Bird Strike

[tommyeflight89]

I have a question to ask you guys.. it is kind of embarrasing :confused:
I was having a tutorial today taught by a Aero. Eng. Masters student. I'll spare the details, but she got into talking about the birdstrike incident over the Hudson River.. Flight 1549.
She explained that the A/C encountered a flock of birds which were injested into both engines... Fair enough.

She went on to say that, just like the were designed to do, both engines broke away from the pylons 'to make the A/C lighter so it could glider better'. She went on to draw two different sloped lines to represent the two glide paths and an explination was to why a lighter A/C glides better.
I asked for her to clear that up, and she further explained that all jet engines break away from the A/C after a serious bird strike so it can glider further since it has no thrust to use.
She says a problem with this is that if one engine takes a bird, it will break off and the other one wont, making the A/C 'unbalanced and not stable'.

Question: What was my TA smoking?.. Or am I supposed to believe this?

[JetPlaneFlyer]

I think they are designed to fall off due to excessive vibration to prevent damage to the airframe but i'm not sure if they did in this case. It's certainly nothing to do with improving the glide.
I heard they broke off on contact with the water anyway?

[timbash]

No, No No. One engine detached when the aircraft hit the water. The other remained attached. On a 70 ton aircraft I'm not sure shedding ~2 tons of engines would dramatically increase the glide ratio. The engines may fall off if on fire (I believe they have attachment bolts that will melt). But no the engines are not designed to be jettisoned to increase glide distance. Wouldn't it suck if you pressed the wrong button?

[kcaldwel]

Decreasing the weight would not help the L/D, but would maybe slightly reduce the stall speed. Sailplanes routinely carry 500 kg of water ballast to shift the best L/D speed higher, but there is no decrease in best L/D with the increased weight. I guess you might see some drag reduction which would help the L/D/ if they came off cleanly. Might be a CG shift though...

I did some work a long time ago on turbine bursts and such. I've never heard of engines that were intended to break loose. I also have photos of the plane coming out of the Hudson, and one engine is definitely still on the airplane then. I believe they were both on the airplane up to water contact, as timbash said. It wouldn't make any sense to have them purposely fall off.

Kevin

Edit: I think people living around airports would be very excited if they heard 2 ton engines were designed to fall off airplanes if they have a bird strike!

[tommyeflight89]

Thankyou for clearing that up guys. I was sure there is no way such a feature would be designed into a jet, but seeing as how she is doing a Masters and I'm a 2nd yr undergrad, I had to ask other people.
I looked into 1549 and also confirmed one engien was lost... because it got torn off when ditching.
I won't even get into what else this TA explained to the class...!

[nfhill]

I'm not a comercial airplane designer, but I've also heard many times that the engines are designed to 'break off' under some worst case situations. If I recall correctly, there was a very bad crash some time ago when an engine did depart that wasn't designed that way and it tore out so much of the wing that the plane went down. Better to lose an engine than the entire plane.

The engine pylons are designed so the engine will break away cleanly without destroying the systems inside the wing. This is 'planned' for when an engine failure results in severe imbalance and vibration. This could happen from a bird strike.

[HerkS]

I have to say that this brings to mind some blonde jokes.

[timbash]

With smarts like that sounds like she might go on to do a PhD

Thankyou for clearing that up guys. I was sure there is no way such a feature would be designed into a jet, but seeing as how she is doing a Masters and I'm a 2nd yr undergrad, I had to ask other people.
I looked into 1549 and also confirmed one engien was lost... because it got torn off when ditching.
I won't even get into what else this TA explained to the class...!

[SmoothCruizer]

from what my dad tells me, him being a retired marine and seeing and working on different types of jets is that he said the F/A 18C hornet the main jet engine is held on by only 2 pins. can you believe that? only 2 freaking steel pins are holding and keeping that motor centered in the engine bay. so i think she is right in that since, but ive never heard of a plane that could jettison a engine..... What really conserns me is that i seen a similar plane when i drove by on the New Jersey turnpike at Newark International and when i looked over I or me saw the left engine smoking while that plane was inline on the tarmac. Scary to think that the one they can't find or is in the water is the LEFT engine similar to that one that was smoking on that day, I can prove i was there in my logbook, (Truck Driver)

[Neil Stainton]

from what my dad tells me, him being a retired marine and seeing and working on different types of jets is that he said the F/A 18C hornet the main jet engine is held on by only 2 pins.

I guess the jet engine has at least 3 mounting points that take all the forces. Your dad was probably referring to two shear pins that when removed allow the engine to be replaced fast.

What really conserns me is that i seen a similar plane when i drove by on the New Jersey turnpike at Newark International and when i looked over I or me saw the left engine smoking while that plane was inline on the tarmac. Scary to think that the one they can't find or is in the water is the LEFT engine similar to that one that was smoking on that day, I can prove i was there in my logbook, (Truck Driver)

If you are concerned Google the relevant FAA body (or ask here) and contact them. If they think it is relevant they will take it further.

Neil.

[Montag DP]

Well, it would decrease the drag a little and lower the stall speed a little, but I doubt that's why it's designed that way.

[DT56]

With smarts like that sounds like she might go on to do a PhD


Or our new Climate Tsar! :rolleyes:

[ciurpita]

some more pictures (hopefully)

[dusty IV]

Egad! Don't push that button when flying over my house. Is the TA really a blond? She definitely has a long career in front of her, uh, with the FAA.

[theluckyone17]

Something else to keep in mind... I've heard that both engines were shut down after the bird strikes, in the case of the Hudson jet.

I've never heard of being able to feather the turbine itself, though. So if the engine's shut down, and you can't feather the turbine, it continues to spin due to the movement of the air, creating more drag. How much drag? I have no idea :D

[HugePanic]

i am pretty sure that you don't want an engine break away!!


1. if one engine breakes away, the COG is of center
2. tooooo much risk to loose a running engine (with more height, maybe the engines would have started later....who knows???)
3. tooo much weight
4. tooo complicated....


some of the most critical loading cases are vertical gust, hard landing and so on...
i cant imagine that a couple of hundert kilos could create any loads in that "aerea". (ok, birds make x-loads, gust make Z-loads...)

i saw the a318-a321 pylon a lot of times during FAL in hamburg. it looks very tought to me. there are only a bunch of well sized bolts...

[Brandano]

the pylons are extremely robust, however, they are dimensioned so that if an engine is off balance (if the fan has lost a few blades while it was spooled up, for example) and starts to shake itself off it will rip off the pylon before ripping off the wing. It can happen, but it's extremely rare and it has not happened in this case. Of course, losing an engine will alter the CG somewhat, but these are heavy planes with relatively light engines, and the engines are close or behind the longitudinal position of the CG, so the plane should remain stable. what makes a lot of difference is the difference in drag between the left and right wing, that would have to be compensated by careful use of the throttle on the remaining engine. Also, if an engine tears off it will probably cause multiple failures on electric and hydraulic systems, so these have to be designed as redundant circuits that are operated independently by both engines.

[graupman]

It has always been my understanding that the reason for putting engines on pylons is twofold -

1. Reduced risk of structural failure in the event of a severe engine fire. Better to keep the most likely place for a fire away from the wing root structure.

2. Ease of access and maintenance. Getting at parts of an engine buried in the wing or fuselage increases maintenance costs.

There are probably lots of other reasons, but this is what I remember. I think most can agree however that it's not to reduce weight when they fall off...

[Doc Hoehn]

Nevertheless I ask myself how that (blonde and longhaired?) engineer can tell stories like that! For shure there is no feature installed that makes the engines "fall off" the pylons or make them releasable after severe damage...
Like mentioned above, the risk of loosing the running engine (when released manually) would be too high. I see often enough pilots who shut down the remaining running engine in the simulator. Ok, it´s only when they´re led into overstressed situations, but anyway...
There are cases known where one of the three bolts was forgotten (!) after an engine was changed and the aircraft still flew a few hundred hours before it crashed due to engine seperation. So the bolts seem to be strong enough, hm?
To be honest, I don´t know about the CG change when you lose one or both (if two) engines. But when simulated, you don´t really feel a difference. Neither in an old style 737 nor in a 318-321. And most pilots luckily never ever felt the difference in idle power or no-engine glide path.
And even in a case where the engine is out and cannot be restarted, there is still a chance that it produces hydraulic and electric power when it´s windmilling. Depends on the checklist, I believe.
She really must have smoked some real hard stuff... Or she came from the future, like the cyborg in "Terminator 3". Wasn´t she blonde, too...? Nice imagination...
Alex

[ndb8fxe]

The engines on civilian aircraft are NOT designed to depart the aircraft. Could you imagine the damage it would cause on the ground. I doubt many airplanes could handle a CG shift that it would cause either.

[GordonTarling]

As a licenced aircraft engineer of many years, I can confirm that engines/pylons are NOT normally designed to detach in flight. However, the pylon IS attached to the wing with shear pins, which are designed to fail during a crash landing when the engine will normally depart up and over the top of the wing. Naturally, if the forces in flight are sufficient, then those pins will shear and the engine would fall away, but AFAIK this is not the original design intent. Aircraft and engines are designed to survive birdstrikes and an engine which has suffered a single birdstrike is normally expected to continue running and producing at least SOME power for a limited time. It'll be interesting to eventually discover just how many birds did hit Flight 1549's engines.

[ah.clem]

It's bad enough that students get stuck with high tuition and outrageous book costs - having a TA teach courses too "basic" for tenure-track faculty to bother with is insult to injury. Unfortunately, this kind of TA stupidity isn't rare at US colleges and universities. I know firsthand, much of my professional career has been spent at "major" US universities.

You are the customer. Demand better service or go elsewhere. You might start with the professor of record for the course, but he/she might not really care (they most likely appointed the TA - their student). The point is, it's your education - you need to find someone that cares. You might discuss this with the department chair, or the Associate Dean for teaching in your engineering college. Pretty much all of us who attended American colleges/universities as undergrads have TA horror stories, but didn't realize that we had the right to complain about it. Many faculty consider putting up with an idiot TA a "rite of passage" - bullsh*t.

Well, I've probably started a shitstorm for myself, but watching undergrad education suffer because a college is too cheap to hire decent clinical or adjunct faculty to cover the courses tenure-track faculty feel are beneath them while they work on their research is frustrating, and watching kids put down 10K - 30K a year (in some cases a semester!) at a state university thinking they're getting a quality education and then getting stuck with TAs is just, in my opinion, wrong.

/end rant

[gmohr]

Kevin nailed it. A lighter airplane doesn't glide better (higher L/D), but will acheive it's max L/D at a slower speed. Sailplanes carry water ballast to raise their max glide speed for wind penetration on windy days.

Nevermind the whole CG issue involved in breakaway engines (lol).

That story is 100% BS.

[nauga]

Nevermind the whole CG issue involved in breakaway engines (lol).

That story is 100% BS.Concur with everyone's assessment of weight and glide performance, but look at the 1992 El-Al 747 crash in Amsterdam if you think losing an engine will unconditionally put you out of the CG envelope. *Both* engines on the right wing departed the airplane and it remained flyable, for a time anyway.

Pylon-mounted engines are not designed to 'break off' in an emergency, but in many cases they are designed to separate *cleanly* if structural limits are exceeded. Put another way, if the engine/pylon is stressed to the point where it's going to break, make sure it breaks predictably and cleanly. It just doesn't always work out that way.

Nauga,
who has lost an engine but has not *lost* an engine

[vintage1]

It better to lose an entire engine than an entire wing...

Now theres a thought.

The Challenge.

To design a model that will, after the entire engine and nose is jettisoned, be able to glide in BACKWARDS and land safely as a canard.. :o ;) :D

[HugePanic]

gentlman, fix your engines..... ;)

http://farm4.static.flickr.com/3092/2762371261_99d67c778f_o.jpg

[Brandano]

It better to lose an entire engine than an entire wing...

Now theres a thought.

The Challenge.

To design a model that will, after the entire engine and nose is jettisoned, be able to glide in BACKWARDS and land safely as a canard.. :o ;) :D

Hmm, you have to jettison the vertical stab, or have a couple of larger folding ones pop out of the nose. Use tailerons on the horizontal stab and you don't even need to replicate the control surfaces. I'd make the nose into another flyable craft, though, could make a nice routine for a show.

[AndrewBurns]

I guess the jet engine has at least 3 mounting points that take all the forces. Your dad was probably referring to two shear pins that when removed allow the engine to be replaced fast.


Also I think you'll find the mounting system of almost all jet turbine engines quite interesting, as a method of dealing with thermal expansion. If you lock the engine down too tightly the mounting points will be stressed to crazy levels as it heats up so IIRC most turbojet/jet engine mounting systems use a minimal number of attachment points and are designed to accommodate some controlled movement.

[bwalt822]

Yeah your TA was on crack. The engines on commercial jet planes (even the GE 90) are held on by a few really big pins. Like others have said, the pins are designed to fail if the engine rotor becomes unbalanced. A bird strike SHOULD not cause the engine to become unbalanced. The engine will usually pivot up and over the wing hopefully not doing much damage on the way but dont tell that to the people onboard the DC-10 that crashed in Chicago a few decades ago after its engine came off on takeoff.

[harveyweewax]

Yeah your TA was on crack. The engines on commercial jet planes (even the GE 90) are held on by a few really big pins. Like others have said, the pins are designed to fail if the engine rotor becomes unbalanced. A bird strike SHOULD not cause the engine to become unbalanced. The engine will usually pivot up and over the wing hopefully not doing much damage on the way but dont tell that to the people onboard the DC-10 that crashed in Chicago a few decades ago after its engine came off on takeoff.

As I recall, that crash was caused by caused by the maintenance crews using an improper procedure when removing the engine and pylon. Apparently, the maintenance crews would remove the engine and pylon in one piece instead of first removing engine and then the pylon, as per MDs instructions. The mechanics procedure was faster but it would damage the mounting points. It just goes to show that any "safe" design can be undone by impatience and stupidity.

Regards,

Sven

[bwalt822]

As I recall, that crash was caused by caused by the maintenance crews using an improper procedure when removing the engine and pylon. Apparently, the maintenance crews would remove the engine and pylon in one piece instead of first removing engine and then the pylon, as per MDs instructions. The mechanics procedure was faster but it would damage the mounting points. It just goes to show that any "safe" design can be undone by impatience and stupidity.

Regards,

Sven

Yes, it was the maintenance procedure that caused the engine to come off but when it did come off it disabled the slat hydraulics which caused that side to retract. When the pilots slowed down like their manual said to do, one wing stalled and the plane crashed. If the manual said to keep speed up or if the co pilot (who was flying) had a stick shaker then it is very likely that they would have avoided the stall and landed the plane.

I think the NTSB recommended to the FAA that speed is kept higher when an engine departs the aircraft im not sure if they adopted it though.

[Falsifly]

As both a pilot and an airframe and powerplant technician who has worked for Boeing, Cessna and Frontier Airlines, I find this thread most amusing. Certainly not in respect of the devastating results of an aircraft accident but in the respect of many of the ideas and opinions stated.

“Engines designed to break away” What?

“Attachment bolts that melt” Melt?

“The engine pylons are designed so the engine will break away cleanly without destroying the systems inside the wing. This is 'planned' for when an engine failure results in severe imbalance and vibration.” Are you kidding?

“Shear pins.” Indeed!

“Of course, losing an engine will alter the CG somewhat, but these are heavy planes with relatively light engines, and the engines are close or behind the longitudinal position of the CG, so the plane should remain stable.” WOW!

“When the pilots slowed down like their manual said to do, one wing stalled and the plane crashed. If the manual said to keep speed up or if the co pilot (who was flying) had a stick shaker then it is very likely that they would have avoided the stall and landed the plane.” Absolutely amazing!

Please do not infer that I am poking fun at anyone, but some of these statements couldn’t be further from the truth.

[bwalt822]

“When the pilots slowed down like their manual said to do, one wing stalled and the plane crashed. If the manual said to keep speed up or if the co pilot (who was flying) had a stick shaker then it is very likely that they would have avoided the stall and landed the plane.” Absolutely amazing!

Please tell me what is further from the truth about this statement or did you not read that I was talking about a DC-10 crash in Chicago? The only mistake that I possibly said was that the co pilot did not have a stick shaker when the stick shakers may have been powered by the engine that came off, but whatever the case, whoever was flying did not have a working stick shaker.


Also what is incorrect about this assuming the word cleanly is a relative term:

“The engine pylons are designed so the engine will break away cleanly without destroying the systems inside the wing. This is 'planned' for when an engine failure results in severe imbalance and vibration.” Are you kidding?

[JetPlaneFlyer]

Falsifly,
If these statements "could not be further from the truth" then please give your explanation for the use of 'Fuse Pins' an the key wing/pylon joints of the 747 as shown in the attached diagram taken from the aircraft's manual.

These fuse pins are designed to allow engine seperation under extreme load. Do a google on 'fuse pin'.

Steve

[Brandano]

Btw, found the wikipedia page about the DC10 accident, which has some in depth detail about the maintenance issues: http://en.wikipedia.org/wiki/American_Airlines_Flight_191
Apparently flight 191 is a bit of an unlucky flight, since another flight with the same number crashed on landing because of windshear

[Falsifly]

Bwalt82,
“When the pilots slowed down like their manual said to do, one wing stalled and the plane crashed”

Let me begin here: According to the NTSB investigation of AA flight 191, a McConnell Douglas DC 10-10 which crashed CHI 5/25/79: “The engine and pylon assy. detached from the A/C at or just after the A/C had accelerated to V1.”

Upon reaching an airspeed of V1 the flight crew is committed to takeoff and to accelerate to V2 until reaching 800 feet AGL (above ground level) or an Obstacle Clearance Altitude, which would be dictated by the departure procedure for runway 32R. (I think that was the runway in use) If an engine Failure or power loss occurs at this time, the crew is to maintain standard takeoff thrust or go to maximum takeoff thrust if deemed necessary. (Pilots call) This power setting is again to be maintained to 800 AGL or OCA. The AGL of flight 191, according to the NTSB, reached an altitude of approximately 325 feet; far from the minimum altitude at which the A/C takeoff configuration can be changed, as per AA takeoff procedure at that time. In an A/C of that type, at that altitude, and at that airspeed, the last thing the crew would do is reduce power and airspeed.

Now for this: “The engine pylons are designed so the engine will break away cleanly without destroying the systems inside the wing. This is 'planned' for when an engine failure results in severe imbalance and vibration.”

Transport category airplanes are manufactured in accordance with Federal Aviation Regulations. (FARs) In this case FAR part 25-Airworthiness Standards: Transport Category Airplanes. If we go to FAR part 25.303 you will find this: [Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure. When a loading condition is prescribed in terms of ultimate loads, a factor of safety need not be applied unless otherwise specified].

Now, if we go to FAR part 33- Airworthiness Standards: Aircraft Engines, and then go to part 33.23- Engine Mounting Attachments and Structures we find this: (a) The maximum allowable limit and ultimate loads for engine mounting attachments and related engine structure must be specified.
(b) The engine mounting attachments and related engine structure must be able to withstand--
(1) The specified limit loads without permanent deformation; and
(2) The specified ultimate loads without failure, but may exhibit permanent deformation.]

Nowhere will you find in the FARs that any part necessary for the safe operation of an A/C, be required, through a structurally designed load limit, or by any other means, to detach from an airframe. The only reason an A/C engine would depart from the airframe is because of a fault in design, material, maintenance, or imposing loads exceeding the design limits. (Well, there may be other reasons but I think this covers my point)

JetPlaneFlyer,
'fuse pin'.

I can see were the use of the term ‘fuse’ can be misleading if you research the definition of the word comparing it to electrical circuits and such. The proper use in respect to this discussion is: (To become blended or joined by.) These fuse pins are designed as an assembly attachment point fastener to facilitate easy and quick installation and removal of an assembly i.e. pylon, engine etc. They too are subject to Airworthiness Standards, in this case FAR part 21- Certification Procedures For Products and Parts.

Yes, there is even an Airworthiness Standard for bird strikes.

[bwalt822]

Try again falsifly, the NTSB report says that the pilots were above V2 and their manual said something like, maintain V2. So the pilots slowed back down to V2. The manual was updated after the crash to say maintain v2+10 or 15.

http://libraryonline.erau.edu/online-full-text/ntsb/aircraft%20accident-reports/AAR79-17.pdf

The relevant stuff is from pages 48-58 (of the pdf, not the actual document). The co-pilot was flying and he did slow the plane towards V2 using the elevator when it stalled.

Its not an FAR for the engines to detach from the airframe but that doesn't mean it isn't designed in or against FARs.

What happens when the engine exceeds its maximum specified ultimate loads including any safety factors? It can break off right. Now do you want the engine to break off cleanly or do you want it to take the outboard wing with it. The pins are designed to break before the rest of the wing breaks. Otherwise the design loads on the wing would be ridiculously high which would mean really heavy wings.

Aircraft manufactures could certify a plane that has engines designed to stay on at all times but it would require a much beefier structure since the wing would have to be designed for higher loads.

[JetPlaneFlyer]

JetPlaneFlyer,
'fuse pin'.

I can see were the use of the term ‘fuse’ can be misleading if you research the definition of the word comparing it to electrical circuits and such. The proper use in respect to this discussion is: (To become blended or joined by.) These fuse pins are designed as an assembly attachment point fastener to facilitate easy and quick installation and removal of an assembly i.e. pylon, engine etc. They too are subject to Airworthiness Standards, in this case FAR part 21- Certification Procedures For Products and Parts.

Yes, there is even an Airworthiness Standard for bird strikes.

Not according to the Japenese Science and Technology Agency (http://shippai.jst.go.jp/en/Detail?fn=0&id=CB1071013&) : quote " Pylon fuse pin (Pylon is the structural component connecting the jet engine to the main wing. The role of the fuse pin is to allow the engine to separate from the wing under the strong impact load that occurs in the event of a crash or hard landing in order to protect the fuselage from engine fire.)"

Wikipedia tells the same story: http://en.wikipedia.org/wiki/El_Al_Flight_1862
As does the new york Times: http://query.nytimes.com/gst/fullpage.html?res=9E0CE1DC1138F932A25753C1A9649582 60

Such loadings would clearly be outside the maximum design loads and therefore outside the FAR regulations.

[JetPlaneFlyer]

Falsifly,
You may argue that the links I provided in my previous post are not adequately authoritative sources?

How about the National Aerospace Laboratory of the Netherlands in a paper on the El Al 747 crash as Schiphol in 1992 when two engines separated: Link to paper (http://www.nlr.nl/id~4823/lang~en.pdf)

Here is a quote from the paper: The design incorporates six "fuse pins" which are less strong than other parts of the connections. If extreme loads occur on an engine and pylon, for example during extreme turbulence or an emergency landing, the fuse pins are supposed to shear off and allow a clean separation from the wing, thereby precluding damage to the wing and possible rupture of the wing fuel tank

Do you still think the previous statements you referred to "could not be further from the truth"?

It would obviously be ridiculous to actually design the engines to fall off, and thats not the case here. I'd be pretty confident that the engines are designed to withstand all design loads and safety margins just like the rest of the airframe and in accordance with regulations.. However if these design loads are exceeded such as in an emergency (crash) landing or as result of catastrophic engine failure then the fuse pins are designed to fail before the rest of the structure providing a 'safe' failure mode.

Steve

[bwalt822]

It always bothers me when people say wikipedia isnt a valid source because anyone can edit it. They fail to see the references at the bottom. Unless you are looking at the article on evolution or some other heated topic wikipedia is right 99% of the time.

I would never cite it in a technical paper but for internet arguements it is pretty valid.

[Brandano]

Eh, to paraphrase bash.org, "I have it on authoritative sources that Encyclopedia Britannica is edited by baboons" :)

[Brandano]

I apologize for resurrecting a dead thread, I just wanted to integrate with another real life event that I happened to stumble upon: http://aviation-safety.net/database/record.php?id=20041020-0

[Flight Engineer]

Falsifly: WRONG.

You're not looking at the correct regulation I'm sorry to say.
Emergency Landing Conditions
CS 25.561 General
(See AMC 25.561.)
(a) The aeroplane, although it may be damaged
in emergency landing conditions on land or water,
must be designed as prescribed in this paragraph to
protect each occupant under those conditions.
(b) The structure must be designed to give each
occupant every reasonable chance of escaping serious
injury in a minor crash landing when –
(1) Proper use is made of seats, belts, and
all other safety design provisions;
(2) The wheels are retracted (where
applicable); and
(3) The occupant experiences the
following ultimate inertia forces acting separately
relative to the surrounding structure:
(i) Upward, 3·0g
(ii) Forward, 9·0g
(iii) Sideward, 3·0g on the airframe
and 4·0g on the seats and their attachments
(iv) Downward, 6·0g
(v) Rearward, 1·5g (See AMC
25.561 (b) (3).)
(c) For equipment, cargo in the passenger
compartments and any other large masses, the
following apply:
(1) These items must be positioned so that
if they break loose they will be unlikely to:
(i) Cause direct injury to
occupants;
(ii) Penetrate fuel tanks or lines or
cause fire or explosion hazard by damage to
adjacent systems; or
(iii) Nullify any of the escape
facilities provided for use after an
emergency landing.
(2) When such positioning is not practical
(e.g. fuselage mounted engines or auxiliary power
units) each such item of mass must be restrained
under all loads up to those specified in subparagraph
(b)(3) of this paragraph. The local
attachments for these items should be designed to
withstand 1·33 times the specified loads if these
items are subject to severe wear and tear through
frequent removal (e.g. quick change interior


Boeing philosophy is for the engines to detach so they don't break anything. Airbus makes the pylons strong enough so the engine stay attached but don't break anything.