The present experimental study investigates the main parameters governing structure and stability of a natural gas premixed lean flame, close to conditions encountered in gas turbines. A scale-model of a gas turbine combustion chamber has been equipped with a quartz tube in order to visualize flame and to perform measurements of CH* chemiluminescence. The combustion chamber can be pressurized up to 0.4 MPa, and combusting air temperature can be preheated up to 673K. The influence of swirl number, equivalence ratio, pressure, combusting air temperature, and flow rate are studied. Stability domain and possible operating range depend on swirl number. For a given swirler and for fixed conditions of pressure and temperature, different flame regimes are encountered and flame regime limits depend only on equivalence ratio. Moreover blow-off limit can be strongly decreased by increasing combusting air temperature whereas pressure increase has no significant influence. The evolution of mean global flame CH* emission as function of pressure, temperature, and equivalence ratio is found to be similar to that observed by other authors in a laminar flame, except close to the blow-off limit.