(Robert M. Gary) wrote
Once again, its time for the 100 hr AD sign offs for my Mooney.

Yes, but not 93-02-05. That AD has been superseded. The current AD
is 2002-26-01. However, the compliance actions have not changed. We
just have new paperwork to confuse us. But hey - it's the FAA, what
do you expect?

I
still cannot come close to understanding the logic behind the injector
line AD on lycomings. My understanding is that some A&P at some point
accidently bent some of the lines and didn't understand that it would
effect the available pressure to the injector.

Not quite. The real problem is that if they are bent improperly, they
can crack under vibration and dump raw fuel on a hot engine.

The action required is not exactly onerous. Once the mechanic is
familiar with your installation, it's a simple matter of decowling the
engine, taking a look at the lines, and seeing that they are not
cracked or kinked, and are securely clamped in place (generally to the
pushrod shrouds). That's it.

Realistically, an aircraft engine needs a 100 hour inspection anyway.
Mine includes, in addition to the ubiquitous oil and filter change and
plug cleaning/gapping, a cleaning of the injector bleed nozzles,
verification (and if necessary an adjustment) of magneto timing, a
check on the air and fuel filter, and a check on cylinder compressions
(sometimes with tester, sometimes just pulling the prop through). I
find that complying with the requirements of the AD adds at most 15
minutes to the process. What is more, a friend of mine, while
complying with the AD, found a line starting to crack. It's a cheap
and easy replacement - but once it starts dumping fuel, it will get
interesting.

Ok, sounds like maybe
there should be an AD after work is done on injector lines. But no.
The FAA says we must check every 100 hours to ensure an A&P hasn't
made this mistake! This is silly! Has this AD ever actually caught a
real problem??

See above - yes it has caught at least one that I know of. The issue
is that an improper bend puts stresses on the metal. However, the
metal will not fail immediately, and it is not immediately obvious by
external inspection that a bend is improper. Sometimes you don't know
until the cracks start. Sometimes you don't notice until it starts
seeping fuel. But if you don't ever check, your first indication may
be loss of power from one cylinder accompanied by fuel being dumped
onto the hot, running engine.

Michael