spark plugs vs. igniters

spillvalve · Post by **spillvalve** » Fri Mar 03, 2006 11:11 am

here's a question that was asked the other day

Why do we lock wire igniters and not spark plugs?

Spinner · Post by **Spinner** » Fri Mar 03, 2006 12:01 pm

good question:

There is no provision for lockwiring spark plug leads as far as I know. Perhaps it is a shop practice that comes from Pratt etc that is carried on in the field.

How about the pushrod gland nuts on a 985/1340. When I first started we used to lockwire them religously. Now it is never done.

737 Mech · Post by **737 Mech** » Fri Mar 03, 2006 8:09 pm

Probably because history has shown that the buggers just don't fall out and there is no need for lockwire...

as far as the leads go.. if one falls of your jug you lose a couple of RPM like a mag drop test

lead off your Ignitor you probably wouldn't now until you selected that side for start OR you opened the cowl....since you have two or more

the JT8D never used lock wire for the leads or plugs and same goes for the CFM56-3B

Northof60 · Post by **Northof60** » Wed Oct 11, 2006 10:29 pm

imagin lock wireing a 18cy 36 plug engine times two

chubbee · Post by **chubbee** » Thu Oct 12, 2006 2:07 pm

If an ignitor falls out it would be followed by a blast of flame perhaps?
A spark plug loss would decompress the cylinder (no suction) and unless you had boost from the intake manifold you would not have much of a flammable gas leak.

Riverman · Post by **Riverman** » Sat Oct 14, 2006 9:15 am

I think they're referring to ignition lead lockwiring. Not lockwiring of the igniter or sparkplug itself. So no jet of flame or descompressed cylinder.

chubbee · Post by **chubbee** » Sun Oct 15, 2006 4:47 pm

Hmmmnn.... I think there is no difference.
If the electric lead is secured from rotating off. How could the plug it mounts in come completely adrift?
Ignitor lead in a turbine has enuff spark energy to maybe weld/cut its way thru piping or even casings. Asking for trouble not to saftey an ignitor really.

Troubleshot · Post by **Troubleshot** » Sun Oct 15, 2006 5:10 pm

First off there is no safety provisions to lockwire/safety Ignitiors and spark plugs on 90% of engines out there...why... because the copper gasket is normally your safety when dealing with the plug itself ( Ignitior or spark), they are ment to crush and act like a lockwasher, plus they deal well with the heat and don't get brittle like lockwire does and when they get hot they get softer and provide friction.

As for the leads there hasn't been a need to safety them, history has shown if properly torqued they do not fall off, and even if they did as 737Mech pointed out you wouldn't really know till you tried to do a Mag drop test or use that Ignitor to start the engine.

Northof60 · Post by **Northof60** » Sun Oct 15, 2006 6:05 pm

Any body with any time on pistons know that loose ignition leads lead to problems!!!!!!

Troubleshot · Post by **Troubleshot** » Sun Oct 15, 2006 6:42 pm

Hey don't shoot the messenger !! I posed this very question to engine manufacture tech rep's as well as overhaul faclities and they all gave me the same answer "Industry has shown that it is NOT a problem"

and to further the question, why haven't we seen changes by means of AD/SB's to make the changes....

I have never found a loose lead as a source of a ignition problem...lots of bad leads but not loose ones, now before you all freak out at me... this my experience I'm sure some you have but I doubt if it happens alot or the design would have been changed long ago.

***Please lets just have good dicussion and not turn this into "your dumb and I'm smart" pissing match

chubbee · Post by **chubbee** » Mon Oct 16, 2006 9:37 pm

It is a true statement that unsafetied ignitors /Splugs and their leads have typically no snags related to the lack of safety /securing devices.
The point can be made that a turbine engine ignitor and its lead are potentially fairly hazardous if they ever come adrift.
Some turbine ignitors and ignitor leads are safetied perhaps for this reason (both large and small turbines) or possibly because of legal liability? I am unaware of any piston engine with lockwired plugs or leads. It is curious in an era of $100 million dollar lawsuits for Cessna piston crashes that this is still the case. You would think the manufacturers would do it to cover their legal backsides.

Hedley · Post by **Hedley** » Tue Oct 17, 2006 6:52 am

I have never found a loose lead as a source of a ignition problem

I have. The mechanic at the last annual didn't tighten them up