Date:	Wednesday 15 November 2017
Time:	13:09
Type:	Let L-410UVP-E20
Owner/operator:	Khabarovsk Avia
Registration:	RA-67047
MSN:	3010
Year of manufacture:	2015
Total airframe hrs:	1693 hours
Cycles:	1071 flights
Engine model:	General Electric H80-200
Fatalities:	Fatalities: 6 / Occupants: 7
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	1,2 km SSW of Nelkan Airport -   Russia
Phase:	Approach
Nature:	Passenger - Scheduled
Departure airport:	Chumikan Airport (UHHY)
Destination airport:	Nelkan Airport (UHNX)
Investigating agency:	MAK
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
A Let L-410 aircraft operated by Khabarovsk Avia impacted a forest with little or no forward speed, 1200 m short of runway 04 at Nelkan Airport, Russia. Two crew members and four passengers suffered fatal injuries. A young girl was the only survivor. There was no fire.
The aircraft operated on a domestic flight from Khabarovsk to Nikolayevsk-na-Amure and Nelkan. However, due to runway works at Nikolayevsk-na-Amure, it was decided to stop at Chumikan instead.
At 12:35 the crew radioed the Nelkan Tower controller and received the approach and landing conditions and the landing site actual weather. The approach to landing was conducted to runway 04 with the standalone NDB using the right-hand landing pattern.
The approach was conducted with flaps at 18° and the landing gear in the down position. After the crew started to perform the final approach, they reported the readiness for landing and received the respective clearance from the controller. The PIC acted as Pilot Flying. In the course of the final approach, at distance of about 5 km and at height of 400 m, the autopilot was disengaged, and the PIC having the runway in sight decided to continue the landing.
After the autopilot disengagement, both Power Control Levers (PCLs) were set to the fine pitch mode; then the crew performed the landing checklist. The final approach was conducted within the speed range of 100 to 115 KIAS. The crew then set the PCLs to the fine pitch mode.
The abnormal situation started to develop at 13:10:38 at height of approximately 170 m, when the speed was 108 kts. With the pedals' position remained unchanged and with zero roll, the magnetic heading was changed by 10° (to the right) within 5 seconds, then at 13:10:44 when both thrust control levers (TCLs) were set to forward thrust, the no.2 engine entered the BETA RANGE.
A right roll started to develop, and after 4 to 5 s it reached about 20-25°. The crew tried to arrest the roll, but the aircraft began to descend and quickly lost speed.
The crew's control actions aimed to recover the aircraft by applying the TCL of the no.1 engine, as well as the controls for the ailerons, elevators and rudder, failed. The crew did not feather the no.2 propeller and the no.2 engine continued to operate.
At 13:10:53 at the height of 100 m, with a speed of 76 kts, the stall warning sounded. The aircraft started to develop an aggressive right roll and performed a full-circle rotation around its longitudinal axis (barrel-roll).
The aircraft then impacted terrain.

The investigation revealed that the no.2 engine propeller blades uncommanded turned to an angle of -1.8°, which was significantly below the minimum inflight pitch angle of 13.5°.
During certification of the Let L-410 aircraft, the probability of a propeller uncommanded setting into the BETA range was considered to be 10-14.

Conclusion
The direct cause of the L410UVP-E20 RA-67047 A/C accident was the uncommanded inflight RH engine propeller blades setting to the angle of minus 1.8° which is significantly below the minimum inflight pitch angle (13.5°) with TCLs set to forward thrust. It caused the significant rolling and turning moments, the A/C loss of speed and controllability, and the subsequent with the ground collision.
The propeller blades' setting to the negative angles was caused by the failures of two systems: the BETA Feedback system and the Pitch Lock system. As the Propeller Pitch Lock system components that are to be tested during the PITCH LOCK TEST most probably did not contribute to the system malfunction, then it is unlikely that the crews' deviation of the PITCH LOCK TEST procedure could have make any difference in the detection of the said system malfunction before the flight.
The said situation had been classified as extremely improbable during the aircraft type certification, so, there was no required crew actions in AFM for such situations, and the respective crew training was not required.

02:30 UTC / 12:30 local time:
METAR UHNX 150230Z 03004MPS 9999 -SN SCT030 OVC070 M25 /// Q1014 NOSIG RMK QFE733 / 0978

03:00 UTC / 13:00 local time:
METAR UHNX 150300Z 02004MPS 9999 SCT030 OVC070 M25 /// Q1014 NOSIG RMK QFE733 / 0977

04:00 UTC / 14:00 local time:
METAR UHNX 150400Z 03004MPS 9999 SCT030 OVC070 M25 /// Q1014 NOSIG RMK QFE733 / 0977

Emercom
EASA SIB 2017-21
MAK Interim Report

photo (c) MAK; Nelkan Airport; 15 November 2017

photo (c) MAK; Nelkan Airport; 15 November 2017

photo (c) MAK; Nelkan Airport; 15 November 2017

photo (c) MAK; November 2017

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