First Time in IMC and vacuum problem

To have an AI "spool down" when the engine is running is totally
unacceptable. The gyro should spool up in seconds not minutes. You have
either a vacuum problem or the AI needs to be overhauled. It is probably the
AI as I assume that your vacuum guage reads OK since you didn't mention it.
Take this seriously! A failing AI is not something to take lightly.

Mike
MU-2

"Jon Kraus" wrote in message
...
I too had my first experience in IMC yesterday. I got my ticket last summer
too and have kept current but haven't had a chance to go solo. I was going
to go from Indianapolis Executive (TYQ) to Capitol City in Lansing Michigan
(LAN). The weather was 1000 OVR until 50 miles north of TYQ and then it was
clear all the way to LAN. THis was going to be a quick trip because the
weather in Indiana was forecast to get worse as the day wore on.

I was a little bit apprehensive because I have a respect to IMC but I
thought it would be good practice too. I got set up, picked up my
clearance and was off. Just as forecast I entered the clag at 1000 feet.
Right away I spotted something wrong with the attitude indicator. It was
looking like I was in a steep climbing turn. Oh **** I thought great time
for the AI to go out. I had a weird feeling of ending up as an Aftermath
column. I must say that I was pretty scared but strange enough not
panicked. I reduced power, used the Turn Coordinator to level the wings,
used the Airspeed Indicator to level off altitude. I called ATC and told
them that I was having a problem with the AI and needed their assistance.
They asked if I wanted vectors back to TQY to shoot the ILS 36 there. I
said yes. I started back to the field and the AI started to act like I
expected it should. After a few minutes I was still in the clag but all
instruments were working correctly. I thought about just continuing on
back to Lansing but I quickly talked myself out of it.

Really after I "calmed" down and the AI started acting correctly I didn't
have any problems navigating in the clouds. I shot the ILS 36 and broke
out 1000 feet above the runway, canceled my IFR flight plan and made an
uneventful landing. ATC wanted to know if I wanted to refill my flight
plan and I said no thanks. I was glad to be on the ground. I was thinking
about what just transpired and decided to talk it over with my CFI.

We determined that what probably happened was that the extended period of
idling on the ground caused the AI gyro to spool down some. It took
several minutes at cruise power for it to come back up to speed and after
that it indicated correctly.

Here is what I'll do different next time:

1. Make sure that I have had the vacuum indicator "in the green" for
several minutes before departing to ensure that the gyros are spooled up.

2. Have the approach for returning to the airport loaded or in standby
just in case you need to return quickly. I did not do this and it added
needless stress loading everything.

It is true what they say:
"It is better to be on the ground wishing you were in the air, then being
in the air wishing you were on the ground"

Jon Kraus
PP-ASEL-IA
Student Mooney Owner

The consensus that I've heard is that dry pumps should be replaced every 500
hours. I have to say that the more I learn about dry vs. wet pumps, the less
I understand how the latter came to be replaced by the former.

-cwk.

wrote in message
oups.com...
Colin,

That's true--but nobody seems to have any hard data on the MTBF of a
vacuum pump. I've seen some run 2000 hrs plus, and others quit at 200
(factory new.)

Airborne publishes a 'TBO' for their pumps that ranges from 400 to 1000
hrs, depending on the model. That should say something...

Hey, here's a (non)trivia question for you guys...

What is the (technical, operating) differnce between the old
turn-and-bank and the newer turn coordinator?

Gene

I do take it very seriously... I contacted the shop this morning and the
plane goes in tomorrow.. No IFR until it is determined what is broken...
Thanks for your comments..

Jon Kraus
PP-ASEL-IA
Student Mooney Owner

Mike Rapoport wrote:
To have an AI "spool down" when the engine is running is totally
unacceptable. The gyro should spool up in seconds not minutes. You have
either a vacuum problem or the AI needs to be overhauled. It is probably the
AI as I assume that your vacuum guage reads OK since you didn't mention it.
Take this seriously! A failing AI is not something to take lightly.

Mike
MU-2

"Jon Kraus" wrote in message
...

I too had my first experience in IMC yesterday. I got my ticket last summer
too and have kept current but haven't had a chance to go solo. I was going
to go from Indianapolis Executive (TYQ) to Capitol City in Lansing Michigan
(LAN). The weather was 1000 OVR until 50 miles north of TYQ and then it was
clear all the way to LAN. THis was going to be a quick trip because the
weather in Indiana was forecast to get worse as the day wore on.

I was a little bit apprehensive because I have a respect to IMC but I
thought it would be good practice too. I got set up, picked up my
clearance and was off. Just as forecast I entered the clag at 1000 feet.
Right away I spotted something wrong with the attitude indicator. It was
looking like I was in a steep climbing turn. Oh **** I thought great time
for the AI to go out. I had a weird feeling of ending up as an Aftermath
column. I must say that I was pretty scared but strange enough not
panicked. I reduced power, used the Turn Coordinator to level the wings,
used the Airspeed Indicator to level off altitude. I called ATC and told
them that I was having a problem with the AI and needed their assistance.
They asked if I wanted vectors back to TQY to shoot the ILS 36 there. I
said yes. I started back to the field and the AI started to act like I
expected it should. After a few minutes I was still in the clag but all
instruments were working correctly. I thought about just continuing on
back to Lansing but I quickly talked myself out of it.

Really after I "calmed" down and the AI started acting correctly I didn't
have any problems navigating in the clouds. I shot the ILS 36 and broke
out 1000 feet above the runway, canceled my IFR flight plan and made an
uneventful landing. ATC wanted to know if I wanted to refill my flight
plan and I said no thanks. I was glad to be on the ground. I was thinking
about what just transpired and decided to talk it over with my CFI.

We determined that what probably happened was that the extended period of
idling on the ground caused the AI gyro to spool down some. It took
several minutes at cruise power for it to come back up to speed and after
that it indicated correctly.

Here is what I'll do different next time:

1. Make sure that I have had the vacuum indicator "in the green" for
several minutes before departing to ensure that the gyros are spooled up.

2. Have the approach for returning to the airport loaded or in standby
just in case you need to return quickly. I did not do this and it added
needless stress loading everything.

It is true what they say:
"It is better to be on the ground wishing you were in the air, then being
in the air wishing you were on the ground"

Jon Kraus
PP-ASEL-IA
Student Mooney Owner

Mike Rapoport wrote:
To have an AI "spool down" when the engine is running is totally
unacceptable. The gyro should spool up in seconds not minutes. You
have
either a vacuum problem or the AI needs to be overhauled. It is
probably the
AI as I assume that your vacuum guage reads OK since you didn't
mention it.
Take this seriously! A failing AI is not something to take lightly.


I have to go with Mike here. An AI that malfunctions for a little
while, then goes back to normal, is the classic symptom of an AI that
is losing its bearings (no pun intended). Every AI that I've had to
overhaul exhibited this kind of behavior for months prior to its
complete failure (I fly VFR). I would suspect the AI particularly if
you noticed no deviation on the DG and the vacuum pressure was reading
normally.

The main problem with troubleshooting is that it won't do it on every
flight until the bearings get much worse.
John Galban=====N4BQ (PA28-180)

G. Sylvester wrote:

hehehehe. Runway 28L or 28R at SFO for me coming out of SQL
Rwy30. The landing fee will be more than than having a new vacuum pump
installed.

Hmmmm, would they wave the landing fee if you declared an emergency? :-)


--
Jack Allison
PP-ASEL, IA Student, airplane partnership student

"When once you have tasted flight, you will forever walk the Earth
with your eyes turned skyward, for there you have been, and there
you will always long to return"
- Leonardo Da Vinci

(Remove the obvious from address to reply via e-mail)

Colin W Kingsbury wrote:

The consensus that I've heard is that dry pumps should be replaced every 500
hours. I have to say that the more I learn about dry vs. wet pumps, the less
I understand how the latter came to be replaced by the former.

Same here. Maybe they are cheaper to make, but I can't for the life of
me understand why an airplane designer would use a dry pump on purpose.


Matt

The DG had precessed about 30 degrees in 5 to 10 minutes so I am
wondering if it isn't a vacuum problem. Reguardless it is in the shop
tomorrow for a through going thru. I just hope that this doesn't scare
me out of instrument flight... Time will tell.. Thanks!!

Jon Kraus
PP-ASEL-IA
Student Mooney Owner

wrote:
Mike Rapoport wrote:

To have an AI "spool down" when the engine is running is totally
unacceptable. The gyro should spool up in seconds not minutes. You

have

either a vacuum problem or the AI needs to be overhauled. It is

probably the

AI as I assume that your vacuum guage reads OK since you didn't

mention it.

Take this seriously! A failing AI is not something to take lightly.



I have to go with Mike here. An AI that malfunctions for a little
while, then goes back to normal, is the classic symptom of an AI that
is losing its bearings (no pun intended). Every AI that I've had to
overhaul exhibited this kind of behavior for months prior to its
complete failure (I fly VFR). I would suspect the AI particularly if
you noticed no deviation on the DG and the vacuum pressure was reading
normally.

The main problem with troubleshooting is that it won't do it on every
flight until the bearings get much worse.
John Galban=====N4BQ (PA28-180)

On Tue, 04 Jan 2005 01:15:15 GMT, Jon Kraus wrote:

The DG had precessed about 30 degrees in 5 to 10 minutes so I am
wondering if it isn't a vacuum problem. Reguardless it is in the shop
tomorrow for a through going thru. I just hope that this doesn't scare
me out of instrument flight... Time will tell.. Thanks!!

Jon,

Don't let it scare you. This incident will only make you a better pilot.

What you experience was the real deal, and while no simulated practice will
duplicate the adrenalin rush you got, the nice thiing was that the
simulated practice had you well prepared for this incident.

The plane doesn't care if it's IMC or severe clear.

The beauty of ownership is that YOU KNOW what's in the plane, and the care
taken to maintain the mechanical proficiency.

I will be interested to see if indeed it was the AI or vacuum pump.

Allen

Jose,

You are halfway there.

There is a small, but very important difference between the (older)
turn-and-bank instrument (vertical needle, plus ball), and the newer
turn coordinator (symbolic airplane seen from behind, plus ball.)

The vertical needle on the turn and bank deflects in an amount
proportional to the rate of turn. Only the rate of turn.

When autopilots became more common, the designers needed rate of roll
information to feed the autopilot. So, they canted the gyro axis
(typically 30 deg), such that the front end of the gyro is lower than
the back end. In this manner the gyro will respond to both rate of
roll and rate of turn. This makes life easier for the autopilot
designer, but potentially much more complicated for us pilots.

The problem with the turn coordinator is that its deflection is
proportional to our rate of roll if we are rolling, and then to the
rate of turn after we stop rolling. Unfortunately, there is nothing on
the instrument to indicate when it is showing roll rate and when it is
responding to turn rate.

If the instrument were undamped (no internal 'shock absorber'), in
turbulence it would bounce back and forth from full left to full right
indications as the aircraft takes roll hits left and right, and you
would never get to see the rate of turn. That is in fact what it does
if the dashpot wears out, as is true in many a light aircraft,
especially a lot of rentals.

This can be *very* disconcerting if you are, say, in a right turn, but
at the moment you scan to compare the bank on the AI with the turn
rate, the aircraft has just taken a left roll 'hit;' the AI will show
the valid right bank angle, and theTC will show a full left deflection
(which is really a response to roll rate, but again it doesnt tell us
that). It sure looks like a gyro failure. Having been there done
that, I can tell you it ratchets up the pucker factor quite a bit,
especially night IMC.

This effect is largely eliminated by the dashpot (minerature shock
absorber) inside the TC.

It isn't that expensive to OH a TC, and if you ever get caught in IMC
with turbulence (almost all IMC includes turbulence) with a dead AI or
a vacuum failure, you would at that point pay many tens of thousands of
dollars for a newly-overhauled TC.

In fact, the liklihood of making it back to the airport and down an
approach in IMC with an underdamped TC is right up there with the
proverbial 'ice cube's chance in hell.'

My point is, 1) understand what the TC is saying, and 2) check it for
proper damping, and 3) if it fails #2, stay out of the clouds until you
get it overhauled.

Gene

[big snip]
Thanks for the full explanation. I had forgotten how the instrument
was engineered (the 30 degree cant) and don't think I ever realized
how important the damping was. How do you propose to check it on
preflight (and to what tolerance?) I make gentle turns during taxi to
see how it responds, but I obviously can't give it a roll hit very easily.

Jose
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