Missile attack on Boeing 757: What would have happened if it hit?

Factual Questions
21

Ah to be old an cynical :slight_smile:

Although rare, engine failures occur fairly regularly worldwide(large numbers of hours are flown yearly by commercial aircraft) and the vast majority of them are handled without incident. Remember the ones handled without incident are generally not reported by the media.

Don’t get confused by small twin piston engine aircraft that have far smaller performance margins and generally less experienced crew.

There is no doubt that no extraordinary skill is necessary to handle a typical engine failure in flight. It just requires crew cooperation and adherance to procedures.

Of course an engine failure caused by a missile strike would not be typical and there will probably be controllability problems caused by structural/hydraulic/electrical failures.

22

Here is a link to the SA-7 Strella

the older version of the SA-7b Strella M2
http://www.brushfirewars.com/weapons/sa_7_grail/sa_7_grail.htm
Had a poor showing in the Yom Kippur wars.

23

Um, no.

You definitely have not “survived this sort of thing.” Meaning, of course, that you were not sitting in a commercial airliner when a shoulder-fired missile slammed into its engine or fuselage, and sent parts exploding in all directions.

I’m sure you’re a very competent small-craft pilot. But experienced in combat aeronautics? I’m guessing no.

24

Well, “this sort of thing” meaning having an engine out and bits and pieces flying around, Broomstick has survived it. I don’t think she (?) was trying to say she’s survived a missile attack eh? Just saying that if the missile attack resulted in engine failure with minimal structural damage then it should be surviveable. I think it’s pretty obvious that if the missile caused significant structural damage then survival chances would be low.

Oh, and your statement about depending on two functional engines at takeoff is wrong. Two functional engines is highly desireable but takeoff can occur with just the one.

25

Yes, Skogcat, you understand me. tsunamisurfer, the point was not that I’ve survived a missile attack, but that a catastrophic loss of engine on take-off is not necessarially fatal. Rather than wait to be asked for a “cite” I volunteered the source of my knowledge up front. And do go back and re-read where I state that a missile is going to do a lot more damage than the birdstrike we went through.

Just for the record - the Cessna Skymaster, a small twin engine airplane, is capable of taking off on the rear engine alone. This is not usually done, because the rate of climb is very slow, but it is certainly possible. Can’t do it on the front engine alone, though - which brings up the matter of “critical engine”. In most twins, a power loss in one particular engine is more of a problem than the in the other. In the SkyMaster, for instance, a rear engine failure is more serious than a front engine. Other twins, it’s one side or the other being more of a problem. The concept does extend to planes with more than two engines, although losing 1/3 or 1/4 of your total engine power is not quite the same as losing 1/2. Does it take extraordinary skill to handle? No - but it does take prompt action. Low and slow, a wrong guess, or a delayed one, can kill you.

The AirCam, used by National Geographic for photography, is also capable of single-engine operations, including take-off.

There are probably other small twins with the capability, those are just the two I know for sure about. It’s a matter of designing the capability into the airplane, not so much a limitation of physics. Passenger airliners are designed to fly with a loss of engine(s), it’s that simple. Now, whether they can continue to fly with engine loss AND greater damage is another question.

In theory, take-off in a mutli-engine airplane is to be done a speed such that, if an engine was lost on take-off, the airplane would still be controllable. That speed is even marked on the airspeed indicator and is called Vmc or sometimes “blue line speed”. In practice, this doesn’t always happen the way it should. It does require immediate reaction, and you have to get it right the first time. And yes, given the forces operating at take-off, “stomping” on a rudder pedal might be required. From the pilot’s viewpoint, it’s easier to control an airplane with no operating engines than a plane with a “critical engine” not working.

This part of multi-engine flight is common knowledge among pilots, even those of us who don’t fly more than one engine at a time, and has nothing to do with “combat aeronautics”, whatever that is. What makes you think a commercial airline pilot has any notion of combat flight anyhow? Most of 'em these days have never been in the military, and of those that have, most of them never flew combat planes but rather cargo and transport.

26

Very informative. I find this curious:

I would have assumed power and control symmetry for the 757. Can you give a Readers Digest version of why this is? Direction of rotation of the fan blades is all my non-flyer mind can come up with.

27

Just about everything in a commercial airliner is on a redundant system, hydraulics, electric, control systems, etc. They design these things to stay in the air under some pretty hellacious circumstances, hundreds of people lives can depend on it. IIRC the engine housings are designed to contain an engine fragging itself and even if the engine housing comes apart the wings are built to survive having a couple compressor blades rip through them and keep flying.

Serious, yes, fatal…I am still far from convinced. For comparison an AIM-9S Sidewinder carries 10.15kg of explosives, an AIM-120 AMRAAM carries 22kg of explosives.

I just don’t see this lil bugger as having the oomph to drop an airliner with one shot unless it got really lucky.

28

here

I stand corrected by my own research

(bow humbly to broomstick and slink out)

29

This link has been posted a hundred times on SDMB already but it’s such a great story it bears re-posting (if you haven’t read the story do so…very interesting). Anyway, I re-mention the Gimli Glider here because it shows that large commercial planes can glide to a ‘safe’ landing. In this case the plane is a 767 but hopefully close enough for our purposes.

[sub] NOTE: The plane in question suffered no physical damage leading to its having to glide…this only shows that commercial craft can glide.[/sub]

30

Why is this so? Aside from costing money that airlines are loathe to spend is there a technical reason for this not beiong possible? How much would it cost to outfit (say) 500 aircraft of a large carrier with such devices? Would it be considerably more expensive than a single plane getting shot down (not even including the follow-on lawsuits)?

31

Well, drachillix, the first cite from that site (brushfirewars) had some bum info.

They look for the shadow in the background UV radiation that the object causes, and there were versions without UV seeker capability that had all aspect capability, not just tailchasing. That website does not seem to be the definitive source for info.

32

I’ll give it a shot - I’m sure if I get any details wrong someone will be along to correct me shortly.

While the rotation of fan blades does have some effect, it is not the primary one

In a configuration typical of most airliners and multi-engine airplanes, when you have an engine (or two) on each wing, assuming the engines are all producing equal thrust the airplane is being pushed along in a stable manner. The axis of the thrust is lined up with an axis of the airplane and the axis of travel. Very nice and neat. Now, if the right engine quits (for example) that wing isn’t being pushed along anymore, but the left one is still going forward at the same speed. Only problem is, it’s still attached to the right wing, which is going slower (not being pushed and all). The right wing lags, the left goes forward, but, being achored to the slower wing, the airplane veers right. This is called “asymmetrical thrust”, To correct usually requires application of rudder, lots of it, to counteract the right-turning tendency. Reverse left and right in the above for the sceanario with a left engine failure.

(A very somewhat sort-of analogous thing would be a tire going flat in a car – it causes more drag on that side, and the car wants to veer towards the flat.)

Now, one engine or the other will be the “critical engine”. What that means, basically, is that if the critical engine quits it will be more difficult to control the airplane than if the non-critical engine quit. And this is where the direction of fanblade rotation (or propellor rotation), and the airflow over the airplane, and a bunch of other factors come into play. Design can compensate somewhat for this (for instance, the closer the engines are to the centerline of the plane the less assymetrical the thurst will be with an engine not functioning), but not eliminate the problem completely.

With something like a Cessna Skymaster, which is called “centerline thrust” because both engines align with the longitudinal axis of the airplane, the problem is slightly different. No matter how many engines are working or not working, the thrust generated is always symmetrical. But, the front of the airplane is a different environment than the rear. Airflow over the fuselage has an effect, for one thing. Also, the stronger the airflow over the tail, the more effective the rudder and elevator are. In a Skymaster, the rear engine thrust is very close to the tail, but if that engine quits you have only the front engine… and there will be a noticable loss of effectiveness in the rudder and elevators. Not fatal or unmanagable - but noticable. If I recall, there are some business jets that use centerline thrust and don’t have a tail assembly behind the rear engine (probably because the exhaust would melt it). I presume they, too, would have some issues with single-engine operations, but that’s not an area I have any expertise in at all, so I won’t comment on those.

Now, a word or two about slow speeds and airplanes. Airplanes are like sharks - they have to keep moving or die. It’s the air going over the wing that generates the lift that holds you up, and you need that air going at a certain minimum speed to generate the minimum lift required to hold you up. (When no engines are running, you need maintain that forward speed, too, and you do so by a controlled descent. Gravity provides the motive power in that case, the trick is to release the potential energy slowly) With engines operating normally, you can generate more than the minimum, which is how you go up.

Now, the control surfaces - ailerons, rudder, elevator, etc - are mostly airfoils themselves, or modify the shape of the airfoil they’re attached to. So they, too, require a certain minimum airspeed in order to work.

So here’s the hitch. At cruising speed you have LOTS of air going over all those surfaces and everything works very nicely and easily. But when you slow down, you have less air and less lift, so nothing is quite as effective as before. If you want to turn left, for instance, it will require more input into the controls than if you were in cruising flight. Again, in normal flight this is not going to turn into a problem - it’s like the difference in handling between your car in first gear and in fourth.

However, if you get so slow that you’re right on the edge of having enough lift to keep you up, all the controls are going to be on the edge of effective/not effective. It’s somewhat like driving a car on an icy road (airplanes also have the added feature that, in addition to the sloppy feeling in the steering, most of them also tend to vibrate and shake at this point, too. This is good - it helps get the pilot’s attention.)

OK, back to normal take-off. At take-off, the name of the game is to get away from the ground. Why? because if an engine quits, the only way to save your butt is to trade altitude for the airspeed you need to keep the controls effective so you land instead of splat. And to do that, you need altitude. The more the better. What’s altitude? It’s how far away from the ground you are. So you divert most of the engine power to the UP force and less to the FORWARD force. And works just fine – unless your engines quit. Then you’ll have much much less UP and FORWARD. If the UP and FORWARD runs out before you can reconfigure the airplane for a glide, it can hurt really really bad (but, on the bright side, only for a moment…) In take-off configuration, you don’t have much extra airspeed. Which is why you MUST react quickly.

(Contrast this to landing, where you’re using minimal engine power. In fact, the ideal on landing is to have the engines at idle, so you’re essentially gliding in. If the engine quits you’re already in glide mode, which makes the situation less critical at least in regards to airspeed.)

Tired yet? Don’t worry, I’m almost done.

OK, back to our assymetrical thrust sceanario (that means, at least one engine has quit). Alright, we’re taking off - going up - but we’re still low, and we’re relatively slow. Suddenly, half the UP and FORWARD disappears. The plane yanks itself to one side. (Think “blow out of tire on freeway with engine sputtering and coughing”) You have to, above all else, make sure you maintain enough FORWARD to keep your airspeed high enough to generate enough lift to keep you in the air and under control. The only way to do that is to divert some of the UP force to forward - which means you can’t climb very much, if at all. Whatever altitude you’re at — that’s where you’re most likely going to stay, or lower. Meanwhile, because the remaining engine wants to pull to one side, what thrust you do have left is not being used efficiently - that thrust pushing you to one side of directly forward is being wasted from your viewpoint. AND you have to put in a lot of rudder, which increases the drag slightly (normally not a problem, but you’re on the edge here), which further decreases efficiency. If you were way high up, you could lose a couple hundred feet - or even a couple of thousand feet - of altitude in order to make sure everything was set up proper and in control before refining the airspeed for maximum efficiency, and the trade would be a bargain. But close to the ground you have no altitude to trade.

Start to get the idea? A pro can make it look easy, but it does take some skill. And lower you are, the more difficult it is.

In fact, the minimum controllable airspeed (that’s just what it is - the minimum speed at which the airplane can still continue in flight) for a multi-engine airplane with just one engine is significantly higher than the airspeed for two engines. Because assymetrical thrust is so much less efficient.

Thus, standard procedure is to maintain the airspeed at or above “one-engine” speed at all times.

And any damage to the airplane will increase that minimum controllable airspeed. In order to land a heavily damaged airplane the pilot must fly it to the field at a higher than normal speed. If the damage is too great, the drag will be too much, the lift too little… and the consequences severe.

Thus, we return to the reply to the OP that’s been stated several times - survival depends on what damage, other than a destroyed engine, also occurs.

33

Extremely thorough! I hope that wasn’t all for me, I am an engineer, and learnt Bernoulli real good in fluid dynamics and growing up sailing.

So, on a 757 the reason one engine failing is a worse scenario than the other engine failing has to do with the torque imparted on the wing/aircraft by the remaining engine, and whether that exacerbates or compensates for the yaw and roll caused by the drag and assymetrical thrust problems? (If I’m off base, just say so, no need to explain). If so, would (hypothetically) having the fanblades/propellors turning in opposite directions on either wing eliminate that difference? The physics here is complex.

This link looks great for some math behind what you said above. I see what you mean by the plane being OK if one engine is lost at any time during takeoff of flight without further control surface damage.

34

Which was the cabin-class twin Cessna made which would crash if it lost an engine? 411?

Anyway, this was a low-water mark in the history of light twins - the rudder was not large enough to compensate for the yaw induced by engine failure - the company (which was getting its butt sued) set up a demonstration in which a test pilot would deliberately shut down an engine for the cameras. This was an expert pilot who knew exactly when the engine would quit (‘cause he was killing it). He didn’t do too well - the film became a smash hit with the plaintiffs’ lawyers.

Now for the good part - these planes (if any survive) are dirt cheap, have high-maintenance geared engines (big bucks to keep airworthy), and are therefor attractive to air taxi and flight schools.

35

With all due respect, I think you’re missing the point–or at least my point. I would contend that a direct missile strike to a 757 engine WOULD INDEED likely cause “significant structural damage.” In other words, significant explosive damage.

IANAAE, but combining the kinetic energy imparted from the warhead’s velocity on impact plus the warhead’s explosive power plus the angular momentum of the spinning blades within the engine plus whatever collateral damage occurs leads me to think that a missile warhead, even from a crude SAM, is likely to cause waaaay more damage than a bird.

I’d also imagine that a direct strike (and the presumed blown open engine and damaged wing) would have some appreciable effect on lift, yaw, pitch–the whole works–right when the airliner is at its most vulnerable.

BTW, I will again contend that aviation fuel is highly flammable. Remember the inferno trailing behind the ill-fated Concorde’s wing? Wasn’t that tragedy presumably triggered by one shard of metal being (relatively slowly) flung into either one of the airliner’s engines, or through a wing-mounted fuel tank? Imagine hundreds of such fragments being accelerated through a 757 engine/wing/fuselage at exponentially higher velocity.

As for two engines being unnecessary, I trust your expertise. But then I’m sure your scenario doesn’t presuppose a missile attack. We’re not talking about a textbook situation of an engine cleanly depowering and shutting down.

36

The problem here is that the point you are arguing is not the point being argued by Broomstick or I. We have accepted that the attack would likely cause significant structural damage and would not be surviveable.

So I guess the point is that losing an engine per se is not going to be a huge problem as that is designed to be controlable in all multi engine aircraft, at all stages of flight including takeoff, more so in large passenger aircraft The problem is going to come from what ever other damage the missile might do, or more realistically the combination of losing an engine plus having some structural failures.

Broomstick

Correct me if I’m wrong but I think that the critical engine is far more critical in a prop aircraft because the down going blades produce more thrust and so the thrust vector is offset to the side of the prop disc. Thus one engine will have the thrust line closer to the fuselage and the other will be further outboard. The engine with the thrust line close to the fuselage is the critical engine as losing that one will give more assymetric problems. Jet aircraft wouldn’t be susceptible to this as the thrust comes straight from the exhaust nozzles.

37

Please mentally insert or remove punctuation and amend spelling as required. :slight_smile:

38

Nope. I assume other folks are reading, too, even if they aren’t speaking up.

Yes, complex physics, which is why I avoid using numbers and formulas - they aren’t my strong point. I do know many (but not all) twin prop planes have counter-rotating props, but jets are not my area of expertise. It wouldn’t surprise me if they had counter-rotating fanblades, but I don’t have any real knowledge of that. My take on flight comes from the standpoint of what I have to do to make things work, not from books and theories.

Wolfgang Langwische (whose last name I’m sure I’ve misspelled again) explained it quite well in his Stick and Rudder. If you ask an engineer how to fly an airplane with maximum efficiency he’ll say “Simple!” and in the book there appears a quite impressive set of equations. If you ask a pilot the same question he’ll say “fly it at best glide airspeed” or, if you press for more precision, “the airspeed that gives you the lowest rate of descent with no power at all”. Which is just a fancy way of saying “best glide”. One is a very precise, very exact figure. The other you can arrive at quickly while you’re actually in the air and maybe don’t have the time in which to make very precise and exact calculations. Both approaches have their uses, but I incline more towards the latter for my own needs.

Yes, but we should probably acknowledge tsunamisurfer’s point that a missle is going to do more than just trash the engine. Speaking of which…

Well, that is the point of developing such a weapon. So… how likely is a “direct hit”? Is a non-direct hit possible? Is it possible for the missle to fire, aim, and strike yet the warhead not detonate? Another factor might be just how heavily loaded the airplane is (the more weight, the more critical things are on take-off) and just how steeply the airplane is climbing out.

Yeah. Sure gave me the heebie-jeebies. No one is disputing that jet fuel will burn or explode - if it wasn’t flammable, it wouldn’t be fuel. It’s just that jet fuel is not as flammable as gasoline. If you get hot shards of metal and debris puncturing fuel tanks, there’s going to be a fire (on the Concorde, it was the puncturing of the fuel tanks that directly caused the explosion - not the damage to the engines). But a trail of fire off a wing is not the same as an explosion that causes further damage. Certainly it increases the posibility, and is cause for tremendous concern, but an airplane on fire does not always explode. A cut fuel line may simply burn until all available fuel is exhausted. Or, it may actually set the structure of the wing on fire, in which case death comes from a lack of lifting surface and control, but that’s not an explosion. As UncleBill has pointed out, the physics can be quite complex.

True enough - but in real life, engines do not always cleanly shut down either. Sometimes, they tear themselves apart. At which point it becomes a question of whether the flying debris hit anything vital. Airplanes can sustain a great deal of damage and keep flying, so long as nothing vital is hit. Think of the airliner that took off from Hawaii and lost a big chunk of fuselage (and an airline attendant and a couple passengers), yet landed with no further injuries. In the Sioux City Iowa crash they lost ALL hydraulics, which meant they couldn’t move the control surfaces any longer, which would be a lot like having the steering wheel in your car fall off while driving, yet 2/3 of the people on board survived the landing.

Granted, even if the airplane did survive a missle attack, you’d likely still have casualties on board from the explosion and debris hitting passengers. A couple years ago the engine on a jet blew while the plane was still on the ground, the housing didn’t contain the debris, which shot through the cabin and killed two people.

Is it likely a jet would survive a missle attack? No, I don’t think so. But it’s not impossible, either. If I wasn’t an optimist I probably wouldn’t fly at all, which probably accounts for my feeling that it’s not certainly death, just highly likely death

As I said, jets are not my area of expertise. Your statement is logical, but as UncleBill has mentioned, there are those high-speed fanblades in the jet engines. I don’t know how much of an effect they have. What you’re describing - the differential in thrust between prop blades - is called “p-factor” and would be absent in jets. I would therefore presume there is less of an off-set in a jet, but that torque from the spinning engine parts might still be a factor. But don’t hold me to any of that - I don’t fly jets and have only very sketchy info on their characteristics in regards to engine operations.

This sort of discussion always reminds me of my old flight instructor’s story about his multi-engine checkride to get his rating. Seems they had gone through the required engine shut-down and procedures, but could not restart the engine. So there he is, sweating bullets with the examiner beside him, and he asks “Have I flunked?”

The examiner said “Not yet?”

“Not yet? What do you mean?”

“I mean if you can land this thing with just the one engine and we walk away… then you pass”.

No pressure, right? :wink:

39

Just thought I’d drop in with an update.

We now how empirical real-world data on missle attacks on jet airplanes in Baghdad: Cite

Relevant quote:

The verdict - SAMs and RPGs seem to be much more effective used against helicoptors than large airplanes.