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FishermanIvan

V1 at high altitudes

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Departing La Paz, which is at 13,000 feet MSL, the V1 is still calculated to be around 140 knots with a full load and 1/3 fuel. There's no way I'd stop the jet if something went wrong at 140 knots at that aiport. At VR you're pretty much on the other piano keys... Am I missing a spot on the FMC?

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Normally you need a special certification from Boeing, including extra performance data, to operate from La Paz, Usual data ends somewhere around 10 000ft I believe.I do not think that FMC calculation method is set so that it accounts for the crazy high pressure altitude.

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Use this sheet http://forum.avsim.net/topic/357790-take-off-landing-performance-tool-sheet-b737-800-cfm56-7b26-v103/page__st__50 (search version 1.11, bottom of the page)See ya!

Departing La Paz, which is at 13,000 feet MSL, the V1 is still calculated to be around 140 knots with a full load and 1/3 fuel. There's no way I'd stop the jet if something went wrong at 140 knots at that aiport. At VR you're pretty much on the other piano keys... Am I missing a spot on the FMC?

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Hi, I made myself some scenery for la paz airport a couple of weeks ago. What a mad place! I've spent a bit of time there in rl, but haven't flown out from the airport.Challenging takeoff in the ng as you said. Thx for link too, will be interesting to see what the real v speed calcs should be.

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V1 is still calculated to be around 140 knots
140kts is 140tks regardless of altitude (IAS), it just takes you longer to get there, and a higher TAS

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140kts is 140tks regardless of altitude (IAS), it just takes you longer to get there, and a higher TAS
And the thing that really matters when you're braking; runway remaining and groundspeed. At 140 kts at La Paz the GS is over 165 knots easily. There's no way to stop it. V1 would have to be like 90-95 knots to get it stopped on the runway.

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And the thing that really matters when you're braking; runway remaining and groundspeed. At 140 kts at La Paz the GS is over 165 knots easily. There's no way to stop it. V1 would have to be like 90-95 knots to get it stopped on the runway.
GS depends on the wind and you should be taking off with a headwind, which will give you a lower GS. For jets you need to check the graphs to see if you have enough runway depending on a lot of factors, weight, density altitude, etc., In FSX it's not a problem, just fly the thing off

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And the thing that really matters when you're braking; runway remaining and groundspeed. At 140 kts at La Paz the GS is over 165 knots easily. There's no way to stop it. V1 would have to be like 90-95 knots to get it stopped on the runway.
And we know that V1 isn't arbitrary. Such a low V1 means that when engine quits at v1 you should be able to continue takeoff, accelerate to vR and fly away on a single engine (and not run out of runway!). Would it be possible at this airport? Perhaps not. Perhaps with this weight, certain temp range, no headwind, etc, there is simply no way to satisfy conditions for proper legal balanced field takeoff. Btw, this is a simulator, no harm done experimenting, with some time at your disposal you could find out on your own what is possible or not (assuming the NGX simulation extends well to such extreme conditions).

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It's possible to takeoff in fsx at la paz using the ng, but from memory it used all the runway to do so. I guess what we're hoping to do here though is work through the real-world procedures and see if the sim holds up in these fairly extreme circumstances.Btw, as you may know the airport is called 'El Alto'. Appropriate.LPB (el alto) to RBQ is a common flight. I've done it by ground transport but not in a plane. Takes you over the high andes and straight down into the amazon basin at close to sea level. Road down is claimed to be the most dangerous in the world.Also, I checked and there's a few 737-300's at the gate of el alto at the moment. Didnt see any ngs listed though.If you want to fly out of this airport in fsx, make sure you use an addon mesh because default just gives you some lame looking hills. I use fs genesis and with it the andes around la paz suddenly appear.

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....with a full load and 1/3 fuel.
This sounds ominous.When Boeing was doing its technical demo on 737-700 to prove it could operate in/out of Paro (Bhutan) airport (7300 ft alt with some challenging terrain), the objective was to show that Druk Air could operate this aircraft at about 120,000 lbs. (way below its 170,000 lbs MTOW), enough to fill all the seats, minimum of cargo and just enough of fuel to reach their other destinations. I suspect you create a problem right up front by insisting on weights completely incompatible with the airport.And by the way, there is no way you could adhere to Boeing's procedures and use up every foot of the runway for takeoff with both engines working normally. If you want to simulate real world procedures you must obey balanced field takeoff requirements, in other words at V1 you must either be able to bring aircraft to complete stop or continue takeoff with one engine out (and if you do that you must be at least 35 t above the ground when you cross the end of the runway).

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So I was messing around a bit last night on this. With flaps 15 for takeoff, which seems like it would probably be used, V1 lowers enough that the jet can stop on the runway.

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With flaps 15 for takeoff, which seems like it would probably be used, V1 lowers enough that the jet can stop on the runway.
With flaps 15 you will have worse climb gradient, it could be OK at this airport but it would not work at many mountainous airports since you have to have sufficient ground clearance when flying with single engine.

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Michal, there is much black magic in the alchemy of a hot and high take-off, trading runway performance for climb performance and vice versa... :) depends on the airport, on the runway, on the direction.... many many variables. :)

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With flaps 15 you will have worse climb gradient, it could be OK at this airport but it would not work at many mountainous airports since you have to have sufficient ground clearance when flying with single engine.
Oh big time. You have to get the jet cleaned up quickly or it climbs like a pig.

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I have a friend who works for westjet and when they are fully loaded with a 738 taking off on that 6000 foot runway in Maui, Hawaii they sometimes take off with flaps 25 and a depressurized cockpit as to not take power from the engines on the initial climb. Of course once flaps are retracted they pressurize the cabin again.

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taking off on that 6000 foot runway in Maui, Hawaii
It is a 7000 ft runway over there ...

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Remember, the FMC values are just QRH numbers. You need to run all your data (runway elevation/length, ambient conditions, etc.) through a takeoff performance calculator (e.g. TOPCAT) or use lookup tables (you'll have to work in the ops department at an airline to get these) to see if the takeoff is legal.

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And the thing that really matters when you're braking; runway remaining and groundspeed. At 140 kts at La Paz the GS is over 165 knots easily. There's no way to stop it. V1 would have to be like 90-95 knots to get it stopped on the runway.
Huh? Vspeeds are calulated on the ground. There is a posibility GS might be lower then IAS as a result of headwind, but V1 calculations include headwinds so that is already accounted for.

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can the NGX be operated at Quito airport (9200 ft) ?
Yes. Both Delta (with their CFM56-7B26 equipped 737-700 "rocket jets") and United 737-700's (I think they are B24's) operate from UIO.EDIT: I'm sure there are others...those are just the US operators.

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Yes. Both Delta (with their CFM56-7B26 equipped 737-700 "rocket jets") and United 737-700's (I think they are B24's) operate from UIO.EDIT: I'm sure there are others...those are just the US operators.
thanks for your reply! I know that in real life 700's and 800's version are operated at quito. I meant with the PMDG NGX 737. Anyway i did SEQU-TNCA this afternoon with 130 pax, around 9,5t of fuel and 2,6t of luggages. I took off without a pb with packs off. There was a 300m margin. thanks TOPCAT!

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