Performance on Cruise altitude (77W)

[Renato Roberto Dos Santos 1]

Hello, guys.

 

I would like to know if anyone has the FPPM to confirm a few information for me.

 

I'm performing a (not so long) flight right now and my actual weight is (in kilos) 254.461kg. According to the cruise page, the optimun flight level is FL354. The MAX is 364 and the recomended has changed to 360 a few minutes ago..

 

But if i climb to FL360 (i'm in FL340 right now), the margin between stall speed and overspeed is very narrow. Any change in wind direction or intensity will result in overspeed or stall .

 

That's why i wil maintain FL340 until i have, at least, 1000ft of margin between cruise altitude and MAX cruise altitude. The max and recomended are so close. I cannot use the auto step climb (at least in my opinion), to avoid any problem like that. It's almost the same behavior on 737, i didn't see in 747v2 yet.

 

Do you guys know if this behavior occurs in the real aircraft? Trying to climb so close to MAX Cruise altitude?

 

I will stay in FL340 for now, because the diference between the whole flight in FL340 (8h35) and step climbs (340, 360, 380) is only 400kg (kilos). According to flightplan, my FOD is 8.749kg and according to FMC, is 12.0 (without step) and 12.4 with step, all calculated using airlineperformance.net

 

Thanks in advance,

 

Renato Roberto

São Paulo / SBSP

Brazil

Edited August 20, 2018 by Renato Roberto Dos Santos

[downscc 1,327]

I am not aware of issues with flying at or near the FMC MAX cruise altitude, but I rarely do it.  It is interesting that you have such small margin between FMC OPT 354 and MAX 364.  Is the SAT normal?

I've seen cases where the yellow brackets are as close together as 15 kt on the speed tape but I agree, I try to stay out of the yellow.  If I'm one knot below the Vmmo buffet margin then I'm okay.  That is what the margin is for.

[Driverab330 74]

On 8/20/2018 at 12:08 PM, Renato Roberto Dos Santos said:

Hello, guys.

 

I would like to know if anyone has the FPPM to confirm a few information for me.

 

I'm performing a (not so long) flight right now and my actual weight is (in kilos) 254.461kg. According to the cruise page, the optimun flight level is FL354. The MAX is 364 and the recomended has changed to 360 a few minutes ago..

 

But if i climb to FL360 (i'm in FL340 right now), the margin between stall speed and overspeed is very narrow. Any change in wind direction or intensity will result in overspeed or stall .

 

That's why i wil maintain FL340 until i have, at least, 1000ft of margin between cruise altitude and MAX cruise altitude. The max and recomended are so close. I cannot use the auto step climb (at least in my opinion), to avoid any problem like that. It's almost the same behavior on 737, i didn't see in 747v2 yet.

 

Do you guys know if this behavior occurs in the real aircraft? Trying to climb so close to MAX Cruise altitude?

 

I will stay in FL340 for now, because the diference between the whole flight in FL340 (8h35) and step climbs (340, 360, 380) is only 400kg (kilos). According to flightplan, my FOD is 8.749kg and according to FMC, is 12.0 (without step) and 12.4 with step, all calculated using airlineperformance.net

 

Thanks in advance,

 

Renato Roberto

São Paulo / SBSP

Brazil

That’s normal. The 773ER’s wings do not like cruising at high altitude unlike its fellow 772 brother and the Airbus A330/350.

In theory, you may climb to REC MAX and still has 1.2Vs1g stall margin ( or 1.3 depends on the certification ).

In real life we updated the FMC CG value from a default of 7.5% to whatever the Loadsheet ZFW CG value - a figure which we deduce from FCOM 3 Supplementary procedure. 

After updating the FMC CG figure to a more aft value (some where around 20% ish) , you will get about 1000ft more on REC MAX. 

To be honest, FL350 - 360 / 370 is what we normally end up at the end of a 14-16 hour flight. The airplane only wants to go up to 380/390 when the ZFW is very light resulting a GW of about 230tons. 

The airplane spend most of its time cruising at FL300-340, which is super annoying flying in South East Asia in summer time bouncing around when dodging thunderstorms. 

This is is in stark contrast with the A359 when the initial cruise altitude is already at FL350 departing out of Newerk for Hong Kong. 

Edited August 22, 2018 by Driverab330

[Renato Roberto Dos Santos 1]

On 8/20/2018 at 1:59 PM, downscc said:

I am not aware of issues with flying at or near the FMC MAX cruise altitude, but I rarely do it.  It is interesting that you have such small margin between FMC OPT 354 and MAX 364.  Is the SAT normal?

I've seen cases where the yellow brackets are as close together as 15 kt on the speed tape but I agree, I try to stay out of the yellow.  If I'm one knot below the Vmmo buffet margin then I'm okay.  That is what the margin is for.

Yeap, is was pretty normal.

 

[Renato Roberto Dos Santos 1]

10 hours ago, Driverab330 said:

That’s normal. The 773ER’s wings do not like cruising at high altitude unlike its fellow 772 brother and the Airbus A330/350.

In theory, you may climb to REC MAX and still has 1.2Vs1g stall margin ( or 1.3 depends on the certification ).

In real life we updated the FMC CG value from a default of 7.5% to whatever the Loadsheet ZFW CG value - a figure which we deduce from FCOM 3 Supplementary procedure. 

After updating the FMC CG figure to a more aft value (some where around 20% ish) , you will get about 1000ft more on REC MAX. 

To be honest, FL350 - 360 / 370 is what we normally end up at the end of a 14-16 hour flight. The airplane only wants to go up to 380/390 when the ZFW is very light resulting a GW of about 230tons. 

The airplane spend most of its time cruising at FL300-340, which is super annoying flying in South East Asia in summer time bouncing around when dodging thunderstorms. 

This is is in stark contrast with the A359 when the initial cruise altitude is already at FL350 departing out of Newerk for Hong Kong. 

Thank you.

 

I will look at CG to see if there is any difference.

 

At the moment (another flight), i kept in default 7.5%, but i don't know if i can use the value that FMC shows in the "payload" page.

 

When you set the passengers/cargo and FOB on that page, the CG goes to around 25%, but i don't put this information on PERF page.