Scheduled Revenue Flight

Bad weather conditions for the aircraft and inappropriate actions by cockpit crew to confront the situation is the main cause of the accident. The following contributing factors were identified:
- The old technology of aircraft systems,
- Absence of a suitable simulator for adverse weather conditions,
- Failure to correctly follow the operating manual by the flight crew,
- Inadequate cockpit resources management (CRM).

A short circuit emerged while the aircraft generators were connected to the aircraft's electrical system after start-up of the engines, via an APU. The short circuit caused a strong fire in the generators compartment in the tail which spread rapidly through the fuselage. The cause of the fire was an electrical arc produced by electrical currents exceeding ten to 20 times the nominal loads when two generators not synchronized with each other were brought online but got connected together instead of being connected to parallel busses. The following contributing factors were identified:
- Poor technical conditions of contacts TKS233DOD responsible for connecting the generators with the electrical busses, that were damaged by prolonged operation without maintenance. A contact normally open was welded and fractured insulation material moved between contacts that are normally closed. These abnormal contact positions led to the connection between #2 and #3 generators.
- Differences in the schematic diagrams of generator 2 and generators 1 and 3. When the switch is moved from "check" to "enable" with no delay in the "neutral" position generator 2 is brought online without time delay which leads to increased wear of normally closed contacts in the TKS233DOD unit.
- The specific design of the electrical systems to ensure power supply to each bus from either the APU or either engine integrated drive generator.

The cause of the accident was the unwise decision taken by the crew to descend without taking the harsh mountain terrain into consideration. Controlled flight into terrain.

Erroneous actions on part of the crew who, while landing in instrument meteorological conditions with one engine running, permitted the aircraft to touch down significantly to the right of the runway.
These actions were the result of following factors:
- The flight engineer inadvertently turned off the fuel booster pumps of the service tank while working the procedures for manual fuel transfer during the climb, which led to fuel starvation, all engines spooling down with the outer engines (#1 and #3) shutting down as well as loss of electrical power for 2:23 minutes due to loss of all three generators
- Failure by the crew to take use of all available possibilities to restore on-board systems after generator #2 was recovered and the APU spooled up and was successfully connected
- Failure to comply with recommendations "flying with two engines inoperative" and "approach and landing with two engines inoperative"
- Lack of leadership and lack of management and distribution of responsibilities by the captain leading to independent but not always accurate actions by the other crew members as result of insufficient training in crew resource management
- A complex wind environment varying with heights which contributed to the deviation from the proper approach trajectory while the crew was flying on stand by instruments rather than regular instruments
- Insufficient training of the crew as a whole as well as each individual to act in emergency and complex scenarios
- The non-implementation of safety recommendations developed in earlier investigations to prevent the flight engineer inadvertently turn off the fuel booster pumps.

It appears that the loss of directional control after touchdown was caused by the failure of the brake systems. The aircraft had already several technical problems with its brake systems previous to the flight, and maintenance was performed by technicians the day before the accident. For unknown reasons, the problem was resolved but no feedback or troubleshooting was performed on part of the technicians or the crew. The Captain was aware of the problem and took the decision to complete the flight despite the risk the problem may persist or happen again.

Sudan's Central Directorate of Air Accident Investigation concluded the probable causes as follow:
The accident cause is a complex set of reasons. The aircraft impacted the ground on three wheels at high forward speed shearing off both engines and propellers and damaging the left main landing gear which put the aircraft in an uncontrollable condition.
Contributory factors were:
- Absence of crew coordination,
- Absence of cabin procedure and check-lists for different phases of flight,
- Unsatisfactory Periodic and Annual job check being reflected on the inoperative Cockpit Voice and Flight Data Recorders,
- Bad planning of the flight and long period taken to clear the recorded defects before departure is considered to be a contributory factor to this accident.

Erroneous retraction of the landing gear following three bounces on the runway due to an unstabilized final approach and poor crew resource management.
Contributing factors were:
- Although the descent and landing checklists were followed, the crew did not review stabilized approach criteria or procedures for a possible controlled flight into terrain and did not take into consideration the possibility of any go around procedure
- Several call-outs were non-standard while others were missing
- Descent was continued under visual flight rules, approach was unstabilized and not detected by crew
- Speed was too high on touch down while the power levers were not into idle position
- Lack of corrective action on part of the crew when the aircraft was bouncing
- Loss of situational awareness led to the retraction of the landing gear.

Flight was proceeding normally until it found itself in extreme meteorological conditions that caused the airplane to ice up severely at an altitude of 20,000ft (6,100m). This, in conjunction with errors by the crew in managing the situation, caused the accident.