View Full Version : Gliding in a 777, 747 etc...Can it be done.?

6th Aug 2001, 00:07
I was just wondering about how far you would be able to glide in a plane, be it a 777 or something like a ATR 72, if you had a total engine failure at say, FL330 or thereabouts. How far would you be able to glide for and if conditions were right, would you be able to do a decent approach and land. Would there be a difference with a high winged plane or a low winged plane or even a Concorde. Also, what would be the best configuration for an emergency landing like that. Would you use full flaps or hardly any at all. Just curious thats all, i am a lowly PPL learner at the moment so please go easy on me if you think its a stupid question.

6th Aug 2001, 00:16
Sorry Danny, I have just realised its the wrong forum.
Off to questions please..!!!!!

6th Aug 2001, 00:21
While I think that this question belongs to the tech forum, I have a few answers for You:

Certainly they ALL can glide, even the concorde, as every normal descent is with idle thrust, but I don't know about the glide ratio.
With the MD80 we had a simple formula for all-engine flame-outs: Double the FL / divide by ten is tha max. recommended distance in NM to the airfield. e.g. from FL 310 You shouldn't aim to a field which is further than about 60 NM out. This formula allows for a normal landing with gear down and full flaps on short final, when You can judge the glide more accurately.

As we used to start descent in normal operation out of FL 290 from 90 NM out with idle thrust and 290 KIAS, the glide ratio should be better than 1:19 which isn't bad at all, and way better than any single-engine prop aircraft.

Hope it helps

6th Aug 2001, 00:23
... & for everything U ever wanted to know about gliding in a 767, check this (http://www.frontier.net/~wadenelson/successstories/gimli.html) out ;) .


[ 05 August 2001: Message edited by: Manflex55 ]

Mr Pax
6th Aug 2001, 00:33
I would imagine that the 777 without power would have the gliding characteristic`s of a wet mattress!!

6th Aug 2001, 00:41
:D ...or a manhole cover!! :D :D

The Guvnor
6th Aug 2001, 01:09
FYI, I understand that the Gimli Glider was recently retired from Air Canada service as part of their cost-cutting programme.

6th Aug 2001, 01:29
A 777 glider ??

Who would aerotow that, 100 pawnees flying in formation ???

6th Aug 2001, 02:36
Indeed, C-GAUN has been retired from the AC fleet...





Dave Incognito
6th Aug 2001, 05:00
You might be able to find out a bit more (especially the Gimili Glider) from this thread that was up a couple of months back:

Have a good one, Dave.

6th Aug 2001, 09:37
I have done this subject before - but I cannot find it on my local disks or in PPrune - so here we go again. Usual caveat from me - granny and her eggs. I will keep it simple - interested parties can try it out for themselves.

The other caveat here is that all of this is the result of simulator work. Simulators are good, but they sometimes skate over some of the details that exist outside of the "normal" flight envelope. That said, the consistency is high on several different sims - so it should be very close to the real world. However all that follows is only a "best guess" as to what will happen in the real event. With that in mind there is lots of leeway ...

Before I start let me assure Mr Pax and 126.9 that a B777 glides as good as anything out there. In fact a good deal of what follows is based on the B777, but most of it is the 767. That said, all modern Jet equipment has similar attributes and this technique is very transferable across types.

OK - this is going to a long one folks ( I have 3 hours to kill before off to XXXX (agghhh)) - fast forward now to skip the intro....

So that I can draw in some of our non-jet and lesser qualified readers - let me do a little mass brief :

| -------------------- Granny Guide Starts Here ----------------------|

Gliding :

All aircraft glide - even helicopters (although not well I must admit). However all Fixed Wing aircraft have a potential glide performance and some are better than others. As a general rule, the more fuel efficient the aircraft the better it will glide. This is simple math since gliding consumes energy just as powered flight does. In the gliding case the energy comes from the potential (Altitude * Mass) reserves rather than from engines and fuel. At the end of the day it is a question of drag. Drag consumes that potential energy, just as it consumes fuel under power. Heavier aircraft (with more Mass) tend to glide better (further) than light ones. This is a quicksand topic and I intend to skate quickly over it - the answer depends on the wind affecting the glide. Let's take wind out of the equation today - this is not a PhD course.

As people have rightly stated earlier, the aircraft is normally fully equipped to glide. Just because the engines stop, does not mean that it falls out of the sky, far from it. The normal descent procedure for a Jet aircraft is to throttle back to idle thrust and use all that potential energy to get it the last 100 miles or so to destination using minimum fuel. Indeed the whole skill is to reduce the enormous amounts of energy that are resident in a 200+ ton Jet at 37000 feet doing 500+ kts to zero by the end of the target runway.

The normal method is simply to take the height (in thousands), multiply it by 3 and add a factor for speed to start a throttles closed descent. Normally this factor is about 15-20 miles. So if you start the descent at 35000 you get (35*3) + 15 = 120 miles. Without the complications of wind, this will allow you to GLIDE (throttles closed) to with 5 miles of your landing. Trying to finesse the problem closer than this is usually a bust since you do need some engine power on the finals to allow you a level of control - but once again this is too much detail at this point.

OK, so assuming a normal Jet at normal altitudes. If all the motors stop more than 100+ miles from an airport - you are looking at a real problem. However if you have a half decent runway (how long is an issue here - but anything tarmac or concrete is better than dirt or water..) nearer than that then you have every chance of a successful glide approach. The trick is knowing how to do it.

| ---------- Granny Guide Ends Here ----------------|

One of the larger problems that is often ignored on this topic (not that this is often discussed or taught) is that of pressurisation. Most twins allow bleed air from the APU to be used only below 14000ft. Most quads don't even have an APU that can be started in the air. So pressurisation will be an issue. Obviously it will depend on the age of the aircraft, condition of door seals etc, but there will be a significant DeltaP reduction once the engines stop. This may be a limiting factor in determining ultimate range - and it is not a trivial one. There may well be an imperative to get the airframe to 15000ft or so PDQ and this will restrict the ultimate gliding rage. However let's assume that is not the issue.

Let us now progress to a no wind day at 10000ft within 30 nm of a suitable airport. It is your day !!! From now on in I will assume we are in a 767 / 777 even a Jurassic 744. (Although I will agree that the situation is less likely in the latter - unless we are talking fuel contamination or similar)

If you have an ILS on your intended runway - life is good. Otherwise work for a 3% / 3 nm per 1000 slot somewhere on finals. You have plenty of leeway above this - but not a lot below it. Work on the profile accordingly.

Configuration is clean / Vref + 80. Use airbrake to adjust. The RAT is out and the APU (if you have one) is on line and all systems are working. Try to adjust now to a 3.5% slope - 400ft / mile and once you achieve that, drop the flap to 5 and reduce to the 5 flap speed. On the ILS this 3.5% looks like 1 dot high. Stay with that using airbrake to control speed and elevators to control slope. Stay with this profile to 400 ft. There is lots of flex here. Nominal zero wind should have you at about 1/3 to 1/2 brake. Ensure that AutoBrakes are OFF.

At 400 ft dump the gear and all the flap. Aim for the threshold and use the extra speed to kill the rate of descent. At this point it is the ROD that will kill you. Get back to a nominal <1000 fpm using the excess speed.

Touch down where you can - the sooner the better. Deploy the speed brakes and wait. All those lovely V squared thingies are coming to your aid here. When and if you get to the last 2000ft then start applying brakes.

There you go - it's almost easy and very repeatable. Give it a try (in the Sim!). Any feedback will be well received.


[ 25 August 2001: Message edited by: MasterGreen ]

6th Aug 2001, 19:00
"I would imagine that the 777 without power would have the gliding characteristic`s of a wetmattress!!.......or a manhole cover!!"

Hey, don't denigrate the humble manhole cover! I read somewhere that a manhole cover was the first man-made object to leave the earth's orbit.... i.e. one on top of an early underground nuclear test site :D

7th Aug 2001, 21:38
Are the pictures above of the aircraft that was flown (and glided) by Bob Pearson?

7th Aug 2001, 21:54
If you have an ILS on your intended runway - life is good. Otherwise work for a 3% / 3 nm per 1000 slot somewhere on finals. You have plenty of leeway above this - but not a lot below it. Work on the profile accordingly.

Do you really think that's sustainable in a glide in a B7x7? 3 degrees (an ILS) requires a L/D ratio of 20. 3% requires an L/D ratio of more than 30.

I don't know what the numbers are for best L/D, but if you can get 20s and 30s they're impressive!

7th Aug 2001, 23:21
Thank you MasterGreen for taking the time and effort to write that out. Very interesting, thanks.

8th Aug 2001, 00:38
A few years ago G-BDXH a 747 did glide after all four engines suffered a flameout due to volcanic ash ingestion. This happened somewhere near Jakarta. I think it got a mention in the Guiness book of records as the biggest glider!! :)

Dave Incognito
8th Aug 2001, 05:47
The Captain of the BA 747 (mentioned in the previous post) made on of the best cabin announcements I have ever come across:

"Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnest to get them going again. I trust you are not in too much distress." :eek:

8th Aug 2001, 12:42
On the Airbus we practice this during conversion.

Basic assumption is a 5 degree slope, so at FL 390 you can glide just under 80 miles, FL200 means 40 miles, 10000 ft equals 20 miles etc. Aim towards the runway then turn onto a downwind 2.5 miles out (use the map display). The base turn loses 2500 ft so a quick calc gives you a clue how far to extend your downwind. Turn back, configure appropriately and land.

Oh and we'd Autoland in this case. Only CAT3A though. Seen it done in the sim, quite impressive and autoland with NO engines running.

8th Aug 2001, 17:26
I have done a glide in B757 simulator using the technique discribed by Mastergreen. Works wonderful but quite a sweat with both engine outnad the apu out too.

8th Aug 2001, 18:36
A few more details on G-BDXH The captain was named Eric Moody who some of you may know as the Sky News “Aviation Expert” who is wheeled out every time there is a major accident. Reading the incident report I recall that when they were on finals, they requested the runway lights to be turned up as they could not see them, this was due to the abrasive affect of the ash on the glass causing it to become more opaque than clear.

Did a search on Captain Moody on Yahoo, found this page on becoming an airline pilot. Found out that: Quote “The basic wage for a newly qualified commercial pilot is between 30k-40k.” Ha!!!


10th Aug 2001, 21:37
Question for Mastergreen. Are the calculations you use different for a fuel starved engine rather than throttles at idle? My point being that an engine at idle is still providing the power to "windmill" itself whereas a fuel starved engine is probably windmilling due to the aircraft's forward speed and causing drag as it does, decreasing your range. And how about where all engines are seized up, as happened to an Eastern Airlines L1011 back in the 70's. If the engines can't turn, how much more drag does that induce? (They were able to get one re-lit and make it back to Miami, only to have it shut down right again after landing.)

12th Aug 2001, 13:35

Nice of you to use the word "calculations" but I am not bright enough for that by far. All my numbers are ex simulator practise.

That said, as far as I can figure the numbers I stated above are for a windmilling motor. You comment about the stalled / static N1 is valid and is an added complication. However I thought of this when I ran it through the systems and the SIM at least gave me enough spare to allow the technique as written enough flex to make it down.

The question about glide angle is valid (on the face of it), but I would caution restraint in comparing a 200,000 Kg swept wing 777 with a Blanik or a Plastic Pig (Astir) . Sure you have a couple of 9 ft windmilling fans and a RAT hanging out, but there is a an awfull lot of potential energy there that needs burning off.

300+ ft per mile is not a problem clean (zero wind) and as I mentioned - get into a 400ft / mile profile before you dump flap to 5. This is easy as .....

I am not trying to invent an SOP here. I am just trying to float a few ideas. Get into the box and try it. What I proposed works for me, but if you have a better mouse trap - I am first in the queue. Gimme.....


[ 12 August 2001: Message edited by: MasterGreen ]

14th Aug 2001, 05:38
Master G:
Good background info, in case one is ever confronted with the Air Canada saga. :cool:

25th Aug 2001, 12:26
Thanks and very well done to the Air Transat crew.......What a landing that was, spot on....

26th Aug 2001, 00:07
Yes he's your man, ably assisted by Maurice Quintal (now Captain) who I believe did his advanced flying training at Gimli.

28th Aug 2001, 03:24
What was the REG of the Air Canada 767

Human Factor
28th Aug 2001, 03:43
I think, when it all goes quiet, all credit to anyone who can make it to an airfield and walk away from it. Well done to the Transat guys!!

As far as Capt EM doing his damnedest to get them going again, I think he managed with some of them ...... bet he was glad he had four to choose from!!


You can only have too much fuel when you're on fire ...........

28th Aug 2001, 04:30

Yes, the photos are of the actual aircraft.


The AC B767 registration is/was C-GAUN.