A method and portable apparatus for servicing a shock absorber on a landing gear assembly of an aircraft in a weight-on-wheels state is disclosed. The shock absorber includes at least one chamber containing both hydraulic fluid and a gas in fluid communication with each other. The apparatus includes a source of gas and a source of hydraulic fluid. The amount of hydraulic fluid in the chamber is corrected, preferably such that the chamber is then filled with a known amount of degassed hydraulic fluid. A pre-set mass of gas is then delivered into the chamber under the control of a gas delivery system of the portable apparatus. More accurate servicing of a shock absorber may thus be provided since account is additionally taken of gas dissolved in hydraulic fluid. By delivering a pre-set mass of gas into the chamber, there is no need to rely on a measure of gas pressure or H-dimension (h) when servicing the shock absorber.