Implementing a proton exchange membrane fuel cell (PEMFC) into an aircraft environment is a challenging task. In order for aircraft manufacturers and airlines to realize the ecological and economic benefits of this technology, it is necessary to make use of the multiple functions that a fuel cell system can provide. In addition to the main product of electrical energy, the fuel cell is capable of delivering further products, which are useful in an aircraft environment. The waste products -water vapor, heat and oxygen-depleted air (ODA) -at the cathode exhaust are valuable for use on board a commercial airplane. This paper describes the multifunctional approach, points out the advantages of the operation strategy as well as describes a prototype system for the multifunctional use of a PEM fuel cell on board a commercial airplane. The stable operation of the aforementioned system was successfully demonstrated in various tests. The emphasis of the work in question is on water and ODA generation/conditioning.