Overview
During pre-flight checks, the captain unintentionally omitted to select the speed selector knob to flight management system (FMS) mode, leaving it in manual mode. This was not detected by either flight crew member. The aircraft departed in manual mode without a target speed set.
Speed Mode Selection
Recorded flight data showed that the speed selector knob had been set to manual as per the operator’s procedure for the copilot’s flow at shutdown following the previous flight and the pre-flight procedures. It also showed the selector was not switched to FMS mode as per the captain’s intention in the before start procedures. Neither flight crew member detected the speed selector knob in manual mode or that the speed colour on the primary flight display (PFD) was cyan instead of the expected magenta during the before start scans or the take-off brief review.
After the aircraft rotated, the controller logic automatically increased the target speed to V1, which was 125 kt. However, as the aircraft was in take-off (TO) mode, the target speed was not affected. The pilot flying followed flight director TO mode pitch guidance, and the system targeted the desired V2 plus 10 kt (about 144 kt) for the take-off, and climb was maintained as expected. Passing 1,200 ft, vertical flight level change (VFLCH) mode engaged. At this time, the flight director began to target the selected airspeed (125 kt) by increasing the pitch, and the airspeed gradually decreased.
Monitoring of Airspeed
During the initial climb in non-controlled airspace, the captain was making the required departure call and monitoring traffic and weather. As the aircraft entered a 25° bank turn to comply with the standard instrument departure (SID), the airspeed further decreased. The speed reduction and increased pitch were not detected by the pilot flying, which may have been due to anticipating a slower climb in flap 4 configuration and a banked turn. The first officer was not effectively monitoring the airspeed and, as a result, did not initially detect the aircraft decelerating.
Flap Retraction
Although the aircraft was slower and pitched higher than usual at that time, it was operating at a safe speed. Manufacturer calculations showed that the top of the low-speed awareness (LSA) amber band was at approximately 125 kt during this time, and the airspeed was decelerating through 134 kt. When the pilot monitoring detected that the aircraft was not accelerating, they retracted flap from 4 to 3 (slat retraction) to reduce drag. The manufacturer’s calculations showed that this resulted in the upper value of the amber range on the LSA indicator increasing to about 135 kt. When slats were retracted, the airspeed was around 134 kt, therefore within the amber band, before further reducing to 131 kt. During that time, the pitch limit indicators would have activated and been displayed on the primary flight display. The manufacturer required that if the aircraft was not performing as expected, the flight crew were required to disconnect the autopilot and manually fly the aircraft.
Documentation Inconsistencies
The manufacturer’s airplane operations manual (AOM) was inconsistent with their standard operating procedures manual (SOPM). Specifically, the AOM required the speed selector knob to initially be set to manual in the before start procedures, which was not an SOPM requirement. While the use of manual speed was valid, it was unnecessary for the AOM to require this step.
The stick shaker did not activate during the incident.