Leaving all engines running at the gate

If you could see the blades turning then the engines coudn't be running.

Karl

"John" wrote in message
...
snowy squirrel wrote:

John wrote:

Recently at SJU I saw an IB A340-600 arrive from Madrid that left all
four engines running during the 2 hours that it was at the gate before
continuing to Santo Domingo.

If you could see the engines turning, it means that they were shut off
and
just slowly turning due to wind.

It would be very hard for maintenance personel to get near the aircraft
with
all 4 engines running. And I suspect extremely hazardous (if not illegal)
to
refuel while engines are running.

It is far more likely that what you saw were just engines turning slowly
due
to wind.

There are situations where engines on one side are left running in
extreme
cold arctic conditions, and all passenger, cargo, fuel is handled from
the
other side. This is to ensure that at least one engine is available to
generate sufficient power to restart the second engine.

Nope, those four fans were running at a pretty good clip. No wind
involved there. Besides, with the size of those things, it would take
a hurricane to keep them turning for two hours.


Was the rotating beacon on? If not the engines were most likely
windmilling.

It would be to dangerous to leave one engine running at the gate. Let
alone four. Too many people and equipment in the area. Turbo fan engines
have a tendency of sucking anything that gets to close. Paper or a plastic
bag or plastic wrap that is use to wrap cargo. That's including people
too. There is just to much crape around the gate just waiting to get suck
in. It doesn't take much to damage one of those fan blades. At 20-30,000
dollars per fan blade (For a RB-211. American Airlines 757 ). I don't
think they will leave them running unless they want to be changing fan
blades more often on the A340.


aptim A&P

"John T" wrote in message ws.com...
"John" wrote in message


Besides, with the size of those things, it would take
a hurricane to keep them turning for two hours.

Have you ever turned a turbine engine?

Yep, the wind easily turns the bypass fans. When I had a friend flying
for UPS, we climbed up into the intake of a 767. You could easily
grab the blades and spin them around at a pretty good clip. We scared
the hell out of the load master who saw the thing start to turn with vigor
and thought the engines were being start on him.

On Tue, 03 Feb 2004 22:27:38 -0500, John wrote:


Fine, I'm willing to concede wind turns turbines, never have doubted
it's possible. In fact, I've seen it several times myself. Turbines
turning lazily in the wind, though not at a fairly constant and pretty
fast clip (wind comes and goes, is not constant, certainly not in this
case). But in this case, 1) none of the other 10 or so other jets
adjacent had all their turbines running while parked at their gates,
and 2) this particular jet in question was with its tail to the wind.
Or rather, at about a 45 degree angle, so the wind would have been
blowing against the side of the engines from the back, not straight
in.

But if it was the wind, well hey, my respects to the Wind God. He
showed his mighty powers that day


Wind coming from the rear at 45 degrees will still turn them fast.
When wind speed drops they will continue to turn fast due to momentum.

MJ

(Robert M. Gary) wrote:

John wrote in message . ..
wrote:
Fine, I'm willing to concede wind turns turbines, never have doubted
it's possible. In fact, I've seen it several times myself. Turbines
turning lazily in the wind, though not at a fairly constant and pretty
fast clip (wind comes and goes, is not constant, certainly not in this
case). But in this case, 1) none of the other 10 or so other jets
adjacent had all their turbines running while parked at their gates,
and 2) this particular jet in question was with its tail to the wind.
Or rather, at about a 45 degree angle, so the wind would have been
blowing against the side of the engines from the back, not straight
in.

But if it was the wind, well hey, my respects to the Wind God. He
showed his mighty powers that day

Perhaps with the APU or the power cart running, the bleed air was open
and pushing the turbines??

This sounds like the most reasonable answer so far to me.

Especially considering, as I've already written, that:

1) All 4 turbines were running at a *constant* speed (and pretty fast
too) for the two hours I observed them.

2) None of the other adjacent jets I observed had their turbines
turning. Had it been the wind, the same condition would have been
observed on at least some of the other jets, no?

And 3) I have seen planes parked at the gate in MUCH windier
conditions and the turbines weren't turning at all.

"John" wrote in message Nope, those four fans were running at a pretty
good clip. No wind
involved there. Besides, with the size of those things, it would take
a hurricane to keep them turning for two hours.

Iberia usually parks at gate 27 where the prevailing wind blows up the
tailpipes. A 4 knot wind is sufficient for spinning a fan disk. If you could
see the blades, the engines weren't running.

D.

John wrote:

(Robert M. Gary) wrote:

John wrote in message . ..
wrote:
Fine, I'm willing to concede wind turns turbines, never have doubted
it's possible. In fact, I've seen it several times myself. Turbines
turning lazily in the wind, though not at a fairly constant and pretty
fast clip (wind comes and goes, is not constant, certainly not in this
case). But in this case, 1) none of the other 10 or so other jets
adjacent had all their turbines running while parked at their gates,
and 2) this particular jet in question was with its tail to the wind.
Or rather, at about a 45 degree angle, so the wind would have been
blowing against the side of the engines from the back, not straight
in.

But if it was the wind, well hey, my respects to the Wind God. He
showed his mighty powers that day

Perhaps with the APU or the power cart running, the bleed air was open
and pushing the turbines??

This sounds like the most reasonable answer so far to me.

Especially considering, as I've already written, that:

1) All 4 turbines were running at a *constant* speed (and pretty fast
too) for the two hours I observed them.

How did you know they were at a "constant" speed? If you could see the turbine blades spinning,
the engines for sure weren't running. If you heard a jet engine noise, that's called the APU.

2) None of the other adjacent jets I observed had their turbines
turning. Had it been the wind, the same condition would have been
observed on at least some of the other jets, no?

Perhaps yes, perhaps no. Different location, different angles, different parts of the nearby
buildings and jetways affecting the wind etc. It doesn't take much wind at all to spin a
turbine, they're extremely well balanced.

And 3) I have seen planes parked at the gate in MUCH windier
conditions and the turbines weren't turning at all.

How do you know? If the turbines are spinning very fast, the human eye won't see the motion.

On 4 Feb 2004 10:24:37 -0800, (Robert M. Gary) wrote:



Perhaps with the APU or the power cart running, the bleed air was open
and pushing the turbines??

This is technically impossible.

MJ

wrote in message . ..
On 4 Feb 2004 10:24:37 -0800, (Robert M. Gary) wrote:



Perhaps with the APU or the power cart running, the bleed air was open
and pushing the turbines??

This is technically impossible.

How so? Isn't that how the engines are started?

On 7 Feb 2004 17:16:58 -0800, (Robert M. Gary) wrote:

wrote in message . ..
On 4 Feb 2004 10:24:37 -0800, (Robert M. Gary) wrote:



Perhaps with the APU or the power cart running, the bleed air was open
and pushing the turbines??

This is technically impossible.

How so? Isn't that how the engines are started?


Bleed air is extracted from the engine to feed the aircraft pneumatic
system. It's taken from the high pressure compressor at low engine
speeds (ground idle) and switches to the low pressure compressor at
high engine speeds. It's one way only. Valves prevent backflow, so air
cannot feed from the pneumatic system back in to the engine. There
are some minor variations and complications depending on engine, but
this is the basic principle.

Engines are started by tapping air off the pneumatic system (which has
been pressurised from the apu or other engines already running) and
feeding it to an air starter. This starter is attached to the engine
gearbox and turns the high pressure compressor and turbine. The front
fan is connected to the low pressure compressor and low pressure
turbine, and runs independently from the high pressure stuff.

MJ