Are grass strips more dangerous than tarmac?

Question

There are a couple of flight schools near me. One is at a large airport, they use Piper Tomahawks primarily to teach. Naturally, they use well maintained, tarmac runways to takeoff and land. This school has had no accidents in the last few years and no fatal accidents for much longer than that.

The other school often use grass strips in fields and use Ikarus C42s and Cirrus SR22T models. This school has had 3 accidents in the past 2 years, one of which involved a fatality and all of which wrote off the air-frames.

I'm pretty sure this isn't due to the type of aircraft (as globally, they all have similar safety records) nor the instructors (both schools use very experienced instructors).

So are grass strips more dangerous to use as a runway and if so, why?

Answer 1

Cloud, you are making a huge inference from a few small data points. But in any case, to the basic question, which is actually a very good one:

In terms of the chance of getting killed, (what you seem to be looking for), maybe, marginally, but not enough to rule out operating from grass. If you know what you are doing, and make allowances, I would say zero. In terms of non-fatal incidents, maybe a bit higher, depending.

On the plus side: A grass surface is more compliant than a paved one because the tires have less traction. Grass is much easier to handle flying taildraggers because there is some lateral give with respect to tire side loading. A tailwheel airplane on pavement is much more skittish and easier to ground loop. This is also true of tri-gears but much less so because they are already naturally stable while rolling. In both cases however, most people will find it easier to maintain directional control while on grass because of the traction compliance.

On the down side: Somewhat less braking dry, quite a bit less braking wet (wet grass is quite slippery, as anyone who tries to run on it without spiked shoes quickly discovers). Rolling resistance is higher so take-off distance can be longer than published numbers, which are based on a dry paved runway, and in marginal conditions this has to be accounted for and this varies with how long the grass is at the time.

Bottom line: If I'm in a taildragger I'll much prefer a grass runway. In a tricycle airplane I'll prefer a paved one. Overall I would expect to see more runway excursion incidents on grass, like landings in rain or in morning dew where pilots slide off into a fence when they discover, surprise surprise, they can't stop, that kind of thing.

That being said, I would never say that a grass runway surface is inherently more dangerous IF the pilot is properly trained in what to expect (especially landing on wet) and makes allowances for it. The only kind of fatality I would directly attribute to grass would be a takeoff fatality where the airplane's take-off run was extended and it struggled into the air at the far end and stalled out.

In the end though, regardless of this factor or that factor, these things really come down to that old standby, BAD AIRMANSHIP.

More than boating, aviation is fraught with hidden hazards waiting to trip you up. But if you are educated and trained, they are neutralized and can't get you unless you let your guard down. You have to approach things in flying this way, or you will worry yourself out of the activity before you ever really get to enjoy it. On the other hand, you are asking the right kind of questions so this is good.

Answer 2

John K already gave a great answer about the runway surface itself and there are some other points that might be worth mentioning too. Grass runways are often uncontrolled, short, rough, obstructed, and generally different from paved ones. That's a big generalization, of course, but it's worth thinking about the wider runway environment.

• Uncontrolled. Whether or not uncontrolled airports are more 'dangerous' than controlled ones is very debatable although a tower does provide some level of information and direction that doesn't exist at uncontrolled airports. Obviously, this applies to any uncontrolled runway, not just grass ones, but a pilot who isn't comfortable with an uncontrolled environment might theoretically be at higher risk than one who is, if only because of issues with situational awareness or radio work.
• Short/rough. Some grass runways are almost as smooth as pavement (Triple Tree, for example). Others are very rough and back country grass strips may not be maintained much, if at all. At least in the US, private pilots are trained in short- and soft-field landings and takeoffs but any piloting skill can degrade over time. As well as actual flying skills, pilots who only fly from long, paved runways might get complacent about performance calculations, which can make all the difference in some cases. Even taxiing can be challenging if the ground is rough and a pre-landing inspection may be useful. Or even a pre-takeoff inspection!
• Obstructed. Especially at private or back country strips, the runway may be close to trees or other obstructions. That requires the pilot to be comfortable with short-field landings in particular.
• Different. A grass runway can attract deer or other animals. You might have to do a low pass to move them off the runway before landing.

Having said all that, private pilots are trained for all of those situations and there's nothing 'dangerous' as such about landing on grass and it's not a big deal at all. Many pilots consider it more fun, especially in a tail-wheel aircraft. I couldn't find any statistics about grass vs paved surfaces, but there are many factors to consider and in general a pilot's personal experience and comfort level will count for much more than the runway surface. As with any new scenario in flying, if you aren't comfortable then find an instructor and go and try it out before you do it solo.

Answer 3

I want to add one more thing that neither existing answer discusses, but which I feel is relevant here.

Grass strips are more difficult than hardened ones to spot from the air, especially if you're not used to them and know exactly what to look for.

This doesn't make them more dangerous per se (as a pilot, you should only continue the landing if doing so is safe, which includes remaining on the proper glidepath toward your intended landing point and not drifting laterally), but my experience is that it's much easier to midjudge your glidepath, or the distance to the threshold, when the runway doesn't stand out clearly from the surroundings.

It's a trap I fell into the first time I tried to land at a field with only a grass strip, being used to a field that has both a paved runway as well as adjacent grass strips (both of which I'd both taken off from and landed on). I lost the strip I was aiming for, as I recall during a traffic pattern turn, and we (instructor and I) ended up going around for another attempt.

A paved runway is plainly visible from well away, and hard to mistake for much else: it looks like a straight stretch of wide, gray road that appears out of nowhere and doesn't go anywhere, clearly cut out from the surroundings almost no matter what the conditions on the ground are. A grass strip, on the other hand, can easily look like nothing more than a slightly different shade of green compared to the surroundings, hopefully with something to mark the thresholds and edges. To confidently recognize that for what it is, from a distance, takes more practice.