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737-800 Q&A

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I'm scratching my head about few things in the NGX particulary, but since that addon is simulating all the stuff very close to the real deal (more or less), this questions are not just about the NGX, it's generally related to 737-800.

 

1. I'm performing all my landings in the NGX with flaps 40, heavy or light plane, short or long runway, doesn't matter. Why? Simply because I found the landings with flaps 30 very difficult, completely opposite of full flaps landings, which are easy , smooth and stable with just right amount of flare. I can nail every landing between 50-150fpm, which is ok.

With flaps 30 I must apply more throttle to keep a decent rate of descent/angle of attack, and I have a problem keeping VREF +5 on final, the speed keeps raising due to applying more throttle, maybe even 10-15% N1 more than with flaps 40. And on top of all I must flare the plane more making the landing really difficult since I can't see the runway. I don't have any of these problems with flaps 40 landings. Is this normal for flaps 30 landings, or I'm missing something?

So, how I can decide which flap setting to use? I guess it depends on airplane weight on landing and runway length? Above which weight and below which runway length is advisable to use flaps 40 in the 737-800? How real pilots are calculating that? For us simmers, I guess top cat calculation tool will do the job?

 

2. Since 737-700/800/900 are using exactly the same engines, it's logical that 700 will climb faster, and will make less noise on cruise to keep that magic 0.78 number, since N1 will be lower than in 800 and especially in 900. In the NGX 737-800 (yeah, my only reference) I'm hearing the buzz from the engines all the time because N1 is usually in the 86-90% range, depending on the wind. On top of all I edited sound.cfg to make the fan buzz sound appear above 87% isntead of 80% just to avoid non-stop buzzing. My question is - in the real 737-800 do you hear the engine fans buzzing during cruise all the time or sound.cfg in the NGX is wrong?

 

3. After takeoff, as far as I know using fs2crew and watching some video, acceleration altitude is 1500ft agl in my case, and at 3000ft agl I will apply climb thrust. Is that generally ok? I'm thinking to change applying climb thrust to 2000ft agl.

 

4. How I can decide which BARO setting to use as decision height? In fs2crew briefing is always 200 as default, and I'm using that all the time. Watching some froogle videos and such, I saw some very strange numbers like 775, 750... I can find that in charts or? On which stuff decision height will depend on?

 

5. Airport altitude bug on the overhead panel is important because of? :) 

 

 

That's it for now, I guess. Thank you in advance! Cheers!  :smile:

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I don't fly the 737 but I'll have a go at 4 and 5.

 

4. I think this is determined by the approach plate and refers to height above the ground according to the radar altimeter, not barometric pressure.

 

5. Because of cabin pressurisation. The system needs to know what the cabin pressure needs to be on landing i.e. it should match the outside pressure. 

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(2) In r/w ops, the engine fan only generates the "buzz" when operating at high power settings at lower altitudes, due to the fact that the air is more dense. Once the aircraft reaches the flight levels, it will not create the buzz, even at high N1 speeds. It would probably be difficult to code the sim to use different sound files for various altitudes though.

 

(4) On ILS approach plates, at the bottom, there will be a series of boxes containing the decision heights for various scenarios. There will be two numbers - the barometric decision altitude , which is the altitude above sea level as shown on the standard altitude display, and the decision height (based on the radar altimeter), which is the actual height above the ground.

 

For example, the chart for the ILS 25L approach at KLAS, shows a baro decision altitude of 2,350 feet MSL, and a radar altimeter decision height of 281 feet AGL. These numbers actually equate to the same altitude. You use BARO decision altitude for a standard CAT I ILS approach. Radar altimeter decision height is used only for CAT II and CAT III (auto land) approaches. Most ILS approaches are flown as CAT I, so you would be using BARO minimums the majority of the time.

 

(5) The elevation of the landing airport must be set on the overhead panel so the the pressurization controller can depressurize the aircraft at the proper rate during descent to insure that it is completely depressurized upon landing. To do that, it needs to know the airport elevation.

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Flaps 30 is the most commonly used setting, but there’s a number of factors that influence landing flap selection including but not limited to runway length, braking action, and missed approach climb gradient requirements.

Without seeing what you’re doing it’s hard to guess at why you’re having challenges with flap 30 landings.
I recommend taking a look at the included docs, there’s a bunch of info in the landing section of the FCTM that should help.

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1. Flap usage is mainly decided by airline SOP but captain has ultimate discretion. Airlines prefer flaps 30 for noise abatement and fuel efficiency purposes. Less flaps = less drag = less engine power required to maintain approach speed. Flaps 30 also benefits approaches made in turbulent conditions because there is a higher margin of tolerance for exceeding flap airspeed limits due to gusting winds. You probably noticed the airspeed can jump around a lot in windy conditions. In calm conditions, pilots seem to prefer flaps 40 because of the same reasons you mention preferring it yourself - it gives them a better chance for a greaser, VREF is lower, plane has more predictable flare behavior, and perhaps stronger ground effect. Most airlines specify flaps 30 for landing though unless there are special conditions like a short runway. Topcat is a great tool, but it will not suggest an ideal flap setting for landing, only for takeoff. It gives you the approach speed numbers required for each flap setting, but you have to decide flap angles yourself.

 

3. 1500ft for acceleration height and 3000ft for climb thrust is fairly standard. This can also vary between airline SOP and airport regulations. Cutback altitude is related closely to acceleration height, so these numbers can be effected by noise abatement rules. Good example is KSNA, where cutback altitude/acceleration height is 800ft and you have to wait (for what seems like an eternity sometimes) till 3000ft for climb thrust. There are remote sound sensors located all around the departure path miles from the airport and if a departing airplane sets off these sensors, the airline can be fined heavily. The longer you are maintaining TOGA thrust and the sooner you go to climb thrust, the more chance you have of violating noise abatement rules. But the safer your departure will be as far as maintaining a higher margin over stall speed and gaining precious altitude sooner. It's a balance of compromises, just like flap choice.     

 

BTW, that John Travolta gif cracked me up. 

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Huge thanks guys for answering!

 

 

(2) In r/w ops, the engine fan only generates the "buzz" when operating at high power settings at lower altitudes, due to the fact that the air is more dense. Once the aircraft reaches the flight levels, it will not create the buzz, even at high N1 speeds. It would probably be difficult to code the sim to use different sound files for various altitudes though.

(4) On ILS approach plates, at the bottom, there will be a series of boxes containing the decision heights for various scenarios. There will be two numbers - the barometric decision altitude , which is the altitude above sea level as shown on the standard altitude display, and the decision height (based on the radar altimeter), which is the actual height above the ground.

For example, the chart for the ILS 25L approach at KLAS, shows a baro decision altitude of 2,350 feet MSL, and a radar altimeter decision height of 281 feet AGL. These numbers actually equate to the same altitude. You use BARO decision altitude for a standard CAT I ILS approach. Radar altimeter decision height is used only for CAT II and CAT III (auto land) approaches. Most ILS approaches are flown as CAT I, so you would be using BARO minimums the majority of the time.

(5) The elevation of the landing airport must be set on the overhead panel so the the pressurization controller can depressurize the aircraft at the proper rate during descent to insure that it is completely depressurized upon landing. To do that, it needs to know the airport elevation.

 

(2) didn't knew that fan buzz noise depends on altitude. Interesting stuff, something new to learn!  :smile:

 

(4) so if I selected CAT II or CAT III ILS approach, it will change from BARO to radio altimeter? It confuses me because BARO coresponds to barometric and that is in MSL, and here is 200, the same as radio altitude:

 

Button-control---All-panels.jpg

 

 

So, BARO = RA only on CAT I approaches?

 

 

 

1. Flap usage is mainly decided by airline SOP but captain has ultimate discretion. Airlines prefer flaps 30 for noise abatement and fuel efficiency purposes. Less flaps = less drag = less engine power required to maintain approach speed. Flaps 30 also benefits approaches made in turbulent conditions because there is a higher margin of tolerance for exceeding flap airspeed limits due to gusting winds. You probably noticed the airspeed can jump around a lot in windy conditions. In calm conditions, pilots seem to prefer flaps 40 because of the same reasons you mention preferring it yourself - it gives them a better chance for a greaser, VREF is lower, plane has more predictable flare behavior, and perhaps stronger ground effect. Most airlines specify flaps 30 for landing though unless there are special conditions like a short runway. Topcat is a great tool, but it will not suggest an ideal flap setting for landing, only for takeoff. It gives you the approach speed numbers required for each flap setting, but you have to decide flap angles yourself.

 

3. 1500ft for acceleration height and 3000ft for climb thrust is fairly standard. This can also vary between airline SOP and airport regulations. Cutback altitude is related closely to acceleration height, so these numbers can be effected by noise abatement rules. Good example is KSNA, where cutback altitude/acceleration height is 800ft and you have to wait (for what seems like an eternity sometimes) till 3000ft for climb thrust. There are remote sound sensors located all around the departure path miles from the airport and if a departing airplane sets off these sensors, the airline can be fined heavily. The longer you are maintaining TOGA thrust and the sooner you go to climb thrust, the more chance you have of violating noise abatement rules. But the safer your departure will be as far as maintaining a higher margin over stall speed and gaining precious altitude sooner. It's a balance of compromises, just like flap choice.     

 

BTW, that John Travolta gif cracked me up. 

 

1. so practically I'm not doing it wrong where all my landings are with flap 40? I'm not following noise abatement procedures. I will practice flap 30 landings just to add some variety to my landings.

 

3. I was mixing climb thrust with Airbus CLB settings, which is lower than FLEX, as far as I can remember. In the NGX I'm using derated takeoffs most of the time (94% N1) so climb thrust is usually at 96% N1. 

Anyway, in fs2crew, climb thrust command will appear right after gear up command, which is not logical since I must wait for 3000ft agl,  and that is a problem because I must raise the flaps fully around 200kts at acceleration height to gain, yep, speed. Must investigate that in fs2crew manual again, something is fishy there.

 

John Travolta GIFS rules.  :P

 

cheers

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BARO vs. RA is not automatic. The aircraft (i.e. the FMS) does not "know" if a particular approach is CAT I, II or III - that is determined by the regulatory authorities who designed it - and the approach category for a given runway can change on any given day or time depending on the current weather conditions. Many ILS runways are only certified to CAT I minimums, while others (especially at larger airports) can be used in multiple categories, depending on the current ceiling and visibility.

 

Also, in order to fly a CAT II or CAT III approach, the aircraft must be certified for those lower minimums, and the flight crew must also have additional specific training and certification to fly such approaches.

 

In any case, it is the pilot who determines which type of minimums to set - either BARO or RA, depending on the current CAT in use. At airports at or near sea level, like KJFK, the BARO and RA minimums will be identical for a CAT I, while an airport at a higher elevation, like KLAS or KDEN, they will be different.

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Thanks :)
 

In any case, it is the pilot who determines which type of minimums to set - either BARO or RA, depending on the current CAT in use. At airports at or near sea level, like KJFK, the BARO and RA minimums will be identical for a CAT I, while an airport at a higher elevation, like KLAS or KDEN, they will be different.

 

That's confusing me since in fs2crew so far I've used only CAT I approaches, and in the panel there is always BARO:200 as default, either for Zurich which is at 1350 MSL or for Skiathos for example.

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Thanks :)

 

 

 

That's confusing me since in fs2crew so far I've used only CAT I approaches, and in the panel there is always BARO:200 as default, either for Zurich which is at 1350 MSL or for Skiathos for example.

I'm not familiar with fs2crew. Is that the program which gives you an automated copilot? CAT I BARO minimums should always be called out as an MSL altitude. If fs2crew is calling out "200" for ALL CAT I approaches (regardless of the actualairport elevation), then there is a problem with the program. The only time that the BARO minimum would be 200 feet is for an airport exactly at sea level.

 

Another issue is that CAT I approach minimums are not always exactly 200 feet AGL. MOST are - but some are higher. In the example I gave earlier for ILS 25L at KLAS, the runway touchdown zone elevation is 2,069 feet MSL. The BARO minimum descent altitude is 2,350 feet MSL, which equates to an altitude of 281 feet AGL, not 200.

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Thanks :)

 

 

That's confusing me since in fs2crew so far I've used only CAT I approaches, and in the panel there is always BARO:200 as default, either for Zurich which is at 1350 MSL or for Skiathos for example.

That is just the default for fs2crew. It has nothing to do with the altitude you should set. Looks like you're using the version before reboot. I don't remember if that gets its info from what is set in the ngx for its DA/DH or what. But, by default in the ngx(maybe even in the real aircraft?), 200 is also the default. So fs2crew may be reading that or just defaulting to 200 on its own. In reboot, you type the actual DA/DH you want to use. It doesn't default a number in there for you.

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1. so practically I'm not doing it wrong where all my landings are with flap 40? I'm not following noise abatement procedures. I will practice flap 30 landings just to add some variety to my landings.

Nah, not really. I'd reserve flaps 40 for calm wind approaches, but you aren't under pressure to meet a certain fuel burn or noise level target so no requirement for flaps 30 all the time. Cool thing about simming is you can follow your own SOP. As you gain knowledge and experience, you can adjust the SOP to be more or less conservative than typical airline SOP. Since there's no fuel cost or noise abatement fines in FSX, you can take the scenic route, jack up your cost index, and flap settings can favor smoother landings over efficiency. As long as you are being prudent and safe, you can have a little fun every now and then. ;)      

 

3. I was mixing climb thrust with Airbus CLB settings, which is lower than FLEX, as far as I can remember. In the NGX I'm using derated takeoffs most of the time (94% N1) so climb thrust is usually at 96% N1. 

Anyway, in fs2crew, climb thrust command will appear right after gear up command, which is not logical since I must wait for 3000ft agl,  and that is a problem because I must raise the flaps fully around 200kts at acceleration height to gain, yep, speed. Must investigate that in fs2crew manual again, something is fishy there.

I'd ignore fs2crew until you find out the logic of their climb thrust command. I don't think fs2crew can read the acceleration height from the FMC. If not, it shouldn't be making up the takeoff briefing. 

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I'd ignore fs2crew until you find out the logic of their climb thrust command. I don't think fs2crew can read the acceleration height from the FMC. If not, it shouldn't be making up the takeoff briefing.

Exactly. As I also thought, just after TO and calls for gear up, heading select and climb thrust, and that will all happen before acceleration height at let's say 1500ft. At 3000ft (reduction altitude) NGX will activate thrust climb. It depends on your settings in the FMC.

 

------

 

- I noticed that cruise speed will vary a lot at CI 10 or 20. It could be .778 or even .758. Is it due to winds, so when it's strong tailwind it will be .758? That doesn't suit me because PFPX will calculate flight time & ETA always with .78 number and I don't know how to change that?

 

- I know that LRC stand for long range cruise, but I don't get it why the cruise speed is faster on longer cruises?

 

- I struggle with descents and VNAV. I can use VNAV without problems on climb and of course during cruise, but on a descent VNAV doesn't do as much. It's the same as I manually manage v/s. I see that you can specify waypoint/height on a descent page in the FMC, but I couldn't managed to insert it, it was something like DEGEH/12980, it wasn't accepted by the FMC. I will probably look for some tutorials but I will appreciate any help here. :smile:

My question is, exactly - how do RL pilots manage descents? Is it up to SOP or it is pilots decision to stay in VNAV, to use lvl chg or complete manual v/s/speed?

 

 

- When do RL pilots call for approach brief and descent checklist? On approach brief they would specify BARO and auto brake setting, at least they do with fs2crew. So if they get runway change after that during descent, they must run approach brief once again with new settings for BARO and auto brake.... or?

 

 

Thanks once again!

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Cost index does take headwinds and tailwinds into account and will give you a higher cruise speed with a headwind than a tailwind. You should be able to use a CI in PFPX by just entering the value in the cruise/cost index field.

 

Long range cruise is defined as losing 1 percent of your maximum range in exchange for a 3 to 5 percent increase in speed. In the 737NG series any CI below around 35 will be slower than LRC in zero wind. MRC is always achieved by using a CI of 0.

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Thanks :)

 

Yes, I experimented with CI in PFPX but the difference in ETA with 0.78 and CI 10 is only 2 minutes, which is negligible at least. The difference should be at least 5-10 minutes on 2 hour flight with 0.78 vs 0.77.

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Not sure how you’re coming up with 5-10 minutes. The TAS difference at cruise altitude between .77 and .78 is only about 6 knots. When cruising at more than 7 miles a minute that’s under 2 minutes for a 2 hour flight.

 

Keep in mind the other side of the CI ratio is fuel. If the CI of 10 used less fuel than a straight .78 cruise at a cost of only 2 minutes the airline bean counters might consider it a win. On the other hand if your aircraft is wet leased those 2 minutes might mean more since someone else is paying the fuel bill. In reality neither the time or fuel values change too much on a per flight basis, but when you scale it to an entire fleet it can make a huge difference.

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Thanks for your clarification, it's now much more logical to me, and on top of all I can rely on PFPX again. :)
I'm not sure neither how I managed to come up with 5-10 minutes. 

 

That is exactly the reason I want to use CI, to save the money using FsPassengers. I guess I can stick with CI 20, which is low cost. Who uses CI 10 or 5? I heard that Ryanair uses CI 5?

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Optimum CI is a function of fuel cost, time cost and fixed cost - If fuel cost is high and time cost is low as is the case with most LCC, then CI would be low. Supposedly real-world airlines had tools to calculate them, but I'm just parroting what I heard.

 

EDIT: Too low a CI would result in a considerably slower cruise speed closer to those of Classics', and probably annoy enroute ATCO's in busy sectors as they try to fit an aircraft cruising at .75 into a stream of other narrowbodies cruising at .78-.79. Way much better than VLJ's cruising at .55 up to FL410, but still...I think I once read something about that.

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Way much better than VLJ's cruising at .55 up to FL410, but still...I think I once read something about that.

 

Believe it. This picture was taken at FL390 on a good day. 

FB5TQ4H.jpg?1

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That's a good tailwind, at least...Still somewhat faster and much higher than most turboprops. Guess that's how most of them sold.

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