The smuggler's plane is trapped, literally -- there's a trapdoor underneath the passenger seats.
From the telephone style in Buck Marshall, Range Detective, it appears this strip is meant to take place in the early 1900s.
Slam Bradley is revealed to have a great singing voice in this story; not surprising, since Golden Age Heroes often happen to have whatever skill they need for the scenario. Maybe this should be handled by a save vs. plot each time. Any inconsistency in skill is only more appropriate for the continuity-lite Golden Age.
For some reason, the radio station that hires Slam buys a $1,500 clock. It's unclear why the clock costs so much. A valuable antique? Slam and Shorty are also hired for a $5,000 reward, so this radio station really likes to toss its money around. The scenario is ridiculously easy to solve too. If microphones are exploding and killing performers, all they have to do is have an engineer take each microphone apart and check it before each program.
(This issue can be read at Comic Book Archives)