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Reading the whiskey compass
When you're flying partial panel, to what precision do you read the
mag compass? To the nearest 5 degrees? Estimate to the nearest degree? How long do you go between readings and rely only on timed turns? For that matter, do you ever try to apply values from the correction card? In IMC or even VMC? -- Ben Jackson http://www.ben.com/ |
#2
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Unless you are flying in unnaturally calm conditions, precision with the wet
compass is hard to come by. IMHO compass turns should be eliminated from instrument training and timed turns emphasized. In my experience, few pilots pay any attention to the compass correction card, probably because the cards themselves are usually out of date. Bob Gardner "Ben Jackson" wrote in message news:3wZ_b.54783$Xp.264494@attbi_s54... When you're flying partial panel, to what precision do you read the mag compass? To the nearest 5 degrees? Estimate to the nearest degree? How long do you go between readings and rely only on timed turns? For that matter, do you ever try to apply values from the correction card? In IMC or even VMC? -- Ben Jackson http://www.ben.com/ |
#3
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#4
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"Michael" wrote:
I really have no clue why anyone would tolerate a whiskey compass in an IFR airplane. In my case, it's because I know of two occasions where VCC installations failed. In each instance the hysteresis error of the compass sometimes exceeded 10 degrees and none of the fixes proposed by the mfr. helped. I hate whiskey compasses. If you have any insights into how to achieve happiness with a VCC, I would be interested to read them. -- Dan C172RG at BFM (remove pants to reply by email) |
#5
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There's a good reason why NDB visibility minima are a mile or more.
You need to be able to see the airport when you get somewhere near it. ---JRC--- "Bob Gardner" wrote in message = news:M0a%b.56799$Xp.269573@attbi_s54... True story: The Boeing 747 building is east of the approach end of = runway 16 at Paine Field. The NDB approach is based on a beacon nine miles away. = On my ATP checkride, the FAA examiner had me shoot the NDB 16 approach, and = I did my very damndest....but when I called "missed approach" and he told me = to lift the hood, the Boeing building was to my right...my approach was = that far east of the runway. "Good approach," he said. =20 As an instructor, when a student shot an NDB with an off-field beacon = and ended up looking right down the runway, I assumed that he or she had = cheated somewhere along the way. Too many variables for an NDB approach to be perfect. =20 Bob Gardner |
#6
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There's a good reason why NDB visibility minima are a mile or more. You need to be able to see the airport when you get somewhere near it. I don't buy that. If you can't see it, you go missed. If you can see it, you land. Shooting an NDB with poor visibility may lead to more missed approaches, and perhaps that's their thinking (why tempt a pilot into attempting an approach that's likely to fail and leave him looking for his alternate) but OTOH, this should also be trained into pilots, and then the visibility thing becomes moot. It might be that, since you will be farther from the airport, you need to see more to avoid terrain, but again, you don't see the runway, you go missed. Jose -- (for Email, make the obvious changes in my address) |
#7
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Bob Gardner wrote:
True story: The Boeing 747 building is east of the approach end of runway 16 at Paine Field. The NDB approach is based on a beacon nine miles away. On my ATP checkride, the FAA examiner had me shoot the NDB 16 approach, and I did my very damndest....but when I called "missed approach" and he told me to lift the hood, the Boeing building was to my right...my approach was that far east of the runway. "Good approach," he said. Yes, I had a similar experience on my check ride. It was a very windy (10G15 on the surface and 40+ at 4,000') and bumpy day when I took my instrument ride. The examiner didn't require a PP NDB approach, but even with a full panel it was hard to set the DG accurately with the compass dancing a jig. ELM is in a valley probably 3/4 - 1 mile wide. The DE told me not to look outside upon reaching the MDA, but to wait for his call. When he said to look for the field, I was probably a good 1/4 mile off the runway, maybe even farther. I thought that was the end of the ride, but he said "good approach, you kept us between the mountains!" and we continued on. It convinced me though that I'd never fly an NDB in IMC to an airport in a valley unless it was the last option I had ... even though I believe the MDA at ELM is slightly above the tops of the surrounding mountains. Matt |
#8
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Bob
I guess I have a different opinion. I have no trouble using the compass even in light turbulence. Moderate turbulence is a different matter. Perhaps this is because the airplanes at my FBO have bad DGs that need to be reset every 5 minutes, and we just got used to reading the compass in bumpy air. Regarding timed turns, they will only get you to the approximate heading. For example, even if you are only 5% off from a standard rate turn (which is hard to tell on the TC), you will be about 10 degrees off after a 180-turn. In order to fine tune that heading, one needs to know about compass errors. I've seen students zig zag their way along a north heading because they didn't understand how to compensate for the banking errors. I do agree that the correction card is often overlooked because the card is out of date or the numbers are simply impossible to read. However, most of the correction cards I've seen are rarely more than 2 degrees off, which is well within the tolerance for flying approaches. "Bob Gardner" wrote in message news:WR5%b.56390$Xp.268321@attbi_s54... Unless you are flying in unnaturally calm conditions, precision with the wet compass is hard to come by. IMHO compass turns should be eliminated from instrument training and timed turns emphasized. In my experience, few pilots pay any attention to the compass correction card, probably because the cards themselves are usually out of date. Bob Gardner "Ben Jackson" wrote in message news:3wZ_b.54783$Xp.264494@attbi_s54... When you're flying partial panel, to what precision do you read the mag compass? To the nearest 5 degrees? Estimate to the nearest degree? How long do you go between readings and rely only on timed turns? For that matter, do you ever try to apply values from the correction card? In IMC or even VMC? -- Ben Jackson http://www.ben.com/ |
#9
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For example, even if you are only 5% off from a standard rate turn (which is hard to tell on the TC), you will be about 10 degrees off after a 180-turn. In order to fine tune that heading, one needs to know about compass errors. No, you do another timed turn. It will be shorter, and (in the above example) you'll only be off by half a degree. That's plenty good. Jose -- (for Email, make the obvious changes in my address) |
#10
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The wet compass will only give you an approximate heading as well.
This is the scenario I use against compass turns: You are flying at night, in turbulence, in the clouds, picking up ice, and your vacuum instruments fail. Your kids are crying, your wife is bombarding you with questions, and the mag compass looks like a washing machine. Would you use a compass turn or a timed turn? If your answer was a timed turn, then you are guilty of suiting the procedure to the situation, which doesn't pay off too well in an emergency. (I tried to put that scenario into the Instrument Flying Handbook, but it didn't get past the FAA editors.) Bob Gardner "Andrew Sarangan" wrote in message om... Bob I guess I have a different opinion. I have no trouble using the compass even in light turbulence. Moderate turbulence is a different matter. Perhaps this is because the airplanes at my FBO have bad DGs that need to be reset every 5 minutes, and we just got used to reading the compass in bumpy air. Regarding timed turns, they will only get you to the approximate heading. For example, even if you are only 5% off from a standard rate turn (which is hard to tell on the TC), you will be about 10 degrees off after a 180-turn. In order to fine tune that heading, one needs to know about compass errors. I've seen students zig zag their way along a north heading because they didn't understand how to compensate for the banking errors. I do agree that the correction card is often overlooked because the card is out of date or the numbers are simply impossible to read. However, most of the correction cards I've seen are rarely more than 2 degrees off, which is well within the tolerance for flying approaches. "Bob Gardner" wrote in message news:WR5%b.56390$Xp.268321@attbi_s54... Unless you are flying in unnaturally calm conditions, precision with the wet compass is hard to come by. IMHO compass turns should be eliminated from instrument training and timed turns emphasized. In my experience, few pilots pay any attention to the compass correction card, probably because the cards themselves are usually out of date. Bob Gardner "Ben Jackson" wrote in message news:3wZ_b.54783$Xp.264494@attbi_s54... When you're flying partial panel, to what precision do you read the mag compass? To the nearest 5 degrees? Estimate to the nearest degree? How long do you go between readings and rely only on timed turns? For that matter, do you ever try to apply values from the correction card? In IMC or even VMC? -- Ben Jackson http://www.ben.com/ |
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