One thing I have noticed with the 737/900 is that the altimeter has to be watched very closely when on approach. For example, you can be descending from 7000 to 1800 feet at, say, 1000 fpm; the object being to level out in time to intercept the localiser. It seems that a change of speed (typically from 250 to 160 knots) and/or a change of course during the descent sends the rate of descent awry andy ou find yourself descending to 2500fpm and well below the 1800 limit. I haven't yet established a cause for this but it happens too often to be written off as pilot error.I am thinking of purchasing the PMDG 747 - dioes this have any similar quirks?Jim

One thing I have noticed with the 737/900 is that the altimeter has to be watched very closely when on approach. For example, you can be descending from 7000 to 1800 feet at, say, 1000 fpm; the object being to level out in time to intercept the localiser. It seems that a change of speed (typically from 250 to 160 knots) and/or a change of course during the descent sends the rate of descent awry andy ou find yourself descending to 2500fpm and well below the 1800 limit. I haven't yet established a cause for this but it happens too often to be written off as pilot error.I am thinking of purchasing the PMDG 747 - dioes this have any similar quirks?Jim

It's not a quirk; it's basic aerodynamics. If you slow down or turn you will lose lift and the descent rate will increase. You're quite right - you do have to watch your rates and altitude closely.DJ

Quite so - something I remember being taught about the time the Comet entered service. However, the point is that if you set a given altitude in the window. the aircraft is expected to level off at that height and not go charging on to its doom at an increased rate of descent. The PMDC 737 autopilot does not seem to be very reliable (or realistic) in tis respect (which has nothing to do with basic aerodynamics).JC

Quite so - something I remember being taught about the time the Comet entered service. However, the point is that if you set a given altitude in the window. the aircraft is expected to level off at that height and not go charging on to its doom at an increased rate of descent. The PMDC 737 autopilot does not seem to be very reliable (or realistic) in tis respect (which has nothing to do with basic aerodynamics).JC

I have to admit that I haven't encountered the behavior that you mention (even in the Comet...) - when I make a coupled ILS approach the plane is rock solid on the glideslope and during the initial descent and approach (using heading, altitude and v/s settings in the AP)to the localizer my altitude and v/s settings are nailed solid. The PMDG autopilot behaves very well indeed. It sounds as though you might be too heavy...DJ

I have to admit that I haven't encountered the behavior that you mention (even in the Comet...) - when I make a coupled ILS approach the plane is rock solid on the glideslope and during the initial descent and approach (using heading, altitude and v/s settings in the AP)to the localizer my altitude and v/s settings are nailed solid. The PMDG autopilot behaves very well indeed. It sounds as though you might be too heavy...DJ

In all of the flights I have done in the NG I have not seen this behavior either. As long as you keep the plane in the envelope the autopilot behaves correctly. Remember when you slow down and change configurations such as adding flaps and putting the gear down, you need to add power accordingly. Once your below 18,000, try flying the decent using the the speed (auto throttle), VS & Heading autopilot modes. Use a 1,200 fpm decent rate, set speed to 180knts and heading as needed. Once you get more comfortable you can vary values as needed. There are a few tutorials out there that may be helpful as well.George

Could weight be the problem? I simply use the existing weights that came with the aircraft. The weight does not seem to inhibit take-off and climb yet the problem described manifests itself on almost every flight.

Could weight be the problem? I simply use the existing weights that came with the aircraft. The weight does not seem to inhibit take-off and climb yet the problem described manifests itself on almost every flight.

Weight could certainly be the problem, but I can't say definitively since I have no idea what your fuel and passenger weight is - I've been running the 737's since they were released and have long forgotten the original settings. I suggest that you run the 737 load manager (FS closed) and set a relatively light weight of passengers and cargo (50% or less) and then load the plane in FS and set the fuel (20,000 pounds will get you there on most intermediate flights) using the payload and fuel menu being careful not to exceed maximums. Then see what happens... DJ

Make sure you are running at Vref plus 15% for the flap setting (clean or otherwise). Make sure you are not running out of trim as with your fuel burn your CG has shifted and the trim must remain within the range of AP pitch control. You should be on at least twenty five degree or more flaps at one sixty knots, even 35 flaps as you slow down for near final approach between the outer and inner marker. Check the required speed range for flaps on the speed tape.I assume you have set the required landing flap settings and then V-Speeds as you started the approach before getting below 10,000 AGL so the speed tape indicates the ranges for each flap setting. The FMC will compute those based on your weight at that time and your chosen landing flaps setting in the FMC in the FS model but real world you'd have to compute those on charts if I recall or have a laptop handy with a custom application.If the terminal is near the end of a long runway some airlines touch down at a higher speed to roll-out longer saving taxi fuel but touchdown speed is also limited by gear tire considerations as they get hot spinning up on ground contact.In gusting winds you use the indicated Vref speed plus half the gust velocity of the headwind component to avoid stalls. In a high headwind component your ground speed is reduced so you could use less flaps and a higher speed by a few knots as you make ground contact.In wing icing situations you also land faster due to wait and the ice causing decreasing lift due to distortion of the wing leading edge and surface shape. Ideally you have anticipated this and turned on wing deicing when needed. You should get an alarm if icing is detected.

I did some test flights last night after having reduced the weight of fuel and payload. Descending from 7000 to 2500 with flaps at 35 and speed at 160knots, flying on automatic plus a/t and everything within the flight 'envelope'. A change of course caused the rate of descent (1200 fpm) to fall to 2500 fpm well beyond the 2500 set in the window.

I did some test flights last night after having reduced the weight of fuel and payload. Descending from 7000 to 2500 with flaps at 35 and speed at 160knots, flying on automatic plus a/t and everything within the flight 'envelope'. A change of course caused the rate of descent (1200 fpm) to fall to 2500 fpm well beyond the 2500 set in the window.

There is something abnormal going on - could you post a screen shot of the panel at the point at which you begin your change of course?DJ

I did some test flights last night after having reduced the weight of fuel and payload. Descending from 7000 to 2500 with flaps at 35 and speed at 160knots, flying on automatic plus a/t and everything within the flight 'envelope'. A change of course caused the rate of descent (1200 fpm) to fall to 2500 fpm well beyond the 2500 set in the window.

Hi,I believe a flap setting of 35 doesn't exist in the 737. Was it 30 or 40?A descent from 7000' to 2500' with flaps 35 and turning seems strange to me.... What kind of maneuvre were you doing?Were you descending in Level Change mode?Best Regards,Bert Van Bulck

[i don't bother with the FMS. Instead I create the route in FS2004 and fly the 737 on autopilot, etc. It seems to work quite well except for this problem with the altimeter. I have tried a couple of flights this evening and in both cases the rate of descent seemed to be thrown by altering the speed. Any reasonable system should be proof against a bit of savage treatment but so far as I can see with the 737/900, you have to set your speed before descending and maintain it until levelling out.

<br />Any reasonable system should be proof against a bit of savage treatment but so far as I can see with the 737/900, you have to set your speed before descending and maintain it until levelling out.<br />

<br /><br /><br />That might be Apple's perspective on computers, but this is an airliner.One of the first things you learn in 737 ground school is this: The 737 can slow down and it can go down, but it can't slow down and go down.

[i don't bother with the FMS. Instead I create the route in FS2004 and fly the 737 on autopilot, etc. It seems to work quite well except for this problem with the altimeter. I have tried a couple of flights this evening and in both cases the rate of descent seemed to be thrown by altering the speed. Any reasonable system should be proof against a bit of savage treatment but so far as I can see with the 737/900, you have to set your speed before descending and maintain it until levelling out.

If you descent on lvl change and change your speed the ACFT has to change its decent rate. Descent in lvl chg means: engines idle and pitch for speed. Thus if you increase the speed, the ACFT will pitch down to pick up speed until it has reached that speed.

hi pilots,1. Be sure you're not using spoilers/gear on descentturns together with lvl-change.2. During descent, 20° bank or greater Turns with lvlch and flaps lower than 15 could result in an excessive produce of drag, which gives automatically a high rate of descent in lvlch mode. Certainly, the weight is also a factor. 3. It could also a possible aircraft.cfg error the reason for it. [flight_tuning]cruise_lift_scalar=1.000pitch_stability=1.000roll_stability=1.000yaw_stability=1.000parasite_drag_scalar=1.000induced_drag_scalar=1.000elevator_effectiveness=1.000aileron_effectiveness=1.000rudder_effectiveness=1.000elevator_trim_effectiveness=0.80aileron_trim_effectiveness=1.00rudder_trim_effectiveness=1.00[Flaps.0]type=1span-outboard=0.690extending-time=35.000system_type=1damaging-speed=260.000blowout-speed=280.000lift_scalar=1.050drag_scalar=1.000pitch_scalar=-6.000flaps-position.0=0.000, 0.000flaps-position.1=1.000, 0.000flaps-position.2=2.000, 0.000flaps-position.3=5.000, 0.000flaps-position.4=10.000, 0.000flaps-position.5=15.000, 0.000flaps-position.6=25.000, 0.000flaps-position.7=30.000, 0.000flaps-position.8=40.000, 0.000[Flaps.1] // Cookingtype=1span-outboard=0.950extending-time=35.000system_type=1damaging-speed=250.000blowout-speed=270.000lift_scalar=1.000drag_scalar=1.000pitch_scalar=-12.00flaps-position.0=0.000flaps-position.1=3.100flaps-position.2=4.000flaps-position.3=5.725flaps-position.4=4.000flaps-position.5=0.000flaps-position.6=0.000flaps-position.7=0.000flaps-position.8=0.000[Flaps.2] // More cookingtype=1span-outboard=0.950extending-time=35.000system_type=1damaging-speed=190.000blowout-speed=210.000lift_scalar=-1.000drag_scalar=-2.550pitch_scalar=12.75flaps-position.0=0.000flaps-position.1=0.000flaps-position.2=0.000flaps-position.3=0.000flaps-position.4=0.000flaps-position.5=0.500flaps-position.6=3.500flaps-position.7=7.200flaps-position.8=8.000[Flaps.3] // KREUGER FLAPStype=2span-outboard=0.001extending-time=7.5system_type=1damaging-speed=250.000blowout-speed=270.000lift_scalar=0.000drag_scalar=0.000pitch_scalar=0.000flaps-position.0=0.0flaps-position.1=25.0flaps-position.2=25.0flaps-position.3=25.0flaps-position.4=40.0flaps-position.5=40.0flaps-position.6=40.0flaps-position.7=40.0flaps-position.8=40.0------------------------I don't know, if these values are original ones by PMDG, but my 739 is in all situations (tested few minutes before ^^) in limits and does not descent faster then 2200fpm and this only in turns with F40/Gear down.hope it helps