Using V/S and setting Missed Approach Altitude problem

[captdini 3]

Hi guys,

 

At the outset, let me apologize for this lengthy post. I am describing a scenario where I feel there is a bug in the system logic on the NGX compared to the real aircraft.

 

I was doing a raw data VOR approach the other day using V/S for descent from the FAF. Prior to reaching the FAF, the aircraft was correctly configured viz., approx 2NM from FAF, Gear Down, F15, Speed brake armed. The DDA was set on the MCP as I was doing a CANPA (no intermediate level off) to minima. FMA was annunciating MCP SPD, VOR/LOC and ALT HOLD as it should and v/s was armed in white which is correct. A/P was engaged. For whatever it is worth, Active waypoint in the LEGS page was RWYxx and a missed approach procedure was active.

 

Prior to reaching the FAF, I selected landing flaps, set Vapp, completed the landing checklist and began the descent from 2500 feet which was the FAF crossing altitude down toward the DDA of 700 feet. V/S was adjusted to maintain the aircraft on profile. FMA correctly annunciated MCP SPD, VOR/LOC and V/S with A/P engaged

 

Now the Boeing FCTM states that approximately 300 feet above the DDA, set Missed Approach altitude, in this case, to 4000 feet. My intention was to keep the A/P engaged just prior to reaching MDA, and then disconnect, recycle the FD's and land.

 

Now this is where the system logic gave me a problem and I think is not correct. With the A/P still engaged and at around 1000 feet (300 feet above DDA) I started to change the MCP Altitude from DDA of 700 feet to the Missed Approach Altitude of 4000 feet. As the MCP altitude selector was going through approximately 1000 feet, V/S disengaged and ALT HOLD annunciated, thereby starting to reduce the Rate of Descent towards a level off. I initiated a Go Around at this point and positioned for another approach.

 

I once again tried the same scenario, but this time I started to set the MCP altitude towards the MIssed Approach Altitude much higher at approximately 2000 feet. Once again, as the MCP altitude came close to the Aircraft Altitude, V/S disengaged and ALT HOLD engaged. I disengaged the A/P, readjusted the profile and stabilized by about 1600 feet and continued for a manual landing

 

Having spoken to a friend of mine who is an NG TRE, he said this problem used to occur in the Classics, but is not an issue in the NG. He went on to say, in actuality, that after you begin your descent towards the MDA in V/S you can set the Missed Approach Altitude at anytime when at least 300 feet below the Missed Approach Altitude.

 

I hope I have been able to describe the scenario clearly. Could I request one of the PMDG staff to replicate this and let me know if you are facing the same scenario? For that matter, if anybody reading this wants to try and replicate this and let me know what you find, I would be extremely grateful.

 

While on the subject of system logic, another issue(very minor) I have come across is the logic of the Displays Control Panel Switch on the OVHD panel. When I do my preflight setup I set the current QNH and Minima (Baro) selector to Thrust reduction Altitude on the Captain's side. As a shortcut, I once put the CONTROL PANEL switch on the OVHD to BOTH ON 1. Correctly, the F/O's PFD also changed the QNH and minima setting to match the Captain's PFD. But once I moved the Switch back to NORMAL, the F/O's PFD showed the previous QNH and Minima setting. On verifying with my friend, this again is wrong because he said that after putting the switch back to NORMAL, the F/O's QNH and minima will not revert back to their old settings but will continue to remain at the changed setting after the switch was moved to BOTH ON 1. Can anybody verify this as well? 

 

If possible, I will ask him to video this on his next flight.

 

Cheers, and once again sorry for this lengthy post.

 

Regards,

 

Dinshaw Parakh

[Driver170 42]

I think you need to turn the MCP ALT alot faster to avoid that ALT HOLD. Have you been turning it at a normal slow rate?

[Stearmandriver 2,270]

In the real airplane:

 

1. It's been a while since I've done a non-precision approach that wasn't in LNAV / VNAV PATH, but I believe you're correct, the plane should not attempt to capture altitude unless you pause the MCP altitude selector near your current altitude.

 

2. I've noticed this one too. Altimeter setting and baro bug value should stick after cycling the displays control panel switch. It's not the best habit, but there are guys that use that as a shortcut, I'll admit I've done it.

[Spin737 102]

 

 

It's not the best habit, but there are guys that use that as a shortcut, I'll admit I've done it.

 

Dear Pro Stans. . . .

[captdini 3]

I think you need to turn the MCP ALT alot faster to avoid that ALT HOLD. Have you been turning it at a normal slow rate?

 

Dear Vernon, I dont think that should matter, because I am continuously turning the Altitude knob(mouse wheel) until I reach the MA Altitude. Besides, I can only scroll as fast as my mouse wheel, hehehe  :smile:

 

 

In the real airplane:

 

1. It's been a while since I've done a non-precision approach that wasn't in LNAV / VNAV PATH, but I believe you're correct, the plane should not attempt to capture altitude unless you pause the MCP altitude selector near your current altitude.

 

2. I've noticed this one too. Altimeter setting and baro bug value should stick after cycling the displays control panel switch. It's not the best habit, but there are guys that use that as a shortcut, I'll admit I've done it.

 

Dear Andrew, thanks for your reply. As mentioned above, there was no pause, just constant rotating of the knob until Missed Approach Altitude. Thanks for clarifying and alluding to the point that there might indeed be a flaw in the NGX logic. I hope the PMDG guys can look in to this and verify.

 

With regards to point 2, I completely agree. I dont do it as a habit at all, because it is a bad habit. And kudos to admitting that, hehehe  :wink: It's just that unlike the real world, simming is a single man operation so sometimes, it's just convenience. But with this bug, taking this shortcut is moot I guess  :smile:

 

Once again, thanks for your comments based on real world ops.

 

Cheers,

 

Dinshaw Parakh

[Driver170 42]

Dear Vernon, I dont think that should matter, because I am continuously turning the Altitude knob(mouse wheel) until I reach the MA Altitude. Besides, I can only scroll as fast as my mouse wheel, hehehe

 

Ok, well i hope you find the answer you are looking for! I will test on sunday once i'm home and see about this matter.

[Stearmandriver 2,270]

Dear Pro Stans. . . .

Hey, I learned it from a check airman... so it must be standard! (It came with the caveat "do as I say...".) ;-)

[scandinavian13 5,192]

 

 

At the outset, let me apologize for this lengthy post. I am describing a scenario where I feel there is a bug in the system logic on the NGX compared to the real aircraft.

 

Not that we discourage getting community input on whether something is a bug or not prior to submitting it to us, but if you're relatively sure something is a bug, it's better to go directly to our support site. We're not guaranteed to act on things here. Though I usually lounge in the forum throughout my day at my day job, I don't have access to our support site, or our bug tracking system. Along those lines, if I see something I usually make a mental note to mention it to the team when I get home, but that's not foolproof: tickets, on the other hand, are tracked and managed.

 

The link is in my signature.

 

For what it's worth, I think we're aware of the shortcut thing, though I'm not sure about the altitude thing (pretty sure we are, but I'm not 100% on it).

[captdini 3]

Not that we discourage getting community input on whether something is a bug or not prior to submitting it to us, but if you're relatively sure something is a bug, it's better to go directly to our support site. We're not guaranteed to act on things here. Though I usually lounge in the forum throughout my day at my day job, I don't have access to our support site, or our bug tracking system. Along those lines, if I see something I usually make a mental note to mention it to the team when I get home, but that's not foolproof: tickets, on the other hand, are tracked and managed.

 

The link is in my signature.

 

For what it's worth, I think we're aware of the shortcut thing, though I'm not sure about the altitude thing (pretty sure we are, but I'm not 100% on it).

 

Dear Kyle,

 

Thanks for taking the time to post your reply. As suggested, I will post a ticket on the PMDG site. I was under the impression that the members of PMDG are quite regular here and the support site was more with problems due to installations, performance, etc. 

 

Thanks for the suggestion

 

Regards and wishes,

 

Dinshaw Parakh

[scandinavian13 5,192]

 

 

Thanks for taking the time to post your reply. As suggested, I will post a ticket on the PMDG site. I was under the impression that the members of PMDG are quite regular here and the support site was more with problems due to installations, performance, etc. 

 

We're regular, but the whole purpose of the ticket system is tracking correspondence. What if it's a holiday right after a release and we're all only casually paying attention to the forum? Right after releases, the forum is slammed with topic after topic, and legitimate issues can easily get buried.

 

The site over there is called the Support Site, because it's there at any time someone needs support. A problem requiring support could be any time the product isn't working correctly. If we butcher a line of code and it's not behaving like the real thing, that's certainly an item that we'd want to know about.

 

Either way, a better description is as we have it in the Intro Manuals:

• Community Support Forum - a place where the community helps each other, and can discuss the products (we're here, but responses are not guaranteed)
• Support System - a place where you're guaranteed to get in contact with us directly for just about anything

[Driver170 42]

So what exactly is the bug or could be?