Managing speed with the MCP & A/T question?

[Thunderbird8 1]

Hoping for some help from you learned folks.. All my experience of a detailed simulation to date has been three years dedicated to the LDS 767. Old habits and all that.... I fly frequently under 'real' ATC control (either VATSIM or my online group) and because of this I often have to depart from full VNAV/LNAV control quite a way from the destination due to separation, weather, vectors etc. One thing I'm still getting my head around (and my eyes went funny searching for it in the FCOM) is the 'correct' way to operate the MCP in regards to speed. I've noticed that if you press either VNAV or LNAV when they are engaged their green light goes out (unlike in the 763). What mode is then active in each case? I know that engaging v/s will also kick out VNAV, and likewise HDG/SEL will kick out LNAV. Secondly, under VNAV I notice the MCP speed window doesn't show anything. If I'm given (for example) an ATC instruction as follows; 'descend FL150, level by XXXXX, maintain 270kts' and I'm in both LNAV and VNAV at the time, can someone talk me through my options? What I would have done in the B763 is engage v/s with a descent rate of about -1500, dial the speed in at 270, and use speed-brakes as and when necessary. The issue I'm having is getting the 737 to respond to the MCP speed without repeated stabs at the Speed button, which makes me think I'm doing something wrong. The MCP speed settings also seem to behave differently in the 737, I've found that if I enter the speed in the MCP window, press the 'speed' button once (if on, to turn it off), then then press it again to turn it back on, the aircraft will then respond to the command. Is there a better way of doing it or do I have to press the Speed button twice? Also, how do I get the MCP speed window to come alive to do a Speed Intervention in VNAV should the need arise? I'm aware I'm rambling, and there are a few questions in this post. I have done the tutorial and read the introduction, and as I said I have tried to find this in the FCOM. I have never flown a 737 before however I'm very impressed with it and apart from these few things I'm getting on with it fine. A virtual beer to the ones who help answer this!

[M_Sauce 6]

Secondly, under VNAV I notice the MCP speed window doesn't show anything. If I'm given (for example) an ATC instruction as follows; 'descend FL150, level by XXXXX, maintain 270kts' and I'm in both LNAV and VNAV at the time, can someone talk me through my options?

No need to leave VNAV. I would just plug in 270kts in the VNAV page, and make sure you have the "level by XXXXX" instruction programmed in the legs page. The FMC will then recompute, during which you will get a transient mode like VNAV SPD, and the AT might cycle through the THRST / IDDLE / HOLD modes. After VNAV recomputes, check out your magenta VNAV glideslope and see how it looks. If you were already in the VNAV PTH descent when the instruction was given and 270kts is slower than your original speed, your new path will likely be lower than your old one, so depending on how high you are, you will need to intervene. You might see a drag required FMC message, so most likely you will need to do something to steepen the path. You could ask ATC if he needs the speed now or if you can cross a little higher. It is preferable to using the speedbrakes. If ATC doesn't need the speed right away, you could open the speed window (speed intervene is the small button next to the speed knob. The 767 / 747 you press the speed knob button itself) and dial up the speed. Since opening the window will put you into VNAV SPD mode, the aircraft will pitch to maintain the higher speed - so it will start diving and will steepen its descent. This will help you get back on path. Just make sure you have iddle thrust if you are in AT HOLD mode (which you most likely will be). Once you are below your VNAV path, you can close the window and the plane should go back into VNAV PTH mode with the speed bleeding back to what you set in the VNAV page. Energy management in VNAV takes years to properly master, it is one of those things in which you never stop learning. Probably has to do with the fact that humans only use 20% of their brains. Some rules which I live by and have helped me tremendously; - Always pay attention to the FMA modes (the autoflight modes displayed on the top part of your PFD). Understanding each mode, and knowing when they come on and why.- In regards to VNAV, if the FMA mode is VNAV SPD - then the autopilot is responsible for maintaining SPD, and you are responsible for maintaining path. If the FMA mode is VNAV PTH - then the autopilot is responsible for maintaining a path, and the pilot is responsible for maintaining the speed. The only exception is when your auto-throttle mode is SPD, like during on approach logic. Or after making a VNAV altitude restriction that is very low on path.- Always look at the current VNAV page, and be very careful using VNAV when you are not in LNAV. If you are getting vectored or deviating around weather, you don't need to leave VNAV - just be aware of what it is gonna give you. Hope that helps.

[Thunderbird8 1]

Mariano Many thanks for your post, I must admit the FMA modes are a bit of a mystery to me at the moment. More reading up I guess!

[curt1 79]

I can fly the NGX alright, but don't always understand why a mode changes. For instance, when descending in VNAV down to an approach fix, what exactly triggers the FMA to annunciate "MCP Speed"? Is it the flap setting, the transition fix, or something else altogether? I can't seem to find an answer in the manual. Thanks for any replies.

[lbowerman737 0]

I can fly the NGX alright, but don't always understand why a mode changes. For instance, when descending in VNAV down to an approach fix, what exactly triggers the FMA to annunciate "MCP Speed"? Is it the flap setting, the transition fix, or something else altogether? I can't seem to find an answer in the manual. Thanks for any replies.

The speed is denoted according to the constraints computed by the FMS. This is also depicted on the NAV display, with a green little circle which tells you that at that point the stage of decelerating will initiate. Then the speed continues to reduce once you start increase flaps incremently, as by its 'law' and safety the aircraft will only decelerate to the minimium clean speed which is indicated on the speed tape as UP.

[martin-w 3,299]

Secondly, under VNAV I notice the MCP speed window doesn't show anything. If I'm given (for example) an ATC instruction as follows; 'descend FL150, level by XXXXX, maintain 270kts' and I'm in both LNAV and VNAV at the time, can someone talk me through my options?

Stay in VNAV, and hit the "speed intervention button". Dial in your speed, simple as that. Same for overiding VNAV altitude restrictions. Enter required altitude and hit the "altitude intervention button"

[Spin737 102]

What I would have done in the B763 is engage v/s with a descent rate of about -1500, dial the speed in at 270, and use speed-brakes as and when necessary. The issue I'm having is getting the 737 to respond to the MCP speed without repeated stabs at the Speed button, which makes me think I'm doing something wrong. The MCP speed settings also seem to behave differently in the 737, I've found that if I enter the speed in the MCP window, press the 'speed' button once (if on, to turn it off), then then press it again to turn it back on, the aircraft will then respond to the command. Is there a better way of doing it or do I have to press the Speed button twice? Also, how do I get the MCP speed window to come alive to do a Speed Intervention in VNAV should the need arise?

Don't touch the SPEED button. They might as well get rid of the thing. If the A/T is on then it's trying to follow the commanded speed. I think most of your problems are self-inflicted. If you need to go slower and you're in VNAV, change the descent speed on the DESC page and/or on the LEGS page or use SPD INT.

[PIC007 82]

I simply engage SPEED mode and dial it in, along with the appropiate VS to get me where I want to go.

[FirstOfficera320 1]

Hoping for some help from you learned folks.. All my experience of a detailed simulation to date has been three years dedicated to the LDS 767. Old habits and all that.... I fly frequently under 'real' ATC control (either VATSIM or my online group) and because of this I often have to depart from full VNAV/LNAV control quite a way from the destination due to separation, weather, vectors etc. One thing I'm still getting my head around (and my eyes went funny searching for it in the FCOM) is the 'correct' way to operate the MCP in regards to speed. I've noticed that if you press either VNAV or LNAV when they are engaged their green light goes out (unlike in the 763). What mode is then active in each case? I know that engaging v/s will also kick out VNAV, and likewise HDG/SEL will kick out LNAV. Secondly, under VNAV I notice the MCP speed window doesn't show anything. If I'm given (for example) an ATC instruction as follows; 'descend FL150, level by XXXXX, maintain 270kts' and I'm in both LNAV and VNAV at the time, can someone talk me through my options? What I would have done in the B763 is engage v/s with a descent rate of about -1500, dial the speed in at 270, and use speed-brakes as and when necessary. The issue I'm having is getting the 737 to respond to the MCP speed without repeated stabs at the Speed button, which makes me think I'm doing something wrong. The MCP speed settings also seem to behave differently in the 737, I've found that if I enter the speed in the MCP window, press the 'speed' button once (if on, to turn it off), then then press it again to turn it back on, the aircraft will then respond to the command. Is there a better way of doing it or do I have to press the Speed button twice? Also, how do I get the MCP speed window to come alive to do a Speed Intervention in VNAV should the need arise? I'm aware I'm rambling, and there are a few questions in this post. I have done the tutorial and read the introduction, and as I said I have tried to find this in the FCOM. I have never flown a 737 before however I'm very impressed with it and apart from these few things I'm getting on with it fine. A virtual beer to the ones who help answer this!

Hi, if I got a request like that I would simply use FL CH. You have some options now. you can delerate first and then decend or decend and then fly level and decelerate. I would fly the second option. so put simply: if you are 300kts at FL270 and you need to decend to FL150 and slow to 270kts. You need to loose 12000feet which would take 40nm in still air. and to loose 30kts would take about 3miles in level flight. so if you are closer than 43nm from the waypoint you are high and if you are further then you are low. At 300kts it decends at an approximate 3 degree angle. you can therefor use the 1 in 60 rule here. You can also watch the green arch. just keep it simple. There is a level of automation for every thing.

[Spin737 102]

I simply engage SPEED mode and dial it in, along with the appropiate VS to get me where I want to go.

Scenario: You're at FL340 at M.78. You get a clearance to slow to M.76 and descend to FL240. What buttons are you hitting?

[PIC007 82]

Scenario: You're at FL340 at M.78. You get a clearance to slow to M.76 and descend to FL240. What buttons are you hitting?

If ATC clearanceSPEED set to .76 (switch to mach if it reading knots) Passing around FL270 I switch to knots.ALT set to 24000VS as needed. If its to a fix I will put the green 'banana' on the fix, if it is 'unrestricted' I use 1500-1800 FPS If not using ATC, I set SPEED to 290 and VS as needed to hit my IAF at the correct altitude.

[Spin737 102]

If ATC clearanceSPEED set to .76 (switch to mach if it reading knots) Passing around FL270 I switch to knots.ALT set to 24000VS as needed. If its to a fix I will put the green 'banana' on the fix, if it is 'unrestricted' I use 1500-1800 FPS If not using ATC, I set SPEED to 290 and VS as needed to hit my IAF at the correct altitude.

So, you're not using the SPEED button, but LVL CHG or V/S.

[PIC007 82]

So, you're not using the SPEED button, but LVL CHG or V/S.

No, I use the Speed button in conjunction with the VS

[Spin737 102]

No, I use the Speed button in conjunction with the VS

I've been flying the 737 for just 4 years, but I think I've touched the SPEED button maybe twice. Do you mean the SPEED/MACH selector dial for the MCP speed window?

[PIC007 82]

I've been flying the 737 for just 4 years, but I think I've touched the SPEED button maybe twice. Do you mean the SPEED/MACH selector dial for the MCP speed window?

Maybe this helps explain it...