Performance

[jdap]

Hi guys, in my last PPC the instructor ask me to prepare a take off data card on B-737/400, the weight wasn't no high so I decide not to use a improve climb instead I use a engine bleed off take off.
He told me that the priority is:
1- Use normal take off.
2-Improve climb.
3-And last resource engine bleed off take off.


Is that true?? if someone have a documentation about that please let me know where I can find it


Thanks.

[john_tullamarine]

Interesting.

In the first instance, an operator can schedule however it wishes so long as the protocol accords with AFM limitations/requirements and any local regulatory matters.

Consider -

1- Use normal take off.

Not a concern for the operation

2-Improve climb.

If you have the runway to spare and no restriction such as a close in noise abatement concern, this is the generally preferred option as it loads the dice towards the crew in the event of a problem during the takeoff. Caveat - not much sense using overspeed if that converts a non-limiting ASDR into a limiting situation.

3-And last resource engine bleed off take off.

Bleed off generally is only a desirable option if the takeoff is limited bleeds on and you can get the last few kilos required with bleeds off. There is little point in going bleeds off for the sake of it as it just interposes an additional risk for a post takeoff reconfiguration screw up ...

documentation ?

Probably not as this is an operator choice matter.


Me, I'd prefer

(a) overspeed (improved climb) if there is plenty of runway and no other considerations of note

(b) normal

(c) bleeds off only if that is the only way to make the RTOW.

[FlyingStone]

It's completely up to the company and/or captain. Some company use improved climb with bleeds off and on, some use it only with bleeds off, so in the end you may have 4 choices.

If you are not too heavy, so you can still use normal climb + bleeds off, you might consider using improved climb + bleeds off with assumed temperature. (There are companies who forbid this, most sensible ones don't though.)

I agree with John, using improved climb on short runways (especially when wet) when not neccessary isn't really very smart thing to do.

Note: Using improved climb will practically eliminate possibility of tailstrike on -400.

[RAT 5]

you might consider using improved climb + bleeds off with assumed temperature. (There are companies who forbid this, most sensible ones don't though.)

The idea of using improved climb and/or bleeds off is because the normal thrust setting will not be enough to haul your heavy weight off the runway within runway and climb limits. Thus you have already tried maximum thrust and found it not enough. Why then would you use the performance enhancing techniques and then use assumed temp? That's like driving and accelerating with your foot on the brake.

Further: why use anything other than normal when NOT at a high weight? I don't get this use of improved climb as the 1st choice. There are many companies that don't have these charts because they are unnecessary in their network. They use extra thrust at higher weights. I don't understand the use of improved climb unless at high weights. The same applies to bleeds off. Why not KISS.

[Denti]

Improved climb can help with second segment limited take offs. In my outfit we use improved climb with credit for backward CG as standard and on the 737 that allows the maximum thrust reduction by combining derate and ATM (airbus doesn't have derates on the narrowbody types) which in turn reduces engine lease rates considerably. However, full climb thrust wherever useful (not the london TMA for example). That combination provides the least cost solution by combining the lowest possible thrust for take off and the least amount of fuel during climbout.

With today's software tools on the usual iPad based EFBs it is rather easy to get the best performance out of the plane, not much to do there except enter the conditions and let the software do its magic. So, why not use the best possible combination? It is as KISS as it gets.

[Skyjob]

As every operator has its own rule, it cannot be commented upon what has been set in place for your outfit.
It should be documented in your Part-B (or equivalent) what configuration order is to be used by crew. Using improved climb (IC) prior to bleeds off makes total sense as you get airborne with a normal air-conditioning system configuration, not one that requires reconfiguring adding to workload that could be avoided.

(There are outfits that always use Bleeds Off performance and reconfigure as part of their SOPs and After Takeoff Checklist, those airlines have optimised their takeoff weight in all cases, saving a bit of fuel on the takeoff and allow crew to assume as normal as this is their normal departure technique, they will subsequently also use Bleed Off IC if the need dictates...)

Unless your instructor can point out where in your manual such requirements for configuration are described, I would say it's up to you.

[piratepete]

JDAP.
For most cases normal performance practices/techniques should be used.An improved climb method brings with it many issues that reduce safety, like higher speed potential aborts for example.Bleeds off is a safer way to increase payload etc, and should be used if normal methodology isnt enough.Then consider IMPROVED CLIMB if absolutely necessary.At the end of the day, its up to both the operator and the PIC to decide the best/safest course of action.Aviation in general isnt a science (except for the laws of physics), its an art form and you are the artist.

[RAT 5]

Denti: Things have obviously changed since my pencil & rubber days. Improved climb was to use excess runway to reach a Vr & V2 and thus give a better gradient for close in obstacles. It always required highest power setting. This idea of using high speeds and low thrust is a new one to me. Obviously the electrons have a different philosophy to my pencil & rubber with finger in the wind technique.
I've only come across its use as a last resort. Most operators I've flown with did not have the charts as they had enough power in hand for their network. As routes lengthened, and sometimes from hot/high airfields, improved climb charts appeared for the odd time it was needed. The whole matter is becoming less simple. And do the majority of operators now use EFB's? What I've noticed since i-pads have been introduced is that the cadets do not understand what they are doing in the same way. As you say they punch in the numbers, let EFB crunch them up and out pops the answer. It's all so fast. I do not see any gross error checks anymore. They do not have a feeling for numbers; are they sensible. They same with load sheets, V speeds, Vref etc. That feeling for "does it make sense?" is disappearing. It's another cog in the TEM wheel of automation. The only cross check of the i-pad performance calculation is both pilots do it independently. Perhaps that is sufficient. Do all operators do that?

[B737900er]

If you use Improved Climb and not use the performance limited weight (your actual weight is lower) then you will get a better derate, hence the lower power.

[Denti]

RAT 5: indeed, things have changed. I did start out with the Binder of performance charts and only using ATM as method since otherwise it would have been too much work to get the right figures. One knew roughly which figures would be the result from which conditions, and as we flew a very limited network, for which runway.

With the switch to the EFB and the combination of ATM and derate that "knowledge" became obsolete, as very very tiny changes could lead to wildly different performance figures. In effect we had three differently powered aircraft in one, flying different variants of a type gave us even more possible combinations so we lost that experience we had earlier. We have to trust the numbers the EFB spits out as there is no real way to get the same numbers with a pen and paper. Now, on the bus we don't have derates (the A330 does, but i believe it is used differently than on the 737), so it has become a bit easier. On the other hand the airbus software usually gives us a range for V1, not a fixed figure and we can choose ourselves in which part of that range we want to have the V1. Using the lowest one is more go-minded, but could come close to Vmcg which can be kinda difficult to handle if there is an engine failure around that moment.

Dual independent calculation becomes very important, although quite a few companies switched to that only a year or two ago, even though there was a precedent with the melbourne case.

[FlyingStone]

Further: why use anything other than normal when NOT at a high weight? I don't get this use of improved climb as the 1st choice. There are many companies that don't have these charts because they are unnecessary in their network. They use extra thrust at higher weights. I don't understand the use of improved climb unless at high weights. The same applies to bleeds off. Why not KISS.

Higher PLTOM with the same actual TOM = lower thrust = more engine life

Each operator defines their policies - most A320 operators for example use packs OFF takeoff as SOP in order to increase flex, even if they could depart safely with packs ON. The only reason 737 operators prefer packs AUTO takeoffs is the complexity of the air conditioning panel and increased chance of not detecting wrong bleed system configuration.

What I don't understand is that people are willing to depart at MTOM using improved climb and other methods in order to maximise traffic load (and thus saving money for the company, which would have to rebook pax to other flights, pay for the HOTAC, etc.), but yet are not willing to use reduced thrust with improved climb (when below PLTOM) in order to save the engines by increasing EGT margin (and thus saving money for the company).