Two pilots looking for the runway; no pilots watching airspeed
The TSB’s Analysis
The TSB focused its analysis on crew performance during the periods when the pilots engaged in non-operational conversation and when both pilots directed their attention outside the cockpit in attempts to obtain visual reference to the runway “at the expense of monitoring the aircraft.” Here's what the TSB had to say:
During the initial stages of the approach to Kirby Lake, the crew was engaged in a conversation that did not directly pertain to the operation of the flight. The casual nature of the conversation between the PF and PNF suggests that they were not overly concerned with the approach and may not have been at a heightened level of attention.
While a majority of the SOP and checklist items were completed during the approach, a number of critical items, such as descending below the minimum sector altitude while diverting to the XIKIB waypoint and failing to announce/confirm the arrival at the MDA, were indicative of lapses in cockpit discipline. The Kenn Borek SOP states that there should be no conversation other than that required for assigned work or for the operation of the aircraft during the descent from 3,000 ft. AGL or top-of-descent, which ever occurs last.
Beyond the distraction within the cockpit, the crew was faced with the additional task of identifying the runway. Although the company SOP did not specify when the PNF should look outside, the automated weather observation system at Kirby Lake indicated that the visibility was 4 sm in light snow. This likely prompted the PNF to look outside of the cockpit at a GPS distance of 4 nm and to identify the runway.
This declaration prompted the PF to look up from monitoring the flight instruments in an attempt to identify the runway. For the remainder of the flight, both crewmembers were focused outside the cockpit. With neither pilot monitoring the airspeed and altitude, the aircraft continued to descend. From the initial identification of the runway, the airspeed decreased to a point that it entered an aerodynamic stall. The aircraft was, however, too low to effect a recovery, despite attempts by the crew to do so.
The loss of control of the aircraft was likely the result of a stall or near stall condition. The ground speed determined by the propeller marks and the high engine power setting during the attempted recovery indicate that the aircraft was in a low energy state. The aircraft's close proximity to the ground prevented a full recovery from the loss of control.
Pilots are often expected to perform a number of concurrent activities. In this case, this involved flying and monitoring the aircraft as well as visually acquiring the runway. During these multitasking situations, the crew may prioritize activities based on their perceived level of importance. In this case, the act of visually finding the runway was categorized as being of primary importance. As such, the crew's cognitive efforts were directed to this activity at the expense of monitoring the flight profile.
The aircraft was equipped with a stall warning system, which did not activate prior to the aircraft entering a low energy state. The aircraft's wing deicing system appeared to be functional throughout the approach and the post-impact inspection of the aircraft did not indicate an accumulation of ice on the critical flight surfaces. The investigation was unable to determine why the stall warning system did not activate.