MarshalN
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How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 4:59 pm

I'm just curious. I remember reading on some thread with someone saying that even when all the engines go out on a jet, the plane can probably still glide for a while. Now, how long can this last? If, say, a 747 somehow loses all engine power but still has its structure/wings intact, what will happen? It'll obviously dive, but at what speed? Will the pilot be able to control it somewhat? How much time is there, given that it's probably not going at free fall? I mean, obviously, it'll eventually crash...
 
PPVRA
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 5:06 pm

Quoting MarshalN (Thread starter):
I mean, obviously, it'll eventually crash...

Not if the pilot gets to a runway. It's happened before, google "AirTransat + Azores" or something like that and read about it.

If it can't glide it can't fly - unless it's a helicopter. Jet's simply glide at a higher speed then props, they all fly on the same principles.

As for how long it can last.... don't know, but I'm sure meteorological conditions will play an important role, especially wind speed and direction.

Cheers

edit: Even the space-shuttle glides! no thrust on approach at all.

[Edited 2005-12-18 09:23:28]
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je89_w
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 5:07 pm

First thing that came to mind was the "Azores Glider" or an Air Transat A332 that lost all power over the Atlantic due to a fuel leak. It glided down all the way to the Azores. There are probably a bunch of threads about it on A.net. I can say that the Air Transat bird did go pretty far!

Don't forget the infamous "Gimli Glider" which is an Air Canada B762.

Both aircraft are still in service.
Running Out Of Fuel Mid Air (by UA777lover Aug 6 2003 in Civil Aviation)#ID1152901
RE: What Is The Story Behind The "Gimli Glider" (by Eric Nov 28 2004 in Civil Aviation)#ID1838604
 
MarshalN
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 5:51 pm

Hmmmm, interesting, thanks for the links, I just read about the Air Transat thing, pretty fascinating.

So, is this something that pilots have to train for? I'd imagine so, eh?
 
Glom
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 7:26 pm

Quoting MarshalN (Thread starter):
It'll obviously dive, but at what speed?

HOOOOOOOOOOOOO NOOOOOOO!!! Most descents are done on idle thrust. The situation is pretty similar. No dive there.

Quoting MarshalN (Thread starter):
Will the pilot be able to control it somewhat?

Of course he will. How else could he control it on the descent when power is reduced to idle?

Quoting MarshalN (Thread starter):
How much time is there, given that it's probably not going at free fall?

No free fall at all. There is still lift being generated as long as the airspeed is maintained. Airliners tend to have glide ratios of around 15 so it will travel 15 feet for every 1 foot of height lost. That means from FL300, it will be able to glide 75 miles, fully under control, provided the pilot maintains the best glide speed.
 
legacy135
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 7:47 pm

The speed for the best ratio altitude versus Descend is amazingly low. The faster you glide, the quicker you will hit the ground Big grin

Aerodynamically the speed for best glide is equal with the speed for optimum climb. This speed, on some aircrafts called Venr on others Vfs is what a pilot would climb the aircraft in a one engine out situation, once flaps (and slats) are up. This is the best speed for Lift versus Drag. If we look at the Embraer Legacy, the maximum landing weight is 18'500 Kg. Vfs at this weight is as low as 159 Knots! If we go at max take off weight - which is 22'500 Kg - it's 172 Knots! So if we assume somebody running out of fuel may be at weights as low as 14'000 Kg or even less, resulting in a Vfs of 145 Knots or less!

Jets in general are much better gliders than propeller driven aircrafts. About the worst to glide are planes like a Piper Arrow, Senecas, the Rockwell Commander AC14 or similar aircraft. Jets are pretty good. I remember once being in the Jungfraujoch (mountain in Switzerland) at 13'000 feet with a Citation. Our intention was to glide down to Bern ( BRN / LSZB ) in idle power and look how far we will come. We thought that at a certain point power would have been necessary. The fact was, we didn't make it, we were to high and had to fly several orbits to come down!

Cheers
Legacy135 Wink
 
757MDE
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 7:47 pm

As long as the air circulating through the wings has enough speed the Airplane will maintain sustentation and fly.
But in a leveled flight some thrust is needed to maintain this airspeed as there are factors opposing the Airplane's movement, when there's no thrust (i.e the engines just caught fire) these factors begin to "win" and the Airplane slowly decreases airspeed until it reaches a stall speed, so the basic thing is to maintain enough airspeed for the airplane to maintain sustentation, but for maintaining this airspeed there's a need to begin a descent, the rate of descent may vary depending on conditions such as the weight, the winds, the aerodynamics of the Airplane...etc, this Airspeed is called "best glide airspeed" I think. Even if on descent, the nose needs to be kept trimmed as possible, the airplane will continue to fly, and for what I know the controls will be pretty much the same (talking about flight controls and surfaces). Remember sometimes normal descents are made with the engines on idle, some sort of "non-emergency glide".

As a side note, the engines provide hydraulics and electric power to the airplane (the APU also provides electric power, and bleed air as well), so when the engines go offline, a little turbine in the back of the plane deploys, it's called the RAT (Ram Air Turbine).
This turbine will only generate enough hydraulics for proper operation above a certain airspeed (130+ kt if I'm not mistaken), this is another important reason for maintaining the airspeed when the engines are offline, because as most of you might know, no hydraulics = no flight control surfaces movement (among other things).
This is regarding a 767, in other Airplanes this sort of device may be different on performance and stats, but I think most Airplanes have it some way or other.

Another thing is that jets are better gliders than turboprops, the blades of the turboprop engine will hinder the gliding when they're just standing there doing nothing, for this matter turboprops have a feature called "autofeather" or something like that, feature that re-positions the blades so they get some "wing shape" and be of a little more help.

There's a simple mathematical formula for obtaining the glide ratio or something like that, but I don't know it. It was posted here some time ago, maybe a fellow member who knows more can enlighten us, and correct me if I'm mistaken as well.

Edit: Grammar and typos!

[Edited 2005-12-18 12:02:57]
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NAV20
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 7:51 pm

To glide in anything you keep the nose trimmed as level as you can, subject to maintaining a reasonable minimum of flying speed.

Powered aircraft (with power off or at idle) tend to glide at a descent rate of around 12:1 (twelve feet forward for every one down). That compares to a sailplane which only descends at 25-30:1.

So I'd expect a jet airliner starting at say 35,000 feet to be able to glide around 70nms. - at a guess, its best gliding speed would be around 170 knots.
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sean377
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 8:30 pm

Quoting Glom (Reply 4):
That means from FL300, it will be able to glide 75 miles, fully under control, provided the pilot maintains the best glide speed.



Quoting NAV20 (Reply 7):
So I'd expect a jet airliner starting at say 35,000 feet to be able to glide around 70nms. - at a guess, its best gliding speed would be around 170 knots.

Absolutely. The top of descent is often commenced at around 100 miles from the destination, which allows for a little ATC intervention, and as has been said, the throttles are brought back to idle. In an ideal scenario, I guess they wouldn't be used again until reverse thrust were needed, but you'd have to be one good pilot to judge that one!

Sean
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 8:48 pm

This may be moved to tech/ops. That may help. Along with the links in Reply 2 about the AC flight in the eighties.


Its called the Vg (or velocity of glide) – from what I recall of my flying days a decade ago. There are a number of settings (trim, pitch) for optimal Vg.

Hope this tidbit helps.
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manchesteruk
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:29 pm

http://www.airsafe.com/events/noengine.htm

this will help and also give some that didn make it, i posted in other forum too !

[Edited 2005-12-18 15:30:47]
 
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longhauler
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:34 pm

How you glide depends on your "mission".

If you wish to maintain the highest altitude, you maintain your best lift drag ratio. For the A320 that's about 220 knots. You will descend about 1500 ft/minute. So from 35000 ft, it will take you roughly 25 minutes to reach the ground. You will travel roughly 90 nm.

To travel the furthest distance, you descend at M0.74/270 knots. Again, from 35000 ft, you will travel roughly 95-100 nm.

To cover a distance the quickest you descend at M0.80/330, but you be gliding like a simonized crowbar. (namely dropping like a stone). You will travel only about 65 miles, but you'll get there quicker!

As someone said above, you have to remember, pretty well all descents are done with the thrust at idle.

Another consideration, is that without engines, your cabin will depressurize. Slowly on newer aircraft, increasing with the age of the aircraft. It is a balance with finding a place to land within your gliding range, but also looking at your cabin altitude rising.
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:43 pm

Quoting LongHauler (Reply 11):
As someone said above, you have to remember, pretty well all descents are done with the thrust at idle.

Generally, most descents are NOT done at idle thrust, especially from cruise altitude. Most VNAV flight director programs provide a relatively gradual descent maintaining cruise speed, and this calls for a fair amount of engine thrust.
 
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:46 pm

Quoting LongHauler (Reply 11):
To cover a distance the quickest you descend at M0.80/330, but you be gliding like a simonized crowbar. (namely dropping like a stone). You will travel only about 65 miles, but you'll get there quicker!

Just out of interest, what's Vne in something like an A320 and are there any circumstances where descending at that speed would be required?

Sean
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sean377
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:48 pm

Quoting RobertS975 (Reply 12):
a fair amount of engine thrust.

What's a fair amount? This can't be right! Why use fuel when gravity does the job for free???
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ltbewr
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:49 pm

There is at least one case of a 747 gliding in air. That was a BA 747 that while at cruise altitude, flew through the plume cloud of a volcano that had blown in Indonesia (?). At one point, all four engines stalled, so it was glide time for a number of miles. They were able to restart one and maybe more of the engines and land safely despite that the windscreen was sandblasted!. Of course, this a/c had to be out of service for a while due to the total ruin of all engines, skin damage, damage to the windows, and so on. One can do a search on Google and find the story of this terrifying event.
 
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:54 pm

Quoting RobertS975 (Reply 12):
Generally, most descents are NOT done at idle thrust, especially from cruise altitude. Most VNAV flight director programs provide a relatively gradual descent maintaining cruise speed, and this calls for a fair amount of engine thrust.

Huh?

Ok, could be. Then let me rephrase that. All the Jet aircraft I have flown, the A300, A310, A319, A320, A321, A330, A340, B727, B737, B767, DC-8 and DC-10 descend from cruise altitude at idle thrust. If whatever you fly doesn't let me know, sounds intriguing.

But if you are not a pilot, you may have a misunderstanding. It is quite possible to descend at cruise speed with no thrust. If your cruise Mach is 0.78, as is the A320, then you maintain that as you descend, with idle thrust. During that time of fixed Mach, your indicated airspeed is increasing. When that matches your planned descent speed, (around 290 for the A320 depending on conditions) then your descent mode changes from Mach to Speed. But rest assured, the whole thing is done at idle thrust.

The only exception I have seen, is the latest A320s we have bought (say, in the last 2 years), use a different "Idle schedule" and N1 slowly decreases from around 50% to 35%, but, it is still "idle".
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OldAeroGuy
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:58 pm

Quoting LongHauler (Reply 11):
If you wish to maintain the highest altitude, you maintain your best lift drag ratio. For the A320 that's about 220 knots. You will descend about 1500 ft/minute. So from 35000 ft, it will take you roughly 25 minutes to reach the ground. You will travel roughly 90 nm

These numbers are pretty representative for all jet transports within plus or minus 5 minutes or 10 nautical miles.
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PhilSquares
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RE: How Long Does A Jet Glide With No Power?

Sun Dec 18, 2005 11:59 pm

Quoting 757MDE (Reply 6):
(the APU also provides electric power, and bleed air as well), so when the engines go offline, a little turbine in the back of the plane deploys, it's called the RAT (Ram Air Turbine).

FYI on the 747 there is no RAT and the APU isn't certified for inflight use. So you're out of luck.

For descent planning purposes on the 744, at average gross weights (250 Tonnes) you can plan on "gliding" about 3 NM for every thousand feet, so from 350 you'd need to start down around 105 NM from the field, then if you add about 10 miles for the configuration you're all set.

However, on the 747/744 since the flight controls are hydraulic there is a very big warning in the AFM about trying to land with windmilling hydraulics. Basically, don't. You won't maintain enough speed with windmilling engines to get an adequate hydraulic supply.
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 12:04 am

Quoting Sean377 (Reply 13):
Just out of interest, what's Vne in something like an A320 and are there any circumstances where descending at that speed would be required?

Sean

Vne is 350 in the A320 (or M 0.82).

Sean, I can't imagine any scenario whereby one would need to descend at speeds like that with loss of all engines. Its a pretty bad day where you have lost both engines, AND you need to get somewhere quickly, (fire?, ill passenger?) But that mission is in the A320 manual so someone in Toulouse must have thought it possible.
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sean377
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 12:10 am

Quoting LongHauler (Reply 19):
Vne is 350 in the A320 (or M 0.82).

Sean, I can't imagine any scenario whereby one would need to descend at speeds like that with loss of all engines. Its a pretty bad day where you have lost both engines, AND you need to get somewhere quickly, (fire?, ill passenger?) But that mission is in the A320 manual so someone in Toulouse must have thought it possible.

Thanks, I was just curious. In a recent flight with an instructor alongside, I was asked at what speed I would decend if I had an engine fire. I was sure Vne would be the wrong answer, but was pleasantly surprised to get it right!

Surely the A320 has a button that you can press in the above scenario  silly 

Sean
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NAV20
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 12:20 am

I'm intrigued by the matter of actually landing the thing.

Gliders (i.e. sailplanes) are virtually the opposite of powered aircraft. Apart from anything else, most types weigh less than a ton; your problem when landing is more often how to make them go down, not persuading them to stay up.  

Because of that, the landing speed of a glider is actually higher than its cruising speed. There is only a narrow margin between cruising speed and stalling speed, so danger would flow from landing too slowly, not too fast.

The basic technique is to extend the spoiler, then push the nose down enough to keep the speed up to a safe level against the extra drag. As the ground perspective kicks in you let the nose come up level, and land normally. You don't flare in the normal sense. OK in a Blanik or something, but I'd hate to try it in a 737.........

I'd have thought that an airliner without power might face the same problem - the risk of losing flying speed in the later stages of the approach (especially with gear and flaps down). I believe that they normally keep about half-power on until they cross the threshold?

The only answer would appear to be to use the gliding technique; approach relatively high, then keep the nose well down until the last moment. Are airline pilots trained (at least on simulators) to carry out deadstick landings?

[Edited 2005-12-18 16:35:21]
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RobertS975
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 12:55 am

Quoting Sean377 (Reply 14):
What's a fair amount? This can't be right! Why use fuel when gravity does the job for free???

The question posed is why use anything other than idle thrust on a standard descent profile... here is an explanation. A jet cruising at FL350 to FL400 will start a cruise descent about 100nm out, and they will maintain their cruise speed, about M .75 or so. In order to maintain that speed and that angle/rate of descent requires somewhere around 50-60% of cruise thrust. Idle thrust would require a far too great of a descent rate to maintain cruise speed.

This discussion has nothing to do with gliding, where one does not attempt to maintain cruise speed. But someone posted that all desents are usually made with idle thrust, and this is simply not the case.
 
sean377
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 1:04 am

Quoting RobertS975 (Reply 22):
The question posed is why use anything other than idle thrust on a standard descent profile... here is an explanation. A jet cruising at FL350 to FL400 will start a cruise descent about 100nm out, and they will maintain their cruise speed, about M .75 or so. In order to maintain that speed and that angle/rate of descent requires somewhere around 50-60% of cruise thrust. Idle thrust would require a far too great of a descent rate to maintain cruise speed.

This discussion has nothing to do with gliding, where one does not attempt to maintain cruise speed. But someone posted that all desents are usually made with idle thrust, and this is simply not the case.

I'm with LongHauler on this one. 50-60% thrust in a descent is just ridiculous. You'd be going up for crying out loud!
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longhauler
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 1:31 am

Quoting RobertS975 (Reply 22):
and this is simply not the case

You're not a pilot are you?

It's very simple. Throttles/thrust levers to IDLE, maintain M 0.78. You will be descending at about 1500 - 1700 fpm down, covering about 2.5 nm/1000 ft of descent. As you descend at a constant Mach, your airspeed is steadily increasing, at your desired descent SPEED you change from constant Mach to constant Airspeed, (say around 290). You will now be descending closer to 1500 fmp, thrust still at IDLE.

At 10,000 feet you slow to 250 knots, you will now be descending at around 1300-1500 fpm, thrust still at IDLE!

If ATC has no input, then you slow at 3000 feet toward your approach speed, slowing the descent to slow the speed, extending flaps/slats and landing gear as required. In a perfect profile, you needn't even touch the thrust till around 1000 feet as you approach your desired approach speed. Gear and flaps extended, say around 130 knots or so.

So, in a perfect profile, the thrust was at IDLE right up to 1000 feet agl, you covered about 100 miles, burnt about 300 kgs of fuel, and it took about 15-18 minutes. All but the last 2 minutes AT IDLE.

Vary the speeds and distances a bit, and it was the same for every jet aircraft I have flown.
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sean377
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 1:36 am

Quoting LongHauler (Reply 24):
Vary the speeds and distances a bit, and it was the same for every jet aircraft I have flown.

 checkmark 

Thank you for that exquisite explanation.
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carduelis
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 2:24 am

Quoting LTBEWR (Reply 15):
There is at least one case of a 747 gliding in air. That was a BA 747 that while at cruise altitude, flew through the plume cloud of a volcano that had blown in Indonesia

Take a look at:- http://www.ericmoody.com/ which gives details of the 747 incident in 1982, written by the BA operating Captain, Eric Moody.
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 4:05 am

A very interesting experiment was made with a Se-210 Caravelle to prove the reliability of this new concept aircaft, on March 15th 1959 :


The Caravelle took off with one engine only from Orly Airport and climbed at an altitude of 13200m, circling over Orly.
Then the engine thrust was fully reduced, and she begun her glide ...to land at the Dijon-Longvic base, located 259km/161mi/140nm south west of Paris.

She glided at an average speed of 200km/h and with a descent rate of 270m/minute.


View Large View Medium
Click here for bigger photo!

Photo © Gerhard Plomitzer

 
PhilSquares
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 4:17 am

Quoting RobertS975 (Reply 22):
In order to maintain that speed and that angle/rate of descent requires somewhere around 50-60% of cruise thrust. Idle thrust would require a far too great of a descent rate to maintain cruise speed.

Please tell me you're not a pilot. Because if you are, you're completely out to lunch!

On the 744, we generally descend at cruise M (.85-.86) until we intercept an indicated airspeed, 295+/- 10 kias generally. During this entire descent we're at idle. At the top of descent your vertical speed is somewhere around 24-2600 FPM. Once you intercept your desired indicated speed, your descent rate is around 1800fpm. If you then have to slow to 250 below 10,000 doing so will reduce your descent rate to about 1200 fpm.

This is all done at idle thrust!!!!
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Stoicescu
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 4:48 am

In the plane I fly best glide speed is 73 kts. With a loss of altitude at about 500 Ft/m. And best climb speed is 79 kts.
 
sean377
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 4:58 am

Does that mean if you lowered the nose a bit in a glide, you'd climb?  silly 
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milan320
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 5:07 am

Quoting PPVRA (Reply 1):
Not if the pilot gets to a runway. It's happened before, google "AirTransat + Azores" or something like that and read about it.



Quoting PPVRA (Reply 1):
As for how long it can last.... don't know, but I'm sure meteorological conditions will play an important role, especially wind speed and direction.

From the info I found, the Air Transat incident was the longest glide of it's kind done by a commercial aircraft.
It glided for 19 minutes over a distance of 120km (65nm) and landed at an estimated speed of 200 knots (which is higher than the normal landing speed of the A330 but then, for instance the flaps were inoperational).

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CO787
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 6:01 am

I remember hearing something on TV that a 757 could fly/glide between 75 and 100 miles if it lost all power or ran out of fuel while at cruising altitude and could maintain about 225kts while on descent. Please correct me if I'm wrong!
 
jafa39
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 6:30 am

Quoting LTBEWR (Reply 15):
flew through the plume cloud of a volcano that had blown in Indonesia (?).

Read the book "All four engines have failed" by Betty Toothill.

In the book it says that a 747 at cruise altitude can glide for approx 160 nm depending on conditions.

In the "Jakarta Incident" they took 15 mins from cruise altitude down to 11,000 ft where....well, I wont spoil it for you, the book is a gripper!!!
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 9:55 am

Quoting RobertS975 (Reply 22):
This discussion has nothing to do with gliding, where one does not attempt to maintain cruise speed. But someone posted that all desents are usually made with idle thrust, and this is simply not the case.

why do i get the feeling that the only flying that you have done is in your seat on MS flightsim?
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Fly2HMO
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 10:10 am

As a side note, the F/A-172, ummm I mean the C172, best glid speed is 68kts, from 10000ft I 've glided down to about 1000 ft agl in about 10-15 mins. That sucker glides pretty well.
 
APFPilot1985
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 10:12 am

Quoting FLY2HMO (Reply 36):
As a side note, the F/A-172, ummm I mean the C172, best glid speed is 68kts, from 10000ft I 've glided down to about 1000 ft agl in about 10-15 mins. That sucker glides pretty well.

I've had an actual engine out on one and we just trimmed it for 68 kts and didnt even have to touch pitch again.....
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PanAm747
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 10:17 am

On April 4, 1977, Southern Airways DC-9 N1335U flew into a particularly nasty thunderstorm and lost both of its engines. Before crashing at New Hope, GA, the DC-9-30 descended from 14,000 feet in 35 miles, something "the aircraft manufacturer calculated is what it should have been able to do", according to author David Gero in his book "Terror In The Skies".


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TheRedBaron
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 10:20 am

My landings at X-plane are always done at idle (so even in a good FS this glide/power still holds true). The trick to a good landing is knowing your rate of decent vs speed, so you loose altitude and keep speeds safe (no everspeed, no over 250 knots below 10 000 feet and having the right speed for the deployment of flaps slats....
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PPVRA
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 10:27 am

Milan320, you're correct. And I believe both pilots were awarded honors for the feat.

Quoting PPVRA (Reply 1):
Jet's* simply glide at a higher speed then** props, they all fly on the same principles.

Sorry, but those two grammar errors are really annoying me:

*Jets
**than

I was really, really tired when I typed it.

Sorry again,
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[Edited 2005-12-19 02:28:54]
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MarshalN
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 10:56 am

So, when you're under 1000 ft altitude, then engine thrust is used again to maintain altitude for a smoother descent, instead of ramming your plane down on the ground?

I do notice a lot of times on final my flight will apply slight engine power, presumably because it's going a tad bit slow or some such.
 
mig21umd
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 1:27 pm

To answer your original question MarshalN - How Long Does A Jet Glide With No Power?

The most correct response would be - Until it hits the ground!  Big grin
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carduelis
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 1:49 pm

Quoting Carduelis (Reply 26):
Take a look at:- http://www.ericmoody.com/ which gives details of the 747 incident in 1982, written by the BA operating Captain, Eric Moody.



Quoting Jafa39 (Reply 33):
Read the book "All four engines have failed" by Betty Toothill. In the book it says that a 747 at cruise altitude can glide for approx 160 nm depending on conditions.

I find it surprising that nobody has taken up the factual information mentioned in the two quotes above, particulalry the Eric Moody one - as they both refer to the same incident when a British Airways 747 lost all power on all four engines after flying through some volcanic 'clouds' over Java in 1982. The BA Captain, Eric Moody, and his crew actually later got some power back and successfully landed with absolutely no injuries. Truly amazing, and very practical stuff! Not hypothesis or theory!
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higney85
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 2:00 pm

all the way to the scene of the crash...
 
mig21umd
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 2:52 pm

Quoting Carduelis (Reply 43):
find it surprising that nobody has taken up the factual information

Carduelis, why surprised?

This topic was started by a member who has contributed over 1200 posts to various AVIATION TOPIC'S in this forum and clearly has very little or no understanding of basic aerodynamic principles of an aerofoil. Even though aerodynamics is not that simple...  Smile

Not trying to be rude to MarshalN, but contributors to airliners forum get their info from all different sources. Including TV  Wow!.
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MarshalN
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 2:56 pm

Quoting Mig21UMD (Reply 45):
This topic was started by a member who has contributed over 1200 posts to various AVIATION TOPIC'S in this forum and clearly has very little or no understanding of basic aerodynamic principles of an aerofoil. Even though aerodynamics is not that simple...

Not trying to be rude to MarshalN, but contributors to airliners forum get their info from all different sources. Including TV .

Well, I think I exaggerated a bit when I posted the original question. I do know that the planes will glide (i.e. not fall like a rock) but I wasn't sure how long a plane flies in those circumstances, thus my question of how far it will go.
 
gorbskow
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 4:25 pm

I think that maybe it is too easy for pilots to assume that since their airplane is flown a certain way, that all airplanes must be flown that way. What I am trying to say is that not ALL airplanes decend using idle thrust. Idle thrust is not a normal operation from altitude in the airplane that I fly. Most times, from 41000 feet, my airplane will require approximately a 2,000 fpm descent from 120nm out or a 3,000 fpm descent from 85nm out. To maintain .78 and 2,000 fpm the aircraft that I fly requires somewhere in the neighborhood of 80-85% rpm initially. Additionally if I were to bring the throttles back to idle to begin my descent i would most defenitely lose the cabin. As we continue the descent the throttles will be reduced further. An earlier poster made a comment of power being added towards the bottom of the descent. This is simply an aerodynamic procedure for airplanes as the plane becomes dirty. It is typical for a learjet to increase to 80% and 700fpm inside the outer marker on an ILS.
 
Glom
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RE: How Long Does A Jet Glide With No Power?

Mon Dec 19, 2005 8:52 pm

Quoting MarshalN (Reply 41):
I do notice a lot of times on final my flight will apply slight engine power, presumably because it's going a tad bit slow or some such.

That's to maintain the glidepath when at a slower speed. In the event of a forced landing without power, the descent path would be steeper.
 
theunclesam
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RE: How Long Does A Jet Glide With No Power?

Tue Dec 20, 2005 1:30 am

It's the first thing that you are told when learning to fly that applies here: Pitch for speed, power for altitude.

In this case, you've lost power (you're going down whether you like it or not), but you still have your speed control (Pitch).

So how long does a jet glide with no power? Well, depends on the jet (Config, weight, etc), the pilot, and probably a little luck.
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