We have travelled many times by plane with the solu-cortef shots (I always carry more than one) and have NEVER been questioned.  Just in case, I carry a note from the dr who prescribed it, written on her letterhead.  We carry it in a small carry-on bag with all of our other prescription medicines (NEVER check your prescriptions - in the event the bag gets lost, you will be without your meds) .  Our bag has gone through the x-ray machine and they haven’t asked about the needles at all.  Strangely, my daughter was picked out in line twice and had to take off her shoes which had orthotics (supports) in them.  They made her take out the orthotic for them and show it to them!