LNAV/VNAV with answer

14.06.2012

Submission:

In a RNP APCH LNAV, airspace constraints compell MAPt to be placed 1NM prior to threshold and also used as TP. As OCA is little high for LNAV, it is acceptable. While assessing APV BaroVNAV for the same approach, corresponding OCH is quite low. As the airspace does not allow MAPt to move closer to THR, the only option is to increase OCH for LNAV/VNAV to allow turn at MAPt. In this case, what value of OCH should be selected for LNAV/VNAV to avoid coding and other operational issues?

Is any other constraint is also foreseen with such APV implementation?

I really appreciates and thankful to Mr. Whitworth and ASAP to maintain this important forum for procedure designers.

Arif Mumtaz - Pakistan Civil Aviation Authority - Procedure Designer



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Answer or Commentary:

First of all, with a MAPt not at THR for Baro-VNAV guidance you might have a problem with some aircraft that cannot use the VNAV guidance due to an avionic issue. For the Baro-VNAV procedure, a turn at the MAPt is delicate, when the MAPt is not at the THR. The earliest MAPt terminates the APV segment and the OCH cannot be lower that the nominal altitude on the VPA at ATT before the MAPt and the latest TP must be calculated according to general criteria (3s+15s to SOC, then reaction and bank establishment time). Then of course, the full validation process according to doc. 9906 vol. 5 applies and will identify any database issues if the occur.


Beat Zimmermann - Air Navigation Institute GmbH - Switzerland

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