Attitude and Sink Rate Control
The most critical and often the most inexcusable error that can be made in the planning and execution of an emergency landing, even in ideal terrain, is the loss of initiative over the aircraft’s attitude and sink rate at touchdown. When the touchdown is made on flat, open terrain, an excessive nose-low pitch attitude brings the risk of “sticking” the nose in the ground. Steep bank angles just before touchdown should also be avoided, as they increase the stalling speed and the likelihood of a wingtip strike.
Since the aircraft’s vertical component of velocity is immediately reduced to zero upon ground contact, it must be kept well under control. A flat touchdown at a high sink rate (well in excess of 500 feet per minute (fpm)) on a hard surface can be injurious without destroying the flight deck structure depending on the design of the airframe and the shock absorbing system. On soft terrain, an excessive sink rate may cause digging in of the nose wheel with the wing and/or WSC aircraft rotating forward into the ground, stopping with severe forward deceleration or tumbling with higher speeds.
A pilot’s choice of emergency landing sites is governed by the:
- Route selected during preflight planning and
- Height above the ground when the emergency occurs.
The only time the pilot has a very limited choice is during low and slow flying or during takeoff if the landing approach is always within gliding distance of the runway.
It should be understood that the amount of area for available landing sites increases at a rapid rate with increased altitude. [Figure 13-4]
As an example, a WSC aircraft with a 5 to 1 glide ratio flying at 500 feet AGL has 500 feet multiplied by five feet horizontal (or 2,500 feet) radius on the ground to select a suitable landing area. For example, use a ½ mile radius. The area of available landing spots is π x r2, approximately 0.8 square miles. At 1,000 feet AGL, this area would be 3.1 square miles; at 2,000 feet AGL, this is about 12.5 square miles; and at 5,000 AGL, this is almost 80 square miles.
Additionally, flying in a downwind direction provides more area to be covered while flying upwind reduces the amount of area that can be covered while looking for a suitable landing area.
If beyond gliding distance of a suitable open area, the pilot should judge the available terrain for its energy absorbing capability. If the emergency starts at a considerable height above the ground, the pilot should be more concerned about first selecting the desired general area than a specific spot. Terrain appearances from altitude can be very misleading and considerable altitude may be lost before the best spot can be pinpointed. For this reason, the pilot should not hesitate to discard the original plan for one that is clearly better. However, as a general rule, the pilot should not change his or her mind more than once.
When the pilot has time to maneuver, the planning of the approach should be governed by three factors:
- Wind direction and velocity
- Dimensions and slope of the chosen field
- Obstacles in the final approach path and the field itself
These three factors are seldom compatible. When compromises must be made, the pilot should aim for a wind/obstacle/terrain combination that permits a final approach with some margin for error in judgment or technique. A pilot who overestimates the gliding range may be tempted to stretch the glide across obstacles in the approach path. For this reason, it is sometimes better to plan the approach over an unobstructed area regardless of wind direction. Experience shows that a collision with obstacles at the end of a ground roll, or slide, is much less hazardous than striking an obstacle at flying speed before the touchdown point is reached.
Since an emergency landing on suitable terrain resembles a situation with which the pilot should be familiar through training, only the more unusual situation is discussed.
The natural preference to set the aircraft down on the ground should not lead to the selection of an open spot between trees or obstacles where the ground cannot be reached. Once the intended touchdown point is reached, and the remaining open and unobstructed space is very limited, it may be better to force the aircraft down on the ground than to delay touchdown until it stalls (settles). An aircraft decelerates faster after it is on the ground than while airborne.
A river or creek can be an inviting alternative in otherwise rugged terrain. The pilot should ensure that the water or creek bed can be reached without snagging the wings. The same concept applies to road landings with one additional reason for caution: manmade obstacles on either side of a road may not be visible until the final portion of the approach.
When planning the approach across a road, it should be remembered that most highways and even rural dirt roads are paralleled by power or telephone lines. Only a sharp lookout for the supporting structures or poles may provide timely warning.
If the only possible landing alternative is a small clearing and it is not possible to land the WSC aircraft, the BPS should be deployed, if equipped, as discussed earlier.
Although a tree landing is not an attractive prospect, the following general guidelines help to make the experience survivable.
For example, if the trees are taller than 15 feet and not dense enough to assure the wing could be set on top of them, use the BPS if so equipped. This provides two possible chances of hanging up in the trees and a slower descent rate if the WSC aircraft does not become lodged in the trees and continues a descent to the ground.
If the trees are estimated to be shorter than 15 feet or a BPS is not installed on the WSC aircraft, landing in the trees should be performed as follows:
- Keep the groundspeed low by heading into the wind.
- Make contact at minimum indicated airspeed, but not below stall speed, and “hang” the wing in the tree branches in a nose-high landing attitude. Involving the underside of the fuselage and both wings in the initial tree contact provides a more even and positive cushioning effect. Hold the control bar with both hands more than shoulder width apart and bend elbows to lessen the impact of the control bar against the chest. [Figure 13-5]
- Avoid direct contact of the fuselage with heavy tree trunks.
- Try to land in low, closely spaced trees with wide, dense crowns (branches) close to the ground, which are much better than tall trees with thin tops; the latter allow too much free fall height. (A free fall from 75 feet results in an impact speed of about 40 knots or about 4,000 fpm.)
- Ideally, initial tree contact should be symmetrical; that is, both wings should meet equal resistance in the tree branches. This distribution of the load helps to maintain proper aircraft attitude. It may also preclude the loss of one wing, which invariably leads to a more rapid and less predictable descent to the ground.
- If heavy tree trunk contact is unavoidable once the aircraft is on the ground, it is best to involve both wings simultaneously by directing the aircraft between two properly spaced trees. However, do not attempt this maneuver while still airborne.