Too fast and too high

[kekstrom 1]

Hi. Almost every time I start my descent as programmed/calculated by the vnav, I end up way too high and/or too fast for my approach and I have to circle several times to set up for a stable approach and landing. I always have to use a lot of speedbrakes also. I know somebody will reply that I should input winds to the fmc as it matters if I have tailwind but the problem seems to be every time. And its not every time I have tailwind, sometimes headwind etc. Is the vertical flight path calculation realistic on the ngx? Any suggestions? My autothrottle seems to idle on the descent (it says "arm" and end up about 40% N1), that should be correct?

 

Thank u!

[hopskip 253]

When you get to 10,000ft are you already high? Does the plane slow to 240kts?

 

At about 4000ft is it slowing down to ~220kts? if so, deploy flap 1 (even before you hit the glideslope).

 

By the time you hit glideslope at 3000ft or 2500ft you should have flap 5, be at less than 180 knots, and select the gear down (arm speedbreak, turn on cont ignition) at Glideslope capture, and select flap 15 once you have 3 green, you'll want to be well onto a deceleration to 160kts at 2000ft. As the aircraft gets nice and stable at 160kts go flap 25.

 

Passing outer marker, or 3 miles out from the runway, slow to Vref+additive(140ish kts) and flap (30 or 40).

 

I usually stick to VNAV/LNAV till either 160kts or when the speed window becomes active on it's own if I'm on an RNAV STAR which ends at the runway.

 

I'm generally finding the aircraft nails the profile perfectly most of the time unless I am late deploying flaps. ANY time you see VNAV selecing the green flap marker speed, deploy the next stage of flap. LESS THAN 180kts and flap at 5 or 10 at glideslope is a must. Intercepting glideslope from below at 3000ft above airfield is quite important, and to get down from above glideslope or to be at 180kts from 2000ft is going to be a problem.

 

If you intercept glideslope with the gear up, and fly down the 3°, you WILL accelerate.

 

Idle decent is perfectly normal. Just try to keep it idle all the way down to glideslope intercept (by deploying flaps when you reach the green flap marker speeds).

 

Here's a video I did not long ago of a full flight in the NGX, skip up toward the end to see proof it works

[por930 51]

Hi Kekstrom,

If possible, I will start down maybe 5nm early or ensure by about 30nm from my destination, I slow my descent, while at the same time bleeding off airspeed. When I am comfortable all under control, I monitor my descent speed and ensure it is within a reasonable envelope. No doubt though, she is a slippery girl.

I recall seeing in the forum a RW driver providing a video of his approach and demonstrating bleeding off airspeed during the approach. His main comment was to slow down as early as possible. Do not recall what the posters name was.

BTW, we prefer real names in this forum.

 

Regards

[Iccccie 1]

 

 

If you intercept glideslope with the gear up, and fly down the 3°, you WILL accelerate.

 

 

 

 

Naaaa, the aircraft is designed to fly a 3° GS with flap 5 with gear up and it does it fine in RW and so does the PMDG.

Good weather conditions we take the gear down at 4 miles it's about 1300-1400' so well down below G/S interception

[Vagabondo 23]

Hi. Almost every time I start my descent as programmed/calculated by the vnav, I end up way too high and/or too fast for my approach and I have to circle several times to set up for a stable approach and landing. I always have to use a lot of speedbrakes also. I know somebody will reply that I should input winds to the fmc as it matters if I have tailwind but the problem seems to be every time. And its not every time I have tailwind, sometimes headwind etc. Is the vertical flight path calculation realistic on the ngx? Any suggestions? My autothrottle seems to idle on the descent (it says "arm" and end up about 40% N1), that should be correct?

 

Thank u!

 

Make sure you're in VNAV PATH at the top of descent. Once high it might trip into VNAV SPD which, in all probability, will make you even higher.

 

You should also crosscheck your height vs your distance to go in the PROG page. Very roughly speaking, if your height/1000*3 is 10 less than your distance to go when above 10,000' you're good (by height I mean altitude less landing elevation). If doing the sums is too much like hard work, press the MTRS button on the EFIS Control Panel, this will display your altitude in meters, this is handy because if you divide the meters by 100 you have the magic 3º gradient distance to sea level. Again this should be roughly 10 less than the distance to go with a correction for landing elevation.

 

For distance to go estimation below 10,000. First use the PROG page, if given vectors, use LVL CHG and use VOR or ILS DME (or the FIX page if no navaids) as a straight line distance and estimate additional miles to a sensible point on final using the radar range scale. When downwind or straight in, use the DME or FIX page. When using a VOR/DME for distance take account of where the beacon is located, you may need to add or take a mile or two depending on its position relative to the landing threshold. A base turn takes 3 to 5 miles.

 

In a clean configuration at 250 kts bank on about 5nms need to slow. Once below clean speed with some flaps the height/1000*3 or MTRS should be <= miles to go. You're pretty safe then.

 

These height vs distance crosschecks can be done at 20,000, 10,000, 5,000, 4,000, 3,000 then as continuously as you can manage it. If you are high on a cross check deal with it then, it is much easier to correct further out.

 

If above approximately 17,000 and you need to slow to 250 at 10,000, instead of using the speedbrake, try using level change and increasing your speed to 320 knots or more. Try to stay withing 5000 fpm rate of descent. At about 700' below the descent profile, reengage VNAV PATH and it will pitch up and decelerate back to FMC descent speed and get back on profile.

 

You distance to go needs to be wind corrected too. Add or subtract 1 nm for each 10 knots of head/tail wind.

 

I'm sure I've not made some points as clear as perhaps they could be, just ask more questions if so.

[megs8888 20]

Anyone willing to produce a tutorial with this as I have the same issues, should the throttles be physically retarded prior to descent?

 

Would be nice to see a video on this if I knew I would do one

[Sam 68]

My autothrottle seems to idle on the descent (it says "arm" and end up about 40% N1), that should be correct?

 

Thank u!

 

Engine anti-ice on then? Make sure you have entered it on the des forecast...

Idle w/o engine anti ice is lower, and if the desent path is calculated for tai off, and it is on, you will be to high and eventually to fast...

[HighFlyer310 21]

I always use the DES NOW feature about 5-10 nm back from T/D. It helps the autopilot to join the idle path by coming up underneath it with the thrust pulled back a bit. If you let it "run into" the T/D it will almost always overshoot and spend about 2-3 thousand feet trying to get back on path. LVL CH is a good tool to use for maintaining a constant airspeed descent.. at that point its just becoming familiar with the distance required for a given speed.. it takes practice and familiarization.

[Vagabondo 23]

I always use the DES NOW feature about 5-10 nm back from T/D

Just as a point of info for yours or other readers benefit, alternatively, just press the ALT INTV button on the MCP after setting a lower altitude. This is the same as the FMC, DES NOW feature.

[scandinavian13 5,192]

Anyone willing to produce a tutorial with this as I have the same issues, should the throttles be physically retarded prior to descent?

 

There are two included with the plane, and yes, the physical throttles should be placed at idle.

[hopskip 253]

There are two included with the plane, and yes, the physical throttles should be placed at idle.

 

Actually no, the throttles should place themselves to idle (autothrottle). The throttle position during decent should be fully back, but there's no need to grab them with your hand to get them there. (or press F1). If you have a throttle quadrant that you use for Flightsim, pushing it to idle isn't a bad idea to avoid control spikes from the hardware.

 

Real aircraft's throttles would move on their own.

[LABOX 40]

What cost index are you using? High CIs (>30) and (as said before) not entering engine anti ice in the descent forecast page can be causes for this.

[megs8888 20]

What's the recommended CI for ngx given its a sim please?

[squerble 300]

Less than 30 as a CI is a good shout. My VA uses 22 for the -700 and 26 for the -800 and I never have descent path issues.

 

As above, are you using Engine Anti-Ice? The biggest killer for the des path is not entering wind forecasts in the 'DES' page on the FMC.

[LABOX 40]

There are a couple of inofficial lists on this forum regarding CIs. Try a search :rolleyes: Low cost carriers sometimes use 15 or less. Many airlines use different CIs for climb, cruise and descent, which means you can always change the cost index in flight...