Title: FIS - Invalid default value for the ATIS type

PDR Reference:              		99040001
Originator Reference:            	
SARPs Document Reference:         	FIS SARPs, Section 2.4.4.2.1
Status:                       	RESOLVED
Impact:					B (Bug)
PDR Revision Date:              	17/05/99 (PROPOSED -> RESOLVED)
						20/04/99 (SUBMITTED -> PROPOSED)
PDR Submission Date:           	01/04/99
Submitting State/Organization:    	STNA
Submitting Author Name:          	Picard, F 
Submitting Author E-mail Address:  	picard_frederic@stna.dgac.fr
Submitting Author Supplemental 
Contact Information:               	tel. +33.5.62.14.55.33
						fax. +33.5.62.14.54.01
SARPs Date:                      	IV2.3 (Doc 9705 Ed1) 
SARPs Language:                  	English

Summary of Defect:

The ADSP Manual in part V section 6.4.4.10 requires that the pilot be allowed to not indicate explicitly which type of ATIS (arrival, departure or combined) is requested.

In Doc 9705 Edition 1, the ASN.1 description of the ATIS Request makes "arrival" the default value for the ATIS type. As a consequence, if the pilot does not specify an ATIS type in his request, the ground system receives automatically a request for an arrival ATIS. This is not operationally acceptable.

The ATIS type should be made optional.

Assigned SME:                    	Sub-Volume II SME

Proposed SARPs amendment: 

In 2.4.4.2.1, change in type ATISRequest from:

ATISRequest ::= SEQUENCE
{
aerodromeID				Aerodrome,
arrivalDepartureIndicator	ArrivalDepartureIndicator  DEFAULT arrival
}

to:

ATISRequest ::= SEQUENCE
{
aerodromeID				[0] Aerodrome,
arrivalDepartureIndicator	[1] ArrivalDepartureIndicator 	OPTIONAL
}

Impact on interoperability

This change in the ASN.1 does change the bit on the wire encoding. The meaning of the extra bit when no indicator is provided indicates in the first case that an arrival ATIS is requested, in the second case that the ground is free to chose the type of ATIS to return as follows:
a) if available, provide a combined ATIS,
b) if both arrival and departure available but combined ATIS not available, provide an arrival and a departure ATIS,
c) if only arrival ATIS available, provide arrival ATIS
d) if only departure ATIS is available, provide departure ATIS, or
e) send a reject message indicating is unavailable. 

Therefore, there is no technical interoperability problem but a potential operational interoperability problem.

SME Recommendation to CCB: 		-

CCB Decision:                    	atnp_ccb_chair: SUBMITTED (01/04/99)
						atnp_ccb_chair: PROPOSED (20/04/99)
						CCB-9 (Naples): 17/05/99