E/D wrong altitude

[boeing247 0]

I had only performed ILS landings up until a few days ago with the NGX, so this was never a problem, but when I tried to perform a VOR/DME approach with VNAV, I noticed that the FMC said that the E/D was around 40 feet higher than it actually was, which resulted in the plane wanting to land in the trees beyond the runway. The glide path seemed to work just fine, though--had the airport been at the altitude that the FMC said it was, I would have touched down right on the runway. I checked this at another airport and it still holds true. The main problem is that you can't change the E/D altitude. Any ideas? Do I have to update my Navigraph data?Thanks,boeing247

[Spin737 102]

Time to earn your virtual stripes and turn off the autopilot: There is no autoland. As a wise Captain once told me: Fly the freakin' jet.

[boeing247 0]

I did "fly the freakin' jet" after I found that VNAV wasn't going to do the job (I had the flight saved shortly before approach). However, all of VNAV's calculations set the plane up for a landing 40 feet above the airport. I had to bring the plane down very hard, very fast.

[Houghton11 12]

VNAV is not supposed to be utilized as guidance to the runway threshold. If you had set up an IAP correctly you may have gotten closer, but I doubt it.Take a look at that chart you are using for a VOR/DME approach. Read the minimums listed. I bet you they say at least 500 feet. At 500 feet, you transfer your primary reference to the outside, and look for the runway. If you can see it, you disconnect the autopilot, and visually continue the approach and landing.The computations around VNAV are good, but not good enought to provide perfect guidance to the threshold. That's why we have ILS's. WAAS and IAP procedures may one day get around that...but it's still a long way off.Bram, you got to take a peek at some of the FCTM topics, specifically around those regarding the landing and approach phase. You'll get a much better idea of what the procedures and capabilities are.

[daniel.burke01 1]

VNAV is not supposed to be utilized as guidance to the runway threshold. If you had set up an IAP correctly you may have gotten closer, but I doubt it.Take a look at that chart you are using for a VOR/DME approach. Read the minimums listed. I bet you they say at least 500 feet. At 500 feet, you transfer your primary reference to the outside, and look for the runway. If you can see it, you disconnect the autopilot, and visually continue the approach and landing.The computations around VNAV are good, but not good enought to provide perfect guidance to the threshold. That's why we have ILS's. WAAS and IAP procedures may one day get around that...but it's still a long way off.Bram, you got to take a peek at some of the FCTM topics, specifically around those regarding the landing and approach phase. You'll get a much better idea of what the procedures and capabilities are.

Yes This is very true!VOR/DME is simply a way to calculate a safe altitude at each reference point along the approach. It really is a visual approach as a VOR/DME would not ever be rated for autoland. I think the reason its giving you a 40ft. difference is also because the 737 NG has a 50ft Minimum max. If you don't see the runway by 50ft you would conduct a go around, unless you were on a CAT3 ILS approach where in this case you could continue with the autoland as the ILS approach would be rated for this.~DAN BURKE~

[Spin737 102]

The 50ft difference is that the FMC is giving you guidance the to the threshold, and the height of the jet at the threshold is. . . 50ft.You should have the autopilot off long before this.

[boeing247 0]

The 50ft difference is that the FMC is giving you guidance the to the threshold, and the height of the jet at the threshold is. . . 50ft.You should have the autopilot off long before this.

Okay, that makes sense, but when would I disengage the autopilot, and how would I know what descent speed to use?I know very little about landings other than ILS (in jetliners, that is, of course). Since I didn't know how to perform a VOR/DME approach, I went to the NGX manuals. I followed its instructions and got the results I posted above.Here is the line from the manual:

If suitable visual reference is established at DA(H), MDA(H) or the missed approach point, disengage the autopilot and autothrottle.Maintain the glide path to landing.

As per the instructions, I maintained the glidepath, but like I said, the glidepath wanted to set the plane down past the runway. Thus, I increased my descent speed and ended up bringing the plane down very hard (it's a wonder I didn't crash). So what do I need to do differently?

[Spin737 102]

As per the instructions, I maintained the glidepath, but like I said, the glidepath wanted to set the plane down past the runway. Thus, I increased my descent speed and ended up bringing the plane down very hard (it's a wonder I didn't crash). So what do I need to do differently?

As Patrick said, this is the realm of the FCTM.So at the MDA/DDH you see the runway environment and you continue to land. You turn off the autopilot and handfly from there. If you keep the same descent path, you should end up in the touchdown zone. Keep your approach speed until the threshold and you should touchdown at about Vref.

[Tabs 2,790]

I think you need to read about the difference between precision and non-precision approaches in IFR flying. (this is a basic instrument flying concept, not something that's in the NGX manual) There's a minimum descent altitude (MDA) on a non-precision approach that is the lowest you can go before disconnecting the AP and landing manually. If you can see the runway at that point, you land manually, if you can't, you go around and try again. A VOR approach shouldn't even have a glidepath technically unless you're using a built VNAV path or the NG's Integrated Approach Navigation feature. If you were in VNAV, then the reason you were high is likely because the approach and the VNAV path stopped at the MDA, not at the runway.VOR approaches are normally flown with a "dive and drive" method - each segment of the approach has a minimum altitude and once you pass each DME fix on the approach, you can descend further. There's nothing that's going to lead you right to the runway - non precision approaches get you in the vicinity of the airport so you can make a visual landings. If the weather is bad enough that you need to get right to the runway then you shouldn't be doing a non-precision approach - you need an ILS.The vast majority of real world landings are not autolands. Even most ILSes are not.

[FirstOfficera320 1]

Hi Bram,As the others have said you need to know what the different type of approaches are and their limitations. Also note about VNAV and the IAN. They are not pressure and temp corrected. So on a chart it may say "LNAV/LNAV procedure valid to 0C"For the actual VOR approach for this time being don't listen to Ryan Maziarz, because in heavy jets we don't do the "dive and drive" method. It's simply too unstable and you won't have enough visual cues when flying level flight at MDA. You see in the oldern days and in small planes what you do with a NPA is decend down to MDA+50feet and level off. Then fly there untill you hit a decision point which you select based on where you MAPt is located. The DP can either be a time from a beacon or DME from a beacon.What we do in a heavy jet is fly it as a stable approach down to MDA+50feet *IF* we do not see the runway there we go around. Simple as that. So how do we do that. Before reaching the FAF you should be in Landing Configuration. 0.3nm before the FAF(shown as a maltesecross) you dail in the FPA that you need to decend at. This number is printed on your approach chart. Also on the chart will be Altitude/Distance crosscheck. Then it's just a matter of clicking off the A/P and land it.Kind regards,

[Tabs 2,790]

Martin,Airbus procedure is probably different - there's no FPA AP mode on an NG... IAN or VNAV are what would be used, which I did mention. I think the dive and drive is the best way for someone who isn't familiar with what an NPA is to get the idea, even if that's not 100% the way it'd be flown by real pilots.

[NoahBryant 26]

Also, many VOR approaches aren't even designed to get you pointed at the runway properly. They simple get you to a place where you can see the airport and land visually. http://dtpp.myairpla...-1/09041VDA.PDF That's an example of a VOR aproach that takes you in almost perpendicular to the runway.Check this out, http://www.navfltsm....om/vor-appr.htm

As per the instructions, I maintained the glidepath, but like I said, the glidepath wanted to set the plane down past the runway.

What "glide path" are you referring to? At that point, you should be looking at the PAPI lights next to the runway and nothing in your plane except your speed, but what it comes down to more is just knowing your airplane and practice. You really should never be looking at your VS during an approach either, it really has no purpose at that point.With the runway in sight, the AP should be off, and you should be looking outside to get your plane to the runway and glancing at your airspeed occasionally. If you're too low, based on looking at the runway and the PAPI lights, increase power a bit or decrease your power if you're too high, (again no auto throttle here either).

[FirstOfficera320 1]

Martin,Airbus procedure is probably different - there's no FPA AP mode on an NG... IAN or VNAV are what would be used, which I did mention. I think the dive and drive is the best way for someone who isn't familiar with what an NPA is to get the idea, even if that's not 100% the way it'd be flown by real pilots.

Hi Ryan,I know there are differences from how airbus and boeing does things. Instead of using FPA mode which isn't available you can simply select a VS. What VS you need is also on the chart. I also wrote why I thought he shouldn't do the "dive and drive" technique. The basic flying techique is the same. Once you get to grips with the CDFA it's a joy and much much more like a ILS.This is straight from the 737NG FCTM: "Over the past several decades there have been a number of CFIT and unstabilised approach incidents and accidents associated with non-precision (non-ILS)approaches and landings. Many of these could have been prevented by the use of Continuous Descent Final Approach (CDFA) methods"regards,

[boeing247 0]

Thanks for all the help, guys. As I said, I'm just starting to fly NPA's, s I don't know much about them. So just to be clear, I would let VNAV take the plane to the MDA, then disengage the autopilot and land manually, right? (and I should be at VRef at that point, no?)Just one last thing--could somebody give a quick explanation of IAN? I found some info online, but not a whole lot, and considering the information I found on VOR/DME approaches was apparently insufficient, I want to be sure I know what I'm doing. Thanks!

[IFR7700 228]

Also, a simple point, but sometimes overlooked ... make sure you contact the local ATIS before landing and adjust the altimeter to local settings. I find that when I forget, I am wildly off the natural glide path on a NPA.