I fly a lot in and out of Canadian Airports, most of them are pretty small and have RNAV Approaches. When I look at the charts for these Approaches they say; "LNAV/VNAV: NOT AUTHORIZED" in the minumins section. So if I want the autopilot to fly this approach I can ONLY use LNAV + VS correct? The only time I can use VNAV/LNAV is if there are published Mins?

 

Cheers

You can still use VNAV to step down to the LNAV MDA, you just wont have the glideslope and there will be no incentive ie lower mins for doing so

So, if the chart says LNAV/VNAV not authorized, why would you use VNAV then? Makes no sense..

Reduces workload...

 

You're not constantly fiddling with the MCP

I fly a lot in and out of Canadian Airports, most of them are pretty small and have RNAV Approaches. When I look at the charts for these Approaches they say; "LNAV/VNAV: NOT AUTHORIZED" in the minumins section. So if I want the autopilot to fly this approach I can ONLY use LNAV + VS correct? The only time I can use VNAV/LNAV is if there are published Mins?

 

Cheers

Can you provide an example?

Well now wait a minute I know I CAN use VNAV but is this what the RW pilots would do?

You are correct in assuming that VNAV is not authorized for many of those smaller RNAV approaches...

 

The reasoning is that terrain will conflict with the VNAV path a lot of the times.

 

An example is the RNAV RWY 33 in Smithers, or the infamous approaches into Castlegar. If you just follow your VNAV path in there you'll most likely smack into the side of the mountain.

 

The exception of course is the fancy RNP stuff into Kelowna.

So if there are no published VNAV mins then just dont use it correct?

So if there are no published VNAV mins then just dont use it correct?

Which approach are you seeing this note on?

Here's an example Matt:

 

LNAV/VNAV minima to a DA(H) is not provided likely due to obstacles in the visual segment of the final approach, penetrating what is know as the glide path qualification surface (GQS). Therefore, only LNAV minima to a MDA (H) is published.

 

Nothing prohibits the use of VNAV on this approach; however, the pilot may not descent below the MDA using LNAV only minima without the runway environment in sight. Typically, pilots will apply an additive of approximately 10% of the vertical speed (some operators use 50 feet) to the MDA and apply it as derived DA when using VNAV to ensure that the aircraft doesn't descend below MDA during a missed approach.

 

Once below LNAV MDA, the VNAV path will NOT provide assurance of obstacle clearance. Pilots need to see and avoid any obstacles below the MDA.

 

Hope this helps.

 

Rich Boll