Under what condition may foul time be issued?

Foul time may be issued when the track is clear but authority is withheld. This situation typically arises when there is a need for caution or safety, even though the track is physically clear of trains. The issuance of foul time serves as a precautionary measure to prevent any potential accidents, ensuring that crews are aware of the conditions that could pose a risk, even if trains are not currently on the track.

In this context, withholding authority means that while the track may be clear, it is important to control movements cautiously, often due to ongoing maintenance or inspection activities. This ensures safety in operations, as even a clear track may not always be safe for movements if there are other operational considerations in play.

The other options do not align with the conditions under which foul time would typically be issued. For example, when all trains are operating normally, it wouldn't be necessary to issue foul time, as normal operations imply that no special precautions are needed. Malfunctions indicating a reporting of issues also wouldn’t inherently necessitate foul time unless specific circumstances dictated it. Finally, scheduling foul time exclusively during a maintenance window is too restrictive, as safety can require foul time in various other scenarios beyond set schedules.