Investigation Summary
The accident occurred during an automated CAT II ILS approach in low visibility conditions (RVR 350-400m). The crew arrived at the TOKPA reporting point higher than the prescribed altitude, crossing at FL092 instead of FL060. Because they were high, the aircraft's ILS systems captured a false glideslope lobe at an angle of approximately 9 degrees while the aircraft was only 1.1 nm from the threshold. Shortly after capture, the signal became invalid, causing the autopilot to transition to an 'inertial path' mode, which maintained a constant 3 degree descent based on internal data. The crew, under high psycho-emotional stress and suffering from fatigue during a long duty day, failed to verify their altitude against distance markers. They crossed the runway threshold at 110 feet, far above the normal touchdown zone, and continued descending over the entire length of the runway. A go-around was initiated at just 58 feet radar altitude, but the aircraft struck a concrete fence and houses in the village of Dacha-SU, located just past the airport boundary.
Final Conclusions
The Interstate Aviation Committee (MAK) concluded the cause was Controlled Flight Into Terrain (CFIT) resulting from the crew's lack of monitoring of the aircraft's position relative to the glideslope. Contributing factors included the capture of a false glideslope signal, the design of the Boeing 747-400 autopilot which continues descent on an inertial path without a prominent red warning when a glideslope signal is lost after capture, and the crew's failure to execute a go-around despite EGPWS 'Glideslope' alerts and the lack of visual contact at decision height. The investigation was completed on February 17, 2020.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
İbrahim Dirancı, aged 59.
First Officer
Kazım Öndül, aged 59.
Systems & Failure Modes
Autopilot Flight Director System (AFDS)
The system captured a false glideslope and, upon losing the signal, defaulted to an inertial 3 degree descent path (FMA FAULT 2) without disengaging.
Enhanced Ground Proximity Warning System (EGPWS)
Triggered 'Glideslope' alerts five times during the final descent, which the crew failed to act upon by immediately initiating a go-around.
Instrument Landing System (ILS)
The ground-based ILS emitted side lobes that allowed for a 'false capture' because the aircraft was positioned too high during the approach.
Interesting Facts
- 01All 4 crew members and 35 residents on the ground were killed.
- 02A total of 36 residents, including 17 children, sustained injuries of varying degrees.
- 03The aircraft destroyed 19 homes and 12 outbuildings in the Dacha-SU village.
- 04The aircraft was carrying 85,618 kg of cargo at the time of the accident.
- 05The crew initiated the go-around only after overflying the entire length of the runway.
- 06The investigation found the Jeppesen charts used by the crew did not explicitly mark a Final Approach Fix (FAF) for Runway 26.
Safety Actions & Advisories
Autopilot Logic Review
Source ↗The investigation recommended that Boeing review the AFDS logic to provide more prominent alerts when the system transitions to inertial descent mode after a glideslope signal loss.
ATC Monitoring Procedures
Source ↗Recommendations were made to update Tower controller instructions to include monitoring for significant aircraft deviations from established approach charts when technical equipment is available.
Location
APPROXIMATE POSITION · AIRPORT LEVEL · Coordinates are the estimate published in the entered by an editor. The ring shows the accuracy the record supports, not the point of impact.