Would an airline pilot ever shut down an engine on descent to save fuel?

Question

I was on an MD-80 flight into Seattle, sitting by the right engine, and during descent I noticed that the fan blade was not spinning at all. Even when I heard the power increase, the blade did not spin.

After landing, when we taxi'd, it sounded like the left engine/side of the plane was louder than the right.

Nothing else about the descent or taxi seemed unusual.

At the gate, I asked the pilots if they shut down an engine on descent. The copilot said, "No. We idled them back but we didn't shut one down."

But at idle setting wouldn't the fan still spin or at least windmill?

I'm not too familiar with the older turbofans.

Thanks!

Answer 1

Just because the power is idle, doesnt mean the fan wont spin.

"Idle" is still around 25% power, and (on A320) using around 1000lb fuel per hour, so no, they probably didnt shut the engine down.

On taxi, it might have seemed louder, or maybe even was louder, because you may have been turning in that direction, and it is sometimes easier to increase power than actually turn the nose wheels.

Answer 2

i cannot understand a non spinning front fan. Even in a mild breeze on ground, many of them windmill.

Answer 3

Fan blades will windmill at idle power.  They will also windmill with the engine shut down.  As previously mentioned, you were probably looking at the stator.  The fan blades turn so fast, you can look right through them... just like a propeller looks nearly "invisible" when it is running at full speed.  In between jet fan blades are stationary stator blades that force the air to move in the proper direction for the next stage of blades.

Pilots will never shut down an engine in flight unless there is a problem.  Idle power descents are very common.  In fact, that's the most efficient way to fly.  Some airlines allow an engine to be shut down during taxi to save fuel, but never in flight.

Answer 4

Thats not a fanblade, its a stator. If it werent running and they shut it down it still would be spinning.

Answer 5

No, you're right, it sounds like they might have shut one down, but they never do it to save fuel, only in an emergency if the engine isn't operating properly. However, some turbofans have a fixed set of vanes ahead of the rotating disc with vanes in it, which helps direct the airflow as it enters the engine. This is more likely what you were seeing. If they had a real engine failure, they would probably have diverted to the closest major airport after it happened.

Answer 6

Pilots routinely idle engines on descent.  Modern airliners are slippery and glide well, and often the only way to descend at the desired rate is to set throttles to idle.  However, even at idle, the front fan of the engine still turns at a relatively high speed.

An engine that is shut down will still windmill.  On aircraft with many engines (such as a 747 with four), the windmilling alone can provide emergency power for essential systems even with all engines shut down, and these aircrafts don't require extra ram-air turbines (RATs).

Are you sure you were looking at the front fan?  Some engine assemblies have stationary vanes in front of the fan, and I think the MD-80 might be in this category.

Answer 7

This sounds like the "Well we still have two good ones left". If it wasn't windmilling, it probably had a catastrophic failure within landing distance of your destination. So no change in flight plan, no announcement to scare the heck out of everybody.  Now the idle back comment is accurate. NASA discovered during their preparations to design the space shuttle that a power off landing is everybit as safe as a powered landing. Then they took the idea to the airlines-who said "you have got to be $hitting me" and threw them out. But when the price of gas went batty in the 70's They came back and wanted to know more. The idea took hold and the airlines have been saving fuel by the bucket ever since.

Answer 8

a single-engine landing is an emergency, you'd have seen emergency vehicles on the ground and other air traffic suspended.

Answer 9

you obviously are not too familiar with the younger turbofans either.

one, even an idiot would not shut down an engine to save  fuel. the fuel required for the approach is more on one engine than two.

two, if the crew did perform a precautionary shut down it makes no sense to tell the passengers about it if they're at the scheduled destination on time. i'd sure lie to you if you asked.

and three. there is no way to stop the fan from windmilling in flight. you simply did not see what you think you saw.