When is the NATO T marking used in relation to altitude?

The use of the NATO T marking is specifically associated with the coordination of helicopters operating at or above certain altitudes. When flying at or above 500 feet AGL (Above Ground Level), the T marking serves as a visual cue for pilots and ground personnel, indicating that the area is safe for helicopter operations. At altitudes below this, there are different considerations for visibility and landing zone safety, which do not warrant the NATO T marking.

This marking helps to standardize communication and ensure safety in joint military operations, particularly when multiple units and different types of aircraft may be present. The altitude threshold of 500 feet AGL is significant because operations at this altitude are generally less susceptible to ground obstacles and provide better options for recovery and landing. Therefore, recognizing the T marking while operating at or above this altitude aids in effective situational awareness and coordination in the field.