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#1
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Backup gyros - which do you trust?
There are several things you can add to help with the identification, In my
plane I have a low vacuum warning light (part of the precise flight backup) mounted between the AI and DG. The AI is one of the sigmatec ones with a vacuum flag, so that if vacuum is lost in the instrument but not in the system I still know about it right away. These warnings cover identification of the more common cause of loss of the AI. The other failure mode would be failure of the gyro, in which case I don't believe you get the insidious gradual spin-down like you do with loss of vacuum. I also fly with the GPS on the HSI page to offer yet another source of redundancy. Personally, I think the instrument scan typically taught relies too heavily on the AI given its relatively low reliability. Unfortunately, the alternative is a scan that works a bit more like a partial panel scan using the AI as supporting, not primary. Such a scan is much harder to master and requires considerable finesse to keep from chasing the needles. It is not one I would expect to be able to teach someone just learning to fly by instruments. -- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#2
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You have three sources of bank information in a typical panel: the attitude
indicator, the turn coordinator, and the heading indicator. If two agree and the third does not, it is faulty. Add a fourth source and it makes elimination that much easier. Bob Gardner "Steve House" wrote in message ... I've been reading with interest the several threads where a number of people have strongly pointed out the advantages of a backup electric AI to supplant a vacum driven main AI. But I'm reminded of the saying "A man with a good watch always knows what time it is. A man with two watches is never sure." So I'm toodling along in IMC with no outside horizon reference and I see my two AIs don't agree with each other. How do I determine which to trust? If I had a third, I could go with a 2 of 3 voting strategy of course, but with only two, what do you do to decide which is operating properly and which one has faulted? Obviously I can look for consistency with other instruments - does my DG or Turn indicator show I'm turning, does the VSI show a climb or descent - but what would be the best strategy given the various ways vacuum or electric driven instruments can fail? |
#3
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The presence of two attitude indicators is especially valuable when they
disagree. That disagreement will direct your attention to the needle/ball and basic flight instruments to help determine which one is correct. With a single AI you could more easily follow a gyro error without noticing a difference in the other basic instruments until it was too late. -- Darrell R. Schmidt B-58 Hustler History: http://members.cox.net/dschmidt1/ "Steve House" wrote in message ... I've been reading with interest the several threads where a number of people have strongly pointed out the advantages of a backup electric AI to supplant a vacum driven main AI. But I'm reminded of the saying "A man with a good watch always knows what time it is. A man with two watches is never sure." So I'm toodling along in IMC with no outside horizon reference and I see my two AIs don't agree with each other. How do I determine which to trust? If I had a third, I could go with a 2 of 3 voting strategy of course, but with only two, what do you do to decide which is operating properly and which one has faulted? Obviously I can look for consistency with other instruments - does my DG or Turn indicator show I'm turning, does the VSI show a climb or descent - but what would be the best strategy given the various ways vacuum or electric driven instruments can fail? |
#4
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"Ray Andraka" wrote in message
... Good reason not to depart in low IMC I guess. I agree, that the AI is a weak link and carries with it some risk. While nice to have, cost and panel space make the back up AI difficult in some aircraft. I think it is a matter of priorities... in an airplane which is IFR certified, it is hard to believe there is not some space or economic compromise which could not be made if a pilot felt this were an important enough issue. I know I will get diagreement on this as always, but I think the electric AI comes first before an IFR GPS. Even C152s sometimes have Garmin 430s/530s nowadays; an electric AI would make much more sense IMHO. As an even better solution, Hal Sheevers of Sporty's has for quite some time been lobbying the FAA to permit an electric AI to replace a turn coordinator... it does not seem as if the issue is getting very far with the FAA, but I do think that would be a very good compromise if we started to see electric AIs installed in place of the turn coordinator on planes where panel space is tight. -- Richard Kaplan, CFII www.flyimc.com |
#5
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The problem isn't just finding a home for it, it is finding a home for it that
is in a spot where it will be in the pilot's primary scan. I don't think it would do much good on the other side of the panel where it might only be referenced once a minute or less. I also agree that an IFR GPS is not necessarily a high priority. Frankly, that (the GPS) is a lot of money for very little added capability. In the case of a GPS/Nav/Comm, it also introduces a single point of failure for all of the electronic nav gear with no back-up other than what might be in your flight bag. It is a shame that many of the simulators do not fail the AI the in the gradual way it fails for real. I think training with realistic failures is the best way to be able to recognize the failure (some of the accident reports indicate even with redundant AI's recognition is not guaranteed). Unfortunately, the failures can't be realistically simulated in the aircraft (at least not without an illegal mod to the vacuum system), so ground based simulators must fill in there. I've hear that some of the high end simulators such as the Frasca's do a realistic AI fail, but the PCATDs I've played with all just pop from working to tipped over instantaneously. Any of the current breed of PCATD's do any better? Mine is a really old version of Elite, from about 1995 or so. Richard Kaplan wrote: "Ray Andraka" wrote in message ... Good reason not to depart in low IMC I guess. I agree, that the AI is a weak link and carries with it some risk. While nice to have, cost and panel space make the back up AI difficult in some aircraft. I think it is a matter of priorities... in an airplane which is IFR certified, it is hard to believe there is not some space or economic compromise which could not be made if a pilot felt this were an important enough issue. I know I will get diagreement on this as always, but I think the electric AI comes first before an IFR GPS. Even C152s sometimes have Garmin 430s/530s nowadays; an electric AI would make much more sense IMHO. As an even better solution, Hal Sheevers of Sporty's has for quite some time been lobbying the FAA to permit an electric AI to replace a turn coordinator... it does not seem as if the issue is getting very far with the FAA, but I do think that would be a very good compromise if we started to see electric AIs installed in place of the turn coordinator on planes where panel space is tight. -- Richard Kaplan, CFII www.flyimc.com -- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#6
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"Ray Andraka" wrote in message ... The problem isn't just finding a home for it, it is finding a home for it that is in a spot where it will be in the pilot's primary scan. I don't think it Put it where the turn coordinator is located and the put the turn coordinator off to the side somewhere.. the regs say you must have a turn coordinator but do not say where the turn coordinator has to be on your panel. tipped over instantaneously. Any of the current breed of PCATD's do any better? Mine is a really old version of Elite, from about 1995 or so. The current Elite software allows a choice between instant or gradual AI failure. They have a reasonable upgrade program for their software as well. -- Richard Kaplan, CFII www.flyimc.com |
#7
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"Gary L. Drescher" writes:
In MS FS2002, the AI fails abruptly, in just a few seconds. But I've heard that FS2004 (due late this month) has more-realistic gyro failures. If you don't want to wait, FlightGear already has gradual gyro failures. You can fail an individual gyro or an entire system (i.e. vacuum or electrical): http://www.flightgear.org/ All the best, David -- David Megginson, , http://www.megginson.com/ |
#8
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I thought one of the reasons for the turn coordinator is that it won't tumble in
unusual attitudes where the AI will. I once tumbled my AI in IMC, and it was not a pretty thing. Gave me a real bad sense of vertigo. At the time I had a needle and ball rather than a TC, but that was the instrument that let me sort things out. I think I would still want either a T&B or a TC in my primary scan. Richard Kaplan wrote: Put it where the turn coordinator is located and the put the turn coordinator off to the side somewhere.. the regs say you must have a turn coordinator but do not say where the turn coordinator has to be on your panel. -- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#9
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Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning
lights on the annunciator panel. If I had an electric AI and a vacuum AI and they disagreed markedly, I would be suspicious of the one having warning lights and flags all over it. Otherwise, comparing them to the other instruments, as you suggested, is the best approach. AOPA Safety Foundation just ran some tests on how long it takes a pilot to recognize that his vacuum system has failed, and how long it takes pilots to recover from those failures. Many times it took over 90 seconds, which is way too long. Some never did recognize the failure. However, none of them were convinced that the vacuum instruments were working and that it was the other instruments that had failed. IIRC somewhat less than half discovered the problem quickly and took quick action. Only about 1/4 of them covered the failed instrument. |
#10
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On 13-Jul-2003, Ray Andraka wrote: The problem isn't just finding a home for it, it is finding a home for it that is in a spot where it will be in the pilot's primary scan. I don't think it would do much good on the other side of the panel where it might only be referenced once a minute or less. Our Arrow has a backup electric AI on the right side of the panel. It is turned on whenever I am in or near IMC. I do not include it in my primary instrument scan, but check it periodically to make sure it is on and stable. I have fortunately never had a failure of my vacuum AI in IMC, but I have practiced under the hood with the vac AI and DG covered, using the electric AI for guidance. For me, it only takes a few seconds to get comfortable with looking across the panel, and sure beats sweating bullets trying to hold attitude and a reasonable course with only the TC, particularly in turbulence. So, the only issue is whether I could detect a failed vac AI before it leads me (or the autopilot) into an unusual attitude. If the problem is (as is most likely) a vacuum pump failure, I have a vacuum warning light right in front of my eyes that would be hard to miss. But a failure of the gyro itself could be trickier. I tell myself that if I can't keep a reasonable course (per the DG) with a wings-level attitude (per the AI), then something is wrong and I need to immediately refer to the TC and the electric AI to sort things out. -Elliott Drucker |
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