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Guest gasebah

Probability of aircraft system failures

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Hi guys,I just downlaoded the little proggie "reliability factor" and have to say that I really like the idea of what it does.Now did anyone ever stumble over material or statistics regarding the probability of failure of different aircraft systems? I would love to take a look at it. Any link would be highly appreciated.Thx,Alex

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My questions seem to be very special as I hardly get any answer recently.Sorry for the BUMP.Alex

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Needles to say it is very small.I know a 737 United pilot - in his 20+ years flying he could not recall a single failure !. Maybe he was very lucky.Michael J.

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Thx Michal,I am aware that it is very small. But be sure I will boost it up a little to get some excitement. My question was not aiming so much on how likely a failure is at all, but what systems are more likely to fail than others. I found some answers at AOPA meanwhile,Alex

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Talking about small GA airplanes - the most dreaded failure is the vaccum pump. This is a serious stuff and 'ideal' emergency to practice in the sim.Next in line got to be loss of the alternator.Running out of fuel - which happens quite often - it is purely pilot's fault.Michael J.

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Aside from vacuum pumps, if the aircraft is well maintained, and preventative maintenance is performed (replacing / repairing something before it breaks), the chances for failures are VERY slim, and often when things do "fail" (aside from vacuum pumps, and certain other items) they may even give you ample warning.Example: A DG that drifts more and more as time passes. This is telling you it is time for an overhaul / replacement of the unit.On the Arrow IV I fly (a rental), the fuel pressure needle vibrates wildly in flight. Now, what's causing this? The gauge itself? The sensor? Something nearby just causing it to vibrate?Well, there's a warning sign. You can heed it or ignore it. So far the FBO has let it go, and I'm not exactly losing sleep over it. ;-)The MAP gauge's needle also does a +/- 1" dancing act!A program that bases failures on time in service is nice, but assumes some neglicence on the part of the aircraft owner, and also the fact that the only way an item may fail is completely, this is not always true, as described above.Another example: FlightSim.com's Nels Anderson replaced the starter on his Archer during the annual inspection this year. Was there anything wrong with the old starter? No, all was fine, and it could have remained in service. It was just that the new starter was considered superior, and weighed several pounds less than the old. Since the airplane was already being disassembled, it was cost effective to do it then.We just got a new ADI in the Archer that I fly. I asked them what happened to the old one, as it appeared to be working fine last time I flew the plane. Turns out the old one was fine, but was getting on in years, and as the owner of the airplane was going for his IFR ticket, he wanted a new ADI to go with new HSI recently installed. He didn't want to take any chances with the old one. Now, THAT's preventative maintenance!We used to do similar on our Cherokee 235, during the annual inspection. Depending upon when a unit was last serviced, we might send out something like the ASI or the DG for a checkup / cleaning /overhaul. The only thing we ever had fail on the 235 was the Bendix T-12D ADF receiver, which one day smoked, smelled, and died. Not much you can do with an ADF receiver as to preventative maintenance, as it was working perfectly before. Turns out some component just decided it was time to fry itself. This can often be the case with avionics. Unless you notice something (like a sticky knob, or some erratic behavior or sounds) you often just have to wait for it do "die". Otherwise, if you send a perfectly working radio to the shop, the technician will look at you and ask "what should I do with it?" At most he will just clean certain components inside, make an adjustment or two, test it and that is about it. Ultimately, the thing could still fail the next day, when a perfectly good looking resistor heads for the hills in a cloud of smoke!As to the vacuum pump, replace it on a set schedule, based on its estimated life (700 hours, whatever), and replace it before then. Of course, many light aircraft have standby vacuum systems installed, so loss of the pump is only a momentary annoyance, as these standby systems, if not the primary system itself, will annunciate a failure.If you consider yourself one who flies a well-maintained aircraft, I would set the program at "minimum", and plan on flying, and flying, and flying for a loooong time without any failures.Yes, with even a well-maintained aircraft, something could always go, even something that is brand new, no doubt about it, but...;-)Regards,http://www.dreamfleet2000.com/gfx/images/F...RUM_LOUF_A2.jpg

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Thx fr the extensive answer Lou.You know, I am sure you are 100% but I think that it is a nice good idea to add a certain probability that something can happen. And.. I guess that aircraft cannot be so much more reliable than anything else that is surrounding you. In my household things always happen in waves. Four weeks ago I received a faulty MCP that I bought for the sim, one of my HDs died, a spring in my PFC Yoke broke, my 1000 US$ espresso machine killed the fuse everytime I tried to get steam out of it, and my DVD player refused to read US disks. No kidding, it all happened..

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In my 13 years of flying I have had more than my fair share of troubles. I maintain my plane by the book-but as a forty + year old craft things happen!-An alternator failure right after I bought my airplane (the mechanic in its' annual forgot to hook it up completely-I do not use that mechanic anymore)-Landing gear stuck in the down position-gear motor burned out-Flaps stuck in down position-flap motor burned out-alternator break off one mount in flight-1 muffler break in flight(sounded like the engine was gone!)-prop overspeed-twice-vacuum failure on my first imc flight-lol (pin sized hole in the vacuum line-autopilot malfunction, vsi/airspeed malfunction, altimeter malfunction,and prop overspeed all at once in imc over hostile terrain(prop overspeed problem and water in the static system)-prop throwing grease so front windshield was very hard to see out ofThere are probably quite a few others but these are the big ones that come to mind.http://members.telocity.com/~geof43/Geofdog2.jpg

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Geof, I was wondering how that vacuum failure was for you. As a student that is taking an instrument checkride on Saturday, one of my worst fears is having a vacuum failure and not noticing it until Im in a full stall or worse yet, a spiral dive of some sorts. Did you notice the failure right away or did it take you a while? Also, sounds like you lucked out with your gear problem. Better to be stuck down than up is what I say. :-lolCraig

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What happened was the plane sat outside (it is used to be hangared) in torrential rains at Knoxville,Mghee Tyson for 9 days. When I got in to take the return flight to Michigan the artificial horizon just rolled to a 45 degree bank-adding vacuum during the runup didn't help.I rolled the plane to the mechanic there-he suspected that the oil driven vaccum pump had failed-said it would take 2 weeks to repair. While I watched the steam come out of my wife's ears I called my mechanic back in Flint-he suggested there was a little gauge that could be turned up to increase the vacuum and that that was probably the problem. They did it-I did the runup and it worked!I took off-climbed to 9000 ft. and headed north. South of Toledo after entering solid overcast the gyro just rolled over once again into a 45 degree bank. Knowing that my autopilot derives its own attitude information I just left the plane on autopilot-called approach and told them I had lost vaccum. (On my plane the ah is the only vacuum instrument.) Funny thing was I controlled the plane fine-but couldn't remember the name of the ah to save my life!Anyway-they vectored me in for a precision approach at Jackson, MI-the ceiling was about 600. I found that I had to hand fly the plane partial panel from the downwind on. The controllers were great-the calm voice helped, and I finally broke out. After landing I was very tired and realized how concentrated and stressfull the event had been.My mechanics found a pin sized hole on the hose leading from the vacuum pump to the ah-that is why it was sporadic.The only thing I can say is to keep scanning all the time-the cross references should indicate something-and know the aircraft you are flying! http://members.telocity.com/~geof43/Geofdog2.jpg

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Alex, In my 18 years of aircraft maintenance I see failures of all kinds but usually they fall into this order of frequency:1) Electrical This is more often a shorted or broken wire leading to an electrical component causing it to trip off line. Or a generator abnormality or failure.2) Electronic This is usually a Radio (Nav or Comm) or Autopilot or other Computer such as System coupler or FMC/RNAV malfunction. I was told the secret to keeping the black boxes working is "Don't let the smoke out of the black boxes" Once that happens they stop working. :-)2) Hydraulic Usually a leak or component malfunctions such as flaps/Gear Malfunctions, brake leaks ect..Hyd Pump failures or Hyd line cracks/leaks.3) Engine Related Usually Oil leaks. Or power reductions due to internal engine component or seal failures, or electronic/mechanical engine managment systems malfunctions causing power loss...ect. (I only work on Turbine Engine aircraft)4) Pneumatic/Pressurization Aircraft Cabin Pressurization/Air conditioning and heating. Pneumatic and bleed air system malfunctions such as clogged filters and sticky air operated valves. ect...5) Fuel System related. Usually small leaks (drips) in fuel tanks or fuel line plumbing or tank level sensors, or fuel pump failures or valves that stick.I know this is not an accurate assesment for all aircraft but for the ones I work on and see most often this is what I see.Hope this helps a little.Ken

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There was a great article in Flying (I think this is the mag that had it could be wrong) about how most partial panel accidents do not happen immediately. 20 min. was the cutoff they stated when an accident was likely to occur. They used the Carnahan accident in Mo as the example.I had a vacuum pump failure, thankfully I was in VMC. Now I always bring something to cover them up just in case. It was awfully hard to not stare at the bad instruments.Also, Geofa what FBO where you at in KTYS? We landed there two weeks ago in cold/cloudy conditions and went to Cherokee Aviation in a Cirrus SR-20. After we dropped the owner off we did a preflight and found 1/8" of ice on the leading edge surfaces. Not only did Cherokee refuse to service use (they wanted $50 to put our airplane in a heated hangar for 15min.) but the other FBO, Knoxair, wanted a flat $100 fee plus $10/gal for alcohol. Thankfully a check hauler heard our plight and offered some of his from his Baron. That clear ice was a bear to get off! Moral of the story is the FBO's at KTYS are not customer friendly in the least (they care only if you use Jet-A).

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I also went to Cherokee-but only required a tie down so didn't really experience the type of problem you did. Everytime I fly down there though my plane doesn't seem to like the humidity/rain-but it sounds like a hanger might not be an option from your experience!How did you like the Cirrus?-I haven't had a ride in one but I always drool over them at Oshkosh.http://members.telocity.com/~geof43/Geofdog2.jpg

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Thx to all of you. You have been of great help like always.Cheers,Alex

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