It actually happened today!! Vacuum failure in IMC.

skym wrote:
Departed Asheville NC today into IMC enroute to Columbia SC. Well into
IMC and about 6500 MSL the DG started to slowly just start rotating and
the AI started to lean over. Backup vacuum-no help.

As others have already said, I'd appreciate some elaboration on why your backup
vacuum was no help.

I couldn't
believe this was happening in IMC; I only fly it about 5% of the time.
Columbia was just a bit above minimums. I was not prepared to try an
ILS with no operative DG, and most of the GPS approaches at CAE want a
WAAS capable GPS, which my G430 isn't.

Putting aside the anthropomorphism implied by approaches "wanting" a WAAS
capable GPS, I'd like to understand how this figured into your planning. All the
RNAV approaches at CAE have LNAV MDAs, so could be flown with your GPS. Why was
the lack of WAAS a consideration?

Second, I'd like to understand in what way you felt prepared to fly an RNAV
approach without a DG, but not an ILS approach. I'd think the workload is about
the same. Do you think having vertical guidance would be a distraction?

Congratulations are in order for handling your emergency safely and competently!

Dave

What was the reason for the 7700? Were you in controlled airspace?
Didn't ATC already have a positive ID on you before you changed the
transponder code?

-Robert, CFI

skym wrote On 10/06/05 17:26,:

3. An STEC A/P which runs on the TC, rather than the vacuum
instruments, is the way to go.

I agree, the STEC even has a separate altimeter (actually a
differential pressure transducer) with its on dual air inlet
placed midsection.

One question: was the A/P engaged during the AI fail ? Do you
think that would have made a big difference in keeping the
aircraft under control ?

If it wasn't engaged, did you engage it immediately ? Did you
wait to get the aircraft under control with the T&B before
engaging it ?

Thank you, and congatulations on your sucessful handling of
the situation.

Greg Farris wrote:

I'm curious about that too.

As am I. And which type of backup is it that didn't work for you?

- Andrew

Victor J. Osborne, Jr. wrote:


That's why I'm looking at the Mid-Continent Sporty's electric AI
replacement T/C.

And what will you do if that AI tumbles for some reason in IMC? That's been
my big concern about replacing the TC with an AI, and the relevent AC
doesn't even refer to that particular vulnerability.

Are there tumble-free AIs?

BTW, the Sporty's unit is not the Mid-continental; it's a Castle-something
(IIRC). The Mid-continental is more expensive than the Sporty's.

[...]
Keep in mind that even George w/ bail on you if the vacuum/pressure goes.
(S-Tec aside)

If George is, like most (all?) S-Tec units, rate-based then it'll survive a
vacuum failure in NAV mode. HDG mode, of course, will be unavailable
(unless you want to circle with the DG {8^).

Or is my understanding incorrect?

- Andrew

Dave Butler wrote:

Second, I'd like to understand in what way you felt prepared to fly an
RNAV approach without a DG, but not an ILS approach. I'd think the
workload is about the same. Do you think having vertical guidance would be
a distraction?


For that matter, the 430/530 has the ability to display track. That's even
better than heading for approach purposes.

[In fact, it's easy to become *too* dependent upon track, desired track, and
x-track error.]

- Andrew

I'm on a road trip and not near the plane right now, so can't tell you
the name. However, it is an electric pump, not the Precise Flight
model that draws off the manifold (or whatever), and is not dependent
on the throttle. They are still looking at things, and believe that a
shuttle valve either stuck or that something may have somehow gotten
sucked into the plumbing. The backup pump is, itself, working. I 'll
let this answer some of the other queries about what happened, until I
know more.

Dave,
I'll use this to answer both you and Barry, since you have both raisede
the WASS question, but you have a second one.

The rnavs 5,11, 23, and 29 at CAE have an entry that is "LNAV/VNAV".
I'm new to the panel GPS, having just gotten it about a month before
this trip so, although I have flown the approaches when familiarizing
myself with it, I had not thoroughly studied the GPS approach plates.
Before I left AVL, I'd looked at the plates and saw those notations,
and didn't look further. They require WAAS. I now (for the first
time) see that there are also simply LNAV approaches. I'm more
familiar with ILS than GPS approaches (obviously), and planned on an
ILS approach anyway, so hadn't really studied the GPS approach plates.
As for flying the GPS rather than the ILS into CLT, I've been so
indoctrinated into flying headings rather than "chasing the needle" on
an ILS that I had to rule that out. Although I was wrong about the
need for WAAS, I believed that I had no choice at that point-I'd do the
best I could with the GPS approach. The ceilings and vis were better
at CLT than at CAE (which was close to minimums) so it was less of a
risk (in my mind) to do the GPS approach at CLT even though I wasn't
(erroneously) properly equipped with WAAS.

It is my understanding that 7700 is what we are supposed to dial into
the xpdr when we declare an emergency. I was in controlled airspace.
Does that make a difference?

On 10/7/2005 6:02 PM, skym wrote:

It is my understanding that 7700 is what we are supposed to dial into
the xpdr when we declare an emergency. I was in controlled airspace.
Does that make a difference?


You only need to do that if you need to get someone's attention.
If you're in radio communications already, all you need to do is
declare it. There is no *requirement* to change your xponder code.


--
Mark Hansen, PP-ASEL, Instrument Airplane
Sacramento, CA