Emergency Landing - 2

Ground Speed and Stopping Distance

Ground speed and stopping distance will govern the abruptness of deceleration. The most critical aspect is speed, where the severity of deceleration is inversely proportional to the ground speed. Doubling the ground speed means quadrupling the total destructive energy. Even a small change in ground speed may affect the outcome of a crash landing. An impact at 85 knots is twice as hazardous as one at 60 knots. It is three times safer to crash at 60 knots than 104 knots (104-squared is about three times greater than 60-squared).

Sudden stops injure. Manufacturers design the typical general aviation airplane to provide protection in crashes up to 9 g's in a forward direction. Compression (vertical descent) will cause serious injuries and death more readily than forward decelerations. The human body may withstand as much as 40-50 g's in the forward direction, but very little g's in the vertical direction. If you have to land on trees, do not "drop it in."

Most pilots will instinctively, and correctly, look for the largest available flat and open field for an emergency landing. But, very little stopping distance is required if the speed can be dissipated uniformly, that is, spread evenly over the available distance.

It is interesting to compare the minimum required stopping distances at various speeds, if crash deceleration takes place at a uniform 9 g's. At 50 mph the required distance is 9.4 feet, while at 100 mph it is 37.6 feet (twice the speed means four times the distance). Understanding this allows the pilot to make touchdown decisions that spread the deceleration over a distance, avoiding the abrupt stop.

The nose attitude and sink rate at touchdown often determines the outcome of an emergency landing. With an excessive nose-low pitch, the nose may "stick'' in the ground. With the nose too high, a high sink rate resulting in compression will get you. The sink rate should be reduced to zero upon ground contact, as with any landing.

Terrain Appearance

Terrain appearances from altitude can be very misleading and considerable altitude may be lost before the best location can be pinpointed. Do not hesitate to change your landing site for one that is obviously better, but not too often, or too low. Generally you should not change your mind more than once. A well-executed crash landing in bad terrain can be less hazardous than an uncontrolled touchdown on an established field.

Use of Flaps

Flaps should be used during the final approach. Flaps improve maneuverability at slow speed and lower the stall speed, allowing a slower touchdown speed. Exercise judgment when using flaps since they increase drag and decrease the gliding distance. Premature use of flaps may jeopardize an otherwise sound plan.

Landing Gear

No strict rule can be given concerning the position of a retractable landing gear at touchdown. The military advocates extending the landing gear for all emergency landings. In rugged terrain and trees, an extended gear has a protective effect on the cockpit area. A gear-up landing on level, soft terrain may result in less aircraft (and occupant) damage than a gear down landing.

Aircraft Control

Positive aircraft control during the final part of the approach has priority over all other consideration, including aircraft configuration and cockpit checks.

Slope Landings

In mountainous terrain, valleys and open areas may be a scarcity. Sometimes a slope landing (maybe steep) is unavoidable. Slope landings should be made upslope. This requires special technique. Excess airspeed is necessary to change the aircraft's descending flight path to that paralleling the slope before a normal landing can be made. As much as 20 to 30 knots or more additional approach speed is necessary for this transition. For example, descending at 50 knots and 500 fpm produces a glide angle of about six degrees. If the upslope has a 30-degree angle, the airplane must change its pitch 36-degrees nose up just to parallel the slope. To execute the landing requires additional pitch. After touchdown, while the rudder is still effective, turn the airplane sideways to the slope to prevent it from slipping backward.

Peace of Mind

The pilot who knows his aircraft and understands the techniques that will insure a survivable emergency landing under adverse conditions, has no reason for morbid preoccupation with the possibility of being forced down. The peace of mind associated with this knowledge should improve the pilot's overall performance, which may prevent an emergency or benefit its outcome.