the crew had to cope after the twinjet was crippled by an explosion in Russian airspace.
The E190 sustained multiple penetrative impacts – many of them rectangular in shape – from fragments which damaged its hydraulic circuit tubes and reservoirs, its stabiliser pitch-trim electric drive, and the empennage including its fin, elevators and rudder.
Similar damage affected its left wing and left-hand GE Aerospace CF34 engine.
The crew of the aircraft – operating a Baku-Grozny service on 25 December – had abandoned attempts to land at the Chechen capital, after losing GPS navigation capability and encountering difficult weather conditions including haze, reduced visibility, and overcast cloud at about 240-420m (790-1,380ft).
After the pilots opted to return to Baku, the aircraft was climbing through 3,500ft when, at 08:13:31 local time, its cockpit-voice recorder captured a “sonic boom” noise, says the Kazakhstan air accident investigation commission.
Flight-data recorder traces reveal that the autopilot disengaged and, over the next 23s, all hydraulic pressure bled away before another bang was heard.
The data provided in the commission’s preliminary findings show that routine variations in both inboard and outboard elevators immediately ceased, with the elevators’ traces flatlining at slightly different positions.
Cabin altitude instantly began to rise, coinciding with the E190’s actual altitude after about 20s, indicating depressurisation.
The aircraft, which had been cleared to 15,000ft, continued to climb to about 8,000ft, before briefly sinking back to around 6,000ft, and then climbing again to 10,000ft.
According to the commission the cabin-altitude warning sounded and repeated eight times. One of the pilots informed Grozny tower that the aircraft was unable to proceed to 15,000ft, stating: “I can’t maintain [flight level] 150, we have high pressure in the cabin.”
The pilot also said the aircraft was “losing control” and that it had suffered hydraulic failure.
Some 14min after the explosion, Grozny tower transferred the flight to Rostov controllers. The crew informed Rostov that the aircraft would head for Baku, and the controller instructed them to maintain 9,000ft.
The pilots, having been recommended Makhachkala for diversion, told Rostov that the aircraft’s engines were running, but the aileron and elevator control systems had failed, and declared they were heading for Aktau in Kazakhstan.
Data from the flight recorder shows that the crew were constantly manipulating the thrust levers, advancing and retarding them across half of their range, and using differential settings, in an effort to stabilise the damaged aircraft’s flightpath across the Caspian Sea.
As a result of the difficulties in control, the aircraft fluctuated both laterally and longitudinally, continually rolling from left to right and back, with bank angles exceeding 40° at times.
Pitch was similarly unstable, the recorder traces suggest, frequently alternating between some 10-20° nose-up and about 10° nose-down.
The aircraft’s captain had substantial experience flying the Embraer E-Jet family, with over 7,000h on type out of a total of more than 15,000h. Although the first officer was much less experienced, with only 830h in total, these included 670h on E-Jets.
Between them they nursed the aircraft to Aktau, where the attempt to land on runway 11 was ultimately unsuccessful. The aircraft crashed about 5km northwest of the airport.
Both pilots were among the 38 fatalities, but 29 of the occupants – including two cabin crew members – survived.
Azerbaijan’s president, Ilham Aliyev, commended the efforts of the pilots and flight attendants during an event in early January, stating: “Had the pilots not demonstrated such exceptional professionalism and courage, there would have been no survivors from this tragic incident.”
