All About Altitude, not attitude

I'm just about sick of going over and over and over this. But I must remember not everyone has read everything I have read. And we are all very different people with different lives, habits, and abilities.

So let's start with the basics from the source.

For Kollsman Specifications go here:
Kollsmans Inc Instruments

You will find several documents, let's look at the Servoed Altimeter, since this is the one most likely used by commercial cargo fleet.

A41322 PDF
Accuracy: +- 20 Feet

I will continue my break down later. Work calls...

UT,

Thank you!

This is an area I obviously have tons to learn. One of the things about looking into all of this is that it requires multiple specialties. The learning curve can be harsh.

As part of this thread maybe you could post what the .csv file says about altitude, pressure and heading for the first and last minute of the flight. That would help very much since I am developing some graphics (if they can be recovered from my hard drive).

I am looking forward to your developing this thread.

Russell

This is the type of altimeter found in transport category aircraft.


Highly accurate.

Russell.. dont you have the .csv file and the animation?

If not.. the csv file can be downloaded here

off-topic

This post has been edited by UnderTow on Sep 27 2006, 01:55 AM

off-topic

This post has been edited by UnderTow on Sep 27 2006, 01:55 AM

off-topic

This post has been edited by UnderTow on Sep 27 2006, 01:56 AM

You do realise that the altimeter in the cockpit, per se, plays no part in the DFDR altitude data?

Yes, there is data about what QNH was set in the Kollsman window - but the DFDR was taking its pressure altitude data from the Air Data Computer.

What is important is the sensor system that was providing information to the ADC, and the ADC itself.

Some background reading for you:

http://www.ssec.honeywell.com/pressure/datasheets/AN104.pdf

Actually that is somewhat incorrect. The ADC, Alitmeter Gauge, FDR, (and other sytems) are linked together and cross check each other with reliabilty signals every second.

And from your document

One factor discussed in ARINC Standards is Accuracy

This is the total accuracy of the input data before recording as described in Section 4.1.1 of ARINC 573 and ARINC 717. Some factors included in the accuracy figure are:
-- Sensor tolerances.
-- FDAU tolerances.
-- Non-linearities of the analog to digital conversion process.

For example:
Parameter Range || Accuracy (±)
x < 10000 ft || 20 ft
10000 < x < 30000 ft || 25 ft
x > 30000 ft || 30 ft


Another factor discussed by ARINC is Transport Delay.

Example:

----

Redundancy is the backbone of every aircraft.

Nice job UT...

A beg to differ, but you are somewhat incorrect.

The ADC feeds the data to the altimeter and to the DFDR. In case of ADC failure, there are backup modes.

The altimeters can both fail entirely and it will not affect the DFDR Pressure Altitude data unless the ADC or the DFDAU fail / are in error.

Excerp from the B757 manual:

The other quote is correct. That is the accuracy required by the ADC according to that standard. By that, you would have to say that the DFDR pressure altitude data is within +/- 25 feet.... if the system is within its certified operating range.

As was pointed out on another thread, you have to find out if the sensors and ADC were accurate when operating some 100 knots faster than Vmo. Until you do, the DFDR pressure altitude data may be in error. The airspeed sensors are rated for that speed but the altitude data may not be.

Perhaps we are saying the same thing.

Vmo is aircraft specific.. not instrument specific.

These ADC's and DAU's are used in all types of aircraft with all types of Vmo's.

You dont start getting into instrument error on these Air Data Computers until you hit transonic/supersonic ranges. And from what i understand, they just make a slight "tweak" to the ADC if it is going into a supersonic aircraft.

Hanging onto "errors" in order to not disturb govt theory is reaching in its purest definition of the word.

I have already covered lag issues and/or instrument error. If you think in any way, shape or form that aircraft was low enough to hit the light poles.. the descent rate would have been too great to pull out of that dive instantaneously to have been level across the lawn.. (it is at that point right now without errors)... as shown in the DOD video.


Again.. what good is an FDR that cannot record valid parameters outside the aircraft envelope?

This is the type of altimeter found in transport category aircraft.


Highly accurate.

Like, for example, a C130, like the one spotted above the Pentagon and the one spotted in Penn. air space near where everybody has been lead to believe F93 crashed?