What happened
On June 28, 2008, a De Havilland DHC-6, registration V2-LFL, was performing a scheduled passenger flight from Antigua to Pointe-à-Pitre. While the crew initially intended to fly under Visual Flight Rules (VFR), approaching thunderstorms near the destination forced a transition to Instrument Flight Rules (IFR).
During the ILS approach to runway 11, the crew attempted to avoid a convective cloud by extending the outer marker leg. During this maneuver, the aircraft descended to 2,200 ft in a sector where the minimum safety altitude was 3,600 ft. An air traffic controller noticed the abnormally low altitude while the aircraft was executing a procedure turn toward rising terrain and instructed the crew to climb back to 3,600 ft. The aircraft subsequently intercepted the localizer at 2,600 ft and completed the landing without further incident.
The investigation
The BEA examined the aircraft's equipment, specifically the Terrain Awareness and Warning System (TAWS). Investigators found that the installed Sandel ST3400 unit had outdated terrain and airport databases, with the terrain data dating back to May 2006. Furthermore, the unit's serial number did not match the aircraft's maintenance records.
Discrepancies were also noted regarding the aircraft's radio altimeter. While the Minimum Equipment List (MEL) indicated no radio altimeter was installed, one was present; however, it was causing frequent false TAWS alarms during taxiing. The investigation also reviewed the crew's experience and the operational environment, noting that many Carib Aviation flights are conducted under VFR, and crews were less accustomed to full IFR procedures.
Findings
- The aircraft descended into a high-terrain area while the crew was focused on avoiding weather.
- The crew demonstrated a lack of preparation for IFR procedures, effectively mixing VFR and IFR principles during the approach.
- The crew's decision-making was hindered by the pressure of the sudden change in flight rules and the need to avoid convective activity.
- The TAWS was unreliable due to outdated databases and a miscalibrated radio altimeter signal, which led some crews to frequently disable the system to avoid nuisance alarms.
- There was a lack of effective crew resource management (CRM) during the critical phase of the approach, as the pilot monitoring did not challenge the commander's descent decisions.