Let me pose a general fud-4-thot question. 6

[WKTaylor]

OK Guys...

Let me pose a general fud-4-thot [I loved "the Farside"] question.

Note. This thread has the intent of raising the hairs on Your neck... and stimulating discussion. Hopefully it will also raise general awareness as to how amazingly vulnerable airframe structures are to a variety of damaging factors. Relatively new engineers... or those not involved with mishap investigations and damage repairs [depot liaison, field support, etc]... will gain some insights from those of us "gray-hairs" who have "been-there, seen-that, done-that...

For all airframe structures only... NOT including engines, landing gear, instruments/electronics, mechanical/electrical/environmental systems, etc [maybe we'll try this same question for each of these later]...

Identify obvious, and NOT-so-obvious mechanisms, for structural damage.

Sub points to carefully consider:

There ARE substantial differences regarding the aircraft Type, IE: para-sails; Ultra-lights; GA; Commuters/corporate; Medium and heavy transports; Cargo; Military [USAF, USN, USCG, USA, IE: Trainers, Fighters, Bombers, Helos, etc]; Light helos; Heavy helos; LTAs, etc...

There are substantial differences regarding the aircraft construction Type, IE: all fabric; Tube-fabric; Wood; Sheet metal; Machined-metal; Composites-metal mixes; all composite; etc...

There are differences regarding Mission type, IE: training, commuting, airlines, cargo, tactical, etc...

I'll lead the parade…

Examples of damage mechanisms.

Some environmental factors. Ice/slush, "Arizona dusty road", rain, hail, airborne volcanic dust, bird/critter-nests...

Operational factors: overstress [g, airspeed], hard landings, taxi collisions, severe turbulence, bird-strikes, lightning strikes...

Assembly and Maintenance factors: force-fitting parts, poorly drilled holes, loose/incorrect fastener installations, sealant adhesion failures...

Exposure to corrosive or abusive fluids/materials: urine, salt water, detergent wash-water, jet-fuel additives, hydrazine, deicing compounds...

GOT the concept??? Your comments appreciated.


Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[MintJulep]

Collision from service vehicle. Closing door or hatch on obstruction. Counterfeit parts. Over tightening fasteners. Poorly written or ambiguous maintenance instructions. Misinterpretation of inspection results.

 

[KENAT]

Deliberate sabotage be it by malcontent employees or terrorists.

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[MikeHalloran]

Collateral damage from salvage ops.
{
Super Cub banner plane went down off local beach some years ago.
Cylinder head stud failed, cylinder fell off, engine lost power.
It looked okay until they pulled it through the surf to get it on a truck.
Probably should have torn off the fabric while it was still in deep water.
}


Mike Halloran
Pembroke Pines, FL, USA

 

[Sparweb]

Turboprop airplanes landed regularly on unpaved runways: propellers throw rocks at the fuselage and "golf-ball" the skin around the nose and break pilot's window.

Airplanes in arctic/antarctic land on ice runways, park overnight, then the skis freeze into the ice. Ground crews try to free the aircraft by pushing sideways on the tail (there's a FAR for this load condition!). Sometimes works sometimes breaks the oleo scissor.

Speaking of the oleo scissors: usually broken by ground crew putting the tow bar on the nose wheel, then driving the tractor away without un-pinning the scissor. Meanwhile the control locks inside some airplanes (eg Piper Navajo) prevent the nosewheel from turning. Something breaks. Sometimes many things break.

Boss was replacing fabric on his Piper Pacer. Discovered some previously fabric covered sheet metal part with a bullet hole in it. Hole too big to be a screwdriver drop so...

I could go on and on and on.

Steven Fahey, CET

 

[thruthefence]

De-Bogging an aircraft in an unapproved fashion. Tow straps on anything that looks handy, & so forth. Damage is ofter hidden, for example, a powerful enough tug will snatch most any airplane out of the mud, by pulling on the nosewheel, there's some stuff up in there that ain't designed to be yanked on.

exceeding turn limits while towing.

 

[KENAT]

On military aircraft problems on release of items in flight.

Not just the classic of the store dropping down, getting caught in some kind of slip steam or similar and then coming back up to the A/C but also issues like the snatch disconnect on MIL38999C connectors on smart stores failing and the store pulling a bunch of cabling out of the A/C and damaging associated structure or similar.

Also accidental detonation of stores on A/C.

Heck, just loading the stores in the first place is fought with potential issues of driving weapons loaders into aircraft on the ground, connecting lanyards etc incorrectly and so on.

Did anybody say FOD yet?

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[berkshire]

Wil did not put sailplanes on the list, but they are not exempt.

Example: several years ago an FAA Licensed repair station in Virginia undertook the annual inspection of a sailplane made by Glasflugel in Germany. They took the rudder off to inspect the hinge mechanism as part of the annual. On this aircraft the rudder is operated by a pushrod and swash plate mechanism, not rudder cables. It is possible to re-install this upside down, and the station did. The aircraft was signed off and returned to service. The owner discovered that the system was upside down on take off (The control sense is reversed.) he released and almost got the aircraft stopped before instinct took over and he pushed the rudder pedal the wrong way. The resulting course deviation put the glider through a barbed wire fence tearing holes in both wings.
At no point did the repair station before release or the owner do a control check to see that the controls were working in the correct sense I.E. right foot right rudder left foot left rudder.

This same manufacturer sent me an aileron belcrank for another aircraft that was for the wrong wing, upon doing a control check we noticed that the ailerons were going up and down in unison like flaps, not one up one down like they should.

For those in light aircraft in the USA who think this cannot happen to them, Bellanaca used the same knuckle drive on their ailerons.
B.E.

 

[moon161]

I've flown around 20% of the miles i've driven, statistically, I'm due for a plane accident. I'll still sleep if I don't get the window seat.

 

[lisa247]

How does that make you due a plane accident moon161?

 

[rb1957]

bogus material
faked certs
effed up analysis
invalid testing
over-confidence (analysts or pilots mainly)
political influence in the design/cert process

 

[IRstuff]

Getting one's tail assembly whacked by an A380 wingtip
Whacking a CRJ700 tail assembly with one's wingtip
Vibration
Pressurization cycles
Wing loading and flexure
Not following engine R&R procedures, ala AA DC-10
Not following maintenance procedures in general

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[MiketheEngineer]

Without my knowledge - nose wheel fell off on take off - metal fatigue.

Didn't need much braking upon landing.. and quite surprised when composite propeller shattered into a thousand slivers.

 

[berkshire]

IR stuff.
I guess the A380 rates as a taxi collision, as refered to in Wil's original post. We have also had the 737 unzipping problem.
I wonder what will show up next.
B.E.

 

[KENAT]

Over pressurization during fueling.

Posting guidelines faq731-376

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[verymadmac]

Landing slightly short and having fence posts leaving marks on the underside of the wing.

Forgetting to set park break on a sloping strip and having the aircraft roll off down hill.

Using rope as a long line on a helicopter, managing to break it & having it recoil up through the rotor-head.

Use of SRM repairs outside of limits.

Overloaded operations
i.e ag spraying in R22
with Instructor + student + spray gear + min fuel = over gross and still nothing in the spray tanks.

 

[Sparweb]

Have all you guys seen the photo of the Cessna Caravan with a caved-in wing leading edge, and 50 feet back, a dead giraffe on the runway?

If anyone wants to see I can dig up the photo.


Steven Fahey, CET

 

[der8110]

Let's not bring the internet to a grinding halt... but here's a few unusual ones, with no FAR (yet!):
- wire rope indentation on leading edge (radio station guy wire)
- seat belt half hanging out door, beating up door and fus.
- antenna not screwed down, beat up fairing until departing aircraft
- overzealous pressure refueling
- 3" long fully threaded screw, more than long enough for interior trim (poked through)
- door stay chains, caught between door and frame
- passenger stepping on stairs before fully lowered, tore out chunk of door frame
- antenna removed by sawing off screws (hacksaw between fus. and base)
- antenna pried off with what must have been a can opener

 

[Andries]

You have convinced me - I'm not flying any more!

Andries

 

[verymadmac]

Parachute rig fouling tail plane
Parachutists hanging onto / climbing onto tail plane / fin