What happened
On December 10, 2015, a SAAB 2000, registration HB-IZW, was operating a scheduled flight from Berlin-Tegel to Billund. During the initial approach to Billund, the crew encountered issues with the glidepath transmitter display. At an altitude of 800 feet above ground level, which was 250 feet below the required minimum height, the captain initiated a go-around.
Due to the ongoing display issues, the crew attempted a second approach using a non-precision method via the localizer. During this second attempt, the aircraft descended too steeply, dropping below the required minimum altitude. This descent triggered a "terrain ahead, pull up" warning from the Enhanced Ground Proximity Warning System (EGPWS). The crew responded with another go-around, reaching a minimum altitude of 346 feet above ground level during the maneuver. Following the incident, the crew decided to return to Berlin.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) conducted the inquiry, supported by the Danish authorities. The investigation reviewed radio communications, radar data, and Quick Access Recorder (QAR) data, alongside crew statements. Investigators examined the flight planning, the crew's fatigue levels, and the technical characteristics of the approach charts used during the flight.
Findings
- The primary cause of the serious incident was the inadequate monitoring of the vertical flight path by the crew.
- The crew's approach planning regarding the vertical path was insufficient.
- The pilot flying's performance was likely reduced due to fatigue.
- The approach chart lacked a distance/altitude table, which made monitoring the descent more difficult.
- The crew did not strictly follow the established EGPWS escape procedure following the terrain warning.
Safety action
Following the investigation, several measures were implemented by the operator, Etihad Regional/Darwin Airlines:
- The involved crew members were removed from line operations during the internal investigation.
- The Minimum Equipment List (MEL) was updated to include additional restrictions for flights operating without EGPWS or GPS.
- Standard Operating Procedures (SOPs) were revised to include specific call-outs, such as "one thousand – on profile" and "five hundred – stable," to ensure stabilized approaches.
- Flight Data Monitoring (FDM) was utilized to track the ratio of unstabilized approaches to go-arounds.
- Simulator training was updated to include scenarios similar to this incident.
Additionally, Jeppesen updated the relevant approach charts to include recommended altitude descent tables for specific DME distances.