Investigation Summary
The aircraft, a 1984-built Let L-410UVP, had been recently returned to service in 2018 after being stored for eight years in Ukraine; it underwent a full overhaul between 2016 and 2017 before being acquired by Slav-Air. On the morning of the accident, the crew departed Juba without obtaining a weather briefing. The flight was operated by South West Aviation under a charter for Baby Air Tours and Travel. As they approached Yirol, visibility significantly deteriorated due to thick fog. Despite the worsening conditions, the crew did not divert to their alternate airport, Rumbek. Post-crash analysis of the wreckage revealed that the altimeter was set to an incorrect pressure value, causing it to indicate an altitude of 1,780 feet while the aircraft was actually much lower. This instrument error, combined with the lack of visual references in the fog, led the pilots to fly the aircraft into the surface of Lake Yirol. Additionally, investigators discovered that a faulty propeller had been replaced in Pibor prior to the accident without proper documentation or notification to the safety department, though the primary cause remained the crew's operational errors in poor weather.
Final Conclusions
The Ministry of Transport and South Sudan investigation committee concluded the crash was caused by a combination of factors: the crew's failure to divert to an alternate airport despite severely bad weather, pilot error in setting the altimeter which resulted in flying at a false altitude, and the unauthorized replacement of a propeller without following safety department release protocols. The final report was completed in October 2019.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Altimeter
The pressure-sensitive instrument used to measure altitude; it was found set to an incorrect pressure value, leading the crew to believe they were higher than their actual position.
Flight Recorders
Both the CVR and FDR were recovered but contained no data for the accident flight because the recording media (tapes) had reached their end and were not serviced.
Propeller System
A propeller had been replaced in Pibor shortly before the accident without official maintenance release documents.
Interesting Facts
- 01The aircraft was leased from the Ukrainian carrier Slav-Air.
- 02The Flight Data Recorder and Cockpit Voice Recorder were found to be non-functional as the recording tapes had run out and were never replaced.
- 03The altimeter recovered from the wreckage indicated 1,780 ft despite the aircraft being at lake level.
- 04Three people survived the initial impact: two children and an Italian doctor.
- 05The airline failed to provide the crew with a weather briefing prior to departure.
Safety Actions & Advisories
Maintenance Oversight
The investigation highlighted the need for strict adherence to maintenance release protocols after the discovery of undocumented propeller replacements.
Location
ACCIDENT SITE · Coordinates taken from the wikidata coordinate.