The FITS files produced with the hiClass task in HIPE on HIFI data can be read in CLASS with the following commands
file out MyHIFISpectra.hifi mul
fits read MyHIFISpectra.fits
#
# Now you have a CLASS file named MyHIFISpectra.hifi (you can use whatever you want as an
# extension) you can access like you always do in CLASS:
#
file in MyHIFISpectra.hifi
find
get first
set unit f i
device image white
plot
For PACS data or any spectum1d product, you can try the this script (remove .txt extension before you load it in HIPE).