On 12 February 2019, an Airbus A320 under the command of a Captain reportedly undergoing line training supervised by a Training Captain occupying the supernumerary crew seat was slow to follow ATC instructions after breaking off from an unstabilised approach at London Stansted caused by the First Officer's mismanagement of the approach and lost separation at night as it crossed approximately 600 feet above a Saab 340B climbing after takeoff. The Investigation found that flight crew workload had been exacerbated after the Captain under supervision unnecessarily delayed taking over control and had then not done so in the prescribed way.