What happened
On October 4, 2013, a Boeing 747-200 aircraft bearing registration 5N-JRM, operated by Kabo Air Limited, was conducting a charter flight carrying 512 passengers and crew. The flight, designated QNK617, departed Mallam Aminu Kano International Airport (DNKN) en route to Jeddah, Saudi Arabia, with a scheduled stopover at Sultan Abubakar Airport in Sokoto (DNSO).
While airborne, the operator instructed the crew to alter their routing to include Sokoto for additional passenger pickups. Upon reaching Sokoto airspace, Air Traffic Control initially cleared QNK617 for an Instrument Landing System (ILS) approach to Runway 08. However, the flight crew reported sighting the airport and requested permission to switch to a visual straight-in approach for Runway 26. ATC granted this request, cautioning the crew that the approach lighting system was of low intensity.
During the final phase of the night approach, the aircraft descended below the intended glide path. It struck the localizer antenna and associated approach lighting structures before touching down approximately 100 meters short of the Runway 26 threshold. The aircraft continued its landing roll along the runway surface before coming to a stop. Post-landing inspections revealed that two tires on the right main landing gear had burst, but there was no fire or significant structural damage requiring evacuation.
The investigation
The Nigerian Accident Investigation Bureau (AIB) examined the flight data, cockpit voice recordings (which were unfortunately overwritten), and witness statements. Key facts established include:
- The aircraft was within maximum structural landing weight limits.
- Weather conditions were favorable with calm winds and good visibility.
- The Visual Approach Slope Indicator (VASI) for Runway 26 was unserviceable at the time of the incident.
- The crew elected to use a 2.5-degree descent angle rather than the standard 3-degree profile typically planned for such approaches.
Findings
The investigation determined that the primary causal factor was an inappropriate visual approach profile flown at night without vertical guidance. Contributing factors included:
- The decision to land on Runway 26, a non-precision runway, during nighttime operations despite the availability of a precision ILS approach on Runway 08.
- The unserviceable VASI on Runway 26, which removed critical vertical guidance for the pilots.
The crew's choice of a shallower glide path likely resulted in the aircraft arriving at the runway threshold with insufficient altitude, leading to the impact with the lighting infrastructure and the short landing.
Safety action
Following the incident, the Nigerian Airspace Management Agency (NAMA) issued a Notice to Airmen (NOTAM) prohibiting the use of Runway 26 at night when the approach lighting system is unserviceable. Additionally, safety recommendations were made to Kabo Air regarding the preservation and maintenance of flight recording devices to ensure data integrity in future investigations.