United Flight 93, What actually happened ? [somewhat edited by JT]

[SUPERMNNN]

I am not a pilot, while doing some research, I have some questions for professional commercial pilots. I would highly appreciate your help:

1. How hard is it to fly a Boeing 757 with only one engine?

2. If a plane flying at 7000 ft, 500 mph, suddenly lost one engine and decending. How long does it take the plane to drop to 6000 ft, and 5000 ft, comparing to a free fall? (It takes 11 seconds for a free fall to drop 2000 ft. )

If you are a professional pilot who would like to help me with an very important research, please email me: [email protected]

Thank you.

[extreme P]

1. Easy.

2. Will not "drop". Level flight will be maintained.

2a. Can't fly at 500mph at 7000'.

[Genghis the Engineer]

At 5,000ft, and a sensible cruising speed, most aircraft in that class, at most conditions should be able to maintain level flight. The pilot's likely to have to modify his speed however, and there may be a small loss of altitude (a couple of hundred feet maybe) whilst adjusting speed and power (on the other engine) to maintain level flight.

If you are a writer or journalist, have you tried: http://www.scitalk.org.uk/

G

[chornedsnorkack]

Originally Posted by SUPERMNNN

Why Boeing 757 can not fly at 7000 ft altitude and 500 mph speed?

This is connected with the concept of Vmo.

Basically, the faster an aircraft flies, the larger the drag (at the same height). But the higher the aircraft flies, the lower the air density and therefore the less drag there is.

If an airplane tries to fly too fast, then the drag forces can break something. Therefore, aircraft are not allowed to fly faster than a certain speed, named Vmo. This speed increases with altitude, because at a higher altitude the air is less dense.

A 757 is not allowed to fly at 500 mph at 7000 ft altitude for Vmo reasons.

However, it seems they actually can. The Vmo is restricted with some safety margin, so a plane might exceed Vmo and get away with it. It is said that the 757 that rammed Pentagon exceeded Vmo and did not break up in air before hitting target...

[Genghis the Engineer]

However, it seems they actually can. The Vmo is restricted with some safety margin, so a plane might exceed Vmo and get away with it. It is said that the 757 that rammed Pentagon exceeded Vmo and did not break up in air before hitting target...

Entirely possible - there are always significant safety margins (usually around 10%) on any airspeed operating limit.

For the purposes of what I presume is some kind of work of fiction, there is no good reason to fly a 757 at 500mph (that's 434 knots, or 67% of the local speed of sound) / 7,000ft, it's just too fast for economic cruise at those sorts of altitudes - so Boeing have probably just not bothered proving it's safe to do so. Typically it'll cruise much higher (say around 30,000ft) at around 0.8Mach, but a much lower airspeed (0.8Mach at 30,000ft equates to about 242 knots (279mph) true air speed, or 148 knots (170mph) indicated airspeed.

The relationship between true airspeed, indicated airspeed and Mach number changes with altitude, but most modern airliners are designed mostly to operate at a high altitude, high subsonic mach number, low indicated airspeed, but reasonably high true airspeed (and thus groundspeed). The only good reason to be as low as 7,000ft normally is climbing or descending from/to a runway; that's likely to be done at reasonably low airspeeds (almost certainly below 250 knots / 288mph).

G

[Mad (Flt) Scientist]

Originally Posted by chornedsnorkack

This is connected with the concept of Vmo.
Basically, the faster an aircraft flies, the larger the drag (at the same height). But the higher the aircraft flies, the lower the air density and therefore the less drag there is.
If an airplane tries to fly too fast, then the drag forces can break something. Therefore, aircraft are not allowed to fly faster than a certain speed, named Vmo. This speed increases with altitude, because at a higher altitude the air is less dense.
A 757 is not allowed to fly at 500 mph at 7000 ft altitude for Vmo reasons.
However, it seems they actually can. The Vmo is restricted with some safety margin, so a plane might exceed Vmo and get away with it.

Vmo isn't much to do with drag - it's mainly to do with lift. The drag is very unlikely to break anything meaningful - but the wings are definitely capable of creating more than enough lift to break at those speeds.

Now, you say, I'm flying at 1'g' so there's no more lift than at any other 1'g' condition, and this is true of course. But Vmo arises fundamentally from consideration of Vd - the design dive speed - and required margins between Vd and normal operations i.e. Vmo. And Vd will usually be determined either by manoeuvre loads or by flutter margins - both of which arise, in the most part, due to lift (wanted or unwanted)

Since a plane should remain structurally sound up to Vd, that's the speed above which you could be said to have "got away with it"; below that its pretty much a sure bet the plane stays in one piece. Whether the flying characteristics are acceptable between Vmo and Vd is a whole new question ...

[Mercenary Pilot]

SUPERMNNN

I’ll try to answer seriously but your questions are a little odd and seem to show even a basic lack of understanding in regards to modern aircraft operations and design? If the crew wanted to, a 757 could easily lose 1000 feet in less than 20 seconds whether it has 1 engine working or 2. On the other hand it doesn’t have to drift down on 1 engine at those altitudes so could maintain 7500' until it ran out of fuel.

Try doing some research on the Laudair 757 which had a reverser sleeve deploy in flight, it broke up and crashed. Im sure that investigation would give some of the answers you’re looking for.

[SUPERMNNN]

I’ll try to answer seriously but your questions are a little odd and seem to show even a basic lack of understanding in regards to modern aircraft operations and design? If the crew wanted to, a 757 could easily lose 1000 feet in less than 20 seconds whether it has 1 engine working or 2. On the other hand it doesn’t have to drift down on 1 engine at those altitudes so could maintain 7500' until it ran out of fuel.

Thank you. This is very helpful. What if one engine is totally gone (physicall), with less weight on one side, can 757 keep balance and maintain the altitude?

I am sorry to bore some of you. I don't pretend to understand morern aircraft operations and designs, simply and humbly I ask professionals for help. I am not supporting any theories, but try to think before believing. (If that's ok with whoever upset with my posting. I appologize for wasting some of your time by reading these.)

Try doing some research on the Laudair 757 which had a reverser sleeve deploy in flight, it broke up and crashed. Im sure that investigation would give some of the answers you’re looking for.

I will try to find Laudair 757 info. Thank you again for your professional info.

[Mercenary Pilot]

What if one engine is totally gone (physical), with less weight on one side, can 757 keep balance and maintain the altitude?

Yes. All Boeing jets are designed to withstand this type of damage and remain controllable. Also "Engine fire, severe damage or separation" (as the drill is known) is something airliner pilots train for often.

[john_tullamarine]

I've probably edited a bit more heavily than necessary so my apologies if appropriate.

It is not the role of mods to adjudicate on the value of topics per se .... rather to keep things on a reasonably even keel and generally cause the thread to follow the wishes of the site owners.

I think that the conspiracy things are best left to other sites .... while the techie bits certainly can remain here ...

[flyboyike]

Originally Posted by SUPERMNNN

I will try to find Laudair 757 info. Thank you again for your professional info.

Except that it was a 767.

[Mercenary Pilot]

Except that it was a 767.

Yes it was, my mistake.

[SUPERMNNN]

Originally Posted by john_tullamarine

I've probably edited a bit more heavily than necessary so my apologies if appropriate.

It is not the role of mods to adjudicate on the value of topics per se .... rather to keep things on a reasonably even keel and generally cause the thread to follow the wishes of the site owners.

I think that the conspiracy things are best left to other sites .... while the techie bits certainly can remain here ...

John:
Is it possible to have a copy of deleted original posts? Many replies are very helpful, especially the ones regarding the transponder and cel phone?

I would appreciate it if you could email them to me: [email protected]. Thank you.

(Is this normal for this site? Who are the site owners? )

[chornedsnorkack]

Originally Posted by Mad (Flt) Scientist

Vmo isn't much to do with drag - it's mainly to do with lift. The drag is very unlikely to break anything meaningful - but the wings are definitely capable of creating more than enough lift to break at those speeds.
Now, you say, I'm flying at 1'g' so there's no more lift than at any other 1'g' condition, and this is true of course. But Vmo arises fundamentally from consideration of Vd - the design dive speed - and required margins between Vd and normal operations i.e. Vmo. And Vd will usually be determined either by manoeuvre loads or by flutter margins - both of which arise, in the most part, due to lift (wanted or unwanted)
Since a plane should remain structurally sound up to Vd, that's the speed above which you could be said to have "got away with it"; below that its pretty much a sure bet the plane stays in one piece. Whether the flying characteristics are acceptable between Vmo and Vd is a whole new question ...

Or above Vd.

The 757 that rammed Pentagon is said to have flown at 530 mph. Definitely above Vmo (it is said to be 350 Kias, so about 390 or so mph). What is the Vd of a 350?

It then seems that a 757 that refrains from sharp maneuvers can easily fly faster than Vd, stay in one piece and undertake controlled maneuvers within a restricted envelope. At least, the plane that hit Pentagon reached the target... is it correct that it was structurally intact and in controlled flight at impact, so all wreckage ended up in ruins?

Now, what about the plane that crashed in Pennsylvania? Did it ram the ground intact leaving wreckage at one impact spot, or did it suffer damage before impact? The thread above is heavily edited, I think there was some description of wreckage...

[SUPERMNNN]

More simple minded questions:

1. Do you need to turn on the transponder before landing, especially if you were preparing an emergency landing to a small airport?

2. For a 757 to land, how long a runway does it need?

[Genghis the Engineer]

Originally Posted by SUPERMNNN

More simple minded questions:

1. Do you need to turn on the transponder before landing, especially if you were preparing an emergency landing to a small airport?

2. For a 757 to land, how long a runway does it need?

(1) The transponder is normally turned on throughout the flight, only the code is changed according to ATC requirements, or occasionally to signal an emergency. If you happen to forget, or it fails, the aeroplane flies just as well however.

(2) Depends upon weight, wind, surface conditions, slope, altitude, temperature.... The actual value is calculated for each landing, and can vary massively. If you want a very crude rule of thumb - it probably needs for an emergency landing about 2/3 of the length of the shortest runway that you can find operating the type.

G

[SUPERMNNN]

(1) The transponder is normally turned on throughout the flight, only the code is changed according to ATC requirements, or occasionally to signal an emergency. If you happen to forget, or it fails, the aeroplane flies just as well however.

Thanks G. Do you need the transponder for landing? I mean can you land without the transponder?

(2) Depends upon weight, wind, surface conditions, slope, altitude, temperature.... The actual value is calculated for each landing, and can vary massively. If you want a very crude rule of thumb - it probably needs for an emergency landing about 2/3 of the length of the shortest runway that you can find operating the type.

Could you look at this airport and help me to see if 757 can land here?
http://www.airnav.com/airport/2G9
I believe that you have to fly from N.E to S.W. (roughly) to land on the runway?

[Gary Lager]

1) No. Yes.

2) Looks a bit short to me (1500m?), for anything other than a very lightweight 757. Perhaps a current 757 driver could be more specific.

With any kind of control problem/asymmetric thrust configuration I would suggest that it would be nigh impossible to do so safely.


I almost hate to ask...why?

[chornedsnorkack]

The transponders, I believe, are only necessary for the ATC, and perhaps the TCAS systems of other airplanes, to be aware where the plane is. If it fails or is deliberately turned off, the plane would be a hazard for midair collisions, but fly, and land, normally.

Are the airfield navigation beacons active at all times, or only when the airfield ATC expects a landing plane?

The 757 landing distances can be found, e. g. in
http://www.boeing.com/commercial/air...ps/753sec3.pdf
pages 35-36.

[Tarq57]

Thanks G. Do you need the transponder for landing? I mean can you land without the transponder?

Yes. The TCAS won't function, I believe, and the ATC radar may not maintain aircraft identification (depending on the particular ATC system), but it's somewhat analagous to parking the car with the radio off. The aeroplane still flies, turns, lands.

Could you look at this airport and help me to see if 757 can land here?
http://www.airnav.com/airport/2G9
I believe that you have to fly from N.E to S.W. (roughly) to land on the runway?
Today 22:42

Not being a 757 pilot, not sure, but I think it could be done in an emergency. It would be tight.Real narrow too. And at max weight, probably not. If it did get in in one piece, the only way it would get out would likely be in parts on a truck. The bitumen probably isn't strong enough.