Mission Hindenburg - C. Alexander London

Never turn your back on the Cahills . . . The most powerful family
history has ever known returns with a vengeance in The 39 Clues:
Doublecross!
The Cahills are the world's most powerful family, but their strength
is being tested. A sinister man calling himself The Outcast has
targeted the family and set them an impossible test. He's recreating
four of history's worst disasters and challenging the young
Cahills to find and stop the tragedies before it's too late. Now,
with one disaster behind them, siblings Dan and Amy Cahill and
their friends have just days to discover what the Outcast's next
move will be.
Their frantic search seems to be pointing toward a terrifying air
disaster, the explosion of the Hindenburg airship. But no one travels
by airship anymore -- what do the Outcast's cryptic messages
mean? The young Cahills must split up and take to the skies to
try to find the answer . . . before their whole world comes crashing
down.