Altimeter questions

One aspect of the Gillham code (gray code) is that for each increment in 100 foot altitude change, only a single bit is modified. This is done to prevent erroneous readings when the altitude is changing. If multiple bits changed at the same time, it would be possible to report an erroneous altitude, because in reality, there is a small time period during the transition that the bits being changed could report either state. With only one bit changing, the altitude readout is either the previous altitude or the next 100 foot higher altitude if the aircraft is climbing.
 
denverpilot said:
Here's some fun for you: If the controller gives you 29.92 and you accidentally set 29.82, how far off the real altitude he wants you on, are you, and which direction, above it or below it? (And thus, how much closer to the aircraft he just sent under/over you.)
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Depends on the altitude.
 
Tom-D said:
that is the syndrome the 210 pilot last year at PAE, he like to push the limits too. the first thing he saw was the approach lights in the top of his windscreen, and that was the last thing he saw in his life.
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Obviously you weren't in the cockpit, so you don't know what he saw or what caused the accident. For all we know, it was an altimeter error detectable by my suggestions which caused the wreck.

And per the NTSB records, the last 210 to wreck at PAE was in 1998, and involved a pilot with severe medical problems and narcotics in his blood.
http://www3.ntsb.gov/aviationquery/brief.aspx?ev_id=20001208X06968&key=1
 
Ron Levy said:
Obviously you weren't in the cockpit, so you don't know what he saw or what caused the accident. For all we know, it was an altimeter error detectable by my suggestions which caused the wreck.

And per the NTSB records, the last 210 to wreck at PAE was in 1998, and involved a pilot with severe medical problems and narcotics in his blood.
http://www3.ntsb.gov/aviationquery/brief.aspx?ev_id=20001208X06968&key=1
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WoW time flys when you are having fun,,,,,, seems like yesterday When the WPA cleaned up that mess, and I didn't know he was on drugs for heart problems. But he was still below minimums that morning in the fog and beyond his limits.

I still won't push the mins. I don't trust the old equipment that much. and I won't fly a known bad altimeter, no matter how good I am with math. and calculations

IFR aircraft are required to have the altimeter/transponder checked every 2 years, why wouldn't you have the altimeter reset at that time?

as much as you preach safety, I don't understand why you would advocate doing the math, rather than getting the altimeter corrected.
 
John Collins said:
One aspect of the Gillham code (gray code) is that for each increment in 100 foot altitude change, only a single bit is modified. This is done to prevent erroneous readings when the altitude is changing. If multiple bits changed at the same time, it would be possible to report an erroneous altitude, because in reality, there is a small time period during the transition that the bits being changed could report either state. With only one bit changing, the altitude readout is either the previous altitude or the next 100 foot higher altitude if the aircraft is climbing.
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A very nice side-effect of system engineering of "soft" features (implemented in "software") by someone who's not "abstracted" from the hardware by a compiler... something rarely seen these days. :D

I miss the days when a good software engineer knew that voltages take time to transition from "on" to "off", and wrote accordingly. Heck, I'd just settle for software engineers that didn't trust the IP network explicitly and added some error-correction to their home-grown UDP junk. :)
 
Tom-D said:
that is the syndrome the 210 pilot last year at PAE, he like to push the limits too. the first thing he saw was the approach lights in the top of his windscreen, and that was the last thing he saw in his life.

Do the google maps thing, I believe you can still see the tail of the 210 sticking out of the light tower before you get to the clif. ( ILS 16R)
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Not seeing it. Is this the spot you're talking about? http://goo.gl/maps/LWin
 
flyingcheesehead said:
Not seeing it. Is this the spot you're talking about? http://goo.gl/maps/LWin
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I believe so, but it looks different after all the years.

The wires and pole he hit was the approach standard, and of course he was way low the runway is at least 1/4 mile beyond the accident scene.

It's more than probable that the last thing the guy saw was the thing he hit.
 
Ron Levy said:
Given his medical condition and drug levels, he may not have been seeing anything at all.
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That's a possibility, but giving the drug and its effects, I doubt it. His reaction time was slow, but the drug should not have impaired his vision.

Plus the fact the witness on the ground heard the engine come up on power just prior to the impact, leads me and many others, to believe he saw something coming out of the fog. more than likely the bright lights of the approach system.

It was a sad accident that points out you don't push the envelop specialty when you are impaired. or the aircraft or its systems are not working properly. such as the altimeter needles do not agree with the kolhsman window.

I read the preliminary report shortly after he accident, the toxicology reports were not in at that time, thus I did not know he was on drugs until I re-read the report after you pointed it out.

This is one of the best bad examples we have.
 
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Tom-D said:
That's a possibility, but giving the drug and its effects, I doubt it. His reaction time was slow, but the drug should not have impaired his vision.
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The combination of a narcotic and a heart condition might have rendered him unconscious, and unconsciousness has a way of impairing your vision. All in all, it seems:
  1. pretty unlikely that this one had anything to do with altimeter accuracy, and
  2. that it is irrelevant to a decision by a competent pilot who meets FAA medical standards to fly approaches to published mins.
 
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Ron Levy said:
The combination of a narcotic and a heart condition might have rendered him unconscious, and unconsciousness has a way of impairing your vision.
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bring power up right at the end, disproves that theory.
 
Baron2PG said:
OK, same topic different direction. For those IFR folks out there; when do you change your altimeter to match the field rather then ATC assigned? For example, I frequently fly into the western NC mountains. The "last" altimeter pressure setting provided by ATC is from the big airport east of the mountains. The difference from the field pressure and the assigned can be as much as a couple hundred feet.

My assumption and what I do is change to the field pressure when "cleared for the approach".
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You can ask the controller for a new altimeter setting at any time. Last time I visited Center (a long time ago), there was a huge whiteboard overhead with the wx conditions (including alt setting) for a whole bunch of airports written on it.

Bob Gardner
 
bobmrg said:
You can ask the controller for a new altimeter setting at any time. Last time I visited Center (a long time ago), there was a huge whiteboard overhead with the wx conditions (including alt setting) for a whole bunch of airports written on it.
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Which center was that? Spokane? Great Falls?
 
roncachamp said:
Which center was that? Spokane? Great Falls?
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Huh... I had no idea there was ever a Great Falls Center.

During most years, 28th Air Division had zero down time because the 28th shared her computer and displays with the FAA Great Falls Air Route Traffic Control Center. Great Falls Center was operated from 1962 to 1976 from the Malmstrom AFB SAGE site. As the first computerized ARTCC in the FAA, Great Falls was generally ignored by the FAA, both as history and technology, because FAA directors had already decided to go for "modern" equipment for the National Air Space System. Never-the-less the Great Falls Center was maintained to console the Air Force after the FAA had rejected most options for sharing equipment. Great Falls Center worked from the beginning with few hitches other than the need for regular programming changes to reinstall separation boxes, which were ignored when "vanilla" SAGE software versions were released. Great Falls Air Traffic Controllers were among the most productive in the country, which they advertised whenever controllers in Chicago or New York got raises to compensate for the immense workload at those centers.
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http://www.eskimo.com/~wow-ray/sage28.html

Edit: Lots of interesting history here, too: http://www.faa.gov/about/media/b-chron.pdf
 
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Ron Levy said:
Or maybe that's when he slumped forward, or maybe that one witness didn't know what s/he heard (c/s props don't "rev up").
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Yep you can what if it to death..
 
Ron Levy said:
Or maybe that's when he slumped forward, or maybe that one witness didn't know what s/he heard (c/s props don't "rev up").
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When the big blue knob is all the way in, as it should be on close final, what happens when you jamb the big red knob all the way in.
 
Ron Levy said:
(c/s props don't "rev up").
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Really? That's quite strange because I am pretty sure that when I go full throttle on a go around, I see the RPM climb from 1800-1900 or so on up into the 2500 range, and on take off they go from 800-1000 RPM or so up into the 2500 range, as well.

Must be a magical world you live in where CS props are always turning at max RPM.
 
EdFred said:
Really? That's quite strange because I am pretty sure that when I go full throttle on a go around, I see the RPM climb from 1800-1900 or so on up into the 2500 range, and on take off they go from 800-1000 RPM or so up into the 2500 range, as well.

Must be a magical world you live in where CS props are always turning at max RPM.
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I find it quite unusual to have the RPM down at 1800 on an instrument approch with a c/s propped airplane, but perhaps that's just personal technique.
 
Ron Levy said:
I find it quite unusual to have the RPM down at 1800 on an instrument approch with a c/s propped airplane, but perhaps that's just personal technique.
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don't you set the prop to high RPM setting on approach? almost every one I fly with does. and if the prop is on the low pitch stops, it will go from what you have set as power to Full RPM when you stab the throttle.
 
Ron Levy said:
I find it quite unusual to have the RPM down at 1800 on an instrument approch with a c/s propped airplane, but perhaps that's just personal technique.
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90kts, lightly loaded, my prop is not at max RPM for the manifold pressure generated. And I am almost always lightly loaded because it's just me in the plane, so I'm usually less than 80% MGW. But I am 1800 on base and final.
 
Tom-D said:
don't you set the prop to high RPM setting on approach?
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No, I don't -- not until I commit to land.
almost every one I fly with does.
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I can't speak to the experience and training of "almost every [you] I fly with."
and if the prop is on the low pitch stops, it will go from what you have set as power to Full RPM when you stab the throttle.
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Yes, it will, if the throttle is that far back, but on a plane like the 210, it isn't during an ILS.
 
EdFred said:
90kts, lightly loaded, my prop is not at max RPM for the manifold pressure generated. And I am almost always lightly loaded because it's just me in the plane, so I'm usually less than 80% MGW. But I am 1800 on base and final.
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The question involved flying an ILS in a 210. Different situation, that, from a normal traffic pattern.
 
Ron Levy said:
The question involved flying an ILS in a 210. Different situation, that, from a normal traffic pattern.
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You said c/s props, and did not limit it to c/s props on a 210 on an ILS. If I come in guns a blazing on an ILS, I'm gonna use up a ton of runway. The prop is off the stops for me when I do. The fact is, c/s speed props DO rev up - contrary to your statement.
 
Wow, typical thread creep. We went from altimeters to constant speed props.
 
Greg Bockelman said:
Wow, typical thread creep. We went from altimeters to constant speed props.
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That's one of the things that keeps PoA interesting, not to mention a really great resource for an inexperienced pilot like me.
 
EdFred said:
You said c/s props, and did not limit it to c/s props on a 210 on an ILS.
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The context was the accident to which Tom referred, not c/s props in general. Sorry you didn't realize you were jumping into the middle of an ongoing discussion.
 
Ron Levy said:
The context was the accident to which Tom referred, not c/s props in general. Sorry you didn't realize you were jumping into the middle of an ongoing discussion.
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Oh, I read the whole thread, but you are so quick to try and show everyone else how much you think you know, that you often don't clarify yourself. Even so, Comanche and 210 performance numbers are somewhat similar, and the prop comes off the stops during approach - ergo they will rev up if given throttle. So it is entirely plausible the witness was accurate in describing what they heard.
 
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Tom-D said:
User ID: Greg Bockelman)
En-Route
Pilots Of America Managemen
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What does that have to do with anything Tom? You're consistently not making much sense lately...
 
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