Title: FIS - ASN.1 definition of VisibilityNautMiles 

PDR Reference:	                      97080012
Originator Reference:                   VisNautMile
SARPs Document Reference:               FIS SARPs, Section 2.4.4.2.1
Status:                                 ADOPTED
PDR Revision Date:                      22/09/97 (SUBMITTED -> ACCEPTED)
						     06/10/97 (ACCEPTED -> PROPOSED)
							29/10/97 (RESOLVED)
PDR Submission Date:                    18/08/97
Submitting State/Organization:          ATNP / WG3 / SG2
Submitting Author Name:                 Picard, F
Submitting Author E-mail Address:       picard_frederic@stna.dgac.fr
Submitting Author Supplemental 
Contact Information:                    ph 33 5 62 14 55 33
                                        fx 33 5 62 14 54 01
SARPs Date:                             IV1.1, March 97
SARPs Language:	                      English

Summary of Defect:

The following ASN.1 definition of VisibilityNautMiles:

VisibilityNautMiles ::= SEQUENCE
{
 nautMiles            INTEGER (0..127)
 -- units = nautical mile, range (0..127), resolution = 1
 fractionsOfNautMiles INTEGER (0..240)
 -- units = 16ths of Nautical Mile, range (0..15)
}

allows to specify more than 15 16ths of Nautical Mile per Nautical Mile (up to 240).
If used, such values could be mapped by SARPs compliant implementations onto a wrong operational value.
The specification of a non valid visibility distance is a safety issue and shall be corrected. 

If the defect is not corrected, SARPs compliant implementations could interpret differently the value specifying the visibility.

Assigned SME:                           Sub-Volume II SME

Proposed SARPs amendment:

Actually, as indicated in the ADSP Manual, the visibility values must be expressed in statute miles (SM) as opposed to the currently identified nautical miles. The current definition in nautical miles must be replaced by a definition in statute miles.

Change in the ASN.1 section from:

VisibilityValue ::= CHOICE
	{
	 meter 		[0] INTEGER (0..49),
-- units = meters, range (0.4900), resolution = 100
	 kms			[1] INTEGER (5..10),
-- units = kms, range (5..10), resolution = 1
	 nautMiles        VisibilityNautMiles
	}

to:

VisibilityValue ::= CHOICE
	{
	 meter 		[0] INTEGER (0..49),
-- units = meters, range (0.4900), resolution = 100
	 kms			[1] INTEGER (5..10),
-- units = kms, range (5..10), resolution = 1
	 statuteMiles     [2] VisibilityStatuteMiles
	}

Delete ASN.1 definition of VisibilityNautMiles.

Add ASN.1 definition of VisibilityStatuteMiles:

VisibilityStatuteMiles ::= CHOICE
{
 	 oneSixteen		[0] INTEGER (0..6),
	 -- unit = Statute Mile, range (0..3/8), resolution = 1/16th 
	 oneEigth		[1] INTEGER (3..16),
	 -- unit = Statute Mile, range (3/8..2), resolution = 1/8th 
	 oneFourth		[2] INTEGER (8..12),
	 -- unit = Statute Mile, range (2..3), resolution = 1/4th 
	 one			[3] INTEGER (3..15),
	 -- unit = Statute Mile, range (3..15), resolution = 1
	 five			[4] INTEGER (3..10),
	 -- unit = Statute Mile, range (15..50), resolution 5
	 morethanfifty	[5] NULL
}

SME Recommendation to CCB:              -

CCB Decision:                           atnp_ccb_chair: SUBMITTED (18/08/97)
						     atnp_ccb_chair: ACCEPTED (22/09/97)
							CCB-3: RESOLVED