With the opening session of action already delayed for 40 minutes because fog had prevented the helicopter from taking off, the session had to be stopped shortly after it began because of further problems with the aircraft.
The FIA later explained that the original medical helicopter had encountered a technical problem, which meant a replacement had to be flown in from Austin. The issue was a loose antenna which meant the helicopter was unable to communicate with the tower.
Until that replacement arrived, the FIA suspended track action, which meant the first practice session did not get going again properly until there were just 32 minutes remaining.
The early morning fog that caused problems had burned away by then though, and the second session on Friday afternoon will go ahead as scheduled.