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Energy management on initial approach

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  • Jetman
    replied
    Serge my perspective unless you are actually a real 737 pilot i dont think any of us simmers or private/commercial can really understand what it takes to fly for an airline day in day out from the political BS, to the huge level of knowledge thats required to safely perform, and to be expected to always be near perfect, in some ways we are better off flying the ngxu as we always get to choose and enjoy. Hats off to the boys and girls who fly these amazing machines. Wish it was me but i dont miss all the pressure and drudgery that surely goes with it, after the first 5-10 years would become a job, high paid and sometimes fun but still a job.

    Leave a comment:


  • MeatServo
    replied
    Originally posted by Emi View Post
    Seriously, the 737's A/T is not very good.
    I agree with this 100%.

    Leave a comment:


  • serge_s
    replied
    Originally posted by Emi View Post

    Pay me for it..... ah, my airline paid 80 million bucks for the airplane already!

    No seriously, it is clear that no automation can perform 100% perfect, however then don't write into the FCOM that it does.
    Same with the speed brakes "the 737 has very effective speed brakes"... yeah, sure it does!
    NOT!
    Hi Emi, I understand your point of view completely and believe me your end-user feedback is very important to drive future improvements. I don’t work for Boeing and definitely not the guy who negotiates contracts or writs checks, but the process for escalating issues to the manufacturer is essentially the same. Your company must have an SOP on how to do this. If you feel so strongly that a piece of equipment is not working as it should, my suggestion (as unpopular as it may be) is to follow your company procedure. That said, I can tell you that more likely than not, the particular issues you are experiencing have already been brought up, evaluated, well understood, and prioritized. Some things get fixed immediately (MCAS) and some non-safety items are upgraded and improved incrementally over time. Otherwise, we’d all be flying PMDG 200s now. Also, don’t forget, since we’re discussing 7-3 specifically here, the basic airframe design has really no changed much in over 50 years (hard to believe I know).

    To keep things in perspective, look at it on a bright side, you have one of the best jobs in the world where it’s always sunny in the office! Any one of us simmers and landlubbers would gladly trade places with you.

    Now that we've completely mangled the original intent of the OP's question, I believe it's a good topic to discuss and perhaps should be split off into a separate thread.

    Cheers my friend - Serge

    Leave a comment:


  • Emi
    replied
    Originally posted by serge_s View Post

    In the eyes of end user, it's ALWAYS automation fault But guess what guys, if you get off the butts for a minute and participate in the design process, we might even get it right once in a while.
    Pay me for it..... ah, my airline paid 80 million bucks for the airplane already!

    No seriously, it is clear that no automation can perform 100% perfect, however then don't write into the FCOM that it does.
    Same with the speed brakes "the 737 has very effective speed brakes"... yeah, sure it does!
    NOT!

    Leave a comment:


  • Emi
    replied
    You have to give it 100% accurate input, then VNAV will give you a very good output.
    As always with computers... **** in, **** out.

    Leave a comment:


  • Ephedrin
    commented on 's reply
    Haha very true! I come from that business too, in the wider sense not software developing though..

  • serge_s
    commented on 's reply
    Dan, now we know what you do for a living, my friend. LOL Small world.

  • Stearmandriver
    replied
    Originally posted by Planeblogger View Post
    In short, it helps to stick to several rules when descending in the 737NG (real and NGXu) :

    - don't use VNAV
    I simply don't understand where this notion comes from, that VNAV somehow doesn't work in the airplane. I mean, you're not the first person I've heard say it, it's just that my experience is quite different.

    A significant portion of our route structure involves flying in LNAV/VNAV from off the ground until back on it, on hops that consist of complex RNP departure and approach procedures connected by a short enroute segment. Coming out of VNAV simply is not an option, and there's never a reason to anyway. I've been doing this for years and haven't yet had to fight VNAV, or whatever the urban legends say might happen.

    I said this elsewhere: if the plane actually had half the VNAV problems that are claimed, it never would have received RNAV approach certification, let alone RNP certification. Instead, it is actually the platform that was used to invent RNP approach technology.

    Leave a comment:


  • serge_s
    replied
    Originally posted by Ephedrin View Post

    If developed properly 😝
    In the eyes of end user, it's ALWAYS automation fault But guess what guys, if you get off the butts for a minute and participate in the design process, we might even get it right once in a while.

    Leave a comment:


  • DDowns
    replied
    There's a lot of compromises made in designing or tuning a PID controller, and with something like a throttle there is never a chance that it will work perfect in every case. Tune the loop to be right on top of rapid changes such as gusts and you end up with a throttle that wanders back and forth aimlessly in steady cruise. The PID loop needs to be tuned such that the hysteresis or time it takes to spool up or down does not turn into something dangerous.

    I'm amazed that autothrottle works as well as it does.... and I suspect it's not simply a single PID loop but a network of loops.

    Leave a comment:


  • Ephedrin
    replied
    Originally posted by serge_s View Post
    LOL, Emi, I really enjoy reading your posts. But, as an engineer, if I only had a dime every time I heard that from an operator. To your credit, you guys are the ones who have to deal with the reality of the situation and be responsible for passengers and cargo. I agree, it's not perfect, but you can't argue that automation makes you safer and more efficient if used properly.
    If developed properly 😝

    Leave a comment:


  • serge_s
    replied
    LOL, Emi, I really enjoy reading your posts. But, as an engineer, if I only had a dime every time I heard that from an operator. To your credit, you guys are the ones who have to deal with the reality of the situation and be responsible for passengers and cargo. I agree, it's not perfect, but you can't argue that automation makes you safer and more efficient if used properly.

    Leave a comment:


  • Emi
    replied
    Originally posted by serge_s View Post
    A/T is a finely-tuned PID controller and as such is capable of monitoring a setpoint, predicting, and controlling output much more effectively than a human can. Automation can be a friend if used properly.
    Oh boy, I had to laugh hard at this one.
    Seriously, the 737's A/T is not very good. You constantly need to correct it during turbulence. Many people just disengage it altogether during gusty conditions as it won't hold you speed very well, heck nobody would be surprised it if just flew you into the overspeed.
    Talking about overspeeds, guess where it's usually going and where you usually have to intervene with the speed brake during cruise with some turbulence.

    Leave a comment:


  • Ephedrin
    replied
    Planeblogger I have found a way that works well for me to keep the throttle at idle with AT on: Hold F1. (Or assign it to the idle position of your hardware throttle via FSUIPC). Works great but in the latter case you have to remember to move it out of idle.

    Leave a comment:


  • serge_s
    replied
    A/T is a finely-tuned PID controller and as such is capable of monitoring a setpoint, predicting, and controlling output much more effectively than a human can. Automation can be a friend if used properly.

    Leave a comment:


  • Peter Webber
    replied
    Originally posted by Emi View Post
    Disconnecting the A/T for the purpose of removing the low speed protection would be a big no no in my company.
    If the A/T is working against you, you have not set up proper modes in your MCP.
    Of course sometimes you temporarily hold it back, but if you need to hold it back longer than 2-3 seconds you should reconsider your MCP selections.
    Agree. The MCP is very underated these days with the younger "magenta" generation of pilots.

    Leave a comment:


  • Planeblogger
    commented on 's reply
    Good thing we are flying our desk and don't have to stick to SOP's.
    Essentially, we do not disable A/T to remove the low speed protection (we are getting nowhere near stall speed when we level off in a 330KIAS descent). You just temporary switch to manual engine control.
    Holding the throttle back a few seconds as you describe is often just enough to make things work the way you like them to work.
    But with FS controls, this is hard to achieve. Not many of us have motorized throttles at home. If you can show me a better way to make the NGXu level off at altitude from steep descent without it adding power, I am all for it. Bring it on! ;-)

    Erik

    EDIT: you can also try selecting V/S in the final part of the descent and thereafter lower MCP SPD to eg 250KIAS.
    Last edited by Planeblogger; 17Dec2019, 16:20.

  • Emi
    replied
    Disconnecting the A/T for the purpose of removing the low speed protection would be a big no no in my company.
    If the A/T is working against you, you have not set up proper modes in your MCP.
    Of course sometimes you temporarily hold it back, but if you need to hold it back longer than 2-3 seconds you should reconsider your MCP selections.

    Leave a comment:


  • Planeblogger
    commented on 's reply
    You don't, because then the aircraft will raise the nose too early to first capture the set speed, then continue descent to altitude and it will still add throttle.
    Especially when you come from very steep descents, the aircraft starts to add power even thousands of feet above the set level off altitude which is not what you want.
    IRL pilots prevent this from happening by physically restraining the throttle in idle position. It is a dirty fix, but it works. In FS, your only option is to temporarily disable A/T, set a lower speed and only then re-enable A/T.
    A/T is not a speed protection or was it ever intended as such. It is not a FBW aircraft. You are still flying this airplane.

    Erik

  • DDowns
    replied
    Erik, I'm uneasy with your suggestion to remove speed protection by disconnecting A/T in LVL CHG mode. You achieve the same thing by simply reducing your MCP SPD 10 kts.

    Leave a comment:


  • Planeblogger
    replied
    In short, it helps to stick to several rules when descending in the 737NG (real and NGXu) :

    - don't use VNAV
    - descent OR slow down, don't try to do both at the same time.
    - no SOP, but it works: disengage A/T when descending using LVL CHG. If autopilot levels off and you haven't received further clearance, it will prevent the autothrottle from spooling up the engines and adding fuel/energy to the equation while you are actively trying to loose energy. While levelling off, the speed will bleed off and when you continue descent using the original airspeed, you will have an extra steep angle at first when the aircraft tries to reach the MCP speed, compensating for the temporary level off.

    Still too high? Increase the speed and throw out spoilers. At 330IAS with full speedbrakes you easily hit 5000fpm. As drag increases exponentially with speed, a higher speed gives you a steeper descent angle. This obviously is valid for any airplane. Another thing: IRL speedbrakes are most effective above 250. Below 220, they barely have any effect at all. I have found the NGXu to be quite accurate also in this regard.

    When arriving at FL100, keep the speedbrakes out, level off and speed will decrease to < 250KIAS in about 5 miles. (just like the real aircraft)

    If you use the tools above, I have found the NGXu is perfectly capable of meeting a 1 in 3 glide path, which is a rule of thumb for most airliners (3nm per 1000ft altitude that needs to be lost).

    I hope this helps.

    Erik

    Leave a comment:


  • serge_s
    replied
    Dan, we're in agreement on this. "UP" is essentially 210 KT, and the rest is on schedule. I might have cludged up what I typed before; trouble connecting the brain to my fingers, LOL. Take care bud.

    Serge Saakov

    Leave a comment:


  • DDowns
    replied
    Originally posted by serge_s View Post
    I could be wrong, but I thought Boeing allows flaps 1 at 210 kt? Anyways, I'm usually leveled off at patter altitude doing 210 kt with flaps 1 on downwind, or within the 15 nm arc from the runway if straight in, and then drop to 180 kt a few miles before glideslope intercept, as well as gear down and flaps 15 at that point. At FAF (about 5 min out), I usually reduce speed to APR +5 depending on conditions. <<<Usually>>> Of course it "always" goes to plan . Landings are like a "box of chocolates" you never know what you're gonna get.

    Serge Saakov
    I think Flap 1 is much higher than 210; regardless, I try to stick to the flap extraction schedule: Flap 1 at speedtape "UP", Flap 5 at "1", Flap 15 at "5" or Gear Down...etc (FCOM NP 21.68)

    Leave a comment:


  • serge_s
    replied
    I could be wrong, but I thought Boeing allows flaps 1 at 210 kt? Anyways, I'm usually leveled off at pattern altitude doing 210 kt with flaps 1 on downwind, or within the 15 nm arc from the runway if straight in, and then drop to 180 kt a few miles before glideslope intercept, as well as gear down and flaps 5 at that point. At FAF (about 5 mi out), I usually reduce speed to APR +5 depending on conditions. <<<Usually>>> Of course it "always" goes to plan . Landings are like a "box of chocolates" you never know what you're gonna get.

    Serge Saakov
    Last edited by serge_s; 16Dec2019, 22:34.

    Leave a comment:


  • pijnackerpilot
    replied
    Originally posted by serge_s View Post
    Hi Daniel,
    1. It's difficult to descent and slow down at the same time, you have to pick one or the other, but not both. This takes some planning ahead. One option is to add a pseudo waypoint with the final target altitude several miles head of where you need to arrive, from there you will be level and can slow down more effectively before you arrive at the target fix.
    2. Disengage VNAV below 10K and control altitude and airspeed with MCP bugs.
    3. Enter a hold at a fix to buy yourself time, lose altitude/airspeed, and get things back under control.
    3. Deploy speedbrakes to help slow down. This generally helps to make small incremental changes (i.e., increasing rate of descent slightly, etc.) but it's not going to solve major discrepancies.
    4. Plan to land into the wind to help slow groundspeed (also buys you more time) as opposed to having tail wind which puts you at a disadvantage.
    5. Go around. It's not as uncommon as most people think.
    1. I know this from experience with the NGX. Usually, I tend to set myself up for a speed around 180kts at 10nm (with range arc). I select flaps 5 at passing 10, following by gear down and flaps 15 about 2 miles later. In the NGX I usually have no trouble slowing down because I tend to set a speed constraint of around 220-210 around 15 dme away. However in the NGXu I don't get that far. As soon as the a/c reaches its F100 decel point to decel to 240, it is my experience that the descent rate during this calculated period of speed reduction is to steep, preventing me from not reaching the required speed at the second green dot. This is followed by an even steeper descent which forces to aircraft to pick up speed again.

    2. Above FL100 Lvl change does good work for me, below I prefer to use VNAVspd. But then again, a very very shallow speed must be commanded to maintain velocity (of 240), much shallower than I am used to in the NGX.

    3. Nah, holding is not an option. I prefer to anticipate without using a hold (I rarely do) and if possible without the use of speedbrakes.

    4. I always land into the wind. I don't always arrive and approach into the wind

    5. Agreed, but I prefer not to.

    Originally posted by Snowfalcon View Post
    What program if any are you using for your flight planning.? Are you using a ATC program?

    The -800/900 is notorious for needing time to slow down. "You can go down or slow down not both." If the approach has time it will slow first then descend. if not you will come in high and hot. The default ATC and RC4 will FUBAR your descent every time.
    I plan my flight in PFPX using a profile from aircraft performance profiles. I don't use ATC, but I do fly on VATSIM and that can be a challenge at times when it comes to energy management. Especially on fields that I am not familiar to.

    It seems to me that the descent behaviour is radically different compared to the NGX, might be something I need to get used to, but still...

    Daniel Westdijk
    pijnackerpilot
    Last edited by pijnackerpilot; 16Dec2019, 22:14.

    Leave a comment:


  • DDowns
    replied
    Originally posted by threegreen View Post
    I've had a bit of trouble myself slowing down both the 800 and the 900ER on approach. Getting down from about 210 kts (or whatever the speed constraint is) to around 180 kts for flaps 1 is a bit of a struggle. I've had to throw out the gear already when speed still didn't permit to go to flaps 10/15 to slow down, even with headwind.
    I'll often set a speed constraint at 9 nm for 190 kts and let the FMS slow it down for me. Also, the VNAV path seems intent on not intercepting the GS until at the FAF so I almost always switch to V/S and manage my descent at somewhere around 500-600 fpm to intercept the GS/GP earlier. This makes slowing down a lot easier.

    Just gotta stay ahead of the airplane. Does it have bugs? Yes... but they are consistent and easy to work with if you stay ahead of the airplane.

    Leave a comment:


  • threegreen
    replied
    I've had a bit of trouble myself slowing down both the 800 and the 900ER on approach. Getting down from about 210 kts (or whatever the speed constraint was) to around 180 kts for flaps 1 is a bit of a struggle. I've had to throw out the gear already when speed still didn't permit to go to flaps 10/15 to slow down, even with headwind.

    Leave a comment:


  • DDowns
    commented on 's reply
    Regarding the deceleration to 250 at 10000: The NGXu -800 is too slippery and PMDG is looking at it so if you are coming in with 20 kt tailwind then plan on a touch of speedbrake to get down to 250 by that second green dot. Take advantage of the VPI to see where your descent is going and if slowing also where you are expected to reach the slower speed. Helpful when descending to a constraint with tailwind.

  • Snowfalcon
    replied
    What program if any are you using for your flight planning.? Are you using a ATC program?

    The -800/900 is notorious for needing time to slow down. "You can go down or slow down not both." If the approach has time it will slow first then descend. if not you will come in high and hot. The default ATC and RC4 will FUBAR your descent every time.

    Leave a comment:


  • Jetman
    replied
    Very good post,thanks

    Leave a comment:

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