This study is to evaluate if add-on treatment with inhaled NVA237 (50 µg) once daily (o.d.) via single-dose dry-powder inhaler (SDDPI) further improves lung function and health status and is well tolerated compared to placebo in symptomatic COPD patients with moderate to severe airflow limitation who are already receiving maintenance therapy with inhaled fixed-dose-combination of salmeterol/fluticasone propionate (50/500 µg) twice daily (b.i.d.) via multi-dose dry powder inhaler (MDDPI).

Inclusion Criteria:

• Current or ex-smokers who have a smoking history of at least 10 pack years (e.g., 10 pack years = 1 pack/day × 10 years, ½ pack/day × 20 years, etc.).
• COPD (Chronic Obstructive Pulmonary Disease) patients with moderate to severe airflow limitation (Spirometry classification: GOLD 2 or 3) at Visit 2:
• Post-bronchodilator FEV1 (Forced Expiratory Volume in one second) ≥30% and <60% of the predicted normal, and,
• Post-bronchodilator FEV1/forced vital capacity (FVC) <0.70
• Patients on maintenance treatment with fixed-dose combination of inhaled salmeterol and fluticasone propionate (50/500 µg) b.i.d. delivered via a proprietary MDDPI (multidose dry powder inhaler) device for at least 30 days prior to screening visit (Visit 1).
• Patients in category Gold B or D with a CAT (COPD Assessment Test) total score ≥10 at screening (Visit 1) and before randomization (Visit 3).
• Patients with a history of at least 1 moderate or severe COPD exacerbation within the previous year.

Exclusion Criteria:

• Pregnant or nursing (lactating) women
• Women of child-bearing potential, unless they are using effective methods of contraception during the study
• Patients with a history of long QT syndrome or whose QTc measured at run-in (Visit 2) (Fridericia method) is prolonged (>450 ms). (These patients cannot be re-screened.)
• Patients with evidence (upon visual inspection) of oropharyngeal candidiasis at baseline with or without treatment.
• Patients who have not achieved an acceptable spirometry result at run-in (Visit 2) in accordance with American Thoracic Society (ATS)/European Respiratory Society (ERS) criteria for acceptability and repeatability.
• Patients who have had a COPD exacerbation that required treatment with antibiotics or oral corticosteroids or hospitalization in the 6 weeks prior to screening (Visit 1).
• Patients who have had a respiratory tract infection within 4 weeks prior to screening (Visit 1).
• Patients requiring long term oxygen therapy prescribed for >12 hours per day.
• Patients with allergic rhinitis who use an H1 antagonist or intra-nasal corticosteroids intermittently. (Treatment with a stable dose or regimen is permitted.)
• Patients with concomitant pulmonary disease (e.g., lung fibrosis, sarcoidosis, interstitial lung disease, or pulmonary hypertension), clinically significant bronchiectasis, or history of pulmonary lobectomy, lung volume reduction surgery, or lung transplantation.
• Patients with active pulmonary tuberculosis, unless confirmed by imaging to be no longer active.

Other protocol-defined inclusion/exclusion criteria may apply.