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Dear:

I was making VOR approach to RW 13 of LIBR. AP, FMS NAV and VNAV were engaged. I was coming from LIBD. During initial approach the plane was at 3000 ft with VNAV on. The pitch mode was PATH. Then I seleted alt 2000, descend in PATH continued ok. But when I selected 600 Ft Minima, the plane descended up to approx 1000 ft. then ALT mode green came in without any action, armed mode became ALTV white. I couldn't descend any more. I tried to select VS mode and turned the VS wheel to descend to MDA 600 ft. But no help. Then I disconnected AP and landed manually.

 

1. Why the plane leveled off at 1000 ft when 600 ft was selected and VNAV was engaged?

2. Why I could not use VS mode to descend to 600 ft from 1000 ft?

 

Regards,

Haseen Ahmad.

 

 

 

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1. Sounds like an altitude constraint to me.

2. If you try to use VS with VNAV, it will only work until it reaches the vertical path again and then automatically switch back to PATH, so if the snowflake is already in the middle, VS will not even activate.

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Dear Hans:

 

2. But if I want to cancel VNAV mode and engage VS, what should I do?

 

3. Is there any write up describing the Autopilot Control Panel buttons including the VNAV button?

 

Regards,

Haseen Ahmad.

 

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Real world RJ driver here. 

 

Leaving VNAV engaged for the actual approach section (initial fix and afterwards) is only authorized for LNAV/VNAV and LPV approaches.

 

While in VNAV, selecting VS will put you in VVS mode, which is simply a VS mode with the PATH armed for recapture. At this point deselecting VNAV will just revert to VS mode. 

 

The VNAV switch can be deselected anytime, and it should revert to the corresponding mode. 

 

As for VOR approaches real world, we use VS mode without VNAV, using the CDA method if within tolerances for the autopilot (slope has limits), and our MDAs get rounded up to the nearest 100ft in our particular operation.

 

There's a lot of pilot preference in this, but my personal way of doing it is levelling off prior to the IF, then turning off VNAV. This both allows for slowing the plane and transitioning the autopilot from VALTS to ALTS by turning VNAV off,so we don't fall into the less desirable pitch mode. 

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Dear A_Pilot:

Thank you so much for your comprehensive and satisfactory reply. I'll try the approach again the way you described. If any issue, I'll post.

Regards,

Haseen Ahmad.

 

 

 

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Dear A_Pilot and Hans:

 

1. Just out of curiosity, I tried the same approach (VOR approach to RW 13 of LIBR) with VNAV on. At 2000 ft, the mode showing PATH green, I selected 600 ft in the AP control panel, pressed VS button, but pitch mode showed ALTS green. The plane leveled off at 1000 ft. I was expecting to see VALT green as VNAV still engaged. Then I pressed VNAV button, VNAV button light went off but ALTV white is showing. At this point I got totally confused, I pressed ALT button, VS button, ALTS or ALT green are still on and can not engage VS mode to descend. ALTS OR ALT mode do not go! I just want to cancel VNAV and engage VS mode. But Could you please help me? Does the real CRJ behave the same way in that phase of flight? It's scary,  very close to final.

 

2. Actually, I need to read about AP control panel VNAV functions, mode indications in the FMA in detail. Is there any book (soft copy) available? Is Aerosoft CRJ Pro VNAV and ALTS behavior during approach match the real world CRJ?

 

Regards,

Haseen Ahmad.

 

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1 hour ago, haseen said:

Dear A_Pilot and Hans:

 

1. Just out of curiosity, I tried the same approach (VOR approach to RW 13 of LIBR) with VNAV on. At 2000 ft, the mode showing PATH green, I selected 600 ft in the AP control panel, pressed VS button, but pitch mode showed ALTS green. The plane leveled off at 1000 ft. I was expecting to see VALT green as VNAV still engaged. Then I pressed VNAV button, VNAV button light went off but ALTV white is showing. At this point I got totally confused, I pressed ALT button, VS button, ALTS or ALT green are still on and can not engage VS mode to descend. ALTS OR ALT mode do not go! I just want to cancel VNAV and engage VS mode. But Could you please help me? Does the real CRJ behave the same way in that phase of flight? It's scary,  very close to final.

 

2. Actually, I need to read about AP control panel VNAV functions, mode indications in the FMA in detail. Is there any book (soft copy) available? Is Aerosoft CRJ Pro VNAV and ALTS behavior during approach match the real world CRJ?

 

Regards,

Haseen Ahmad.

 

 

We're entering a realm that the RJ isn't supposed to be operated in, so we're finding errors that won't be explained in the books and can't reasonably be expected to be fully programmed by Hans because the info just isn't available. 

 

That being said, VNAV relies heavily on proper database data (altitudes) and will behave erratically if any of the data is inconsistent with the approach. Keep in mind you're supposed to be doing an RNAV approach with vertical guidance of some sort if you're leaving VNAV engaged.

 

Given you're doing a VOR approach, this data is likely not available, or incompatible with the VNAV function, so its getting confused. Manual edits of approach segment altitudes effectively renders VNAV useless in the real plane.

 

Long story short, in a real world level D sim training session, I'd be letting you go down the way you did to display to you the real mess that you've out yourself into to impress on you the importance of disabling VNAV prior to the approach. The only safe solution in real world ops from there is a go-around, or continue visual if possible. 

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Looks like I forgot to answer your last question!

 

VNAV and ALTS behaviour doesn't sound expected, I'll go try to replicate it on a for approach and see what I find. 

 

That being said - VNAV during approach is a different beast, as mentioned. On a proper LPV or Baro-VNAV approach, ALTS modes are inhibited upon interception of the final Glide Path, in the same way that ALTS are inhibited after GS capture on an ILS. 

 

Since you're not supposed to be using VNAV for a VOR approach, (you either VS your way through an SCDA descent, or you VS your way through a chop and drop.

 

Don't, for the love of your personal god, fly an approach in DES mode, or my hand with emerge through your computer screen and slap you for your decision-making.

 

*edit* Hans hasn't programmed the slap feature yet, so maybe that'll come in SP2. 

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Dear:

 

1. Is there any write up of description and operation of the Autopilot Control Panel buttons including the VNAV button?

2. Any Video or PDF tutorial on VNAV?

3. Will VNAV work if I use pilot defined waypoints i e Place-Bearing/Distance with speed/alt constraints inserted?

 

Regards,

 

Haseen Ahmad.

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1. Not that I know of. To be honest, even the official documentation we use in the plane leaves a lot to be desired. 

 

2. I could try and make something this week if you'd like, I'm no pro at video making though, so it might come as a bunch of pictures and a story instead. 

 

3. It should. FMS programming is one of the hardest things in the Flightsim development world though, so if it doesn't work, let us know so we can poke at it. I know right now VNAV has a couple questionarks were working through. 

 

Cheers!!

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