Aeronautical Information Manual (AIM), page 590
AIM 12/10/15 e. Helping the Flightcrew Locate the Scene 4. When the helicopter approaches the scene, it 1. If the LZ coordinator has access to a GPS unit, will normally orbit at least one time as the flight crew the exact latitude and longitude of the LZ should be observes the wind direction and obstacles that could relayed to the HEMS pilot. If unable to contact the interfere with the landing. This is often referred to as pilot directly, relay the information to the HEMS the "high reconnaissance" maneuver. ground communications specialist for relaying to the f. Wind Direction and Touchdown Area pilot, so that they may locate your scene more efficiently. Recognize that the aircraft may approach 1. Determine from which direction the wind is from a direction different than the direct path from the blowing. Helicopters normally land and takeoff into takeoff point to the scene, as the pilot may have to the wind. detour around terrain, obstructions or weather 2. If contact can be established with the pilot, en route. either directly or indirectly through the HEMS 2. Especially in daylight hours, mountainous ground communications specialist, describe the wind and densely populated areas can make sighting a in terms of the direction the wind is from and the scene from the air difficult. Often, the LZ coordinator speed. on the ground will be asked if she or he can see or hear 3. Common natural sources of wind direction the helicopter. information are smoke, dust, vegetation movement, 3. Flightcrews use a clock reference method for water streaks and waves. Flags, pennants, streamers directing one another's attention to a certain direction can also be used. When describing the direction, use from the aircraft. The nose of the aircraft is always the compass direction from which the wind is 12 o'clock, the right side is 3 o'clock, etc. When the blowing (example: from the North-West). LZ coordinator sees the aircraft, he/she should use this method to assist the flightcrew by indicating the 4. Wind speed can be measured by small scene's clock reference position from the nose of the hand-held measurement devices, or an observer's aircraft. For example, "Accident scene is located at estimate can be used to provide velocity information. your 2 o'clock position." See FIG 10-2-6. The wind value should be reported in knots (nautical miles per hour). If unable to numerically measureFIG 10-2-6 wind speed, use TBL 10-2-3 to estimate velocity. "Clock" System for Identifying Positions Also, report if the wind conditions are gusty, or if the Relative to the Nose of the Aircraft wind direction or velocity is variable or has changed recently. 5. If any obstacle(s) exist, ensure their descrip- tion, position and approximate height are communicated to the pilot on the initial radio call. 10-2-12 Special Operations
Page 590 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures