  We report on the prototyping of a plastic scintillator hodoscope with
wavelength-shifting fibre read-out by a multi-anode photomultiplier as part of
the development of a detector for cosmic ray muons to be carried aboard an
aircraft. Light yield and light attenuation measurements on single- and
double-clad wavelength-shifting fibres were performed. Low power,
low-threshold, discriminators were designed. A prototype 16-channel hodoscope
with two planes was built and tested with cosmic rays. After correcting for
geometrical factors a global intrinsic efficiency of $\epsilon > 98$ % was
obtained in both planes. The overall performance of the hodoscope proved it to
be well suited for the {\sc Adler} experiment to measure the high altitude muon
flux.
