A method for frequency and mode stabilisation of a tuneable laser that has at least three sections, such as a Bragg laser or GCSR laser, where measurable magnitudes are measured and the laser has been characterised with respect to a number of operation points, and where the values of the measurable magnitudes are stored in a microprocessor or corresponding device. The getter precursor includes a cation portion and a non-oxidizing anion portion, which is configured to thermally decompose to change an oxidation state of cation to zero. A rear end of the rear flap is moveably and pivotably mounted to the aircraft structure via a movable bearing arrangement, e. to thereby precipitate a solid zinc containing material and gypsum without causing substantial precipitation of magnesium, and separating the zinc containing material from the gypsum.