Mean Time to Failure

[O. Sami Saydjari]

As I reading through my aircraft logs, I noticed several replacements of
the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
Turbo Arrow 3. Is is normal to need to replace these things every 4-5
years?

Does anyone keep statistics or even projections for the mean time
between failures on airplane parts? It sure would be useful to know.
One would think the manufacturers would publish such information.

-Sami

[ArtP]

On Sun, 08 Feb 2004 17:43:43 -0600, "O. Sami Saydjari"
> wrote:

>As I reading through my aircraft logs, I noticed several replacements of
>the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
>Turbo Arrow 3. Is is normal to need to replace these things every 4-5
>years?

I have an 2002 SR20 and my TC was replaced after 10 months, my
directional gyro (Sandel EHSI) lasted 1 year and 9 months.

[Jeff]

were the replacements done with used or new instruments?
I know the place I did my flight training always used used DG's and they
seemed to go out all the time in the warriors, the mechanic said it was due
to using the used parts all the time and not getting the DG's sent in to be
overhauled.


"O. Sami Saydjari" wrote:

> As I reading through my aircraft logs, I noticed several replacements of
> the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> years?
>
> Does anyone keep statistics or even projections for the mean time
> between failures on airplane parts? It sure would be useful to know.
> One would think the manufacturers would publish such information.
>
> -Sami

[O. Sami Saydjari]

They all seemed to be used. -Sami

Jeff wrote:

> were the replacements done with used or new instruments?
> I know the place I did my flight training always used used DG's and they
> seemed to go out all the time in the warriors, the mechanic said it was due
> to using the used parts all the time and not getting the DG's sent in to be
> overhauled.
>
>
> "O. Sami Saydjari" wrote:
>
>
>>As I reading through my aircraft logs, I noticed several replacements of
>>the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
>>Turbo Arrow 3. Is is normal to need to replace these things every 4-5
>>years?
>>
>>Does anyone keep statistics or even projections for the mean time
>>between failures on airplane parts? It sure would be useful to know.
>>One would think the manufacturers would publish such information.
>>
>>-Sami
>
>

[G.R. Patterson III]

"O. Sami Saydjari" wrote:
>
> As I reading through my aircraft logs, I noticed several replacements of
> the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> years?

I had a 25 year old Cessna 150 with what was apparently the original DG and turn
coordinator. IIRC, there was no record in the logs that either had been rebuilt
or replaced. The RC Allen DG in my Maule started drifting about a year after I
bought it, and I had it rebuilt by Ducasse. It's given me no trouble since. I
have a rebuilt turn-and-bank in the Maule, so I don't have a TC referent there.
The Maule's a '95 model.

George Patterson
Love, n.: A form of temporary insanity afflicting the young. It is curable
either by marriage or by removal of the afflicted from the circumstances
under which he incurred the condition. It is sometimes fatal, but more
often to the physician than to the patient.

[Dude]

Have you not sold that thing yet? I can't believe the factory won't buy you
out of it.


"ArtP" > wrote in message
...
> On Sun, 08 Feb 2004 17:43:43 -0600, "O. Sami Saydjari"
> > wrote:
>
> >As I reading through my aircraft logs, I noticed several replacements of
> >the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> >Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> >years?
>
> I have an 2002 SR20 and my TC was replaced after 10 months, my
> directional gyro (Sandel EHSI) lasted 1 year and 9 months.

[ArtP]

On Mon, 09 Feb 2004 04:56:42 GMT, "Dude" > wrote:

>Have you not sold that thing yet? I can't believe the factory won't buy you
>out of it.

Looking for a broker now. While I am certainly the loudest complainer,
based upon postings at COPA, others have serious problems and I don't
think the factory would want to start a precedent of buying out
disgruntled owners.

[Nathan Young]

On Sun, 08 Feb 2004 17:43:43 -0600, "O. Sami Saydjari"
> wrote:

>As I reading through my aircraft logs, I noticed several replacements of
>the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
>Turbo Arrow 3. Is is normal to need to replace these things every 4-5
>years?
>
>Does anyone keep statistics or even projections for the mean time
>between failures on airplane parts? It sure would be useful to know.
>One would think the manufacturers would publish such information.

At some point, the gyros will fail, so the question is whether the
plane is being used for IFR or not.

If so, it makes sense to periodically replace/overhaul the gyro
instruments, and to replace the vaccuum pump.

If it is used only for VFR, who cares. Let the instruments fail, then
replace them.

Gyro life varies widely. Gyros may last years, or only months
depending on a number of factors:
-Manufacturing/overhaul quality
-Time on shelf before install (it is bad for gyros to sit idle)
-Temperature extremes. I've heard cold starts are hard on gyros.

-Nathan

[James M. Knox]

"O. Sami Saydjari" > wrote in
:

> As I reading through my aircraft logs, I noticed several replacements
> of the Directional Gyro and Turn Coordinator. The plane is a 1978
> Piper Turbo Arrow 3. Is is normal to need to replace these things
> every 4-5 years?

Some folks do replace them on a regular basis... The idea being to
replace them before wear causes them to fail at a more inconvenient
time. Does it help? I don't think anyone knows. Probably, when you
consider the incidence of infant mortality that these devices see,
probably not. While they all will EVENTUALLY wear out (whether that
means 5 years or 50 years), more probably fail in the first couple of
months after installation than anything else.

Some things CAN cause premature wear and failure:

o Smoking in the aircraft
o High-G maneuvers
o Long idle periods (and this includes sitting on the shelf in some
avionics shop).

Fortunately, they usually (but not always) give some warning days or
even months before they fail:

o Wind down quicker than usual
o More noise (after engine shutdown) than normal
o Slow to erect, or tends not to return to neutral when the plane does

Most of us, I think, wait and repair them when they *start* showing
signs of needing it. And BTW, in my opinion, a quality overhaul should
be just as good as a factory new in terms of reliability. A quality
overhaul replaces all the wear items.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[Mike Rapoport]

I asked the same question after my only (vacuum) AI failied on a flight
(turbo Lance) and was told 500 to 1000 hrs for vacuum gyros and 1000 to
2000hrs for electric. If you only have one vacuum AI overhauling it every
500hrs seems prudent.

Mike
MU-2


"O. Sami Saydjari" > wrote in message
...
> As I reading through my aircraft logs, I noticed several replacements of
> the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> years?
>
> Does anyone keep statistics or even projections for the mean time
> between failures on airplane parts? It sure would be useful to know.
> One would think the manufacturers would publish such information.
>
> -Sami
>

[O. Sami Saydjari]

Mike, Who did you ask? Tha manufactuerer? Seems like these stats would
be specific to the make and model of the instruments. -Sami

Mike Rapoport wrote:

> I asked the same question after my only (vacuum) AI failied on a flight
> (turbo Lance) and was told 500 to 1000 hrs for vacuum gyros and 1000 to
> 2000hrs for electric. If you only have one vacuum AI overhauling it every
> 500hrs seems prudent.
>
> Mike
> MU-2
>
>
> "O. Sami Saydjari" > wrote in message
> ...
>
>>As I reading through my aircraft logs, I noticed several replacements of
>>the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
>>Turbo Arrow 3. Is is normal to need to replace these things every 4-5
>>years?
>>
>>Does anyone keep statistics or even projections for the mean time
>>between failures on airplane parts? It sure would be useful to know.
>>One would think the manufacturers would publish such information.
>>
>>-Sami
>>
>
>
>

[Mike Rapoport]

I asked a large avionics/instrument shop where I got the failed gyro
replaced, so it was one (experienced) guys observation, not a scientific
study. There isn't a lot of difference between different vacuum gyros that
is going to affect their lifespan. Even with a good filter, there is dust
and grit constantly being sucked through the unit and the bearing grease
eventually dries out as well. There are larger differences between electric
gyros and I asked about the ones installed in my airplane which use a AC and
DC power. Look in your logbooks and see how long yours lasted. I'm sure
that there are a lot of variables too. If your plane sits outside in
Pheonix, the bearing grease will probably dry our faster and if it sits
outside in Barrow, it is going to have a lot of very cold starts.

Mike
MU-2


"O. Sami Saydjari" > wrote in message
...
> Mike, Who did you ask? Tha manufactuerer? Seems like these stats would
> be specific to the make and model of the instruments. -Sami
>
> Mike Rapoport wrote:
>
> > I asked the same question after my only (vacuum) AI failied on a flight
> > (turbo Lance) and was told 500 to 1000 hrs for vacuum gyros and 1000 to
> > 2000hrs for electric. If you only have one vacuum AI overhauling it
every
> > 500hrs seems prudent.
> >
> > Mike
> > MU-2
> >
> >
> > "O. Sami Saydjari" > wrote in message
> > ...
> >
> >>As I reading through my aircraft logs, I noticed several replacements of
> >>the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> >>Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> >>years?
> >>
> >>Does anyone keep statistics or even projections for the mean time
> >>between failures on airplane parts? It sure would be useful to know.
> >>One would think the manufacturers would publish such information.
> >>
> >>-Sami
> >>
> >
> >
> >
>

[Jonathan Goodish]

In article >,
"O. Sami Saydjari" > wrote:

> As I reading through my aircraft logs, I noticed several replacements of
> the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> years?
>
> Does anyone keep statistics or even projections for the mean time
> between failures on airplane parts? It sure would be useful to know.
> One would think the manufacturers would publish such information.


I'm late to the party here, but I'll add my two cents:

I replaced the vac gyros in my Cherokee a couple years ago, with brand
new RC Allen gyros. They're still okay 200+ hour later, but they were
NEVER as good as the overhauled Sigma-Tek gyros that they replaced. I
had the Sigma-Tek's replaced because they had apparently been overhauled
and, presumably, owner installed. No yellow tags, no log entry, so I
assumed that they were 20+ years old original gyros, and I fly IFR.

When the RC Allens go, I'll seriously consider having them rebuilt by a
good overhaul shop, unless there's some compelling reason why I should
go out and invest in Sigma-Tek's again.



JKG

[Travis Marlatte]

Agreed. There are some good statistics out there. Flying had an article not
too long ago talking about lifetimes of vacuum pumps, gyros, etc. You have
to ask yourself, "Do I really want to wait until it fails?"

------------------------------
Travis
"Mike Rapoport" > wrote in message
hlink.net...
> I asked the same question after my only (vacuum) AI failied on a flight
> (turbo Lance) and was told 500 to 1000 hrs for vacuum gyros and 1000 to
> 2000hrs for electric. If you only have one vacuum AI overhauling it every
> 500hrs seems prudent.
>
> Mike
> MU-2
>
>
> "O. Sami Saydjari" > wrote in message
> ...
> > As I reading through my aircraft logs, I noticed several replacements of
> > the Directional Gyro and Turn Coordinator. The plane is a 1978 Piper
> > Turbo Arrow 3. Is is normal to need to replace these things every 4-5
> > years?
> >
> > Does anyone keep statistics or even projections for the mean time
> > between failures on airplane parts? It sure would be useful to know.
> > One would think the manufacturers would publish such information.
> >
> > -Sami
> >
>
>