Silent Enemy by Thomas Young

From Publishers Weekly: "[A]n airborne version of the movie Speed. Soon after takeoff from Afghanistan, Maj. Michael Parson, the pilot of a giant C-5 Galaxy flying patients injured in a terrorist bombing to Germany for medical care, receives the message that there's a bomb on board and it's set to go off if the plane descends to a lower altitude. Besides the bomb threat, they're running out of fuel; they're beset by storms with deadly lightning, devastating hail, and hurricane force winds; an active volcano is spewing ash into the atmosphere; and unfriendly nations that won't allow them to land even if they can defuse the bomb are trying to shoot them out of the air. Aviation thriller aficionados will cheer, and readers of any genre will gnaw their fingernails to the quick."