Question about airworthiness

[cougar6903]

Is a aircraft non-airworthy if one of the cowl fastener's in loose or missing? How about two?

 

[skeezer]

Ok, this is off the top of my head but I believe the aircraft in question is un-airworthy because it no longer conforms to it's type design.

I doubt you will get violated for missing 1 cow fastner, but you should get it replaced for safety's sake, and in case you run in to a fed with a stick up his/her butt.

Skeezer

 

[PaulThomas]

Is a aircraft non-airworthy if one of the cowl fastener's in loose or missing? How about two?

I don't think so, they're known to come lose on 172 due to vibration. The DE and chief pilot pointed this to me but never mentioned about this making a plane not airworthy.

 

[PropsForward]

The aircraft would be unairworthy. You need to get it fixed ASAP. If it is a split cowl, and and the faseners in question are around where the prop comes out, then it is certainly a greater risk to your safety than say if one by the windscreen is missing, but as Skeezer said unless you run into someone with a "stick up his/her butt", you're probably ok. But the correct action is to get it fixed before you fly it.

 

[wheelsup]

I believe in aircraft under 5000 lbs. you're allowed to be missing up to 1 lb. of weight due to nuts, bolts, etc. However I'd think that they cannot be structual compoents...missing one cowl fastener won't bring down the plane.


~wheelsup

 

[avbug]

I believe in aircraft under 5000 lbs. you're allowed to be missing up to 1 lb. of weight due to nuts, bolts, etc.

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Airworthiness is comprises two concepts; one is conformity to approved data. Not necessarily type certification, but to approved data, which may include a type certificate data sheet, authorized manufacturer modifications, supplemental type certificates, field approvals, alterations in accordance with airworthiness directives, etc. The second concept is safety. The aircraft must be in a condition safe for flight.

The first concept is not nebulous; it is exact. The aircraft is either in conformance, or it is not. A loose or missing fastener is not in conformance.

The second question allows some room for judgement, subject to the viewer's discretion. Is it safe? That depends on your perspective. You might not think a microscopic nick in the edge of a rivet or screw hole is unsafe, but it lead to the loss of both wings on one of my airplanes a few years ago. If you think it's not safe, it's due to lack of experience and training...but that doesn't necessarily make it safe...in that case, you simply don't know enough to know it's not.

Therein lies the problem. One may see something and figure it's safe, and pass it off. An inspector or someone eho has a different viewpoint may feel otherwise. You may feel that you know more, that the other person has a critter located upstream in his or her anatomy. This provides you the high moral ground upon which to look down on the more conservative viewpoint. Not necessarily the correct ground, but one of supposed superiority.

A few years ago I watched a young private pilot slam his nosegear in a 172. He taxied to the ramp where I was located and shut down. He was shaking. He had on board two young ladies whom he was attempting to impress. I approached him, identified myself as an aviation safety counselor, and indicated that I would like to talk to him about his landing, if he had a moment.

He felt there was nothing wrong. I asked him what went wrong, then we discussed it. I asked him what he intended to do about the airplane. He said there was nothing wrong. I discussed the various things he could look for, and discussed the need to examine the nosegear, firewall, and engine mount. I pointed out that the tire had been expanded outward such that large distinct scuff marks were inscribed into the tire sidewall from the nosegear forks, and that the shimmy damper was probably blown. He told me he was a private pilot and had all the training he needed, and proceeded to depart. He felt the aircraft was airworthy.

I called the owner, whom I knew. The young man had just made his last flight there, as he soon found out. The aircraft required substantial work, and had not been airworthy. One might argue that it made it back to it's home base safely, but the truth is that it wasn't airworthy. It needed a hard landing inspection, it needed a new shimmy damper, it needed a new nosewheel, and more.

Back to the issue at hand. Does a single fastener make the aircraft unairworthy? Yes, it does. Unless the manufacturer has documentation specifying that a minimum number of fasteners may be missing, the fact that the fastener isn't secured per the aircraft manufacturers approved maintenance documents means that the aircraft is in fact not airworthy.

Will you get caught? Who cares? Fix it.

Does a missing fastener mean anything? Is it unsafe? Consider that when a fastener is missing, it is no longer supporting the surrounding material. It's load is being assumed by the surrounding fasteners. This is not the intended use of those fasteners, else the missing fastener would never have been put there in the first place. There is no provision to be missing a certain number of pounds of fasteners. Nor should you ever assume that the structure is designed X percent over what is required, so a few missing fasteners is acceptable.

What caused the missing fastener to become missing in the first place? Is the underlying structure broken? Is the fastener broken off, and did part of it go where it shouldn't?

I found a row of fasteners working on a medium turboprop earlier this year. The fasteners were driven rivets, adjacent to each other, and each shared one thing in common; they attached a section of wing skin to the main wing sparcap. That a fastener might have been missing was of much less concern than the fact that the common factor was the spar. I immediately grounded the airplane and scheduled a detailed inspection for the entire wing section, which ultimately required repairs.

What about a single camloc fastener on a skyhawk cowl assembly? Can that be missing? You see them missing all the time. The aircraft aren't falling out of the air. But what is happening, not entirely obvious except over a period of time, is chafing. The cowl is wearing, usually at the top and corners, and may be allowing a little extra motion between the faying surfaces. Vibration throughout the assembly changes. This may eventually lead to unacceptable wear, it may also lead to cracking, and under a load, the structure may not hold up.

The obvious soloution is to fix it. This isn't always possible. You're on the road, you're on a trip, can it wait? One thing I'll suggest is contacting a mechanic. Don't expect the mechanic to put his or her stamp of approval on your problem; he or she probably can't, and almost certainly won't, but may give you some under the table insight into weather the problem needs to be addressed right away...and might even be able to do it for you. As the PIC, you're ultimately responsible for it, but getting qualified professional advice isn't ever a bad idea.

Older 172's use four screws adjacent to the propeller to hold the cowling halves together. These are frequently given unauthorized modifications with the nutplates being replaced by nuts and washers, and sometimes with only one fastener. Think about the proximity of these few fasters to the propeller, spinner, and engine output shaft or extentions. Think of the vibration there, and the aerodynamic loads that alternately attempt to push up or down on each surface.

One very common general avaition airplane uses only a few specialized fasteners to attach the upper and lower forward cowl surfaces. Last year I was given one such aircraft to repair, in which a single fastener had not been secured. The cowl opened in flight, striking the propeller, and causing thousands of dollars in damage to the cowl and the spinner assembly. Minor, dressable damage was done to the propeller.

Don't ever assume that simply because it's a single fastener, it's okay. It's certainly not legal, but the okayness of it may be a subjective issue that you may not be qualified to determine.

 

[wheelsup]

So let me guess, you always fly in brand new aircraft that have NOTHING missing on them, right avbug?

If a microscopic nick can bring down an aircraft, I'd better include a microscope walkaround on my preflight...

~wheelsup

Edit: I suppose in a perfect world you'd want everything to be just like it was coming from the factory. It just doesn't happen - tire pressures, bolt torques, etc. can never really be reproduced or checked on a normal everyday preflight...which would, with my understanding, render it unairworthy. So basically what I'm saying is under realistic conditions you'd never really have a perfect airworthy aircraft...or am I missing something

 

[avbug]

As a matter of fact, a small nick or imperfection can bring down an aircraft, and has brought down many aircraft. The case I referred to involved an aircraft I knew well, and the death of crewmembers I knew well. You saw it yourself on television only three seasons ago, as the wings separated in flight. Both of them. That began with a small nick in a rivet hole, and spread as a stress riser, causing a crack which moved between two holes in the wing. This propogated to layers of material above and below the crack, and eventually lead to the entire failure of the wing. The aircraft broke up, caught fire, hit the ground seconds later, and exploded.

Most cracks start that way, and most structural failures, excepting those that go beyond the ultimate load bearing capacity of any given member, occur in this way.

Should you bring a microscope with you? No. But don't take the foolish attitude that a pound of fasteners can be missing, so a few here and there can't be all bad. What utter insanity. Don't accept mediocacy. It's never right.

Edit: I suppose in a perfect world you'd want everything to be just like it was coming from the factory. It just doesn't happen - tire pressures, bolt torques, etc. can never really be reproduced or checked on a normal everyday preflight...which would, with my understanding, render it unairworthy. So basically what I'm saying is under realistic conditions you'd never really have a perfect airworthy aircraft...or am I missing something

You're missing something. Something big.

Bolt torques can never be reproduced? Are you kidding? There's a reason that each torque wrench in the box goes out annually for recalibration. There's a reason that the torque wrench gets used on every fastener called for by the manufacturer, every time that fastener is addressed. It should be exactly per the specifications, and yes, you should be checking tire pressures or ensuring that tire pressures are checked each time.

As a mechanic, I've spent tens of thousands of dollars on the tools in my box for the appropriate tools to do the job, the quality tools to do the job, and yes, they get used.

As a pilot, there should be no need to check the torque of the wheel bolts each time I fly, though I do a visual check. If I learn that the mechanic failed to check them, then heaven help the mechanic, and yes, the aircraft is immediately grounded.

Yes, I check tire pressures. I ensure that inspections are done, and done properly. This year I delivered an airplane for a company to an inspection site, and then made periodic visits to the site to go on the shop floor and ensure that the phases were being conducted properly. I inspected and visited every squawk, every inspection item, for thousands of items, at the request of the company who operated that aircraft. I found much of it done properly, some that didn't need doing, and some that wasn't done right.

I found a squawk for an engine oil tube, for a nick in the tube. the tube was worth several thousand dollars, and the mechanic was going to replace it. I visited the mechanic on the shop floor, and queried him. He told me that the nick was greater than 10% of the diameter of the tube, and therefore subject to removal. We looked up the reference together in the maintenance paperwork. I then asked him the depth in thousands of an inch. He said he didn't know. I asked him about the calibration of the micrometer used to make the determination, and he admitted he hadn't used one. I procured one, and made the measurement with him, and determined that the tube was in fact within tolerances.

Do I expect that every item in the aircraft is airworthy and within manufacturer specifications. You bet your bottom dollar.

I'm alive because of that attitude. Do I fly brand new aircraft? Right now, Yes, I do. I also fly 20, 30, 40, even 60 year old aircraft. Guess what? I expect the same standard of maintenance on each one, and accept absolutely nothing less. If you do accept less, you face some big problems in your future. I only hope you survive them.

 

[nosehair]

Right on, Avbug! Your attitude is the one we all should be sleeping with. I suspect the reason we GA types have to suffer with these old, decrepant, aging, *crappy* airplanes is because of the generally accepted idea that "a few missing screws* is ok.

Yeah, a missing cowl screw or some such is *probably* ok 99%, or even 99.9% of the time, but if you fly for a living for a life time - that .1% will eventually get you.

The point here is: If we all didn't accept "minor deficiencies" in airworthiness, we all would be flying much better maintained equipment.

Exactly the same as if all us flight instructors didn't accept starving wages, we wouldn't be living starving careers.

We are all our own worst enemy.