Terminology questions
What does "SITU" acronym mean ? I know what it is and what it's for, but what does each letter
"stand for" .
The tutorial refers to a "sandwich" in the flight plan near to the destination. I have never used
this in any flight plan. What is it's purpose? I have been unable to find a definition....
Thank you,
Ken
Comments
SITU isn't an acronym, it's an abbreviation for Situation.
I'm not familiar with the sandwich but the name would imply popping something in between two other entries.
ckyliu - Proud supporter of www.ViaIntercity.com, over 950+ J41 & Q400 flights and 200+ for A320
So, it's the SITUation bag ~:)
Thank you for the info.
Ken
Regarding the "sandwich". I assume you are referring to the double entry of the IAF, seperated by a little designator, which indicates the type of the approach. "R" stands for RNAV approach, "I" stands for ILS approach, and "D" stands for VOR DME approach. (see screenshots below). So for example, a VOR approach onto Runway 28L would be displayed like this in the FPL: 'D28L'
Everything above the designator belongs to the "normal" part of the routing (or the STAR in most cases), everything below and including the approach type designator, belongs to the transition onto the approach. Hint: You can display this approach segment by hitting FPL->MENU PAGE 2/2->APPR PLAN 2/5 up to APPR PLAN 5/5.
https://i.imgur.com/1jePQvf.png
https://i.imgur.com/QEH3FTF.png
https://i.imgur.com/uAV28Q4.png
As you can see, the "sandwich" consists of IAF, followed by the Approach Type Designator, and again the IAF to finish it off.
Thank you for the _**excellent **_/ detailed "Sandwich" information.
The images helped also.
Is this flight planning detail (the "Sandwich") peculiar to the
Q400 ? I've not noticed it in other AC (Boeings, Airbusses, etc) .
How does it make the planning more safe or better otherwise ?
Best regards,
Ken
Yes, as far as I know, there is no other aircraft, that has these kind of sandwiches in their FPL. Also, I'm not really sure about the exact benefits of this method.
All I know is that the FMS is programmed in such a way to determine the base leg automatically, and upon reaching it, it will activate the approach mode on the NAV page by itself.
The activation of the approach mode causes the FMS to:
1. Draw an extended centerline.
2. Arming the Go-Around-Modes, bringing up the "MISD APPCH" on the NAV page and making the plane responsive to the GA button. (Pressing one of those would cause the FMS to skip the route disco between the "RW__*" waypoint and the missed approach procedure.)
3. Reduce the RNP when passing the final approach fix, which is crucial for some RNAV approaches.
The sandwich kind of serves as a "barrier" between STAR and final segment, or in other words, between normal FMS NAV operation and the NAV Approach Mode.
Therefore, my assumption would be that the advantage of having these sandwiches in the FPL is to help the pilots understand which mode the FMS is currently operating in and when it will switch into approach mode.
AWESOME explanation !! Very much appreciated. I am saving it, and adding
a hard copy to my MJC Q400 (manila) folder ~:)
Seems like the more I learn about this plane, the questions arise. Would you
happen to know if it's possible to set the cruise altitude in the FMC ? I can find
nowhere to enter it and it seems to default to FL230 for many of the mid flight
waypoints. Or perhaps there is provision to add a default Crz Alt in some
external way (ie. an ini or cfg file, etc.). Or do we just need to add them to
all the waypoints individually >> one at a time as necessary / desired ?
Best regards,
Ken
You don't need to enter a cruise altitude at all, neither as an altitude restrictions in the FPL nor on any other page of the FMS. As the Q400s VNAV is not designed to give you vertical guidance during climb phase, but only during descent, there is no need letting the aircraft know how far up you are aiming to go. The Q400 could not use this data for calculation in any way.
Most of the time you would aim for the highest FL possible, as the Q400s cruise altitude restriction (MAX FL250) isn't a performance restriction, but rather comes from the fact that most Q400 cabins are not equipped with oxygen masks. Meaning, technically a Q400 could climb a tad higher, but the safety equipment doesn't allow to.
Obviously, if the flight is really short you would not climb the highest you can. Also, the aircraft's weight would have an effect on the altitude selection on those flights. But in any other case, you would generally aim to cruise at the highest FL possible.
Thank you again for the info and for taking the time to prepare such detailed
explanations. Much appreciated.
Best regards,
Ken
Yes, nice explanations. That's good stuff lgl3592. Well done.