I've watched several iFly tutorials, even some by a real-world 737 pilot.

Despite the fact the plane has VNAV, everyone seems to be constantly dialing-down altitudes on the MCP during descent almost two waypoints ahead, and using speed brakes a lot, and then dialing in flap speeds on approach. Doesn't the plane follow constraints for altitude and speed automatically?  Why is everyone dialing in future altitude and speed constraints?  Is that a normal part of the workflow or just compensating for the fact the plane cannot stick to what's programmed?  I even see tutorials where someone is dialing in more VS descent rate to reach a constraint because there's no way the plane is going to hit that constraint left unchecked - the green banana is well beyond the constraint waypoint until the pilot reigns it in.

Is this all normal?  Is the iFly plane bugged or this is just how 737 Max descents are managed?

Edited August 5, 2025Aug 5 by Virtual-Chris

1 hour ago, Virtual-Chris said:

Is this all normal?  Is the iFly plane bugged or this is just how 737 Max descents are managed

Are they using atc? If so they will usually be given altitude restraints they MUST enter on MCP to override the vnav. If no atc they may still prefer to be in manual control. VNAV is not always dead accurate irl depends on winds for a start (did they enter the predictions correctly during flight plan prep?). 

Hi ,

 

Real world 737-8 pilot here.

Vnav is great when it works well IRL, which most of the time it does. However, ATC may ask us to climb or descend early in which case there are several modes we could use, in the climb or decent a simple click of vnav alt near the ALT selector knob with vnav engaged will climb/decend the aircraft in VNAV. if you want to step down a level you could use LVL change, where it will then pitch for speed and climb at the commanded speed. V/S is also another shout but we refrain from using that as it is speed unprotected and not monitoring the aircraft during this mode is a big risk.

If your cleared for an approach, it is then your responsibility to following altitude constraints- so what i like to do is around 2nm before the next waypoint constriction ill change the MCP altitude knob to that restriction to keep the aircraft descending in VNAV PATH- if we don't do this the aircraft will level off to what's on the MCP and go into VNAV alt in which case you know need to do something to bring it back on its optimal decent profile. several ways to this - stay in vnav- and open the speed intervene window and increase speed, similar to level change, or go level change or V/S.

Now to your question-There comes a point the aircraft will go into approach logic during the decent and you'll see decel points on your N/D as long as you stay in vnav pth its telling the aircraft right i need to slow down at this point even more and should do automatically provided you are on the correct path and full use of automatics are engaged, now below the UP speed if you don't do deploy flaps it will just hold you at that speed until flaps are taken, and from there youll take your stages of flaps as you need and the speed will be commanded for that flap setting until you reach your landing flap and speed should then be at VREF automatically. In the real world i normally use VNAV to help with the path but ATC may radar vector you off, leave you high ETC.. so then its up to us to bring it back to its optimal path with the virous ways I've mentioned above. most of the time of drop it to level change and V/S to get CDA approach done at the latter stages when on an ILS. RNP is a different case totally.

Everyone has their own way of flying- some people make it more complicated with constantly faffing and using different modes and not understanding what the aircraft is doing.

I hope this makes sense, any other question let me know ill me more than happy to help.

 

 

4 hours ago, Bilal2104 said:

Hi ,

 

Real world 737-8 pilot here.

Vnav is great when it works well IRL, which most of the time it does. However, ATC may ask us to climb or descend early in which case there are several modes we could use, in the climb or decent a simple click of vnav alt near the ALT selector knob with vnav engaged will climb/decend the aircraft in VNAV. if you want to step down a level you could use LVL change, where it will then pitch for speed and climb at the commanded speed. V/S is also another shout but we refrain from using that as it is speed unprotected and not monitoring the aircraft during this mode is a big risk.

If your cleared for an approach, it is then your responsibility to following altitude constraints- so what i like to do is around 2nm before the next waypoint constriction ill change the MCP altitude knob to that restriction to keep the aircraft descending in VNAV PATH- if we don't do this the aircraft will level off to what's on the MCP and go into VNAV alt in which case you know need to do something to bring it back on its optimal decent profile. several ways to this - stay in vnav- and open the speed intervene window and increase speed, similar to level change, or go level change or V/S.

Now to your question-There comes a point the aircraft will go into approach logic during the decent and you'll see decel points on your N/D as long as you stay in vnav pth its telling the aircraft right i need to slow down at this point even more and should do automatically provided you are on the correct path and full use of automatics are engaged, now below the UP speed if you don't do deploy flaps it will just hold you at that speed until flaps are taken, and from there youll take your stages of flaps as you need and the speed will be commanded for that flap setting until you reach your landing flap and speed should then be at VREF automatically. In the real world i normally use VNAV to help with the path but ATC may radar vector you off, leave you high ETC.. so then its up to us to bring it back to its optimal path with the virous ways I've mentioned above. most of the time of drop it to level change and V/S to get CDA approach done at the latter stages when on an ILS. RNP is a different case totally.

Everyone has their own way of flying- some people make it more complicated with constantly faffing and using different modes and not understanding what the aircraft is doing.

I hope this makes sense, any other question let me know ill me more than happy to help.

 

 

Let’s forget about ATC for a moment. None of the tutorials we’re using ATC.

So if I have an approach programmed in that goes as follows and VNAV, LNAV, AT enabled…

- Waypoint A at 10,000

- Waypoint B at 4,500 feet

- IAF at 3,000 feet

- FAF at 1,500 feet

I feel the only thing I should have to do is press APP mode after B. The plane should fly this down to the threshold without me doing anything… true or false?

Every tutorial I’ve seen has the pilot dialing in an altitude well before… like 4500 before A, 3000 before B etc… what’s the point of that? 

It’s been awhile, but if I recall correctly, the Airbus will fly the path automatically and the only time you’re touching the AP controls is when ATC overrides your programmed path. Is the Boeing not capable of this as well?

 

Edited August 5, 2025Aug 5 by Virtual-Chris

When do you think the new altitudes should be dialed in on descent? 

Here's an example of what I'm talking about... 

At 1:38 he says: 

Quote

If you are descending in VNAV and there are several altitude restrictions along your route you basically need to set the next altitude restriction on your MCP until you are within one nautical mile of the Waypoint and meeting the Restriction is assured when that is the case you can dial the altitude down to the next lower way point this is standard Boeing operating proceedure

Is he doing this as a backup in case the plane doesn't fly the profile properly? Or is it what's driving the decent?

Edited August 5, 2025Aug 5 by Virtual-Chris

2 minutes ago, T_Bone said:

When do you think the new altitudes should be dialed in on descent? 

They are programmed into the FCU and part of the VNAV profile. Shouldn't the plane fly the profile without me dialing it in? It's like VNAV is broken or something.

Edited August 5, 2025Aug 5 by Virtual-Chris

Just now, Virtual-Chris said:

They are programmed into the FCU right and part of the VNAV profile. Shouldn't the plane fly the profile without me dialing it in? It's like VNAV is broken or something.

If you were descending from FL380 to 10,000 via the STAR for instance, you could dial in 10000 and it should meet the constraints if there are any and keep you on path. The plane in VNAV will not descend unless you dial in a lower altitude. Same with Airbus, they just call it managed descent. Is that what you're referring to? 

6 minutes ago, T_Bone said:

If you were descending from FL380 to 10,000 via the STAR for instance, you could dial in 10000 and it should meet the constraints if there are any and keep you on path. The plane in VNAV will not descend unless you dial in a lower altitude. Same with Airbus, they just call it managed descent. Is that what you're referring to? 

Maybe I recall incorrectly, as it's been a couple of years, but when I was flying the FBW A320 in MSFS 2020, I thought the plane would fly the decent without any intervention on the AP panel from me. In other words, it would fly down according to speed and altitude constraints automatically. I gather from what you're saying that I remember this incorrectly. You're saying both planes won't follow a VNAV path unless you manually enter the next lower altitude?  If that's the case, what's the point of VNAV then?

Edited August 5, 2025Aug 5 by Virtual-Chris

11 minutes ago, Virtual-Chris said:

Maybe I recall incorrectly, as it's been a couple of years, but when I was flying the FBW A320 in MSFS 2020, I thought the plane would fly the decent without any intervention on the AP panel from me. In other words, it would fly down according to speed and altitude constraints automatically. I gather from what you're saying that I remember this incorrectly. You're saying both planes won't follow a VNAV path unless you manually enter the next lower altitude?  If that's the case, what's the point of VNAV then?

Correct. Technically, you can dial in the field elevation and VNAV would take care of things. It rarely happens though because of several factors.  You must dial in a lower altitude though. That's just how it is or the aircraft will stay at cruise altitude. 

2 hours ago, Virtual-Chris said:

Is he doing this as a backup in case the plane doesn't fly the profile properly?

I guess so. It may be how they do it irl.

In the sim, I can tell you that both Airbus and Boeing aircraft can descent to platform altitude (let's say 3000ft) from cruise altitude in VNAV without ever changing the dialed in ALT. Edit: Of course, you have to dial in your descent target once before starting the descent. Depending on conditions or how accurate the VNAV is modeled, you may have to use speed brakes to stay on the profile.

Edited August 5, 2025Aug 5 by NovemberUniform

8 minutes ago, T_Bone said:

Correct. Technically, you can dial in the field elevation and VNAV would take care of things. It rarely happens though because of several factors.  You must dial in a lower altitude though. That's just how it is or the aircraft will stay at cruise altitude. 

But after you get it started, will it not descend and follow constraints automatically on the way down... you shouldn't have to keep telling it the next lower altitude at every way point should you?

6 minutes ago, NovemberUniform said:

I guess so. It may be how they do it irl.

In the sim, I can tell you that both Airbus and Boeing aircraft can descent to platform altitude (let's say 3000ft) from cruise altitude in VNAV without ever changing the dialed in ALT. Depending on conditions or how accurate the VNAV is modeled, you may have to use speed brakes to stay on the profile.

Thank you for a simple clear answer!

Just now, Virtual-Chris said:

But after you get it started, will it not descend and follow constraints automatically on the way down... you shouldn't have to keep telling it the next lower altitude at every way point should you?

 

1 minute ago, Virtual-Chris said:

But after you get it started, will it not descend and follow constraints automatically on the way down... you shouldn't have to keep telling it the next lower altitude at every way point should you?

 

7 minutes ago, NovemberUniform said:

I guess so. It may be how they do it irl.

In the sim, I can tell you that both Airbus and Boeing aircraft can descent to platform altitude (let's say 3000ft) from cruise altitude in VNAV without ever changing the dialed in ALT. Depending on conditions or how accurate the VNAV is modeled, you may have to use speed brakes to stay on the profile.

How would you descend without dialing in a lower altitude? 

37 minutes ago, T_Bone said:

If you were descending from FL380 to 10,000 via the STAR for instance, you could dial in 10000 and it should meet the constraints if there are any and keep you on path. The plane in VNAV will not descend unless you dial in a lower altitude. Same with Airbus, they just call it managed descent. Is that what you're referring to? 

100% correct. 

 

As mentioned here, if you are on a STAR and start from FL380 to FL 100 or 10,000 FT, and ATC says descend and maintain FL 100 or 10,000 FT, there are a few scenarios:

 

When in VNAV or not, set MCP ALT to 10000

Descend to FL 100 or 10,000 FT, which means you start descending now and act accordingly.

 

Descend at your discretion to FL 100 or 10,000 FT, and let VNAV do its magic.

 

Descend FL 100 or 10,000 FT via STAR. Now, you can have multiple step-downs or altitude restrictions, but you still dial 10000 in the MCP window, and the VNAV will honor these very well, unless there is a problem and pilot intervention is necessary.

 

What that guy is doing by dialing "next altitude for the waypoint" in VNAV with multiple step-downs on STAR or SID, IT IS NOT A BOEING/AIRBUS PROCEDURE, it might be a company procedure, or someone who does not understand the systems.