181204 Intermediate Segment Response Letter and Action Plan



800 Independen Ave

Washington, DC 20591





 



DEC O 4 2018

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Maximum Design Bank Angle AVS Action Plan

Recommendation: Amend the procedure design criteria in Order 8260.58A regarding maximum bank angles

and remove the breakpoint for RF leg design at RNP 1. Set the new, maximum bank angle for RF legs to 25

degrees for all RNP values, including RNP values less than RNP 1.0 (RNP<1.0).

Discussion: Full analysis and reasoning behind the recommendation is contained in the MITRE paper

“Analysis of Radius-to-Fix (RF) Bank Angle Margin Requirements”, Cramer/Herndon/Sprong, April 2009,

MP090076.

Reference DO-236C, Paragraph 2.6 Lateral Control Performance for the control authority requirement of 30

degrees for future systems.

Reference AC20-138D, Appendix 7-1c for the bank limit tested to in the RF demonstration for approval to use

RF.

Task 1: Update guidance in Order 8260.58A

Responsible Office(s)

Expected Completion Date

AFS-420

Tentative: 8/31/2019

Proposed: Update guidance in Order 8260.58A to authorize a maximum design bank angle for RF legs of 25

degrees for all RNP values.

Intermediate Segment Length Increase AVS Action Plan

Recommendation: The Navigation Working Group (Nav WG) recommends that 8260.58A take exception to

the sentence related to intermediate segment length in 8260.3C, Section 2-5-3, item (b) (1). 8260.58A should

be changed to add the following text:

1. “The intermediate segment length may not be greater than 15 NM unless the nominal track of the entire

segment is within 15 NM of the airport reference point. If the intermediate segment requires a stepdown fix,

increase the segment Required Obstacle Clearance (ROC) for the segment preceding (as flown) the stepdown

fix by 5’ per tenth of a track mile between the stepdown fix and the final approach fix. The maximum distance

from the stepdown fix to the final approach fix is 15 NM.”

Discussion: Working Group discussion focused on why the requirement might have been limited to a total

segment length of 15 NM. Since the standard ROC for the intermediate is 500’, it appears that the segment

length limit was a way to limit the errors in barometric altitude that could result from the aircraft being an

excessive distance from the altimetry source. In cases where a remote altimetry source is used, the intermediate

segment ROC is increased from 500’ by an amount governed by distance between the source and the

procedure airport, as well as by an amount that reflects the elevation difference. The group concluded that the

segment length was an attempt to limit the distance from the airport where the airplane is only protected by the

500’ ROC. The revision to the requirement that the WG is recommending solves this problem while

simultaneously allowing the segment to have a total length more than 15 NM where needed, as long as the

entire path is within 15 NM of the airport. Further, to limit exposure to the smaller 500’ ROC when a stepdown

fix is employed inside the intermediate segment, the recommendation employs an additive to the segment ROC

prior to the stepdown that depends on distance from (elevation above) the final approach fix.

Task 1: Update guidance in Order 8260.58A

Responsible Office(s)

Expected Completion Date

AFS-420

Tentative: 8/31/2019

Proposed: Update guidance in Order 8260.58A to authorize an intermediate segment to be longer than 15NM

provided the segment remains within 15NM of the ARP and to applies a 5’ per 0.1NM additive for stepdown

fixes.