Request for more information on MCDU pages

[ahinterl 1]

Anyone knows if and where I can find in-depth and background information on these MCDU pages:+) weight init+) fuel init (ballast fuel)Please no answers "read the product manual" or "do the tutorials".

[FLEX1978 373]

Anyone knows if and where I can find in-depth and background information on these MCDU pages:+) weight init+) fuel init (ballast fuel)Please no answers "read the product manual" or "do the tutorials".

Let me get this right, you want in depth information on MCDU pages but you dont want to read the MCDU documentation??

[Cirrus22 9]

If the PMDG documentation doesn't cover the information you're looking for, this might:http://www.smartcock...1/systems/0010/It covers some things in more detail.

[ahinterl 1]

I asked because I'd like to know "the story behind" the items on the weight init page. I guess there's a lot more to say about them than just "1r, 2r, 5r, and 6r (block, togw, tocg and zfwcg) appear as boxes"...The importance of several values (e.g. RTE RSV/%) for me as the pilot aren't clear enough, and I ask what e.g. TOCG is used for at all. Let aside that I don't understand what "before eingine start, none of the calculations of weight data (zfw=togw+taxi-block) account for ballast fuel[...]" means exactly.Hope someone is a "good story teller" and can enlighten me...

[FLEX1978 373]

I asked because I'd like to know "the story behind" the items on the weight init page. I guess there's a lot more to say about them than just "1r, 2r, 5r, and 6r (block, togw, tocg and zfwcg) appear as boxes"...The importance of several values (e.g. RTE RSV/%) for me as the pilot aren't clear enough, and I ask what e.g. TOCG is used for at all. Let aside that I don't understand what "before eingine start, none of the calculations of weight data (zfw=togw+taxi-block) account for ballast fuel[...]" means exactly.Hope someone is a "good story teller" and can enlighten me...

TOCG is your Take off center of gravity, it's all explained clearly in the docs, you need it to set your take off trim and confirm the aircraft is within cg limits. It's a lot to go into and I really would suggest reading the documents like the rest of us, none of us where born with the knowledge and we all put a fair bit of studying in, thats kinda the point of a study simulation like PMDG. Hopefully someone with more time will come along and help.Regards

[Cirrus22 9]

Hope someone is a "good story teller" and can enlighten me...

I'll try my best!UFOB (1R) = Usable Fuel on Board. The TOTAL amount of fuelthat you have on board the aircraft is UFOB minus ballast fuel (ballast fuel isentered on the FUEL INIT page, 3/3 on the INIT function key). Ballast fuel isfuel that must not be used – eg for weight and balance purposes, or to make theaircraft weigh more than the minimum takeoff weight.BLOCK (also 1R) = The usable fuel that you intend to leavethe gate with.TOGW (2R) = This is the gross weight of the aircraft at takeoff.Zero Fuel Weight + Block fuel + Ballast fuel – Taxi Fuel = Takeoff weight. Thisis calculated automatically once you’ve entered the zero fuel weight and blockfuel.ZFW (3R) = This is the Zero Fuel Weight of the aircraft. Iethe dry operating weight (250996lbs for the freighter, can’t remember the paxversion off the top of my head) + Payload. LW (4R) = This is the landing weight. TOGW – Trip Fuel =Landing weight. This is calculated automatically. This is calculatedautomatically once you’ve entered the zero fuel weight, block fuel and route.TOCG = Takeoff center of gravity. This is the center ofgravity of the aircraft at takeoff with all of the above values taken intoaccount, expressed as a percentage of the Mean Aerodynamic Chord (MAC). ZFWCG = As above, but for the Zero Fuel Weight Centerof Gravity.You enter those so that the FMC can calculate the horizontalstabiliser setting for takeoff, and also to aid it in fuel distribution in thecruise. The MD-11 has a tail tank that it uses to adjust the center of gravityto minimize drag in the cruise. I’m enroute now from HNL to SYD (on a test run for our MD-11 training product), and I have 9700lbs in the tail tank at themoment. The aircraft decides how much to pump back there based on the ZFWCGentry. These C of G values MUST be within limits, or you’re not safe to fly.For any of the pilot alterable entries on the right columnof this page you can right click on the LSK and it will fill out the currentACTUAL value in the scratchpad. This is very useful if you don’t have theloadsheet easily to hand!Moving over to the left column:TAXI (1L) = is the amount of fuel that you have factored infor taxiing. Default is 1.5, I usually use 0.9 unless it’s a particularly longtaxi.TRIP/TIME (2L) = This shows the FMC computed fuel for theflight, not including reserves etc. It’s important to have your route fullyprogrammed if you want a really accurate figure here for the route you intendon flying. The time is simply the time en route. This isn’t pilot alterable.RTE RSV (3L) = This is the reserve fuel for the ROUTE.Different regs require different values here, you can use a simple quantity(weight), or a % of the trip fuel.ALTN (4L) = This is the FMC computed fuel for the trip fromyour destination to the alternate. Like the trip fuel, you can’t edit thisyourself.FINAL (5L) = This is any extra reserve you have specified.Once you’ve entered a quantity, it’ll calculate how much flight time thatequates to.EXTRA (6L) = Takes into account all of the above. It showshow much extra fuel you have on top of all the reserves you’ve entered. If thisvalue gets into the negative, that’s when you get the INSUFFICIENT FUEL scratchpad message.I hope that all makes sense!

[ahinterl 1]

Thank you, Nick, your explanation was very descriptive. But things are still not clear enough for me:1.As the MD-11 controls CG during flight by relocating fuel in the tanks, I can imagine that TOCG is required as basis for CG calculations and therefore fuel relocation actions. Is this correct?BTW: Which other plane controls CG in flight like the MD-11?2.Am I correct to say TOCG determines the amount of TO stab trim required?3.What tool provides ZFWCG in real world, how is that value determined?4.How is TOCG calculated? The manual states it's the result of a calculation where only ZFW and BLOCK are involved, I don't understand why ZFWCG has no relevance in this calculation.5.What is the practical meaning of the relationship to trip fuel when RTE RSV/% is expressed as percentage of trip fuel?6.I can imagine RTE RSV/% has a relationship to certain airline SOPs. Me as an armchair pilot without such airline policies, how do you recommend I use that value for my flights?7.Why is the fuel required for a hold at the alternate labeled FINAL?8.The advanced tutorial says that the CG value from the secondary engine page should be taken for TOCG on the weight init page. I don't understand what these two values have in common.

[FLEX1978 373]

Until Nick gets back do yourself a favour and purchase this - http://www.topcatsim.com/

[scandinavian13 5,192]

The only knowledge I have of the systems is what I have gained on the interwebs and through this simulation, so this post is not to be assumed authoritative in that regard.1.As the MD-11 controls CG during flight by relocating fuel in the tanks, I can imagine that TOCG is required as basis for CG calculations and therefore fuel relocation actions. Is this correct?BTW: Which other plane controls CG in flight like the MD-11?The CG entered is compared to the CG calculated by the aircraft and it will warn you on engine start if your entered value is too far from the calculated value. This is important, because like you said, it uses it in decisions for relocation action.Concorde uses fuel to augment CG as well.2.Am I correct to say TOCG determines the amount of TO stab trim required?I believe this is used in the FMC calculation of the appropriate trim, yes.3.What tool provides ZFWCG in real world, how is that value determined?Proprietary software, used by the airlines and cargo operators. FedEx, for example, uses a very specific proprietary program that optimizes cargo weights and locations for the most efficient ZFWCG. In the sim realm, TOPCAT is a phenomenal program that will take care of this and more for the MD-11, B744 and others.4.How is TOCG calculated? The manual states it's the result of a calculation where only ZFW and BLOCK are involved, I don't understand why ZFWCG has no relevance in this calculation.To put it simply, you are going to use a weight and balance calculator to find the CG (in the case of ZFWCG, you simply do not figure the weight of the fuel in the calculation. The FAA actually has a decent weight and balance handbook, if you're interested: http://www.faa.gov/library/manuals/aircraft/media/faa-h-8083-1a.pdf .ZFWCG is ignored because the calculation used to get ZFWCG is the same calculation for TOCG, they just include the fuel as part of the calculation. Trying to calculate TOCG from ZFWCG would be more work than it's worth.Weight * Arm = MomentEach storage location (sections of the cabin, fuel tanks, forward cargo, etc) will have a specific distance from the reference point (Arm), so a different Arm value. Each location's weight, times the arm gives you a moment. The total of the moment, divided by the total weight equals the CG. If the totals of the arm and weight calculated before fuel, this is the ZFWCG; if it is calculated after, it is essentially the TOCG.5.What is the practical meaning of the relationship to trip fuel when RTE RSV/% is expressed as percentage of trip fuel?6.I can imagine RTE RSV/% has a relationship to certain airline SOPs. Me as an armchair pilot without such airline policies, how do you recommend I use that value for my flights?7.Why is the fuel required for a hold at the alternate labeled FINAL?

§ 121.645 Fuel supply: Turbine-engine powered airplanes, other than turbo propeller: Flag and supplemental operations.(a) Any flag operation within the 48 contiguous United States and the District of Columbia may use the fuel requirements of § 121.639.(B) For any certificate holder conducting flag or supplemental operations outside the 48 contiguous United States and the District of Columbia, unless authorized by the Administrator in the operations specifications, no person may release forflight or takeoff a turbine-engine powered airplane (other than a turbo-propeller powered airplane) unless, considering wind and other weather conditions expected, it has enough fuel --(1) To fly to and land at the airport to which it is released;(2) After that, to fly for a period of 10 percent of the total time required to fly from the airport of departure to, and land at, the airport to which it was released;(3) After that, to fly to and land at the most distant alternate airport specified in the flight release, if an alternate is required; and(4) After that, to fly for 30 minutes at holding speed at 1,500 feet above the alternate airport (or the destination airport if no alternate is required) under standard temperature conditions.(c ) No person may release a turbine-engine powered airplane (other than a turbo-propeller airplane) to an airport for which an alternate is not specified under § 121.621(a)(2) or § 121.623(B) unless it has enough fuel, considering wind and other weather conditions expected, to fly to that airport and thereafter to fly for at least two hours at normal cruising fuel consumption.(d) The Administrator may amend the operations specifications of a certificate holder conducting flag or supplemental operations to require more fuel than any of the minimums stated in paragraph (a) or (B) of this section if he finds that additional fuel is necessary on a particular route in the interest of safety.(e) For a supplemental operation within the 48 contiguous States and the District of Columbia with a turbine engine powered airplane the fuel requirements of § 121.643 apply.

Basically, that whole page is an augmentation of the Part 121 fuel requirements of the FARs. That percentage default is a requirement outlined by Part 121.645(B). As far as using that value in armchair flying, it is best to leave it at or above 10%. This is to accommodate holds, winds other than forecast, and other unanticipated delays.The reason you can use either percentage or hard value, is the requirement is outlined by a percentage (10%), but if your dispatcher put it into your dispatch sheet as a hard value (6200lbs or 6.2, for example), you could enter it that way too. It's just to give you options.The fuel for a hold at the alternate is listed as FINAL because it is essentially your FINAL option. At this point, you have exhausted your destination fuel, the 10% extra, and the alternate fuel to get to the alternate. If it comes to the point of a hold at your alternate, you're on your last legs. You can hold on that fuel, or you can hope to use it to divert to another alternate. Conforming to the requirements of filing for an alternate (1 hour before and after ETA, 2000' ceilings and 3SM visibility) however, this situation is unlikely.8.The advanced tutorial says that the CG value from the secondary engine page should be taken for TOCG on the weight init page. I don't understand what these two values have in common.The value should come from the SECONDARY DISPLAY - ENGINE page. At the top, in the middle, the calculated CG is displayed. This may be entered into the FMC instead of a pre-calculated value (that would be found on a dispatch release). It is acceptable, but in the case you have a release, you should enter the value on the release. The system will then compare it to its own calculated value and if it is not within tolerances, it will notify you. It's just another measure of safety. If the plane is loaded correctly, the calculated should be very close to the dispatch sheet TOCG. Keep in mind, however, that the value displayed on the SD - Engine page is the current calculated CG at this exact moment, while the TOCG is going to be the current CG minus the changed caused by burning the taxi fuel.

[guitarjava 1]

I also would highly recommend Topcat, fantastic program, very interesting and in-depth. The loadsheets, takeoff and landing reports can also be printed out and give a great overview of things. It helped me begin to understand things like weights and de-rated takeoffs on the MD11 and 747.Chris Bremmer

[ahinterl 1]

Thank you, Kyle, this was very informative.

[scandinavian13 5,192]

You're welcome. I had an hour to kill at work and I'm an instructor, so explaining is what I get paid to do, so off I went rattling away on the keyboard. If you have any other questions, keep on posting or send me a PM. If I don't know, I can probably find someone who does.

[Vulcan 14]

Just idly browsing the forum and came across this thread which looked interesting.Can I say a big thank you to Cirrus22 and scandinavian13 for taking the trouble to answer the OP's question in such a detailed way.I would just blindly enter the correct values into the FMC without giving much thought to the 'whys and wherefores' but I found both your posts informative and interesting; thank you guys.Dave

[ahinterl 1]

I would just blindly enter the correct values into the FMC without giving much thought to the 'whys and wherefores' but I found both your posts informative and interesting

That's what I want to leave behind me in the future.Surprisingly the PMDG MD-11 is motivating enough for me so that I try to understand most things, not simply doing them because the QRH or a checklist says so. I'm sure I can handle emergencies better when I know the backgrounds of the plane's systems (once I get to this poing, I'll start using the failure generator :()...

[scandinavian13 5,192]

Glad it helped, and I'm really glad it's helping to truly understand the aircraft instead of just running by simple reflection of the tutorial. I love tutorials, don't get me wrong, but they only teach the 90% process. What about the other 10%? Without an understanding of the aircraft, those 10% irregular ops will not be pleasant. Sometimes your failure won't fit the book exactly, and that's where you supplement the book with the knowledge.