Friday practice for this weekend's Eifel Grand Prix was cancelled when fog prevented the medical helicopter from operating during the morning and afternoon sessions.
The two 90-minute practice sessions failed to get underway and were eventually called off by the sport's governing body, the FIA. Low clouds in the local area meant the medical helicopter was unable to fly to the Nurburgring's designated hospital in Koblenz in case of an on-track emergency.
Under FIA regulations, a Formula One track session can take place only if the transit time to the designated hospital can be guaranteed in under 20 minutes.
Koblenz is a 45-minute drive away, meaning a green light for any track running this weekend is dependent on the medical helicopter being able to fly.
The Nurburgring, which has not featured on the F1 calendar since 2013, is known for bad weather, but a grand prix has never been held at the circuit this late in the year.
"We've been seeing it [the weather] come in and out all day, so we've been operating on the 30-minute interval with updates, working with local air traffic control, with the helicopter pilot, for the medical helicopter," F1 race director Michael Masi said. "There's certainly unique weather conditions in the Eifel region!
"The main problem -- the wet weather and dampness is fine -- it's just the medical helicopter is not able to fly to the receiving hospital due to fog, so even though we have the broadcast helicopter that's flying only around the circuit, to go from here to any of the hospitals should something happen, it's not possible, and therefore from a safety perspective, we would not start the session.
"The forecast looks better [for the rest of the weekend], but we're also working on some backup plans should we have a similar situation to be able to try and work around.
"We'll work on the backup plans and then advise everyone accordingly at the same time."
Better weather is forecast for the rest of the weekend, although low temperatures and rain could still affect the remaining sessions.
Friday's conditions prevented Mick Schumacher, the son of seven-time world champion Michael, from his planned grand prix weekend debut during first practice.
The Ferrari junior driver was due to drive Antonio Giovinazzi's Alfa Romeo in the session, and his Formula Two championship rival, Callum Ilott, was scheduled to drive Romain Grosjean's Haas.