Time to step climb?

[B737900er]

Hi guys/ girls

I have a question which I can't find the answer to.

Lets say your flying along (b737) at 370 and on the CRZ page you see 372/392 and you would like to climb to 390 but, you want to climb when the max = 395

What's the best way to calculate the time till you can climb to this level

Example 100kg fuel burn = 100ft in altitude

I personally would be happy to climb to 390 if the conditions are smooth and there wasn't a penalty for it but some newer captains from the older 73's are bit hesitant about it.

[beamer]

Remember that climbing is not always the best option !

[bfisk]

Rule of thumb for the 737-800 is about 800' pr hour. So, if you are missing 300', you are looking at 20-25 minutes.

Before climbing above optimum, that for specific fuel consumption, you are better off 1000' below optimum than 1000' above. If you are below the tropopause, your true airspeed will also decrease for a given mach number. It's not always worth it...

[de facto]

Lets say your flying along (b737) at 370 and on the CRZ page you see 372/392 and you would like to climb to 390 but, you want to climb when the max = 395

Better not fly into a mass of warmer air then,your max will go down quicker that it came up.
Have a look at your fcom,under opt/max graph and watch out for temp changes on your flight plan.

[Agaricus bisporus]

Hurry hurry hurry, higher higher higher, faster faster faster.

It's always better, isn't it?

[BOAC]

If you want a ball-park figure, add the diff between opt and max to cruise and that will give you an idea. In your case, enter 410 as cruise to see the step.

1) Do take note of de facto's post
2) Don't forget to put cruise back to 370.
3) Ideally you want to see 372/400 for economy unless 'tactical' considerations dominate.

[misd-agin]

Seen this written before - every 1000 lbs of fuel burn equates to 150' increase in OPT/MAX ALT for the 737NG.

bfisk's 800' per hour example - 5000 lbs/hr fuel flow x 150'/1000 = 750' per hour.

Same basic math.

[737ngpilot]

100 foot in optimum every 7 min...so an increase in 1000f in optimum altitude will take 70 min

[captjns]

100 foot in optimum every 7 min...so an increase in 1000f in optimum altitude will take 70 min

Bingo! In the 800, I use 400 kgs for every 100 for a WAG. Great for before leaving VHF land so a message can be relayed to the guys in HF land for a time to climb.

[Jwscud]

In the NG, you can just put 395 in the "step" window in the FMC. It will calculate the step point to 395, at which point you can happily climb to 390 knowing you have the margin you want.

[captjns]

Doesn't quite work that way in the Sub-continent during Monsoon season where you can experience ISA spikes of up to between 25 to 30 degrees above ISA. Last thing one wants to see is "Buffet Alert" when 500' below the step climb altitude.

[B737900er]

Thanks for the responses, the 100 feet per 7-8mins worked out nicely last night.

Ive experienced a 'buffet alert' on the CDU just after take off, is that even possible or is it an error?

[BOAC]

Originally Posted by jwscud

at which point you can happily climb to 390 knowing you have the margin you want

- but probably higher than econ FL!

[mustafagander]

When it comes to step climbs I usually wait until the optimum is at least 100' above the half way altitude. This means that in CRZ F330 with 2000' steps, I will climb to F350, all things being equal, when OPT shows F341. That allows for a bit of error in actual gross weight. Remember that anytime you are not at OPT level you lose fuel but you can claw a bit back by reducing speed when below but when above you just lose. Tactical thinking may, of course, make an early climb the best bet overall. Break even winds too need to be considered.