 Tracheal intubation requires alignment of oro-pharyngeal-laryngeal axes. When these three axes are not aligned, intubation becomes difficult. In the researchers study, the investigators simulated difficult laryngoscopy situation by using a rigid neck collar. This neck collar renders intubation difficult not only by restricting neck movement, but also reducing mouth opening. The investigators compared the performance of Macintosh, MacCoy and Airtraq laryngoscope in simulated difficult laryngoscopy using a rigid neck collar. 