Aviaco Flight 260

Investigation

The Comision De Investigacion De Accidentes De Aviacion Civil of Spain investigated the cause of the accident. Analysis showed that at the moment the crew started their final approach to the runway, they were slightly above the glideslope but relatively on track towards the runway. It was found that the aircraft had descended below the glidepath during the approach to Vigo-Peinador Airport approximately 10 seconds prior to impact. At an altitude of 125 feet, the "Glide Slope" alarm from the Ground Proximity Warning System sounded during this time, but the crew failed to hear or respond to the warning alarm. 5 seconds prior to impact, at an altitude of 60 feet, the alarms changed to a "Sink Rate" alarm until the aircraft was 50 feet above the ground, where the alarm changed for a third time to a "Whoop, whoop, pull up" alert, 2 seconds prior to impact, indicating that a collision with terrain was imminent. As well, it was also found that at the time the crew transmitted a message to ATC stating that they had the runway in sight, thick fog obscured their view of the runway ahead and the crew lost sight of it. This could have caused the pilots to become spatially disoriented, having no visual references, and felt that they were in an ascent, explaining the increase in the rate of descent in the final seconds prior to impact. The excessive descent rate caused the GPWS system to signal an "excessive descent" alarm but the crew failed to hear this alarm as well. As well, the crew was continually increasing the rate of descent up until impact and maintained a steady rate of descent (approximately 850 feet per minute) until the minimum altitude, at which point the descent rate was decreased slightly before it was increased again only steeper, reaching an average of 1,035 feet per minute. This was in violation of aviation guidelines, which stated that the rate of descent must be decreased upon reaching the minimum altitude. In addition, due to the reduced visibility because of the fog, the crew may have misinterpreted the approach path lights as the lights of the runway, which is why the aircraft impacted the ground just short of the runway threshold. This could have been caused by the crew's expectation of seeing a runway and interpreted the first lights that appeared through the fog as the runway lights, causing them to ignore all other signs the aircraft was flying too low and not on the correct approach path. Their focus on spotting the runway caused them to "cancel out" all other stimuli such as the aural warnings.

The final report concluded that the cause of the crash was the crew going against company procedures by increasing their descent rate in reduced visibility, despite not being able to see the runway and their failure to maintain a steady rate of descent and a stabilized approach.

The CIAAC also implemented several recommendations as a result of the accident:

The use of cockpit microphones and headsets must be mandatory in all aircraft and the sterile cockpit rule must be applied up until an altitude of 10,000 feet, with the crew only engaging in discussions relevant to the flight and eliminate all non-pertinent conversation about matters unrelated to flying the aircraft. As well, cockpit microphones should record the conversations and sounds from a headset for an additional crew member, if applicable.

Installing flight recorders with better audio quality and easier retrieval of data

Crew should be trained on the use of GPWS in emergency situations/scenarios

Airline operators should closely monitor the procedures for an instrument approach to the runway