Gliding Heavies

[paulo]

I'd been meaning to ask for years. Excuse me for raising this in the spectre of the recent story, but I'm curious.

My guess is that it's normal ac stuff (i.e same rules no matter what the size) in that it's nose down and high rate of descent time. Otherwise speed can be kept normal.... Big sharp flare at the end? Do you practice in the sim?

[Milt]

The best glide angle for anything is calculated by the ratio of least drag to lift at that speed.

A glider having a L/D ratio of 20/1 should glide 20,000 feet for every 1000 feet of height which is probably somewhere near the capability of a "heavy" he says making a WAG!.

Can someone come up with actual numbers and best glide speeds?

[411A]

Dependant on weight (or as the Euros now call it, mass, which sounds quite silly IMO) and, in the Lockheed tri-motor, is approximated at 'round about V2+110 knots, in the clean configuration.

[777fly]

All jet aircraft descend from cruise altitude with the engines at idle thrust, initially.A rough indication of range in nautical miles to touchdown is given by multiplying the cruise height in thousands of feet by 3 (eg at 35000 feet, range is 35 X 3 = 105nm). In an ALL ENGINE-OUT condition, the only difference, at first, is the loss of flight-idle thrust. If the aircraft is then flown in the glide at the FMC engine-out descent speed, the X 3 rule is still fairly accurate. No extreme nose-down attitudes or high speeds are required. However, you need to allow a margin for manoueving when in the vicinity of a suitable airfield and should plan to be overhead, or abeam the field, at about 10,000ft agl. This effectively reduces the gliding range by about 30nm. Thus a B777 cruising at 35,000 could be expected to glide to and get into an airfield within approx 70-75nm (still air).
We used to practise the glide-to-land in the BA simulators, if time permitted, after the flame-out/relight scenario. However, it is not known if the simulator performance is valid in the no-engines condition, so the following is a guide only.
Below 10,000ft, a speed of about 230 kts seemed a good manoeuvre speed. This is close to best L/D and gives a reasonable radius of turn. At average weights, the wings level ROD was about 1500fm, up to 2500fm in a 30deg. banked turn. You can do the mathematics from there to plan an approach from the abeam or overhead.
With the aircraft (simulator) postioned at 8-10 miles out, in 'clean' configuration and on the 3 deg. G/S, it would descend at approx 1200fm and maintain the speed (this was in still air.) Within 5nm, the speed was reduced to a sensible value by use of gear,flap and speedbrake - this was when the finer judgement was required. Better to touch down at 200kts than than stall on the approach - lack of a 'go-round' option helps the concentration! With the APU and RAT powering electrics and hydraulics, in the B777, a perfectly good autoland could be made. An alternative technique was to cross the outer marker at twice the normal height, but at normal speed and configuration.This data may give a rough guide, but might not be anywhere near valid for YOUR aircraft.

[BOAC]

Ballpark figure (from 737) is twice the height ie 30,000'=60nm. Any more than that is a luxury. Speed around 220kts.

[javelin]

A330, practised the Transat scenario in the sim.

Once all the ECAM malarky is done with, at a 'full' load weight albeit without fuel, it settled at 210kts with a r.o.d. of about 1500fpm which gives loads of time from 30,000' plus. It is a real challenge for CRM for the first 5 minutes because the non flying pilot has so much to deal with, then it settles down to the inevitable landing !

Planned a 10 mile centre fix approach, no flaps, slats only, app speed 210kts, over the threshold at 170 ish. Kept checking the profile and stayed a little high, widened out to about 12 miles, flew the ILS 1 dot high 'til 1000', gear down by manual overide, back on profile, crossed the threshold on speed and landed normally. Accumulators only for the brakes so one monitored application keeping 1,000 p.s.i. on them and rolled to a halt.

One of the most challenging and rewarding excercises I have ever done in the sim :ok:

[Old Smokey]

The published Holding Speeds for Jet aircraft closely approximate Vmd, and this should be close to your optimum gliding speed if (God forbid) you should ever have to do an engineless glide.

Yes paulo, we used to practice it in the Sim, about 10,000 feet over the top of the field was about right for a successful mini-circuit and glide approach. The advent of ETOPS has made it Politically Incorrect to now consider such a scenario:D

Regards,

Old Smokey

[paulo]

Cheers chaps... sounds like the same principals apply then. Go flaps clean and save them for too fast/too high.

[alexban]

Well, on the 737 we do it,in the sim using,first, a speed around LR speed,depending on weight, something around 250-280kts.This would give a longer distance on the ground compared to 210 kts glide.
On the last part of the glide,mostly on final app, you should use 210 kts,with flaps up till landing.No flaps,only gear down bellow 1000'(manual ext).
210 kts will give you around 1200'/min vert speed.Of course there are some dif between classic and NG.

[BOAC]

Alex - are you without APU? Normal procedure is to put the APU on the appropriate bus for gear and flaps (in the Classic).

[javelin]

BOAC,

No fuel, no APU :{

[BOAC]

Oh Javelin - I'm going to be inflamatory:eek: Alexban was talking Boeing, not Airbus, so ......................... fuel :ok: :) :)

Sorry, couldn't resist it.

[javelin]

BOAC,
And pray, why would you be gliding in the first place :confused:

[foxmoth]

Most heavies are almost gliding in the descent anyway (if you have got it right) and lower speed ("Green dot" for Airbus) will give an even better range so actually not a lot of difference from a normal approach in many ways until the end - I have done the same as Javelin and as he points out the big difference in the 'Bus is that with no fuel you have only one stage of slat plus the gear (I aimed for 5nm/1500' at Green Dot and that worked pretty well).

[BOAC]

BOAC,
And pray, why would you be gliding in the first place - ask the BA Jumbo pilot. We practice 737 double engine failures in the sim and they can be caused by a few things other than no fuel! Volcanoes, ice for two.

.....and yes, I would pray :)

Alternative answer (to make trouble:rolleyes:) 'cos I'm in an Airbus.:)

[chevvron]

I know it's not a 'heavy' but I did a practice 'one in one' in a Hunter once. Clean, it did about 500ft/nm at 250kt, and to achieve the required 1000ft/nm r of d, it was 'dirty'. Starting from about 14000ft near Greenham Common, we easily made it into Boscombe Down - great fun!!

[Milt]

An extended glide approach for a straight in surely checks out those dormant flying instincts/judgements.

But if you are in one of those heavy Deltas or a swing winger with the wings swept having the gliding angle little better than a brick you had better be somewhere close to overhead at a high key of about 15,000 ft to be able to make a go of it! The space shuttle is a good example.

[Blip]

Something else to keep in mind for the B737 flyers...

Above around 180 kt, engine windmilling allows the engine driven hydraulic pumps to supply enough pressure for normal flight control operation while below 180 kt, it starts to feel like manual reversion.

If you get too slow and feel the need to select more flap, say flap 10 at 180 kt you create the situation where the rate of descent has to be increased to maintain speed. The descent path now steepens much more than 3 degrees, and the rate of descent increases significantly (around 2000 fpm). You then require a huge flare as you approach the ground which causes the airspeed to bleed off rapidly, which then causes the manual reversion to come back again which means you can't really flare enough and/or the stick shaker starts to go off and you're now really short of the runway anyway and ... yuck.

Much better to come in above glide slope (one dot as suggested would be good) and keep the speed up around 210 kts. The speed won't increase too much with the engines windmilling (It is interesting to note at this time just how much two engines at idle thrust contribute to the gliding performance). Once you think the momentum will carry you, take flap 1 and then maybe flap 5 and then when you're really sure, take the gear down. But don't let the speed go below around 180-190 kt to avoid the manual reversion!

So from my experience in the sim...
Approaching the flare point at the runway threshold with flap 1 at around 190 kt with a vertical speed around 1000 fpm with enough flight control authority to arrest the rate of descent in a "normal" flare :ok: is way way beter than falling short of the runway with flap 15, an airspeed of 170 kt and decreasing, and a rate of descent of 2000 fpm, whlie losing sufficient hydraulic pressure and having nothing happen when you make one last pull back on the control column just before ground impact, exept maybe causing the stick shaker to go off!:uhoh:

[Alex Whittingham]

For the L1011 a high key of 4500ft and low key of 1500ft, both clean, worked quite well in the sim.

[alexban]

Boac : we use did it with the APU connected,so electric hydraulic pump on ,or without the APU.
Blip: from our sim experiences,the best way to do it is with flaps up.Flaps up speed,let's say 210 kts,will be aprox 1,6 stall speed .So ,you'll have a stall speed around 130 kts,very easy to manage during landing.
No need for flaps,mostly due to the problems that you've mentioned before ,Blip.

[RJM]

Look up 'Gimli Glider'. Well-known incident in which an Air Canada 767 ran out of fuel at 41,000 ft and managed to glide to an airstrip using a RAT emergency power device, luck and a lot of skill.