A Study to Evaluate the Efficacy and Safety of QVM149 (Indacaterol Acetate / Glycopyrronium Bromide / Mometasone Furoate) Versus Salmeterol Xinafoate/Fluticasone Propionate in Children From 12 Years to Less Than 18 Years of Age With Asthma.

This is a double-dummy, double-blind, randomized, active controlled, two-way two-period treatment (12 weeks duration each) cross-over study. The study duration of 36 weeks includes: * a screening period of up to 15 days (rescue medication: short acting β2-agonist (SABA) salbutamol 100 μg or albuterol 90 μg via a Metered-Dose Inhaler (MDI) to use as-needed throughout the study). * a run-in period of 14 days (run-in medication: salmeterol xinafoate 50 μg / fluticasone propionate 250μg bid delivered via Girohaler® or equivalent DPI device) * two treatment period of 12 weeks each (either QVM149 150/50/160 µg od and placebo to salmeterol xinafoate/fluticasone propionate 50/500 µg bid, or salmeterol xinafoate/fluticasone propionate 50/500 µg bid and placebo to QVM149 150/50/160 µg od, separated by a 3 week washout period (wash-out medication: salmeterol xinafoate/fluticasone propionate 50/250 µg bid) * a safety follow up period of 30 days during which the participant will be back on standard of care treatment as appropriate.