Landing a helicopter in an area that wasn't specifically built for a helicopter can be a dangerous but required task. The US Army lands helicopters in fields, on buildings, on streets, and any other place imaginable in order to provide air transportation to troops on the ground by inserting or picking them up.

In order to establish a Helicopter Landing Zone, or HLZ for short, an area large and sturdy enough to allow the aircraft to approach, land, and then take off must be identified. In order to do so, typically there are forces on the ground coordinating the aircraft on their approach and pre-establishing the HLZ. In other cases, the HLZ has been previously checked out and identified as a decent HLZ by forces on the ground, perhaps days, weeks, or even months earlier. However, it is not uncommon for a flight to approach their designated LZ only to realize that it is not serviceable. Typically in cases like this, the aircraft will get as close as possible to the ground and then release their troops/payload.

HLZ Selection and Considerations

In the case where there are personnel on the ground before the aircraft arrive, a proper HLZ is established. An HLZ's requirements are decided by the number and type of aircraft that are to use the HLZ.

Space requirements start at the center of the HLZ and extend outward in a circular direction. In addition to this requirement, approach and departure distance is needed. This is calculated with a 10 to 1 ratio - a 10 foot treeline needs 100 feet for an approaching or departing helicopter to clear. This distance can be increased or decreased by a number of factors including wind speed and the weight of the load that the helicopter is carrying.

Some diameter requirements for HLZs of various types of aircraft are listed below:
* UH-1, AH-1 "Littlebird" - 35 meters or 115 feet
* UH-60 "Blackhawk", AH-64 "Apache" - 50 meters or 170 feet
* CH-47 "Chinook" and other cargo helicopters - 80 meters or 260 feet

A single Blackhawk helicopter landing in a clearing with a 30 foot tall treeline on all sides would require an HLZ that is 770 feet long by 170 feet wide. Each additional Blackhawk that intends to land simultaneously would require an additional 170 feet added to the length of the HLZ.

In addition to size, there are also terrain and condition requirements. A helicopter cannot land on rough or uneven terrain. Landing on rocks or tree stumps will cause obvious problems for the aircraft and landing on a slope of more than 15% can cause issues when the aircraft is attempting to take off.

Helicopters are to approach and depart into the wind. This will decrease the amount of distance required. A tailwind will increase the distance required.

Marking a Helicopter Landing Zone

Once the proper location is selected in accordance with the requirements, it must be marked. How a HLZ is marked depends on if it is during day or night.

Day

A soldier acting as a ground guide will stand at the beginning of the HLZ and use a predesignated method of marking himself as the beginning of the HLZ. This can be by holding up a VS-17 High Visibility Panel or his weapon above his head, or another method. A smoke grenade can be used, however it is preferable to have a soldier standing at the location as the smoke is more visible from the air and less visible as the aircraft approaches the HLZ as the rotor wash will push the smoke away quickly. The soldier can also indicate to the pilot how close to the ground the aircraft is as the soldier on the ground can see that distance much better than the pilot can. The lead aircraft lands at the soldier on the ground and any trailing aircraft follow the lead aircraft on approach.

Night

Marking a HLZ at night presents additional problems. Visibility is limited, even with NVGs (Night Vision Goggles) or other Night Observation Devices (NOD). To increase visibility of the HLZ, lights, typically chemlights, are used to mark the HLZ for each aircraft. The pattern used to mark the HLZ is an inverted Y. See the image below for a visual reference.

The lead aircraft lines itself up with the base directional markers and lands between the left and right stem markers; attempting to line up the cockpit with the imaginary line that they form. Trailing aircraft only need the left and right stems marked on their landing spot because they line themselves up with the aircraft in front of them.

The chemlight colors preferred for the HLZ markers by pilots are, in order: Blue, Yellow, White, Green. Red is reserved for marking hazards on or near the HLZ.

Hazards should be marked by a red chemlight. It is preferred to put the chemlight on the top of the hazard or the highest point possible in a spot that the pilots will be able to see from the air as they make their approach or departure.

Sources
* SH 21-76 US Army Ranger Handbook
* Images copied from SH 21-76