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What Happens When You Pull The Emergency Brake On the Subway?

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If you've ever ridden in a New York City subway car—or pretty much any city's mass transit rail cars—you have probably seen the emergency brake. It's hard to miss, what with its bright red handle and big placard that reads "Emergency Brake." But if you've ever read the emergency instructions that are also posted to the wall, you'll notice repeated caveats for every scenario: "Do Not Pull The Emergency Cord."

So When Should You Pull the Emergency Cord?

According to the MTA's website, "Use the emergency brake cord only when the motion of the subway presents an imminent danger to life and limb." The New York Times, which looked into the matter, relayed transit officials' instructions, who said the only reason you should ever pull the brake is in the event someone gets caught in the door or between train cars and "is about to be dragged to an unenviable fate." Unenviable, indeed.

Pulling the cord during a fire or during a physical attack by one of your fellow straphangers will only hinder emergency workers from getting to your car, which is now stuck underground.

But What Actually Happens When You Pull That Cord?

The emergency brake cord is no joke. It's not like a bus cord that politely dings and tells the conductor, "Stop, please." MTA officials described the process to the Times:

The emergency cord activates compressed-air brakes; an onboard conductor must then notify train traffic controllers, who can contact the Police Department. The braking system must be reset by the train’s crew before the car can start moving again, a process that usually takes 5 to 15 minutes and can delay tens of thousands of passengers traveling on a particular route.

Those compressed-air brakes are pretty powerful, as this video of the MTA testing them will attest:

So yeah, unless someone will be hurt by the motion of the train and that alone, don't pull that cord. A sizable amount of compressed air will hiss out onto the brakes and you won't be going anywhere for a while.

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Big Questions
How Does Autopilot Work on an Airplane?
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How does autopilot work on an airplane?

Joe Shelton:

David Micklewhyte’s answer is a good one. There are essentially a few types of features that different autopilots have. Some autopilots only have some of these features, while the more powerful autopilots do it all.

  • Heading Hold: There’s a small indicator that the pilot can set on the desired heading and the airplane will fly that heading. This feature doesn’t take the need for wind correction to desired routing into account; that’s left to the pilot.
  • Heading and Navigation: In addition to holding a heading, this version will take an electronic navigation input (e.g. GPS or VOR) and will follow (fly) that navigation reference. It’s sort of like an automated car in that it follows the navigator’s input and the pilot monitors.
  • Altitude Hold: Again, in addition to the above, a desired altitude can be set and the aircraft will fly at that altitude. Some autopilots have the capability for the pilot to select a desired altitude and a climb or descent rate and the aircraft will automatically climb or descend to that altitude and then hold the altitude.
  • Instrument Approaches: Autopilots with this capability will fly preprogrammed instrument approaches to the point where the pilot either takes control and lands or has the autopilot execute a missed approach.

The autopilot is a powerful computer that takes input from either the pilot or a navigation device and essentially does what it is told to do. GPS navigators, for example, can have a full flight plan entered from departure to destination, and the autopilot will follow the navigator’s guidance.

These are the majority of the controls on the autopilot installed in my airplane:

HDG Knob = Heading knob (Used to set the desired heading)

AP = Autopilot (Pressing this turns the autopilot on)

FD = Flight Director (A form of navigational display that the pilot uses)

HDG = Heading (Tells the autopilot to fly the heading set by the Heading Knob)

NAV = Tells the autopilot to follow the input from the selected navigator

APR = Tells the autopilot to fly the chosen approach

ALT = Tells the autopilot to manage the altitude, controlled by the following:

VS = Vertical Speed (Tells the autopilot to climb or descend at the chosen rate)

Nose UP / Nose DN = Sets the climb/descent rate in feet per minute

FLC = Flight Level Change (An easy manual way to set the autopilot)

ALT Knob = Used to enter the desired altitude

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

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Big Questions
What's the Difference Between Vanilla and French Vanilla Ice Cream?
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While you’re browsing the ice cream aisle, you may find yourself wondering, “What’s so French about French vanilla?” The name may sound a little fancier than just plain ol’ “vanilla,” but it has nothing to do with the origin of the vanilla itself. (Vanilla is a tropical plant that grows near the equator.)

The difference comes down to eggs, as The Kitchn explains. You may have already noticed that French vanilla ice cream tends to have a slightly yellow coloring, while plain vanilla ice cream is more white. That’s because the base of French vanilla ice cream has egg yolks added to it.

The eggs give French vanilla ice cream both a smoother consistency and that subtle yellow color. The taste is a little richer and a little more complex than a regular vanilla, which is made with just milk and cream and is sometimes called “Philadelphia-style vanilla” ice cream.

In an interview with NPR’s All Things Considered in 2010—when Baskin-Robbins decided to eliminate French Vanilla from its ice cream lineup—ice cream industry consultant Bruce Tharp noted that French vanilla ice cream may date back to at least colonial times, when Thomas Jefferson and George Washington both used ice cream recipes that included egg yolks.

Jefferson likely acquired his taste for ice cream during the time he spent in France, and served it to his White House guests several times. His family’s ice cream recipe—which calls for six egg yolks per quart of cream—seems to have originated with his French butler.

But everyone already knew to trust the French with their dairy products, right?

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