In what scenario is it forbidden to take off?

Taking off is specifically forbidden in the scenario involving a NIL braking action report. A NIL report indicates that the runway conditions are such that the braking ability of an aircraft is severely compromised. This situation poses a significant safety risk, as insufficient braking action could prevent the aircraft from stopping safely after takeoff or during landing. In aviation, maintaining safe and effective braking performance is crucial for ensuring the safety of all operations, particularly during critical phases such as takeoff and landing.

On the other hand, other scenarios such as after a runway inspection may indicate that conditions are deemed safe for takeoff, while reduced visibility can sometimes be managed with appropriate procedures and approvals. Normal operating conditions would not typically restrict takeoff unless there are specific advisories or limitations noted, making the scenario of NIL braking action a paramount concern that directly influences the decision to take off.