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Tired (gyro) Attitude Indicator: what kind of maintenance needed ?

Hello,

I had my IFR check ride today, and after an approach, go around and initial climb, I leveled and noticed that the back-up artificial horizon was still in the descent… [which it was not for the first part of the flight].
A few minutes later (5-10 minutes), the AI went back to normal indications, and so on for the remainder of the flight.
I should had that, even when completely wrong in pitch, it was still giving good roll informations.
VAC pressure was in the green. VAC filter is changed as advised.

This is the first time I notice a problem with this instrument. It is 10 years old, and suppose it has never received any maintenance. For information PN is S-3326-2.

Any idea about what is happening and what should be done to cure ?


I think it’s time to consider euthanasia for that poor old windywheel, and replace it with a brainchild of James Clerk Maxwell (who happens to be buried in our village kirkyard).

In about 800 hours of flying “mature” (you might say junk) aeroplanes equipped with vacuum gyro(s), I think I can count five or six failures of pump or gyro. So every hour I spend in IMC seems to carry a 1 in 160 chance of enjoying some real limited panel cloud-drilling.

Fun though that might be, I think I’m in broad agreement with the FAA – that the safest use for vacuum instruments is for target practice and land-fill.

Last Edited by Jacko at 21 Sep 21:49
Glenswinton, SW Scotland, United Kingdom

I had a very similar situation in May, except that mine had troubles with roll rather than pitch. 125 EUR worth of cleaning brought it back to life.

P.S. In my case it also happened on an IFR checkride. Damn.

LKBU near Prague, Czech Republic

True Jacki but what choices does PCV have?

Get it overhauled about 400 quid in the UK or get a new one for about 1200 pounds are the options.

It would appear I’m a bit more fortunate with instrument/vacuum failures than you. But sadly not by much.

We really should be allowed to fit something safer in this day and age.

PetitCessnaVoyageur wrote:

I should had that

I meant ADD

Jacko wrote:

I think it’s time to consider euthanasia for that poor old windywheel, and replace it with a brainchild of James Clerk Maxwell (who happens to be buried in our village kirkyard).

Thank you Jacko for the suggestion, but, as a back-up instrument, in my Cessna equipped with just one alternator (+ 1 main and 1 back-up batteries), I guess it works with Vacuum for redundancy. I suppose that some electric gyro can also have an internal back-up battery, but that would mean a modification of the aircraft, and the investment in a new instrument. I would prefer another way

Ultranomad wrote:

I had a very similar situation in May, except that mine had troubles with roll rather than pitch. 125 EUR worth of cleaning brought it back to life.

125€ is a good deal ! I guess your bearings were still in a good fit, and I don’t know if it is the case for me.
It’s nice to you to give me an idea of the cost, so that I can appreciate in a better way the quotation(s) I’ll get.

Bathman wrote:

Get it overhauled about 400 quid in the UK or get a new one for about 1200 pounds are the options.

400£ is more than 125€ , but OH may imply replacement of some parts ?
1200£, is it the cost of a new electric AI ? Actually, the gyro AI made by Cessna (S3326-2) is $5000 !!! (here)

Bathman wrote:

We really should be allowed to fit something safer in this day and age.

To be fair, this is the back-up instrument, and the main one (AHRS) should be much more reliable. Or am I wrong here ?

Last Edited by PetitCessnaVoyageur at 22 Sep 06:04

I just put a new sigma Tek DI in and it was 1200 quid. AH were a similar price and this was unlit and with no heading bug.

RC Allen were cheaper at about 900.

The DI I replaced was overhauled 5 months and about 200 hours earlier

Last Edited by Bathman at 22 Sep 06:39

Electric is better and simpler and avoids the vac pump etc but as stated above it is no good running two horizons off the same single alternator

That is where vacuum comes in. Even if you get a total loss of electrics, the mail instrument needed in IMC will still be there.

The various battery backed up electronic (LCD display) AIs – plenty of threads on them here – all cost thousands.

This might be relevant.

Administrator
Shoreham EGKA, United Kingdom

I do understand the principle of having a totally independent backup, if it is reliable. I’m less convinced of the sanity of backing up a somewhat reliable glass panel with a system which is known to be unreliable. It seems a bit like carrying a parachute bought in a flea market.

So I see the options as

  1. Pay EUR 2,000+ over the next few years to keep the vac system going, plus 1,000 for a Dynon D2 to keep in your flight bag.
  2. Pay 2,000 now for a Garmin G5 with STC and 4 hour internal battery and buy Mrs PCV a handbag with the change.
Glenswinton, SW Scotland, United Kingdom

Peter wrote:

This might be relevant.

Yep, I remember that, kind of premonition :-)

Jacko wrote:

I do understand the principle of having a totally independent backup, if it is reliable.

I understand your statement, even if the probability to get both of them fail at the same moment, should not happen. And I know the rule “if something can happen, it will” :-D

Jacko wrote:

So I see the options as

Pay EUR 2,000+ over the next few years to keep the vac system going, plus 1,000 for a Dynon D2 to keep in your flight bag.
Pay 2,000 now for a Garmin G5 with STC and 4 hour internal battery and buy Mrs PCV a handbag with the change.

You’re right, I will inquire Mrs, to check which option she prefers :-)
More seriously, do you really think that this failure is announcing several / frequent other ones to come, and a high budget to maintain it other the years ?

Could the G5 be fitted as back-up in G1000 set-up ?
Could it be connected to the informations of the G1000 (gps, heading…) ?
Can it be configured as a AI alone ?

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