Getting Soft

There is perhaps no more appropriate application for the term “grass roots” than when applied operating an airplane from a so-called soft field. Grass runways evoke a certain goggles-and-white-scarf nostalgia, but the demands they impose do confer more than just some bragging rights. Besides the obvious benefits of improved skills, there’s also the advantage those landings (and hopefully, subsequent takeoffs) will give if ever your plans don’t take you, where your plane did

Many tricycle-gear airplanes have a section in their POH for soft field takeoffs and landings. Most will advise landing slowly, with full flaps, keeping the nose wheel off the ground as long as possible, lowering it gently, and using only gentle braking (or none, if field length isn’t an issue).

It could be argued that partial flaps might work better because the pitch change in the flare is smaller (where the approach angle is less steep) but in that case you’ll likely carry more speed, and speed is counterproductive. Some advise adding a gentle amount of throttle right after touchdown, to help keep the nose wheel up, as you’re slowing down. Techniques differ, but it’s also best to do whatever you need to do to allow the wings to support the airplane’s weight for as long as possible. On a soft field, a full stall landing is best. You want to dissipate as much forward speed as possible before touchdown. And if the field is really soft and soggy, don’t stop until you’re at or near the tiedown spot. Do what you can to watch for rocks, tree stumps, gulleys, sinkholes, quicksand… Well, you get the picture.

That part about keeping the nose wheel up in the air (or for a tailwheel airplane, keeping that stick honked back) is really important. You should start and maintain even just your taxiing with the controls in their full aft position. That allows the slipstream from the propeller to provide more downward force on the tail, reducing the weight on the nose wheel (or keeping the prop from hitting the ground, in a tailwheel airplane). The only time this might not apply is taxiing with a strong tailwind.

Taxiing to the takeoff end of the runway might involve traversing an area that makes you feel like you’re trespassing on private property, or it might be one of your first introductions to back-taxiing (since many grass strips don’t even have parallel taxiways). Your instructor will no doubt have already pointed out that you should be careful about selecting a run-up spot lest your prop dislodge, ingest, and expel gravel and rocks. The experience is none too kind for your propeller fuselage and tail group. Many POHs have recommended flap settings for soft field takeoffs (usually something like 10 degrees, to maximize lift). Note: If the ground is really soft, you may not have the luxury of stopping for a run-up. (Of course, if you’re practicing on a hard surface, you should be pretending that it really is soft…) As soon as you start your takeoff roll, pull back to get the nose wheel clear — or forward, for a tailwheel airplane, to reduce drag. (If you did this during a takeoff from a paved runway, some might call this over-rotation.) Many advise lifting off as soon as possible and accelerating while still in ground effect.

Use your resources. The locals can probably point out to you the less-than-ideal rough spots that any soft field likely has. Call ahead to inquire if you can even land there in the first place; heavy local rains can turn a meadow into a mud pie. And speaking of landing somewhere for the first time, the thing about grass runways is that they can be much harder to find. The only thing that might make them stand out from all the other rectangular fields is that you might happen to notice a few airplanes parked in a row inside one of ’em. So plan on an early reconnoiter with a sectional (as well as the A/FD for additional information) to pre-select a few nearby landmarks for reference, bring along that savvy flight instructor, or both. If you’re unsure and alone, there’s nothing wrong with doing one of the few legal buzz-jobs that remain for a modern-day airplane, which is “dragging the field.” Fly over the runway at a low altitude to get a close-up look at what you might be getting yourself into (hopefully, just fun), and do not let yourself get behind the power curve!

In The Details:

  • Stable approaches most often lead to better landings. A controlled descent rate and airspeed makes it easier to be consistent with correct and well-timed control inputs.
  • Pick your spot. The beginning of the runway might not always be best; land where it looks friendly (assuming you still have enough real estate in front of you).
  • Don’t forget the wind and what you might have to do to correct for it.
  • If the grass is tall and dry, rollout distances can be astonishingly short, and conversely, take-off distances will be longer. Use whatever performance data might be in your POH, and apply it — but assume your performance will be 25% worse.
  • Keep that back-elevator pressure in. (Did I say that already?)
  • On takeoffs with the controls in the aft position, remember that the airplane’s nose will probably go higher than you want. You’ll probably need to reduce backpressure during the roll, and when lift-off occurs, you’ll need more precise (and opposite) application to stay in ground effect.
  • Directional control — The fact that the grass field is probably wider than your average asphalt runway doesn’t mean you can relax as far as directional control. You may need it more than ever, in fact.
  • The locals (fauna). Animals are more likely to feel comfortable wandering on a soft field than a paved one. Watch out.
  • Be extra conservative. If things don’t look right, go around.

What if the field is soft and short? Well, hopefully, this is an academic question for you; or else you’ve been there, done that, and gotten the tee shirt. But in case you’re curious… First off, most POHs don’t cover this territory. With a short field, the usual procedure is to get to the end of the runway, hold the brakes, apply full power, let it roll, and be ready to abort if anything doesn’t feel right. Rotate as soon as you would for a soft field, and climb out of ground effect as soon as you reach Vx, the best angle-of-climb speed. Once obstacles are cleared, accelerate to Vy, best rate.

Arrival: Landing where it’s soft and short means the heck with waiting to land 200 feet from the threshold because that’s where the ground is most even. You want to put it down as close to the start of the runway as obstacles allow. (If there were none, you’d just use the POH short field approach speed.) And in cases like these, a firmer touchdown is best, and not retracting the flaps is better: If it’s short and rough, the wheels may be bouncing around too much, and you would likely get better braking from full flaps instead. The best short and soft technique is probably a controlled steep descent using a slip, followed by the above (and if things get really tight, killing the mixture at touchdown will remove any idle thrust).

Departure: For soft fields that are also short and have a slope, it’s (almost) always better to take off downhill. If you have to wonder between downhill and downwind, if practical wait until there is no wind. If the temperature is up there too, consider a dawn or dusk departure, but ask the locals about dew or obstacles that may be hard to see in dim light. Many grass strips are located in mountainous terrain and will have spots nearby where downdrafts and turbulence often lurk. In the end, these factors may conspire to throw your obstacle clearance calculations out the window.

THE BOTTOM LINE: In a way, a soft field landing is a caricature of a normal landing … or maybe it’s the other way around. If you get used to “landing soft” as a matter of habit, your landing gear and the rest of your airplane will thank you, as will your passengers because you will be more precise and a better pilot.