Date: 201910
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Gulfstream IV / G350 / G450
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Final Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Autopilot
Component problem: Improperly Operated
Reporter organization: Fractional
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Human-Machine Interface; Fatigue; Distraction; Workload
Anomaly: Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Regained Aircraft Control
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: During a visual approach to ZZZ; I was the pilot monitoring during a visual approach to Runway XXL. The Pilot Flying was a highly experienced PIC hand-flying a right base to final. There were multiple aircraft in the pattern at ZZZ including training aircraft to the parallel runway to the west and helicopter traffic to the east of our runway. During the base to final turn; I was preoccupied with maintaining visual separation from a Cessna that appeared to be overshooting his runway to our right and a helicopter to our left that was approaching to land on the east ramp. After rolling out on final; I noticed that the pilot flying had selected an altitude below field elevation in the altitude alerter without calling it and also selected Flight Level Change on the guidance panel. This had caused the autothrottles to pull back to flight idle and the speed had decayed to approximately REF minus 10-15 kts and the stall awareness bars had appeared in the PFD. I called 'speed way low' and the pilot flying had already seen it; disconnected autothrottle; added power; and reduced pitch to recover correct speed. Correct approach speed was quickly obtained; the approach was stabilized prior to 500 feet; and we continued to a normal landing.Despite having trained multiple times in recent years to avoid this exact scenario; the 'FLCH Trap' continues to be an issue. Personally; I NEVER use FLCH for descents for exactly that reason but I am reluctant to correct a 'technique' utilized by a fellow pilot; including the use of FLCH for descent. The company has rightly prohibited the use of FLCH during 'approaches' but its use during visual approach is something of a gray area. I believe the use of Flight Level Change should be PROHIBITED FOR ALL DESCENTS below 5;000 feet AGL. In my opinion; FLCH is the most dangerous button on the Flight Guidance Panel. As the pilot monitoring; it was my job to make sure the proper flight path and energy state of the aircraft were maintained but the distraction of multiple aircraft in close proximity and a 'Traffic; Traffic' TCAS alert forced greater attention OUTSIDE the cockpit than inside. In the future; I will be more proactive in refusing to allow my flying partner to utilize Flight Level Change.




Synopsis: G450 pilot reported selecting an incorrect autopilot mode during approach that resulted in excessively slow airspeed.