Within the Standard Model of particle physics only two parameters, the first element of the Cabibbo-Kobayashi-Maskawa matrix Vud and the ratio of coupling constants lambda are required to describe neutron decay. On the other hand many more observables are accessible experimentally. Precision measurements of several neutron decay observables are combined to test the V-A structure of the SM and to search, e.g., for right-handed currents.The aim of this proposal is to measure the proton asymmetry parameter C in polarised neutron decay with a fivefold improved accuracy.The combination of the spectrometer PERKEO III and a pulsed neutron beam reduces both statistical and systematic uncertainties.Redesigned combined electron and proton detectors improve detector uniformity and high voltage stability.