TG990
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Aircraft Falling Out Of The Sky?

Wed Sep 07, 2005 9:36 pm

Just reading about some of the crashes that have happened recently, why are aircraft falling out of the sky?

I thought aircraft are designed to glide quite a distance?
Is it that they glide as far as they can and still haven't reached a safe area to land and then drop or aren't these planes gliding?
 
NAV20
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RE: Aircraft Falling Out Of The Sky?

Wed Sep 07, 2005 9:53 pm

Depends on the circumstances, TG990. Usually the causes of crashes are things other than engine failure; in fact, that's probably the least likely cause.

Airliners aren't very efficient 'gliders' - as far as I know, they can achieve a descent rate of about 1 in 12 (compared with say 1 in 30 for a sailplane). Landing would be especially tricky - they'd only get the one shot at it, at a steep rate of descent.

Even so, an airliner at say 30,000 feet would have height enough to glide maybe 60-70nms. A Canadian airliner managed to glide its way out of trouble a few years ago, after a 'chapter of accidents' pumped all the fuel out of the aircraft:-

http://aviation-safety.net/database/record.php?id=20010824-1
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
curlyheadboy
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RE: Aircraft Falling Out Of The Sky?

Wed Sep 07, 2005 9:57 pm

Which accidents are you referring to?

Latest have been
-AF A340: Runway overshoot, so the aircraft was not flying when the mishap happened.
-Tuninter Atr 42: Fuel starvation, couldn't glide to a safe landing because closest airport was too far (and 2 non-functioning props add a lot of drag)
-Helios 737: pressurization failed, pilots incapacitated, flew until fuel finished and then crashed into a mountain.
-West Caribbean MD82: Both engine failed+control problems (stall?), crashed into swamp
-TANS 737: Flew through thunderstorm, crash-landed (windshear?)
-Mandala 737: Crashed shortly after takeoff, at very low altitude there is little room for an escape maneuver if a major malfunction (thrust loss, control issues) happens.

An airplane can glide if thrust is lost, but most of commercial airliners are not very efficient when it comes to gliding, there must be an available runway at close range. Things get even worse if other issues happen, such as control problems.
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PositiveClimb
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RE: Aircraft Falling Out Of The Sky?

Wed Sep 07, 2005 10:05 pm

Hi TG990!

Maybe you could be a little more specific to which crash you refer?

Maybe you are thinking about the Helios' crash or the crash of the TunInter ATR72?

In general, you are right, aircrafts can glide even in the unlikely event of a complete loss of power. But, however, this glide must be controlled by the pilots. You must ensure to maintain a glideslope for which your speed does not increase too much, and - in this event maybe even more important - does not decrease too much as it would lead to a stall. In this case the airflow around the wings is disturbed so that the provided lift decreases significantly and the plane could - if it is not recovered - really 'fall out of the sky'.

So, to cut a long story short, yes all aircrafts can glide and the distance they can travel this way can be significant (depending on the altitude, of course - have a look at the famous 'azores glider' gliding 85nm being at FL345

http://aviation-safety.net/database/record.php?id=20010824-1 ), but it is important that control over the aircraft is maintained. For example, regarding the Helios' crash this, sadly, was not the case...

Best Regards,
Fabian/PositiveClimb Big grin
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pilotaydin
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 12:37 am

unfortunately the crahes that have taken place lately, are either low altitude situations, or there is nowhere to land, as the 1st reply efficiently pointed out each crash...there have been times, over and over again in the forums here, of famous incidents, with the Transat A330 and the Air Kanuck 767 that have glided safely...

there will always be a new type of accident...
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miguelss
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 1:14 am

The key to glide or not to glide of an airliner is the center of gravity (GC).

This is related to the load and balance too, the md's are well known for to have a very bad GC, originating the problem for to glide, besides to the number of passengers, baggage and fuel.
 
NAV20
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 1:27 am

Yes - if your recurrent nightmare is being in an airliner that loses all its engines and has to glide in, you'd be well-advised to avoid rear-engined types!  Smile
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
D5DBY
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 2:06 am

Quoting CURLYHEADBOY (Reply 2):
West Caribbean MD82: Both engine failed+control problems (stall?), crashed into swamp

but what caused the stall? at 30.000 feet, if u stall, u are high enough to take back the control over the AC.

I have this theory about the WCA MD-82 crash....

even if both engines flames out...u still need another problem to happen if the MD82 was going 2 crash( pilot said 2 ATC that AC was out of control)

is it likely that 1 or 2 engines fails...and then another problem happens that make the pilot lose control....nahh, i dont think so

not many things can make a MD82, that is flying at 30.000 feet 2 completely lose control and crash.....1 thing can, the jackscrew that controls the horizontal stabilizer...the jackscrew failed due 2 poor maintenance.....isent that very likely?!

if u disagree with me...tell me what can cause this loss of control...on an MD80, flying at cruise speed, at 30.000 feet........
 
NAV20
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 2:20 am

There may be a serious point here.

I was on an MD82 once in the days when the pilots used to come back for a chat. the First Officer chatted to me a little longer than usual because he found out that I'd flown a bit.

After landing (and I do mean AFTER, the main wheels were solidly down) the pilot applied a solid burst of forward thrust. I couldn't believe my ears (or the seat of my pants  Smile) at first - on the face of it, that's crazy - but the First Officer happened to be standing near the door as I disembarked, and I asked him about it. He confirmed that they sometimes did that, on shorter runways and in windless conditions, to make sure that they got the nosewheel down in good time.

Since that time I've tended to avoid rear-engined types. Looks like I was right - very possibly they DO have a slight centre of gravity problem.
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
TG990
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 2:54 pm

Quoting PositiveClimb (Reply 3):
Maybe you are thinking about the Helios' crash or the crash of the TunInter ATR72?

Yeah I was thinking of these ones in particular.

I guess it is extremely hard to control an aircraft during a glide......

Thanks for your replys and links.
 
NAV20
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 3:55 pm

Quoting TG990 (Reply 9):
I guess it is extremely hard to control an aircraft during a glide......

It isn't, actually, TG990 - but it IS challenging, because a lot of what you do is the reverse of normal flying.

Speed is a good example. In a powered aeroplane, speed is your friend; usually, the further it is above stalling speed the better. In a glider, the object is to use your height to travel as FAR as possible; not as fast as possible. Therefore, in a sense, 'speed is your enemy'; if you're going too fast, you're 'wasting' height on it, the glide angle is steeper than it needs to be.

Normal practice is therefore to trim the nose as high as you can to minimise height loss, subject only to not getting too close to the stalling speed. That leads to some odd reversals; sailplanes land at a higher speed than they cruise at, for instance.
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
flanker
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RE: Aircraft Falling Out Of The Sky?

Thu Sep 08, 2005 5:02 pm

hehehee i glide at 80 with the cessna. its fun. spin 
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curlyheadboy
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RE: Aircraft Falling Out Of The Sky?

Fri Sep 09, 2005 8:23 am

Quoting D5DBY (Reply 7):
if u disagree with me...tell me what can cause this loss of control...on an MD80, flying at cruise speed, at 30.000 feet........

You're right, I didn't mean to say it stalled at 30,000', but that they had both engine failure and control issues, maybe a stall, before crashing (according to the ASN report). It is possible to lose engine power and then stall the plane later on the glide, when you're too low to recover.
If God had wanted men to fly he would have given them more money...