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Guest t288msd

Departure runway length calculations

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Guest t288msd

I've scanned the PMDG 747 documentation but can't find how to determine how much runway I'll need to use during my takeoff roll. Take this scenario: I'm parked at Sydney (YSSY) loaded up and ready to get clearance for Bangkok (VTBD). ZFW514000lbs Fuel275000lbs Wind 270/10 Temp 21QNH 1011I'm asked by clearance delivery "Can you accept Rwy25 (2530m) for departure?" I'm not sure and play it safe I advise that I require Rwy34L (3962m). I know my v speeds for each of the flap settings, but can't find anywhere in the manual that shows how much runway I'll need to use to reach that v speed. Therefore I don't know for certain if I can accept Rwy25. With the conditions mentioned above, flaps20 and no de-rate, can I safely depart Rwy25? .... and how do I work this out using the tools provided with this great acft.Matt

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Matt,You are right - there is no data in the manual to derive this information.The problem may be due to the fact that real world 747 pilots rarely need this information. They typically fly for an airline that supplies them with charts for ALL runways/airports they will ever be using. So they know they can use those runways in advance - their only question is how much weight they can carry and what their V1/VR/V2 will be given wind and OAT. If you want to see how such charts look like - read a very recent thread here on assumed temperatures. In essense they are working backwards - given the runway and current weather please tell me what cargo, fuel I can carry and how much I can derate my engines. I am not even sure if in real life clearance delivery would even dare to ask a 747 pilot if he could accept a shorter runway - he already had spent considerable effort preparing for this other longer runway. If you are a Cessna pilot then they won't hesitate to ask!!What you are effectively asking for is a method to determine balanced field requirement given all the parameters you listed. I have not seen anything of the sort either in Boeing's documentation or in PMDG's manuals. Again the reason for this is probably due to the fact that it is a complex calculation involving a lot of other parameters you don't even list (runway condition, runway slope, climb obstacles, etc.). Your aircraft may be either field-limited or climb-limited (again more on the subject in the assumed temperature thread). Airline dispatch centers I believe are equipped to perform such calculations using software provided by Boeing (notice that even FMC doesn't do it!). So faced with a completly new scenario, new runway, new airport, the pilot most likley would turn to his/her dispatcher for help.What's the way around it?You could simplify the problem by neglecting this whole business of "balanced field" and assume that in your simulated world you can use up all the runway (illegal in real world) length - in such case you could probably accept the Rwy25 take-off above. Or you could play safe and decline any but the longest runway at the airport. You could even go step further and by trial and error develop your own simplified version of balanced field calculator by testing what PMDG aircraft can actually do in typical weight configurations that you play with. Sorry that I don't have even a better advice for you.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg


Michael J.

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Hi,are there real world pilots out there to answer this question? FLying a Cessna 172 there are several performance schemes in the Aircraftmanual which allow you to calculate your takeoff distance (which take consideration to weight, runway conditions, density altitude etc). I can't imagine these schemes are not available to 747 pilots. And I have to fly to some smaller airports from my Cargoboss...I must be safe!Herman

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Herman,Usually the crew has the balanced runway lengths on file as Michael stated. There is also a quick guide for balanced field lengths in the 744 AOM taking wind, slope, temperature, pressure altitude and runway conditions in account. If you don't have access to an AOM and it's a matter of a one-time question you might post the airports and runways in question and someone will get back to you with the data you need Also take a look at http://www.vdispatch.ca. I intend to make all that available in a user friendly way.plug>Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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Mats,As and when you're looking for beta testers please feel free to PM me. I have experience in beta / user acceptance testing, in fact I have just gone through a big cycle for a software release at my day job.Come to think of it, I may have already talked to you about this. Oh well, point reiterated!Chrs


Mark Adeane - NZWN
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>I can't imagine these>schemes are not available to 747 pilots. They are available but perhaps in not such an easy format. Whereas your C172 may have a simple look up table that covers a runway 'anywhere' a 747 pilot would normally want a specific calculations for this particular runway and airport - since he may be limited not by runway but by a climb too. Margins can be much tighter with a 747 than with your Skyhawk hence all the precision that goes into it. If you read my above post - it is explained how they do it - yes, they do it differently than you do it in your C172 and than I do it in my Warrior/Archer - actually 95% of the time a Skyhawk pilot doesn't have to concern himself/herself with runway details since there is so much spare length.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg


Michael J.

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Hi Matt,I just use the real-world Boeing specs as a guide - see here for PDF documents showing take-off and landing runway lengths, among other things:http://www.boeing.com/commercial/747family/specs.htmlNOTE: remember to make sure you look at take-off runways for GE engines as this is the FDE for the PMDG 744 (don't look at PW for example, which is more powerful, requiring shorter take-off runways.)Hope this helps.John


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Matt,In the real world we are not so much interested in how much runway we will use but how much weight we can lift off a given runway. I have attached a chart that we use to determine a max TO weight for runway 25 at Sydney. The chart is fairly easy to use. Starting at the top of the page any obstructions in the initial TO fan are listed. Normally with an eng failure you would fly straight ahead until 1500ft and all obstacles in that path (expanding at 12.5% from the end of the runway)would be cleared. When an obstacle exists in the path that would cause a reduction in the minimum obstacle clearance height then the TOW would have to be reduced to allow a better climb gradient or if that was too limiting then a turning flight path would be promulgated. This turning path would be followed by the pilot in the event of an eng fail on TO. The final heading would ensure the required obstacle clearance. You can see this on the RWY 25 chart. With an eng fail on TO you would climb to 800ft and then turn left (15 degree bank angle) onto a trk of 155M.The figures are based on a Flap 20 TO. To find the maximum TO weight (TOW) enter the chart with the Outside air temp on the left and then go across to the column with your wind component. So for 20 degrees celcius and Nil wind you would be able to lift 346.0 tonnes. You then correct this figure for pressure which you find from the next box chart just below called Weight corrections. We use Hectopascals (miilibars instead of inches. 29.92 inches equals 1013 Hp). If the QNH was 998 then you would deduct 2.1 tonne from the figure giving you a TOW now of 343.9. This 343.9 is for a Packs off TO. If you want to do a Packs ON TO then you need to deduct a further 6.0 tonnes which now gives you 337.9 tonnes. This is the maximum weight you can be at the start of the TO roll with the packs on . You can add fuel on top to cover start up and taxy. Anything from say 500 to 1200 Kg depending on how long the taxi and potential traffic delays are. Normally the company will give you a Zero fuel weight ofr the sector. That is the weight of the aircraft.... less useable fuel. It is a simple matter for the pilots to calculate the fuel required for the flight and then add this to the ZFW to get a planned TOW weight. As long as this is less than 343.9 then you can use RWY 25. It is that simple. Say for example the company dispatcher came back with a final ZFW of 250 Tonnes and you had loaded 50 tonnes of fuel . This gives you a TOW of 300 Tonnes which is well below your calculated TOW of 343.9 and less than 337.9 (packs on figure) as well so you can TO with the packs ON. Further more if you go back to the chart you can now work out if you can derate the TO. You will see on the RH side of the chart, toward the top a small box chart called Reduced thrust. All you do is look down the chart until you see a figure that is equal to or just above your actual TOW of 300 tonnes. In this case it would be 300.5 and the assumed temperature would be 43 degrees. This assumed temperature figure is what you will enter into the FMC on the top left of the TO page. You will notice the TO N1 on the top R of the display at a lesser figure than what is the Max figure on the L. Also on the upper EICAS screen you will see the TO limit reduce to this new figure. As long as the TOW does not exceed 300.5 tonnes then you can use this assumed temp figure. At this stage we also take note of the 3 eng acceleration height and put this into the FMC on the TO page as well. Then we go down to the bottom of the chart and get the TO speeds. You can see that for 300 tonnes we would have a V1 of 136 VR of 146 and a V2 of 158. If we are doing a derated TO then we need to reduce V1. The reason for this is that we are going to accelerate slower than when using full thrust and we will be further down the runway for a given speed. To compensate for this we reduce the V1 speed so that we will reject the TO so as to be able to stop in the remaining runway length. To find out how much to reduce V1 by we go to the chart box to right side called V1 corrections. You will see for a dry V1 of 136 we need to reduce V1 by about approx 16 kts. This would give us 136-16 = 120 kts. We also alter V1 for any wind with the corrections that are listed on the same chart. You will notice it says that the corrected V1 can not be less than 123 kts. This is so that you have enough rudder control at V1 to continue the TO with an eng fail (VMCG). In our case we are only 120 kts so we have to increase the V1 to 123 kts. VR is also corrected for tailwind. We then enter these speeds into the FMC.And that is all there is to it. Note that this chart is for Rolls Royce engines.It is quite common for ATC to ask if you can use a different runway if it is going to be more expeditious for you or them.Hope this sheds some light on the subject for you.CheersSteve


Cheers

Steve Hall

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Guest t288msd

cheers Steve. appreciated. Matt

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Guest capntom

It gets a little complicated, but having flown in and out of "Kingsfors Smith" quite a bit, I'll tell you that I have never even considered using 25 for depr. I have considered it for landing on ocassion. There are several considerations besides 'ground roll', the tables we are provided have to factor in takeoff roll (to 35 feet), accelerate stop at V1 (stop or go decision), wind barometric pressure, temp, wind, runway condition etc.We can calculate this manually but seldom do, but use prepared charts for each field and runway. The books that I have in my flight bag, as opposed to the ones on the plane, concentrate on inflight and landing performance. The plane (and at home) I have enough stuff to do complete calculations.A rule of thumb, at max tko wt, ya need about 11,500 ft or so in std conditions. Flaps 20, V2 will be about 180-181 knots. Your mileage will vary.Tom

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Presumeably flying the PMDG 747 you would be on a longhaul departure. Taking into account that the international terminal is on the opposite side to the TO threshold you would be better off departing on 16 or 34. Could take a while to cross 16R/34L.RgdsSteve


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Steve Hall

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Hi Steve,Thanks for the charts. At the bottom where it says Take-Off Speeds, I noticed the lowest weight is 290 tonnes, which translates to 639,160lbs, if I calculated that correctly. Does this mean that this is the lowest operating weight the company operates the 747 at? I was wondering if there're times when the maximum TOW is say around 270 tonnes or even 250 tonnes, even though it's not shown on the performance chart.Ken.

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> Does>this mean that this is the lowest operating weight the company>operates the 747 at? Of course not. These are only the "partial" performance charts to give a perspective buyer an idea what 747 can or can't do or "typical" runway requirements are for typical takeoff weights. These are not charts that pilots or airlines would actually ever use in daily life.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg


Michael J.

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>Of course not. These are only the "partial" performance charts>to give a perspective buyer an idea what 747 can or can't do>or "typical" runway requirements are for typical takeoff>weights. These are not charts that pilots or airlines would>actually ever use in daily life.>>Michael J.Hi Michael,That's what I thought, but the chart Steve posted is the chart he uses to determine the maximum take-off weight for runway 25. I guess you mean the other partial charts. I've seen other technical data posted at Boeing's website but not the chart like Steve posted here. I guess they're given to perspective buyers. Ken.

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