Barry Schiff retired from TWA as a captain in 1998.
A recent e-mail from Graham Clifford, a pilot examiner in the United Kingdom, inquired whether the landing gear of a single-engine retractable should be extended prior to an emergency crash landing.
I replied that conventional wisdom suggests that an emergency landing on irregular and inhospitable terrain (as well, obviously, as when landing on relatively flat ground) should be made with the gear extended. In this manner, the landing gear can absorb some of the crash energy instead of allowing the airframe to take the brunt of the collision. There are exceptions to this rule, and it is for each pilot to evaluate his own situation, but "when in doubt, hang 'em out."
Touchdown speed is perhaps the most significant factor in surviving a crash landing. Every driver has been taught that speed kills, but speed alone does not kill. It is the rapid dissipation of speed that does the damage.
Many do not realize that the threat to survival increases in proportion to the square of the impact speed (everything else being equal). Crashing at 71 knots, for example, is twice as hazardous as striking at 50; it is three times more dangerous to crash at 87 knots than it is at 50.
In other words, land into the wind (if possible) and at as low an airspeed as possible but not so slow as to sacrifice controllability. Insufficient airspeed invites a stall, an excessive sink rate, and an impact with the ground in a nose-low attitude — factors that can reduce the prospects for survival to nil. Touchdown should be made at a minimal sink rate to reduce the vertical Gs. Although the rigid structure of a fuselage can withstand some abuse, the frail human spinal column is much less tolerant of vertical loads.
Emergency landings at high sink rates sometimes result from simulated forced landings when the engine fails to respond immediately to throttle movement. Automatically raising the nose without waiting for power to develop can result in a hair-raising sink rate. During any go-around or missed approach, resist the temptation to begin climbing and do not allow airspeed to bleed until power really is available.
An excessive sink rate and nose-down attitude when landing on soft terrain such as dry sand dunes can cause the nose to dig in, resulting in extreme deceleration.
This leads to another major factor in the emergency-landing equation, stopping distance. Surviving a crash landing depends on using as much distance as possible to bring the aircraft to a halt. In theory, very little stopping distance is required if — and this is a big if — groundspeed can be dissipated uniformly. This is because general aviation cockpits are designed to withstand 9 Gs of longitudinal deceleration.
If an airplane lands at 50 knots, for example, and decelerates uniformly at 9 Gs, the stopping distance is only a remarkable 12.3 feet. Doubling groundspeed to 100 knots, however, quadruples this to 49.2 feet. Such minimal distances, however, have little practical value, because it is impossible to control deceleration so precisely. There simply are too many variables. And although the cabin structure might withstand such a shock, those fragile beings rattling around inside probably cannot.
When a pilot is confronted with having to make a crash landing in a very short distance, he obviously cannot rely on the brakes. He must be willing to sacrifice some or all of the airplane's dispensable structures by using them as shock absorbers. The techniques to use vary with the terrain, and this makes it extremely difficult to offer specific advice. One of the most popular pieces of wisdom, however, suggests aiming the nose of the aircraft for a soft spot, such as between two trees. This may shear the wings from the fuselage, but a considerable amount of destructive kinetic energy will be dissipated in the process.
A pilot does have a few other stopping options such as intentionally ground looping, landing with the wheels retracted at those times when this might help to reduce the rollout distance, and aiming for other soft spots such as brush, bushes, and small, flexible trees that offer the promise of reasonably good cushioning.
The pilot must be prepared to sacrifice whatever part of the airplane is necessary to absorb speed and destructive energy while keeping the cabin and its delicate contents intact. A landing on rugged terrain should be made with the wings parallel to the ground and the aircraft in a somewhat nose-high attitude. Every effort must be made to prevent the nose from burrowing into the ground. In addition to excessive deceleration, a nose-low-attitude can cause an airplane to tumble. Just remember that the idea is to protect the spinner (on singles). If it doesn't get crushed, the odds are that neither will those inside.
Low-wing airplanes usually offer the most protection during a crash landing. They have more structure (carry-through wing spars) beneath the cockpit to absorb destructive forces and are least likely to nose over. High-wing airplanes typically are more top-heavy and prone to flipping.
These are sobering thoughts. Perhaps the best lesson here is to understand that those who modify their routes to avoid threatening terrain probably have the least to fear.
Visit the author's Web site ( www.barryschiff.com).
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