Kazan

Systemic weaknesses in identifying and controlling the levels of risk, non-functional safety management system in the airline and lack of control over the level of crew training by aviation authorities at all levels (Tatarstan Civil Aviation Authority, Russian Civil Aviation Authority), that resulted in an unqualified crew being assigned to the flight.
During the go-around the crew did not recognize that the autopilot had disconnected resulting in the aircraft impacting ground in a complex spatial position (nose up upset). The captain, pilot flying, lacked the skills to recover the aircraft from the complex spatial upset (lack of Upset Recovery), that led to significant negative G-forces, loss of spatial orientation sending the aircraft into a steep drive (75 degrees nose down) until impact with ground.
The go around was required because the aircraft on its final approach arrived in a position from which landing was impossible as result of a map shift by about 4000 meters (aircraft systems determining the position of the aircraft in error), the inability of the crew in those circumstances to combine aircraft control and navigation with needed precision, and the lack of active support by air traffic control during prolonged observation of significant deviation from the approach procedure.
The following factors were considered as contributory:
The captain not having had primary flight training,
The flight crew members being allowed to upgrade to Boeing 737 without satisfying the required qualifications including the English language,
Methodical shortcomings in retraining as well as verification of results and quality of training,
Insufficient level of organisation of flight operations at the airline, which resulted in failure to detect and correct shortcomings in working with the navigation equipment, pilot technique and crew interaction, including missed approaches,
Systematic violation of crew work and rest hours, a large debt of holidays, which could have resulted in accumulation of fatigue adversely affecting crew performance, Simulator training that lacked a missed approach with intermediate height and all engines operating,
Increased emotional stress to the flight crew before deciding to go around because they could not establish the position of their aircraft with the necessary precision to accomplish a successful landing,
Violation of the principle "Aviate, Navigate, Communicate" by both flight crew and air traffic control, which resulted in the flight crew not following standard operating procedures at the time of initiating the go around because the pilot monitoring was diverted from his duties for a prolonged period and did not monitor the flight parameters,
The fact that the crew did not recognize the autopilot had disconnected and delayed intervention by the crew, that resulted in the aircraft entering a complex spatial position (nose up upset),
Imperfection of simulator training programs for Upset Recovery Procedures as well as lack of criteria for assessing the quality of training, which resulted in the crew being unable to recover the aircraft from the upset,
The possible impact of somatogravic illusions,
The non-addressing of prior accident investigation recommendations, geared towards elimination of risks and establishing risk level management, had prevented the prevention of this accident,
Lack of proper supervision of issuance of pilot certificates in accordance with achieving specified requirements and qualifications,
Failure of safety management system (SMS) in the airline, lack of guidelines for SMS development and approval, lack of a formal approach to approve/agree on SMS and pilot training by the related authorities,
Deficiencies in aviation training centers' performance and absence of verification of training quality,
Lack of requirements for flight crew to be proficient in English Language for retraining on foreign aircraft types and lack of formal approach to verify language proficiency,
lack of formal approach to conduct periodic verification of flight crew qualification,
systematic violation of crew work and rest times,
lack of training of flight crew on go around from intermediate heights in manual control potentially leading to complex spatial position (e.g. nose high upset),
The map shifts in aircraft without GPS without training of crew to operate in such conditions,
Lack of active assistance by air traffic control when the approach procedure was deviated from over a prolonged period of time,
Breach of principle "Aviate, Navigate, Communicate".
Translation via www.avherald.com

The exact cause of the accident and the in-flight fire could not be determined with certainty. Nevertheless, the partial disintegration of the aircraft during the emergency descent was the consequence of aerodynamic forces that exceeded the certification of the aircraft. Strong analysis about fuel feed systems, fuel hoses and electrical cables failed to reveal any anomalies.

It was not possible to determine the exact cause of the extension of the flaps to an angle of 30° while the aircraft was in normal cruise with the autopilot system engaged. Various analysis could not define if the extension was the result of an electrical failure or a human action, voluntary or not. The most likely cause for flap release could be moving the handle of the left pilot flap control switch to the 'down' position by an angle sufficient to trigger the switch. The design of the locking device of the ZPPM-45 switch of the left pilot and its geographical situation does not exclude the possibility of an unintentional flap release, which was revealed by a one-time check of these devices on 16 others Tupolev Tu-124 aircraft.

Engine failure at low height after takeoff over a populated area. The main cause of engine failure was a rupture of the cylinder n°8, which caused a leak and overheating. The presence of cracks in the right magneto slider BSM-9 also contributed to the engine failure. This caused the fuel-air mixture in the intake manifold to ignite.

The exact cause of the accident could not be determined with certainty. It is believed that traces of explosives were found on several debris but this was not proven and the Soviet Authorities confirmed there were no military activities in the area at the time of the accident.

Poor judgement and wrong actions on part of the flying crew.

It was determined that the intoxicated crew flew unauthorized manoeuvre at low height shortly after lift-off. Control was lost.

Engine failure in flight caused by the poor quality of the fuel which was contaminated.

In-flight failure of both engines due to a fuel exhaustion. This was the result of a poor flight preparation on part of the crew who failed to fuel the aircraft with a sufficient quantity prior to departure. It was determined that a total of 1,108 kg of fuel was in the tanks, about 550 kg less than the necessary amount for this routing.

Failure of the right engine in flight due to fuel starvation. It was determined that the fuel selector was connected to the left rear tank which was empty. Only 200 liters were added in the tank prior to takeoff and the crew forgot to change the fuel selector in flight to another suitable tank. It is also reported that the crew failed to take the appropriate measures to maintain a safe control of the airplane with one engine inoperative and the captain maintained an insufficient speed of 150 km/h instead of 170 km/h, which contributed to the loss of altitude.