When Flying, Why is Taking Off More Dangerous Than Landing?


Why is taking off more dangerous than landing?Tom Farrier:

Landing is generally considered quite a bit more hazardous (and requires a bit more exacting handling), but both takeoffs and landings can have their challenges. Still, aircraft like to fly; sometimes it can be a little tricky to encourage them to stop doing so at the end of a flight, especially in the presence of unpredictable winds or slippery runways.

This is a graphic from my favorite go-to reference on commercial aircraft accidents, updated annually by Boeing but including all airliner accidents:

The shaded area under the aircraft silhouette shows the amount of time an aircraft spends in each “phase of flight.” At the top, there are two numbers worth looking at carefully. Final approach and landing is when 48 percent—essentially half—of all fatal accidents that have occurred from 1959 through 2016. By contrast, taking off and starting to climb is only about a quarter as hazardous (13 percent). These ratios used to be somewhat different; takeoffs used to see their share of accidents a lot more frequently than today.

The biggest challenge with taking off in the early days of jet airliners was the rate at which they could accelerate during their takeoff roll. Often, a lot of time was required between when the aircraft passed the speed at which the pilots were committed to taking off (V1) and when the jet actually could get into the air with a positive rate of climb. When an emergency would suddenly present itself in that window of vulnerability, sometimes there were no good options, and sometimes the pilots picked the wrong one.

One of the biggest ways pilots (and flight engineers in aircraft that use them) have to earn their paychecks is when something bad happens during a takeoff roll and they have to decide whether to continue the takeoff and deal with the problem in the air, or if the situation is critical enough that it’d be preferable to wrestle the fuel-laden beast on the ground and risk going off the end of the runway.

To try to address the need for added clarity in such situations, some of these early accidents led to recognition of the need for establishing a second speed benchmark (V2), which is the point at which the aircraft is going fast enough to make a successful takeoff with one engine out. Bear in mind that a lot of the biggest early jets had four engines, none of which was nearly as powerful as the current generation (some actually used water injection systems to boost their thrust during takeoff), and which suffered failures a lot more often.

“Rejected takeoffs” are pretty rare occurrences these days, and airport design has gotten better at minimizing the consequences of an aircraft running off the end of a runway if circumstances conspire to make things exciting for its inhabitants. For example, "engineered material arresting systems” are basically long slabs of pavement designed to collapse under the weight of an aircraft, grabbing hold of it and bringing it to a fairly enthusiastic stop.

This may not sound desirable, but some of the places EMAS has been installed (including Boston’s Logan and New York’s LaGuardia Airports) have seen more than their share of aircraft in trouble winding up in bodies of water during what are euphemistically (but accurately) referred to as “runway excursions.”

Such departures can happen either during takeoff or landing emergencies, and it’s nice to know that the chances of surviving both have been improved significantly with one ingenious invention.

This post originally appeared on Quora. Click here to view.

Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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Are Any of the Scientific Instruments Left on the Moon By the Apollo Astronauts Still Functional?

Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Heritage Space/Heritage Images/Getty Images

C Stuart Hardwick:

The retroreflectors left as part of the Apollo Lunar Ranging Experiment are still fully functional, though their reflective efficiency has diminished over the years.

This deterioration is actually now delivering valuable data. The deterioration has multiple causes including micrometeorite impacts and dust deposition on the reflector surface, and chemical degradation of the mirror surface on the underside—among other things.

As technology has advanced, ground station sensitivity has been repeatedly upgraded faster than the reflectors have deteriorated. As a result, measurements have gotten better, not worse, and measurements of the degradation itself have, among other things, lent support to the idea that static electric charge gives the moon an ephemeral periodic near-surface pseudo-atmosphere of electrically levitating dust.

No other Apollo experiments on the moon remain functional. All the missions except the first included experiment packages powered by radiothermoelectric generators (RTGs), which operated until they were ordered to shut down on September 30, 1977. This was done to save money, but also because by then the RTGs could no longer power the transmitters or any instruments, and the control room used to maintain contact was needed for other purposes.

Because of fears that some problem might force Apollo 11 to abort back to orbit soon after landing, Apollo 11 deployed a simplified experiment package including a solar-powered seismometer which failed after 21 days.

This post originally appeared on Quora. Click here to view.