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Estimates of Component Failure Probabilities

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wsimpso1

Joined: 04 Nov 2018
Posts: 32
Location: Saline MI

Posted: Sat Oct 02, 2021 5:26 am Post subject: Estimates of Component Failure Probabilities

I and another EAA chapter member are working on architecture decisions in our respective airplanes. In the process, I have assembled Failure Modes and Effects Analyses for several common options. Unfortunately, we have too small an experience base for confidence in estimating failure probabilities on the many components. We are looking for a broader experience set in estimating a number of things:



    • Likelihood of Failure 

    • How likely individual items are to fail at engine start as opposed to in-flight? 

    • Will we be able to detect the failures using common post-start and pre-takeoff checklist processes?

    • How likely are detection measures in finding impending failures? 

      

If an item is available from B&C, please assume they are the source. My colleague in this exercise is using a Lycoming with factory supplied Surefly Ignition and Bendix Fuel Injection. My homebuilt is planned with SDS fuel injection and ignition. Estimates specific to the hardware are great. 



Please help by giving your estimates of in-flight failure probabilities. Even if all you have is your flight hours and the component failures you have seen, I can collect that sort of data into failure probability estimates. Any other thoughts you might have on detection and failure modes on the following components:



    • Electrical components:

        ◦ Batteries;

        ◦ Carling DPDT switches;

        ◦ Continuous Duty Contactors;

        ◦ Continuous Duty Relays;

        ◦ Alternators;

        ◦ Regulators;

        ◦ Diode packs and Diodes;

    • Ignition Equipment;

        ◦ Conventional Magnetos;

        ◦ E-Mags;

        ◦ SDS Ignition and Coils;

        ◦ Sure Fly Ignition;

    • Fuel Handling;

        ◦ Mechanical Fuel Pumps;

        ◦ Electric Fuel Pumps, Traditional;

        ◦ Electric Fuel Transfer Pumps, Facet;

        ◦ Electric Fuel Injection Pumps, Walbro;

        ◦ SDS Fuel Injection;

        ◦ Fuel Selector Valves, Traditional;

        ◦ Fuel Selector Valves, Andair and Newton/SPRL

    • Sensors supporting electronic fuel and spark;

    • Avionics;

        ◦ Avidyne GPS/NAV/COM;

        ◦ Dynon HDX Display/Processors;

 

Thanks in advance for any help you can give in these estimations.



Billski

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wsimpso1

Joined: 04 Nov 2018
Posts: 32
Location: Saline MI

Posted: Sat Oct 02, 2021 9:44 am Post subject: Re: Estimates of Component Failure Probabilities

15 of you have visited this page and not even one of you will share "I have X many hours in little planes and have had Y of this failure and Z of that failure"?



OK, I shall start. In 2200 hours I have had:

Two plugs on one cylinder foul and cut out the cylinder, with the first cutting out only a couple minutes before the second. The Archer maintained altitude on three cylinders;

Two Facet standby electric fuel pumps failed on the ground;

One alternator failure in flight;

One attitude gyro gave up in flight on an instrument training flight in VMC - that made for an interesting flight;

Two vacuum pumps failed - both in VMC;

One fuel pump sending unit lost its float while IMC, causing a divert to the nearest ILS in case the tank really was draining. It wasn't. And;

Miscellaneous light bulbs. They do not seem to be out when checked on the ground. They must burn out during flight.

No inflight battery or contactor or switch issues, near as I can tell from review of the logs, the switches and contactors all have 6700 hours on them. I will look back through the logs on the airplane for other failures.



Come on guys, let's hear your totals and all the things that have broken. A perusal of the log books for repairs won't hurt either.



Billski

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arcticarrow(at)gmail.com
Guest

Posted: Sat Oct 02, 2021 3:19 pm Post subject: Estimates of Component Failure Probabilities

I’ve been wondering about all the failure preventative measures proposed on this theme. I’m building a Hatz with Verner power hence electronic ignition so have concerns too. However my history over 55 years and 30,000 hr 10,000 in light aircraft isn’t so dramatic:

 9 engine failures, jets, a bleed valve failure, turbine blade disintegration, seizure from starter failure to disengage after start. Recips, massive valve guide disintegration which led to spark plug electrode shorting, oil dip stick failure- parts punched holes through case and let the oil out, fuel vents icing two times, engine fire - broken fuel line on ground, planitary gear drive on GSIO engine. 



Electrical failures: 2 master contractors on the ground, 1 alternator-broken field wire, loose generator drive belt on Lycoming, engine pressure ratio gauge failure, couple dead batteries from neglect. 



Landing gear: main gear tire blew out, metal brake line pulled from fitting. 



Props: 1 while taxing in soft sand, another when a main gear fell into ice covered hole on twin. 



I’m an IA and do my own maintenance, my father started with cars then Lockheed for 35 yrs. which leads me to believe stuff rarely fails but we do. Inspection and preventative maintenance are never wrong. 



Bernie Willis



Sent from my iPhone



 	  Quote: 	
		   On Oct 2, 2021, at 10:10 AM, wsimpso1 <wsimpso1(at)comcast.net> wrote:

 

 

 

 15 of you have visited this page and not even one of you will share "I have X many hours in little planes and have had Y of this failure and Z of that failure"?

 

 OK, I shall start. In 2200 hours I have had:

 Two plugs on one cylinder foul and cut out the cylinder, with the first cutting out only a couple minutes before the second. The Archer maintained altitude on three cylinders;

 Two Facet standby electric fuel pumps failed on the ground;

 One alternator failure in flight;

 One attitude gyro gave up in flight on an instrument training flight in VMC - that made for an interesting flight;

 Two vacuum pumps failed - both in VMC;

 One fuel pump sending unit lost its float while IMC, causing a divert to the nearest ILS in case the tank really was draining. It wasn't. And;

 Miscellaneous light bulbs. They do not seem to be out when checked on the ground. They must burn out during flight.

 No inflight battery or contactor or switch issues, near as I can tell from review of the logs, the switches and contactors all have 6700 hours on them. I will look back through the logs on the airplane for other failures.

 

 Come on guys, let's hear your totals and all the things that have broken. A perusal of the log books for repairs won't hurt either.

 

 Billski

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=503378#503378

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Peter(at)sportingaero.com
Guest

Posted: Sun Oct 03, 2021 2:19 am Post subject: Estimates of Component Failure Probabilities

There isn't much evidence based information available.



My observation is electromechanical devices often fail during use/in flight due to vibration, solid state devices fail at start up. Vibration related failures are difficult to quantify because very few experimental owners have any kind of objective measure of the level of vibration (frequency vs amplitude) their equipment is exposed to. Those who have their engines dynamically balanced may have relatively low levels of vibration (0.2 ips at engine speeds & harmonics?) but how many do that?



The only items I have any experience of failure rates are,



Switches / relays - I've never had a failure in 2000 hours

Alternators - 1 failure in 10x3 hours or less (not B&C)

Magnetos - AvWeb did a survey some time ago, failure rate was 1 in 500 hrs.

P-Mags - Better than magnetos by a factor of 2 to 5 (possibly more going forwards)

SDS & Surefly - too early in their lifetime to really know, probably better than magnetos!

Fuel systems - all pretty reliable, failures are often gradual. Lyc mech pumps have 2 diaphragms so will work with 1 ruptured. Isn't a Facet pump a traditional pump?

Traditional fuel selectors leak all the time, Andair (my favourite) and SPRL are much better.

Sensors do fail from time to time, if the system is well engineered the failure of any one sensor will not take the whole system down and is just an annoyance.

Modern avionics very rarely fail and any failures are often due to installation errors, particularly in Experimentals.



Although you didn't ask, vacuum systems have a failure rate of 1 in 500 hrs (AvWeb survey again), pretty much any EFIS will better that by a factor of 2 to 5 (data is about 8 years old). Installing a back-up attitude indicator with a battery (G5, AV-30, Horis, etc) will bring loss of attitude information into the 1 in 10^6 hours realm.

Smart electrical systems (VPX, Expbus, etc) seem to be about as reliable as alternators in service.

 

Hope this helps, but there just isn't much hard data available.

Peter



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