Hi All

 

I'm new to the forum, hope this is the right place to post this Q.

I'm gradually coming to terms with PMDG FMC. I could do with some help with VNAV. I can't seem to come up with an altitude / speed profile that the FMC is happy with. I wonder if you guys can help. The route I'm trying to work is

 

EGLL - EGNH

 

EGLL BUZAD3K

 

BUZAD

OLNEY

WELIN

SAPCO

TNT

TIPIL

DENBY

POL

BPL

EGNH (ILS28)

 

Thanks in advance

 

Pete O'Tube

Hello Pete

Can you be a bit more specific about what you are trying to achieve?

 

I'll see if I can help

 

Alan

Hi

 

I'm trying to fly from 09L at LHR to 28 at EGNH using autopilot in VNAV & LNAV. I keep getting altitude warning such as unable next alt, unable crz alt, with VNAV drop outs. I'm guessing it's because I'm entering unrealistic climb, descent gradients etc.

The VNAV just won't stay engaged. LNAV seems quite happy.

 

Pete

Hello Pete

 

Unable CRZ means the aircraft can't achieve the next altitude because not enough distance is being allowed to achieve this.

 

For example you are at FL10000 and your next assigned FL is 15000ft but with only say 1nm to achieve this.

 

I would check your flight plan and route first then once entered into the FMC check again the distances between the waypoints etc.

 

Set up the FMC with your route and make sure you are entering all the details of the flight on every page.

 

Make sure you have the correct ALT set in the MCP.

 

Once airborne above 400ft engage VNAV then A/P and it will do the rest for you.

 

Shout if you need anymore help. I'm not a pilot but I used to have this all the time when I first started out

 

Alan

 

I meant engage VNAV

Thanks

 

Do I set the height of the next Waypoint Altitude on the MCP?

Is there a rough rule of thumb for what climb should be achieved in say 10nm?

Same question for descent.

For speed management in VNAV do I just arm the auto throttle or do I need to select SPD / LVL CHNG?

Is there anything I need to tell the FMC which waypoint the cruise sector starts and finishes?

 

Thanks

 

Pete

if you fly the SID as published then you will need to set the MCP to the initial altitude for example 4000ft and once you've reached that point set the next altitude for example 5000ft and then press VNAV after each change of altitude assuming you have the SID entered into the FMC.

 

When I descend I start the descent 10nm before TD at a rate of 1600ft using LVL CHG or V/S. You will notice on the Navigation display a green arc which will settle at the point the aircraft will level off. Excellent instrument to work with.

 

For speed management if you use VNAV the aircraft will fly using the FMC so no adjustment necessary on your part. Of course you will need to take over when landing.

 

Arm the autothrottle when entering the runway

 

Hope that helps a bit

 

alan

First, learning to fly with VNAV has a steep learning curve at first so don’t get too discouraged yet.

I took a look at your routing and I noticed some zig-zagging near the destination airport. This could be keeping the airplane higher than you want as you approach the airport. I noticed that the STAR brings you straight-in to 28, but I also noticed you have to many waypoints near the airport causing you to fly to the airport and then make a 180 course reversal back out to the ILS where you had just come from. You need to delete the way point near the airport and get rid of any route discontinuities. It would make no sense to fly that routing unless there was a mandatory procedure turn.

After you build your routing in the FMC, set the EFIS control to PLAN and STEP through your legs page. Set you ND range to about 10 miles. You will clearly be able to see your routing. Eliminate any zig-zaggiing courses by deleting unnecessary waypoints. Make sure you have at least one mandatory “at” altitude restriction specified on the LEGs page.

I autogenerated a route in FSBuild using the B737 probably might need the 736 due to short runways at EGNH.

 

I am attaching a navlog which uses the FSBuild performance profile.

 

 

 

and here is the the fs9 .pln file showing the altitudes calculated by FSBuild fuel load and performance. I chose a cruise altitude that resulted in a "parabolic" vertical profile which is usually the most efficient plan being at level cruise a minimum of time. I did not plan for headwinds but FSBuild included my last Active sky weather snapshot which it considers for fuel planning and course correction but may not match your FMC. I did not use charts. FSB's AIRAC I use is from DEC 2010 and is later than the PMDG supplied default AIRAC. FSB and the PMDG FMC databases can be updated with a Navigraph subscription.

 

[flightplan]

title=EGLL to EGNH

description=EGLL, EGNH

type=IFR

routetype=3

cruising_altitude=34000

departure_id=EGLL, N51* 28.38', W000* 27.41',+000083.00

departure_position=09L

destination_id=EGNH, N53* 46.17', W003* 01.42',+000034.00

departure_name=LONDON_HEATHROW

destination_name=BLACKPOOL

waypoint.0=EGLL, A, N51* 28.38', W000* 27.41', +000000.00,

waypoint.1=D073J, I, N51* 32.35', W000* 12.49', +04000.00,

waypoint.2=D331T, I, N51* 36.59', W000* 14.23', +06000.00,

waypoint.3=D331W, I, N51* 39.36', W000* 16.44', +07000.00,

waypoint.4=BUZAD, I, N51* 56.31', W000* 33.07', +16000.00,

waypoint.5=WOBUN, I, N52* 01.10', W000* 43.59', +20000.00,

waypoint.6=DTY, V, N52* 10.49', W001* 06.50', +28000.00, UY250

waypoint.7=AKUPA, I, N52* 29.12', W001* 05.27', +34000.00, UT420

waypoint.8=TIMPO, I, N52* 33.32', W001* 09.50', +34000.00, UT420

waypoint.9=ELVOS, I, N52* 42.01', W001* 18.25', +32000.00, UT420

waypoint.10=TNT, V, N53* 03.14', W001* 40.11', +23000.00, UL28

waypoint.11=RODOL, I, N53* 14.17', W001* 51.43', +18000.00, UP6

waypoint.12=KOLID, I, N53* 34.26', W002* 45.20', +05000.00,

waypoint.13=EGNH, A, N53* 46.17', W003* 01.42', +000000.00,

 

 

Waypoints .1, .2, .3 are digital "soft" waypoints in an AIRAC for navigation control such as curve boundaries and are local designators to the airport to provide a digital version of descriptions used on the charts of terminal procedures (SIDs, STARs, and approaches). These soft waypoints are not reserved ICAO global definition waypoints but just good for a radius of 300 miles or so around each airport and are mostly involved in RNAV.

 

The FMC if properly programmed for best fuel, cost index (search for that topic but consider 50 or so) and surface and cruise winds and temperature aloft will offer an optimal cruise altitude that you may make hard in it if you choose. At least it will give you a target to request of ATC.

 

In the FS9 .pln route disregard the 0 altitude at the departure and destination waypoints. The correct altitudes are shown in the departure and destination airport declarations.

 

The other replies here have answered your questions about the control of the aircraft via the FMC and MCP controls. As stated, when climbing in VNAV, the aircraft will not go higher than the MCP altitude and not fly lower than the MCP altitude in descending from above it. To meet published chart crossing restrictions you can place limits or hard altitudes in the LEGS page - see the FMC booklet.

 

There are some on-line tutorials available that others can point you to. I purchased this book by a retired United Airlines captain written especially for B700 series PC simmers. It does not go in to systems very much but in to flight procedures and how to control the aircraft including best practice suggestions:

 

http://www.amazon.com/Flying-Boeing-Series-Flight-Simulators/dp/0936283106/ref=sr_1_1?s=books&ie=UTF8&qid=1338087743&sr=1-1

 

or from his site:

 

http://www.utem.com/shop/index.php?l=product_detail&p=4

 

Be sure to visit his home page to get directed to some "fun" stuff.

 

I'll just say it really helped ease my learning curve of the 737NG series especially the FMC and making choices familiar as I am with GA and turbine aircraft in general principles and real world prop flying (single engine).

 

For idle descents, BTW, a rule of thumb is the 3 in 1 rule adjusted for ground speed:

 

http://en.wikipedia.org/wiki/Rule_of_three_%28aviation%29

 

assuming a constant descent rate between your current altitude and your next altitude.

 

Unless you have placed hard crossing restrictions in the FMC LEGS page, the FMC will show TOD based on constant descent to the destination surface so be aware of that. If ATC requires step descents at some point your real TOD in following ATC commands may be before that as displayed on the ND.