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Comment by wincy | Hacker News Reader

My wife was returning home from Dallas on a flight delayed for thunderstorms. The plane was completely full. They sat on the tarmac for 2 hours before takeoff and to conserve fuels turned off the air conditioner “to avoid refueling” the pilot said. The elderly woman sitting next to my wife vomited then passed out, and they had to taxi back to a gate and drop her off to get medical attention. My wife said it was maybe 80 degrees on the plane. I can imagine higher temperatures would create more issues.

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80 degrees and humid as shit with all those people

Saving fuel seems highly likely to me.

My understanding is that's the cause of the additional turbulence you see these days, since they glide into land rather than stepping down to avoid turbulence. I think they also have planes more tightly packed now subjecting you to more wind vortex from the other planes.

That isn't what causes turbulence. Turbulence is caused primarily by natural winds, especially near storms or mountains. There can also be momentary turbulence when passing through the wake of a large aircraft, but rules on separation haven't changed significant in years.

Commercial airlines don't shut off their engines and glide to land. ATC usually directs them to step down their altitude from cruise in increments until they intercept a cleared approach. Then they make a smooth, continuous descent with minor variations in power to stay on the assigned slope.

My understanding from someone who knows about this (please forgive my lack of knowledge as I am attempting to relay what they told me) was that they used to step down when going to land at fixed points to avoid turbulence and hold those levels.

The levels were picked to provide the customers a comfortable ride, based on reports from other planes and whatever other sources they have.

They have since been told to save on fuel and so don't do this, not "gliding" but lowering the thrust to save fuel when descending which exposes people to the rougher air for longer periods of time.

Please correct my understanding if this is not the case.

Disclaimer, I'm not a pilot so it's very possible I'm wrong. But I think you might want to ask your friend to clarify this as I'm having a hard time understanding.

That said I think there's some terminology mix up. The path of the aircraft is taking when making a landing (the slope the poster is talking about) is called the glidepath. It's got nothing to do with the engines or the aircraft type.

The stepping down might be the pattern used as the plane is being maneuvered to line up with the runway but AFAIK those are just to setup for landing rather then being a part of the actually landing itself once the controller clears the pilot land.

> smooth, continuous descent with minor variations in power to stay on the assigned slope.

Which is called a "glide path" or "glide slope": https://en.wikipedia.org/wiki/Instrument_landing_system_glid...

> they glide into land rather than stepping down to avoid turbulence

This does not sound coherent. Airliners consume more fuel lower down than higher up. And they definietly don’t “glide” them in the aviation sense.

This didn't seem right to me as intuitively thinner air would require much more power to move the same volume to propel you forward. My intuition fell apart based on the altitude which aircraft typically fly. Below typical cruise altitudes, the air resistance seems to overcome the additional thrust produced by the engines leading to lower fuel economy. It's not until you get above typical cruise altitudes that the are gets too thin to be effectively pushed by jet engines. In retrospect it makes sense because of course airlines are going to try to operate at the altitude which costs them the least amount of fuel. Go much higher or lower than those cruise altitudes and your fuel efficiency drops pretty quickly.

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