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1. 03:19 AM - Re: Estimates of Component Failure Probabilities (Peter Pengilly)
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| 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
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com <owner-aeroelectric-list-server@matronics.com>
On Behalf Of wsimpso1
Sent: 02 October 2021 14:27
Subject: AeroElectric-List: Estimates of Component Failure Probabilities
--> <wsimpso1@comcast.net>
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 and 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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http://forums.matronics.com/viewtopic.php?p=503375#503375
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