Safety Publications/Articles

Energy management

Important even when crashing

Nobody teaches how to make good crashes these days. Fortunately, I can help you with that.

Every pilot knows that speed is an important element in any forced landing, but few seem to understand just how important it is. On the rare occasions when you teach how to properly execute a forced landing, you probably tell your students that slow is good, too slow is not good, and fast is bad.

Actually, fast is really, really bad--probably much worse than most CFIs know, and here's why. Kinetic energy, which is the force that crunches airplanes and their occupants in a crash, increases exponentially with speed. If the speed doubles, the energy is quadrupled, and if the speed is tripled, the energy increases by a factor of nine. Put another way, a linear increase in the speed results in a square of the increase in kinetic energy. That's why fast is really, really bad.

The recent accident at Chicago's Midway airport, when a Southwest Airlines Boeing 737 slid off the end of the 6,500-foot Runway 31C and killed someone in a passing car, is a reminder that speed control isn't just a matter for pilots of light aircraft. So what should you be telling your students about how to crash?

Airframe. Most modern single-engine airplanes are required to have a maximum landing-configuration stall speed of 61 knots (70 mph), and an aircraft seat forward G strength of at least nine Gs. Depending on landing area surface conditions, an impact that might be easily survivable with a headwind could be far beyond seat strength with a tailwind. Even with smaller differences in touchdown speeds, such as that between 70 kt and 100 kt, the impact energy is doubled.

Wind. Wind can be good or bad. Directly on the nose is good; on the tail, bad. Suppose you have a 30-kt wind blowing when your engine quits, and you are now on short final for a hostile, perhaps mountainous area. How important is it to have the wind on the nose versus the tail? If your over-the-fence indicated speed is 60 kt, a 30-kt headwind will make your speed at touchdown just 30 kt. With the same wind on the tail, your touchdown speed is 90 kt--three times as fast, making the impact nine times as hard! This exponential increase in crash energy with linear increase in groundspeed is one of the least-known bits of information in our aeronautical playbook.

Wind indicators. Always be aware of the surface wind direction, the same way you play the mental game of picking emergency landing fields as you fly cross-country. During daytime visual meteorological conditions (VMC), classic wind direction clues are easy: smoke, water, trees, grass, cows (which face away from the wind), et cetera. At night and/or in instrument weather conditions (IMC), it's not so easy. Although most GPS units have a function for determining wind direction and speed at altitude, knowing surface winds at night or in IMC is largely a preflight function. The airlines and military used to include a "ditching heading" in the preflight briefing, which took into consideration the state of the sea as well as wind direction. For your own preflight, consider noting the lower-altitude wind direction for your own ditching heading.

Descent planning. Know your minimum sink speed. Particularly during a dark night or in IMC, this indicated airspeed might be the best option. Minimum sink speed is almost always a few knots above your stall speed, and may provide the best overall option for survival if impact has to be made without visual cues.

Groundspeed. Remember that the most important single factor critical to your survival will likely be to acquire the slowest possible groundspeed at your moment of impact. Even a small increase beyond this minimum impact speed produces a significant increase in the kinetic energy that must be absorbed by the airplane structure and your bones. Don't forget the classic pre-crash procedures not covered in this article, such as fuel and ignition off, battery off, door cracked, etc.; review the aircraft POH.

When flying over high terrain, don't forget that your true airspeed--and therefore groundspeed--increases by 2 percent for each thousand feet. At 10,000 feet in most light GA airplanes, that works out to more than 20 kt of additional harmful kinetic energy, compared to sea level. Having the wind on the nose for a forced landing is obviously even more important in the high country.

Other terrain considerations. Flat, unobstructed terrain is ideal for a forced landing, of course, but what if ideal landing areas are few and far between? I fly over the Sierra Nevadas a lot, winter and summer, and in the absence of obvious landing choices--remote forest service landing strips, a straight section of road, and the like--there are no perfect options. Here are some considerations for forced landings in mountainous terrain:

  • Mountain lakes in winter: The thicker lake ice is found at the higher elevations. This becomes obvious in spring when the lower-elevation lakes thaw first. Shorelines in shadows thaw last. Land along the shoreline if possible. Most lakes are in mountain basins, and this may make a steep approach necessary. Note the lowest wall of the basin while still at altitude. Better to pick a long lake.
  • Mountain lakes in summer: Most airplanes (with or without tricycle gear) can flip on touchdown in water. Consider full flaps, gear up. An upside-down airplane in a mountain lake is a bad situation. Crack the door before impact so that it doesn't wedge closed. Run the seat all the way aft, and brace your feet on the panel so your legs don't get crumpled and trapped in the rudder pedal area. If possible, collect the ELT and a window-breaking tool. The water is always cold, so post-crash survival and shelter is a consideration. Remember that any ELT will be worthless under water, and search and rescue will probably not be able to find the airplane if it is in anything other than a shallow area of the lake. The good news--post-crash fire hazard is reduced!
  • Snow fields: Snow is deeper on the lee side of the ridgeline. However, approaching the lee side of the mountain may bring considerable turbulence, followed by the loss of a headwind as you descend below the summit. I have seen streamlined rooster tails of blowing snow coming off the top of the ridgelines, with wind speeds of 70 to 100 mph--much higher speeds than the wind at my cruise altitude a few thousand feet higher. The ridgeline itself may provide the best combination of snow cover, straight-line approach, and headwind. In mid-winter some of these snow banks are deep enough in powder to swallow a small airplane, making search and rescue more difficult, and hiking out impossible. One Mooney pilot and his passenger survived such a crash in the Sierras by staying in the airplane until they were found and rescued. They were uninjured.
  • Trees: Tree landings are generally not good in winter. Deciduous trees in the spring and summer have more flexibility than the evergreens.
  • Mountain meadows: Like lakes, meadows are often surrounded by ridgelines. Consider the low point of a basin wall while still at altitude. In winter, there will be little to differentiate a meadow from a lake--both may be deep in snow.

So, there's my short course in executing forced landings. While sharing that knowledge with your students, also please pass along the famous Bob Hoover advice: "If you're faced with a forced landing, fly the thing as far into the crash as possible."

James Lockridge is a retired military and airline pilot who is now an active CFI in Nevada. He has taught both graduate and undergraduate courses for Embry-Riddle Aeronautical University.

By James Lockridge

Back to the Index of Instructor Reports