The regulation of hot air balloon operators needs to be more in line the airline industry, a US safety official says.
On Saturday a balloon flown by Heart of Texas Hot Air Balloon Rides chief pilot and owner Alfred "Skip" Nichols, hit a power line and plummeted in flames into a paddock, killing all 16 people on board.
The National Transportation Safety Board is still in the preliminary stages of its investigation and has issued no findings into the cause of the crash, nor has it linked the accident in any way to the behaviour of the pilot.
At a briefing on Monday, Robert Sumwalt, who is heading the investigation for the National Transportation Safety Board, said that unlike aeroplane and helicopter pilots, balloon pilots are not required to apply for Federal Aviation Administration medical certificates.
That process screens applicants for drug or alcohol-related convictions and certificates are renewable every six months, Sumwalt said.
"That goes back to the issue of oversight of commercial balloon operators, he said.
"We do see this discontinuity, this disparity in this level of oversight requirements."
The NTSB urged the Federal Aviation Administration in April 2014 to require commercial balloon operators to have a letter of authorisation similar to that required of pilots of tour planes and helicopters, which includes drug testing.
It recommended greater oversight of the hot air balloon industry, saying it was concerned about the potential for great loss of life without more regulation.
The FAA rejected the proposal, saying it did not believe it would have a significant impact on safety.
Sumwalt's comments at the briefing came after news that Nichols, who died in Saturday's crash, had been convicted of drunk-driving offences dating back to 1990 and had at least one drug-related conviction, according to online records.
Records in Missouri's St Louis County showed that Nichols had pleaded guilty to drunk driving charges at least three times between 1990 and 2010 and several other vehicular charges.
In 2000, he pleaded guilty to a drug-related charge and spent time in prison, according to criminal records.
Following his 2010 conviction for drunk-driving, Nichols was sentenced to seven years in prison and released on parole in January 2012.
At the briefing Sumwalt said investigators had found "no evidence of pre-existing failures, malfunctions or problems" in the balloon portion of the aircraft, but there were abrasion marks on high-tension electrical wires near the site.
