2018 South West Aviation Let L-410 Turbolet crash

On 9 September 2018, en route from Juba International Airport to Yirol Airport, a Let L-410 Turbolet aircraft crashed, carrying a total of 23 passengers and crew, of which 20 were killed on impact, including the Anglican Bishop of Yirol, Simon Adut Yuang. The small plane crashed into Lake Yirol amid heavy fog and poor visibility.

Aircraft history
The aircraft, registered UR-TWO, operated by Ukrainian carrier Slaver Kompani for South Sudan-based South West Aviation, had been delivered to Aeroflot in 1984, then transferred to various operators until 2006, when it was placed in storage in Rivne, Ukraine. In April 2018, the plane was acquired by Slaver Kompani and wet-leased since May.

The maintenance log, kept on board the aircraft, was lost in the accident but some documents certifying the maintenance carried out were collected at the Slav-Air headquarters in Ukraine. All certificates of airworthiness of the aircraft were valid. The flight log had been correctly filled out, with the exception of weight and balance, the data for which had some discrepancies with what was later calculated by the investigators.

The fuel used, of the Jet-A1 type, was found to be of normal quality and not contaminated according to post-accident analysis. A week before the accident, the aircraft's power generators had undergone extraordinary maintenance in Pibor but a certificate of authorization for service after the repair, which is a mandatory procedure, was not issued by the national supervisory authority.

The Let 410 UVP had landed in Juba on the same morning as the accident, piloted by a different crew from the one that would then conduct the flight to Yirol.

Accident
On 9 September 2018 at 08.00 local time (05.00 UTC), the Let 410 took off from Juba International Airport with destination Yirol Airport, at approximately 122 NM, for an estimated flight time of 45 minutes. The take-off weight was 5,700 kg, of which 3,800 kg was for the aircraft alone.

On-board the flight deck were two Sudanese crew members. Captain Sami Qeily (57), and First Officer Mohamed Shamseddine (27), were the pilot-in-command and second-in-command, respectively. While both of their flight time logs were destroyed in the crash, they were rated in flying the Let-410.

The weather forecast (Terminal Aerodrome Forecast) at the destination aerodrome between 05.00 UTC and 09.00 UTC reported fog with visibility of 8 km, a few clouds below 3,000 ft and scattered clouds above 14,000 ft. During the flight, however, visibility had dropped to a few meters and the pilots, despite having flown over Yirol, were unable to locate the runway, as it was not served by radio aids and the crew was conducting a visual flight with the aid of GPS. After making a few orbits to acquire visual references with the airfield, the aircraft impacted the surface of Yirol Lake, a body of water about a mile west of the runway.

The airfield had no air traffic and emergency services, except for a doctor: it was the local authorities who rescued the survivors of the accident. The damage reported to the Let 410 UVP was all caused by the impact, as no fires broke out on board. The fuselage was found compressed by the impact, the cockpit deformed and partly shattered. Both engines were shattered on impact and were found submerged in the lake water, still attached to the wings and with the propellers completely deformed. The only part of the aircraft partially intact was the tail section. The accident did not cause damage to property or people on the ground, but the leakage of fuel, engine oil and liquids from the aircraft's hydraulic systems contaminated the lake waters.

There were 23 people on board the aircraft, including 4 children, and the 2 crew members. 18 passengers and all crew members lost their lives in the accident for a total of 20 victims. Three survivors suffered serious injuries. Among the victims was the Anglican bishop of Yirol, Simon Adut Yuang.

Investigation
Despite the Flight Data Recorder being recovered on 10 September and the Cockpit Voice Recorder on 30 September, reading out any information on the two devices was impossible as the recording tapes had run out and had not been replaced. The investigation conducted, based on analyses of the wreckage and interviews with witnesses, allowed the accident to be classified as a controlled flight into terrain (CFIT) and the causes of the accident to be traced back to a series of factors:


 * The airline did not bother to acquire the weather briefings to give to the crew.


 * Taking into account the worsening weather conditions, the pilots should have diverted the flight to an alternate airport but instead continued to fly towards the intended destination despite poor visibility.


 * The on-board altimeter was adjusted to an incorrect pressure value, providing higher-than-real altitude indications. The instrument, recovered from the wreckage on the ground, in fact indicated 1,780 ft.