Investigators are piecing together why a Learjet 60 broke apart over Florida/Bahamas airspace last week, killing nine people, and the emerging picture points to a brutal combination of icing, weather radar failure, and a climb into a growing thunderstorm rather than a single cause.

• The NTSB recovered the cockpit voice recorder and has confirmed the plane broke apart in the air before hitting the ground, with a wing piece found miles from the crash site.
• The crew hit severe turbulence and icing while trying to climb above a storm that grew from a normal cloud to a 48,000-foot monster in just 20 minutes, far taller than the jet could fly over.
• Ice buildup likely raised the plane's stall speed without the crew realizing it, and if the autopilot was engaged, it may have smoothed out the warning signs pilots would normally feel before losing control.
• The plane's 1990s-era weather radar may have shown a "clear" gap that was actually the worst part of the storm, a known flaw where radar signals get swallowed by extreme rain and falsely read as safe.
• Decision-making is a major focus too: standard procedure is to stay at least 20 miles from a storm, and descending or waiting out the weather on the ground were likely safer options than climbing into it.

Outlook: A preliminary NTSB report is expected in about a month, which should narrow down whether icing, the autopilot, faulty radar, or pilot decisions were the main driver.