[Nspcsg] Iono Gradient GAST D Requirement Paper - For Your Review -- suggested changes

[Sam Pullen]

Dear Jim and group,

 

            After briefly reviewing this paper, I suggest modifying the
language (not the meaning) of the proposed new requirement in Section 4.1 on
page 6 for better clarity: 

 

Original Language:

                      

3.6.7.3.4 Ionospheric Gradient Mitigation

 

For FAST D ground subsystems, the probability of an error, |Er|, greater
than the broadcast EIG value in the Type 2 message on the 30 second smoothed
corrected pseudorange at the LTP (Landing Threshold Point), caused by a
spatial ionospheric delay gradient, is not detected and reflected in the
broadcast Type 11 message within 1.5 seconds, shall be less than 1x10-9 for
any approach supporting GAST D

 

Proposed Revision:

 

For FAST D ground subsystems, the probability of an error (|Er|) in the 30
second smoothed corrected pseudorange at the LTP (Landing Threshold Point)
that (a) is caused by a spatial ionospheric delay gradient, (b) is greater
than the broadcast EIG value in the Type 2 message, and (c) is not detected
and reflected in the broadcast Type 11 message within 1.5 seconds shall be
less than 1 x 10-9 for any approach supporting GAST D.

 

            Also, since Section 4.3.1 recommends broadcasting the new
parameter EIG in terms of two separate numbers from which EIG is calculated
by the aircraft, I suggest changing the phrase "greater than the broadcast
EIG value in the Type 2 message" to "greater than the EIG value computed
from the broadcast Type 2 message" to avoid any confusion.

 

            Regarding Section 4.3, I don't have any objections to its
content or the inclusion of EIG in this requirement, but I think the
introduction to this section (the two paragraphs prior to Section 4.3.1)
should give a more detailed explanation of its benefits.  Those of us who
have participated in this discussion can probably infer what is meant, but
the larger audience may not be able to without further explanation.  For
example, point (2) at the end of the first paragraph mentions several
concepts to be traded off, but more information is needed to follow the
train of thought that is implied here.  Also, in Section 4.3.1, it should be
made clear that the calculation shown in Eq. 1 is done by the aircraft,
which means that the aircraft also needs to calculate "D" for the approach
that it is conducting based on its knowledge of the approach path, LTP
location, and GBAS centroid location. 

 

            I'll be on tomorrow's telecon to address these and any other
issues.  Best wishes.

 

-------------------------------------------------

Sam Pullen

Stanford University

Durand Bldg., Room 250

Stanford, CA.  94305-4035  USA

 

Phone: +1 (650) 488 - 3816

Fax:     +1 (650) 725 - 5517

E-mail: spullen at stanford.edu

WWW: www.stanford.edu/~spullen

 

From: Nspcsg [mailto:nspcsg-bounces at aeronav.net] On Behalf Of McDonald,
James (SGNCOE)
Sent: Tuesday, September 23, 2014 12:59 PM
To: nspcsg at aeronav.net
Cc: 'john.warburton at faa.gov'; randy.key at faa.gov; Weed, Doug (SGNCOE)
Subject: [Nspcsg] Iono Gradient GAST D Requirement Paper - For Your Review

 

NSP CSG,

 

Please find attached an initial draft of the working paper summarizing the
requirement modifications we discussed last week.

 

We'll plan to discuss review comments during the next telecon on 9/25.

 

Regards,

 

Jim

 

Jim McDonald

Principal Systems Engineer

Honeywell Aerospace

Guidance & Navigation COE 
8840 Evergreen Blvd. 
Coon Rapids, MN  55433 
763-957-3390 
james.mcdonald at honeywell.com

 

 

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