If Alfred "Skip" Nichols had been a commercial airplane pilot, he probably would have been grounded long ago.

Nichols, the pilot of a hot air balloon that crashed over the weekend in Texas, killing 16, kept flying despite having at least four convictions for drunken driving and twice spending time in prison — pointing to gaps in oversight of hot air balloon pilots.

Whether the pilot's drinking habits had anything to do with the crash was unclear. A former girlfriend described Nichols as a recovering alcoholic. She said he had been sober for at least four years and never piloted a balloon after drinking.

When pilots apply for a ballooning certificate with the FAA, they are not required to disclose prior drunken driving convictions, only drug convictions, said Patrick Cannon, a Balloon Federation of America spokesman.