# Could a runway include a safety device to destroy a plane's landing gear?

The NTSB recently released its final report of a crash at Hanscom field (KBED) in Bedford, MA. The short of it is that the pilot tried to rotate with the gust lock engaged, preventing the plane from lifting off. It rolled past the runway and finally crashed into a ditch, where it burst into flame, killing everyone on board. (I should say that although I've flown in a small 4-seater a few times, I'm not a pilot — so please forgive me if I misused some terminology.)

One thought I had is that if the landing gear had been destroyed at the end of the runway, the crash could have been a lot less severe. In particular, I was thinking that a small wall could have been designed to knock the gear out, making the plane start skidding on its belly and presumably coming to a stop much sooner. It wouldn't be exactly safe, but it seems like it would be safer than relying on just the gear's braking power.

Does such a device exist at any airports? And if not, has it been considered and rejected for some reason?

• hitting the brakes gives more stopping power than sliding on the belly – ratchet freak Sep 9 '15 at 19:46
• An arresting material is very sensitive to the weight of the airplane: A surface that would give way under a 767 would essentially be just an extension of the runway for a Cessna Citation; and material that would stop a small-medium private plane would offer minimal resistance to a jumbo jet. So they are not appropriate for airports with diverse types of traffic. – abelenky Sep 9 '15 at 19:52
• @abelenky What about a multi-layered material? The first layer would be thin and designed to arrest the Citation; the next layer would be a bit more firm and designed to arrest the small-medium plane; and the layer below would be designed to arrest large planes. A large plane would easily tear through the first two layers before being arrested by the third. I imagine the biggest inhibitor there would be cost? – yshavit Sep 9 '15 at 19:56
• Just a note... I think the word "gears" is inappropriate here, as the plural of "gear" (in the sense it is used here) is "gear". My first thought on seeing the title on the hot list was, "What? Planes don't have gears!" – Michael Sep 10 '15 at 15:26
• The landing gear assembly is the strongest part of the plane. You can't "knock it out". – Tyler Durden Sep 10 '15 at 18:28

There is indeed such a system installed at some airports. It is called an engineered materials arrestor system (EMAS). Incidents such as Southwest 1248 have shown the potential safety issues of runway overruns, as you have pointed out. The EMAS solution uses a pad of special material at the end of the runway, designed to allow landing gear to sink into the material. The landing gear is not ripped off, but as the gear travels through the material, the plane is slowed down.

Destroying the gear is not a desirable option. Although the gear on airliners is designed to safely separate from the aircraft, there is still the potential for damaging fuel tanks or other structure. The aircraft will also be even less controllable after the loss of landing gear. If a small aircraft is not going very fast, a small wall could cause it to flip over, worsening the situation.

In the crash you referenced, the aircraft was traveling very fast at the end of the runway, and an EMAS may not have been sufficient to stop the plane. An EMAS typically has a max entry speed of 70 knots, so in incidents like the one linked from the question, this kind of system may not completely prevent a fatal incident. Since the aircraft's gear must break through the material, lighter aircraft may not be stopped as effectively. However, small aircraft have been stopped with such a system.

The FAA is looking at places where these systems could be useful, with a focus on runways that cannot have the recommended 1,000 foot safety area at the end. The runway safety area (RSA) is the best option for a safety buffer at the end of a runway, providing extra distance for an aircraft to stop. The article above notes that the EMAS at Burbank airport took \$4 million to install, and that is a fairly small airport that doesn't usually see anything larger than a 737. Any overrun will incur certain recovery costs, but an EMAS will need to be repaired after any overrun or accidental damage, possibly closing the runway, and will be less effective until repairs are completed. Airports must weigh all of their options for providing a safe facility.

• – abelenky Sep 9 '15 at 19:49
• Small followup: is there ever a reason not to include such a system, other than cost? – yshavit Sep 9 '15 at 19:54
• @yshavit: See my note above, about various weights/types of planes. Also, at an airport that may have a lot of students, minor overruns happen. If the runway just has fields beyond the threshold, it'd be preferable to drag a plane out of the mud periodically rather than frequently repair your arrestor system. – abelenky Sep 9 '15 at 19:57
• This. EMAS systems are very expensive to have to replace tiles every time some tyro in a 150 or Cherokee lands a bit too deep. Similar ideas, like sugar sand pits, are more reusable (just rake them back smooth) and more effective for this kind of runoff, but less effective than EMAS would be for a runoff under power. – KeithS Sep 9 '15 at 20:27
• In addition to the costs incurred after an overrun (inspection and replacement of damaged tiles) EMAS beds require routine periodic inspections to ensure the tiles have not been damaged by weather or other factors, and incur their own maintenance overhead (above what would be required for a simple blast pad / stopway and "adequate" clearway beyond. – voretaq7 Sep 9 '15 at 21:09

The short answer is yes; EMAS and other arresting systems up to and including nets are in place at many airfields of varying sizes. The most common AFAIK is a gravel pit, aka the litterbox; it's filled with sugar sand, a lightweight gravel like pumice rock or a manufactured alternative, that yields and/or crushes much like EMAS panels under the weight of landing gear to increase rolling resistance and stop a plane that rolls off the end of the runway. They are not designed to damage the plane such as by snapping the gear off (though such damage is often par for the course), as that would actually take away the plane's most effective stopping method, its brakes and rubber tires, instead forcing the plane to skid to a stop on its slick underbelly. They're also definitely not designed or intended to stop a plane barreling off the end of the runway under full engine power.

There is no safety mechanism in existence that can 100% replace the human brain in ensuring safe performance of inherently dangerous tasks. In the accident you refer to, several basic yet critical checklist steps were skipped that would have indicated the presence of a gust lock, among them visually inspecting and checking for free movement of control surfaces during the walkaround, and the stick/rudder movement check during runup to ensure the flight controls are unhindered and properly manipulate the control surfaces. The NTSB places the blame for this accident squarely on the failure to perform basic preflight checks prior to the attempted takeoff. Preflight checks exist for this exact reason; to prevent pilots attempting to fly a plane they will not be able to operate safely due to some mechanical defect or hindrance, whether that's a gust lock, water in the fuel tanks, a bird nesting in the engine cowling, or a bullet hole in the rudder. The walkaround is literally the first thing a new civilian pilot learns on their first flight.

There really is no such thing as a foolproof system; fools are too ingenious. The pilot(s) of an aircaft are ultimately responsible for the safe operation of that aircraft, because it's ultimately their lives depending on a safe flight. That's why it's part of their job to do the preflight checks. If a pilot doesn't value his own life enough to do something as basic as this, he shouldn't be anywhere near an aircraft, because when his lack of regard leads to the loss of his life, it's very unlikely his life will be the only one lost.

• fools are too ingenious. +1 for this alone! – FreeMan Sep 9 '15 at 20:28
• Yeah, technically fools are not too ingenious, they are simply so numerous that you can't catch them all, but well said. Especially since that actually is the root issue here. – Ville Niemi Sep 9 '15 at 21:51
• @VilleNiemi - You apparently haven't seen the lengths to which people will go to willfully ignore or circumvent safety systems. Douglas Adams said it best, in the Hitchhiker installment Mostly Harmless: "a common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools". – KeithS Sep 10 '15 at 14:22
• @KeithS Good point. It is astonishing to remember that Chernobyl required, despite its obsolete and exotic design, deliberate effort on part of its controllers before it would blow up... The safeties did not fail, they were deliberately turned off. I wonder,since fools are both ingenious and numerous, why don't they rule the world? Oh, wait... – Ville Niemi Sep 11 '15 at 9:39
• "EMAS and other arresting systems up to and including nets" I think you mean "down to and including", :-) – David Richerby Dec 13 '16 at 15:25