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codechris

PACKS off take-off question

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Tomorrow I'm planning on flying from Bern LSZB to London EGLL, there is a Vatsim event in both places tomorrow evening so should be quite a good flight.

 

However, LSZB  is small with one runway of 1730 meters in length and is 30 meters wide (5676x98ft) and looking on Flightaware the only planes that appear to come and go are E190's. I know nothing of those planes, but they look a similar size to the NGX so I am guessing this is possible.

 

I ran though the flight in Topcat selecting "optimum" Flaps and it gives me a full throttle flaps 25 take off, which I've never seen. I normally manually select Flaps 5 in Topcat and everything is good. But, I called in to question if this would be a scenario which would warrant a packs off takeoff?

 

I've searched around and found answers that involve "airline policy, packs off does nothing, packs off for tired engines, packs off gives more margin" so I'm a little lost as to if I would get anything out of packs off or not, and what situation would warrant this.

 

Does anyone have any better answers? Part of the problem I have in this one is it's currently 35 degrees at least across Europe, and there is no way anyone would want to have packs off take-off given how hot it is and I found people speaking about an APU on take-off to assist while the packs where off for take-off. However, for anyone that has flown in Europe, you know we hate APU's and have very strict times regarding APU usage. BERN is fairly relaxed with a max APU time of 30MIN before EOBT, however I presume that, since engines on take-off far out weigh APU noise, APU on for take-off makes no difference, only for the taxi (which is very small are Bern) but maybe APU on for taxi is also fine?

 

I know it's a sim, and I could do what I wish (I try not to go too mental with this stuff) but I'm at a bit of a loss what to do. I need air-con given the temp, but would packs off be recommended at such a small airport. And, is Topcat correct in that I can take-off with Flaps 25?

 

 

Cheers, as always


I should probably add, with Random Payload I have a ZFW of 54,201 KG in Topcat under Take-off weight I have 60,137, but I'm a fair few KG's away from Max ZFW

 

Just in case there is any confusion; I'm not calling in to question Topcat here, or looking for TC support. It was more the PACKS question

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But, I called in to question if this would be a scenario which would warrant a packs off takeoff?

 

Did you allow TOPCAT to calculate the data with the Packs OFF/ON? If not give that a shot and notice the results

 

 

 

 


I've searched around and found answers that involve "airline policy, packs off does nothing, packs off for tired engines, packs off gives more margin" so I'm a little lost as to if I would get anything out of packs off or not, and what situation would warrant this.

 

Packs OFF takeoffs can be beneficial in various ways, it can be used to reduce the amount of thrust that is required for a given takeoff thus reducing wear on the engine and it also allows you more thrust for takeoff in example your current scenario.

 

 

 


Does anyone have any better answers? Part of the problem I have in this one is it's currently 35 degrees at least across Europe, and there is no way anyone would want to have packs off take-off given how hot it is and I found people speaking about an APU on take-off to assist while the packs where off for take-off. However, for anyone that has flown in Europe, you know we hate APU's and have very strict times regarding APU usage. BERN is fairly relaxed with a max APU time of 30MIN before EOBT, however I presume that, since engines on take-off far out weigh APU noise, APU on for take-off makes no difference, only for the taxi (which is very small are Bern) but maybe APU on for taxi is also fine?

 

Depending on the procedures you follow, you can taxi with the APU off and both packs running, and just as you enter the runway for takeoff, turn the packs OFF, so at least the cabin wont be uncomfortable for more than a minute or 2 until you're airborne. In the NGX i do not usually do APU to PACK takeoffs because before the latest service pack there was a bug in the bleed system that prevented the N1 limit from being calculated properly while the PACKS were running even if the engine bleed switches were off, so i just do packs off takeoff instead of APU to PACK. I do not know if this has been fixed as i havent had time to test it.

 

 

 


And, if Topcat correct in that I can take-off with Flaps 25?

 

I have always trusted TOPCAT with the 737-800, with the -700 theres a little trick that i have to use because the engines on the -700 that PMDG simulates is of a higher thrust rating than the data TOPCAT uses. So if im using the -700 and TOPCAT says to use TO1, in the PMDG -700 i use TO2 with the same assumed temperature, and things usually line up that way.

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Tomorrow I'm planning on flying from Bern LSZB to London EGLL, there is a Vatsim event in both places tomorrow evening so should be quite a good flight.
I am sure you are aware of this thread - http://forum.avsim.net/topic/470480-n1-difference/. You may have even posted in the thread.

 

I would be concerned about F25 recommended  by TOPCAT. Like you I have always used F5 and occasionally F1.  My suggestion would be to enter the appropriate data into the FMC and see if you get any Vspeeds on the takeoff page. It may not even accept 25 on the takeoff page. Good luck.

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If I were your airline chief pilot, I would send a notice to aircrew telling them to use the No Engine Bleed Takeoff and Landing Supplemental Procedure (SP 2.5) whenever high temperature or high aircraft weight are experienced flying to or from LSZB for these reasons:

1) improve aircraft performance (climb gradients)

2) ensure passenger comfort (passenger health)

 

Also in the notice to aircrew, I would tell crew that our EFB Performance Tool (TOPCAT) can calculate takeoff data up to flaps 25. Aircrew are directed to allow TOPCAT to select the optimum flap setting when performing takeoff calculations from LSZB by selecting OPTIMUM in the flap setting field. Flaps 1 and 2 takeoffs are not allowed. If TOPCAT provides data for a Flaps 1 or 2 takeoff, crew are directed to select Flap 5 and re-calculate takeoff data.

 

Last, I would also tell crew that Flaps 40 and a minimum of autobrake 3 must be used for landing at LSZB.

 

Full engine thrust must be used for takeoff and takeoff calculations. Engine de-rates and Assumed Temperature Method not allowed from LSZB.

 

End of notice to aircrew

 

And for the record, yes, takeoffs can be done with flaps 1 all the way to 25.

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I did notice a slightly higher N1 when select packs off, but difference was something like 99 and 100, very marginal. I forgot as well in Topcat it gives you margin for how much runway is left, and it's tiny. So, I would presume that every little counts in this scenario is packs off would be better.

 

 

Depending on the procedures you follow, you can taxi with the APU off and both packs running, and just as you enter the runway for takeoff, turn the packs OFF, so at least the cabin wont be uncomfortable for more than a minute or 2 until you're airborne. In the NGX i do not usually do APU to PACK takeoffs because before the latest service pack there was a bug in the bleed system that prevented the N1 limit from being calculated properly while the PACKS were running even if the engine bleed switches were off, so i just do packs off takeoff instead of APU to PACK. I do not know if this has been fixed as i havent had time to test it.

 

 

I think you're right and I'm over thinking this. At the stand it would be air-con from the ground to keep it cool, APU between ground disconnect and engine start, then packs for aircon all the way up to runway entry procedure when they go off. Once at 1000ft or above packs can come back so, we're speaking of a very small amount of time and I'm sure everyone can cope in that time. You could have a potential problem if when asked to line up and weight you end up with a long delay, but I've never seen a delay that I think would end up causing you a problem in the cabin.

 

 

If I were your airline chief pilot, I would send a notice to aircrew telling them to use the No Engine Bleed Takeoff and Landing Supplemental Procedure (SP 2.5) whenever high temperature or high aircraft weight are experienced flying to or from LSZB for these reasons:
1) improve aircraft performance (climb gradients)
2) ensure passenger comfort (passenger health)

Also in the notice to aircrew, I would tell crew that our EFB Performance Tool (TOPCAT) can calculate takeoff data up to flaps 25. Aircrew are directed to allow TOPCAT to select the optimum flap setting when performing takeoff calculations from LSZB by selecting OPTIMUM in the flap setting field. Flaps 1 and 2 takeoffs are not allowed. If TOPCAT provides data for a Flaps 1 or 2 takeoff, crew are directed to select Flap 5 and re-calculate takeoff data.

Last, I would also tell crew that Flaps 40 and a minimum of autobrake 3 must be used for landing at LSZB.

Full engine thrust must be used for takeoff and takeoff calculations. Engine de-rates and Assumed Temperature Method not allowed from LSZB.

End of notice to aircrew

And for the record, yes, takeoffs can be done with flaps 1 all the way to 25.

 

 

That sounds sensible. I can't find any flights for the 737 out of Bern, and only 2 airlines so finding anything official on this one would probably prove challenging at best. However, if Flaps 25 are fine for T/O then I'll trust Topcat on this one.

 

 

I am sure you are aware of this thread - http://forum.avsim.net/topic/470480-n1-difference/. You may have even posted in the thread.

 

I would be concerned about F25 recommended  by TOPCAT. Like you I have always used F5 and occasionally F1.  My suggestion would be to enter the appropriate data into the FMC and see if you get any Vspeeds on the takeoff page. It may not even accept 25 on the takeoff page. Good luck.

 

 

I had forgotten about that post (still annoyed he never answer my question about how he managed to have the lower EICAS like that :( ) ergh, I see that forum post took a sour turn. Some quite horrible posts. What's horrible is I thought for a long time about this post before deciding I would precisely for the reason of people getting really annoyed at Vernon asking a simple question and making one small mistake of posting a link to material. So, thank you all for the nice replies and I mean that sincerely. Moving on though, that post confused me even more then I was already. Both Packs OFF is allowed and now allowed for a 737 according to the replies. Part of the trap some us fall in I suspect is we see the packs section in Topcat and immediately assume it means that option is available for every plane. But, that isn't necessarily true, it's a tool that can take any plane, but that doesn't mean PACKS off is possible for a 737. However, FS2Crew also has an option for Bleeds on/off at takeoff, so that leads me to suggest that yes you can do it. But, again, that doesn't mean FS2Crew is 100% correct in this mater.

 

Best thing about it being a simulator, is I can try both packs on and off for takeoff and see which is best, or which ends up in a crash! I think that's probably the best option me on this one

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There are other airports with short and narrow runways like Queenstown (NZQN). It's runway is 5830'/98' (1777m/30m). It is 47m longer than the one you're proposing to takeoff from. 737's operate in and out of there.

 

But most airlines flying to these small runways usually have SFP and 26K thrust as a minimum.

 

With regard to BLEEDS off (not PACKS off, because the pack switches don't move from AUTO), it's up to you.

 

I wouldn't do an unpressurised takeoff if the APU was working ok. But my appetite for risk is different to yours. I wouldn't risk another Helios.

 

PS

The airport would need special assessment for suitability. It would then might regulatory approval. Pilots would get special training.

Maybe they don't operate 737's out of LSZB because pavement limitations. If worst comes to worst, just limit the amount of weight you leave LSZB with, like they do in the real world.

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With regard to BLEEDS off (not PACKS off, because the pack switches don't move from AUTO), it's up to you.

 

I wouldn't do an unpressurised takeoff if the APU was working ok. But my appetite for risk is different to yours. I wouldn't risk another Helios.

 

 

Maybe that is the source of my confusion. I was under the impression that "BLEEDS OFF" simply meant turning the Packs to OFF. But, just checking this book on a 737 I have, I always forget about the bottom two switches which are, in fact, the bleed air switches. So, BLEED off is referring to those, not the packs. Good to know how I managed to become so confused with this.

 

So, in Topcat, the option for "Air Conditioning on or off" is referring to the BLEED switches, not the PACK switches. Is that correct? In which case, if the PACKS are left in the auto position, air is still flowing around the cabin it's just unpressurised unless I use APU Bleed air. And what you said, you would, if it was a BLEEDS OFF takeoff, would use APU bleed air until the engine BLEED air came back on. Correct?

 

Not sure I've ever used the word bleed more in all of my life!!

 

 

Just read up on the Helios incident and wow, that a huge series of mistakes

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So, in Topcat, the option for "Air Conditioning on or off" is referring to the BLEED switches, not the PACK switches. Is that correct?

 

 

Effectively, yes.

 

In which case, if the PACKS are left in the auto position, air is still flowing around the cabin it's just unpressurised unless I use APU Bleed air.

Effectively, yes. But the packs are no longer doing anything at all. The recirculation fans are circulating the air. And as you rightly state, the aircraft is "unpressurised" until you use the ENGINE BLEEDS or the APU BLEED.

 

Yes, that's what I'd do out of LSZB. I would use APU BLEED air until I can put the ENGINE BLEED air back on. Basically, I would do the TAKEOFF part of the No Engine Bleed Takeoff and Landing Supplementary Procedure (SP 2.5) found in the FCOM for these reasons:

- Improved takeoff performance

- passenger health

- Reduced risk of depressurisation

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Excellent, sounds like a plan. I think in all of this there is no "answer" to Bleed air as it depends on the airline SOP. That's about the most I can gather from all of this. I notice "very high OAT" as well, but very high in Greenland is very different to very high in Darwin, so again it's hard to get a grasp on what that means.

 

After messing with Topcat some more, I've realised that in my scenario, it's probably better to try both Air Con on and off, and compare the runway margin and de-rate level. If I can get good on both with Air Con on, I'm better to just leave on. However, if it gives me a little extra when I'm not playing with much in the first place, better to have them off and get that extra performance boost.

 

In this scenario I'm better to get a performance boost and get the bleed air on as quickly as possible in a safe manor and let everyone put up with a few minutes of no air, it won't harm anyone (as long as I remember to turn it back on!)

 

Thanks for all the comments, that's really helped me out

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Yes definitely depends on SOP. Airlines have entire departments devoted to nutting this stuff out. Pilots get very comprehensive training and if the airport is special enough, they make specific training and approval requirements for the types of aircraft and pilot that can fly to that airport. This is why everyone says to fly however you want and I'm happy that you're experimenting and developing your own SOP instead of hunting for airline specifc SOP.

 

Don't forget to enjoy the flight!

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(still annoyed he never answer my question about how he managed to have the lower EICAS like that )

 

It's just a lower EICAS frame over a monitor. He could put NETFLIX down there if he wanted to.

(Pic is of a sim pit and not a real plane, or our sim).

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gives me a full throttle flaps 25 take off
A couple of hours ago I was enter info into the FMC for KJFK-KDFW flight using 04L at Kennedy. 04L is an 11000+ ft. runway. I believe I was using a D-2 and 50 degrees. Just for laughs I entered flaps 25 into the FMC. VSpeeds Unavaible message from the FMC. I entered the usual 5 and received Vspeeds. The TOW was around 150000 lbs.

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It's just a lower EICAS frame over a monitor. He could put NETFLIX down there if he wanted to.

(Pic is of a sim pit and not a real plane, or our sim).

 

That makes more sense. I was searching the internet for "PMDG lower EICAS change" but couldn't find anything other then stuff no related. It's just I saw vPilot on that lower EICAS and thought how the eff did he get that on there. If it's not from FSX/P3D though, that makes more sense. I did wonder how he got the screenshot to look very realistic.

 

 

A couple of hours ago I was enter info into the FMC for KJFK-KDFW flight using 04L at Kennedy. 04L is an 11000+ ft. runway. I believe I was using a D-2 and 50 degrees. Just for laughs I entered flaps 25 into the FMC. VSpeeds Unavaible message from the FMC. I entered the usual 5 and received Vspeeds. The TOW was around 150000 lbs.

 

As I've said. it's possible that Topcat just deals with the information it has, rather then knowing the specifics of what a 737-800 can do. It's a tool for everything, not a tool for that plane. So, if you get nothing from Flaps 25, that's probably a good indications I can't. However, it's a sim and it won't stop me (unless the take-off warning horn goes off...?)

 

We'll see. Some testing will prove the answers. I can always pick F.25 and input the V speeds Topcat gives me.

 

 

Yes definitely depends on SOP. Airlines have entire departments devoted to nutting this stuff out. Pilots get very comprehensive training and if the airport is special enough, they make specific training and approval requirements for the types of aircraft and pilot that can fly to that airport. This is why everyone says to fly however you want and I'm happy that you're experimenting and developing your own SOP instead of hunting for airline specifc SOP.

 

Don't forget to enjoy the flight!

 

You're right, and I'm not forced to fly a certain way because I'm paid. I can do what I want. So, I try not to be "It has to be this way and nothing else" because it ruins it for me, but I like to get close to something fairly realistic. I found a lot of documentation for Ryan Air, but funnily I'd never fly with them ever. I've always chosen another budget airline if I've had to. I have a combination of BA and Ryan Air documentation and do what I want to do to make up my "as real as it gets" flying. But, I'm sure neither is correct if I was being paid by them. I'm sure I saw someone state that a certain airline SOP was auto-pilot on a 400 ft, which for me, was far too early, but I've never flown it up to TOC that I see other simmers do. You're right in that fly how you wish, I paid for this thing after all, why fly how I don't want to. But with things like bleed off takeoff, because it's so airline specific, finding an "answer" is probably not the correct way about it. Checking the Boeing documentation and seeing what works for you is maybe a better way.

 

After all, who says Airline X does it correct?

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A couple of hours ago I was enter info into the FMC for KJFK-KDFW flight using 04L at Kennedy. 04L is an 11000+ ft. runway. I believe I was using a D-2 and 50 degrees. Just for laughs I entered flaps 25 into the FMC. VSpeeds Unavaible message from the FMC. I entered the usual 5 and received Vspeeds. The TOW was around 150000 lbs.

The key to being able to use flaps 25 for takeoff is having the short field performance package installed. Pretty sure that's a configuration option in the PMDG menu of the CDU. We do F25 takeoff in real life pretty commonly, in short field / heavy plane situations, like BLI - Hawaii, or out of LIH etc. Bleeds off is common in those same situations, and yeah it's a supplemental procedure.

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You are correct, PMDG does have "Short Field" option. I can't say if it would affect this, but maybe you're right in that one.

 

So Stearmandriver what is your airlines factor for "bleeds off takeoff"? Not that I'm taking your experience as gospel for everything, but some insight would be helpful :)

 

I know weight and high OAT plays factors, but "high OAT" and "heavy weight" mean nothing to us simmers. You use bleeds off T/O for those airports, but whats the reason?

 

Thanks, as always

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To be honest, I can't give exact parameters because I don't know them either. From a pilot standpoint, we use the bleed and flap configuration that our performance data from central load planning says to. Bleeds off = a little more available thrust, a higher flap setting gets you off the runway sooner and so helps with short runways and close in obstacles. sometimes you'll see artificially inflated v speeds that use more runway but launch you with more energy, resulting in a steeper climb that can help clear obstacles farther out in the take off profile.

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Ok thanks, that helps.

 

No obstacles at Bern, however a short runway so I will use Topcat as stated earlier and just work out what gives me the best run way length. I saw some runway margins around 80m but bleeds off and I can get 200m. I'll take the 200m.

 

I'm not a pilot or a dispatcher, but sounds good to me :)

 

Thank you for contributing

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There are other airports with short and narrow runways like Queenstown (NZQN). It's runway is 5830'/98' (1777m/30m). It is 47m longer than the one you're proposing to takeoff from. 737's operate in and out of there.

 

But most airlines flying to these small runways usually have SFP and 26K thrust as a minimum.

 

With regard to BLEEDS off (not PACKS off, because the pack switches don't move from AUTO), it's up to you.

 

I wouldn't do an unpressurised takeoff if the APU was working ok. But my appetite for risk is different to yours. I wouldn't risk another Helios.

 

PS

The airport would need special assessment for suitability. It would then might regulatory approval. Pilots would get special training.

Maybe they don't operate 737's out of LSZB because pavement limitations. If worst comes to worst, just limit the amount of weight you leave LSZB with, like they do in the real world.

Helios wasn't caused by packs or bleeds being switched off and your after takeoff checks should ensure packs are on. Not really a risk.

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Packs have nothing to do with this Kevin as we have learnt in this post, it's bleeds. I was wrong in quoting packs when infact I meant bleeds. This was a misunderstanding on my part. I quote from Helios

 

"After the aircraft was returned into service, the flight crew overlooked the pressurisation system state on three separate occasions: during the pre-flight procedure, the after-start check, and the after take-off check. During these checks, no one in the flight crew noticed the incorrect setting"

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Helios wasn't caused by packs or bleeds being switched off and your after takeoff checks should ensure packs are on. Not really a risk.

You're right on both counts. In the interest of brevity, I didn't and won't elaborate.

 

I would still consider a bleeds off, unpressurised takeoff a threat and brief it as such because the only guard against forgetting to reconfigure air would be the after takeoff c/l, until you get the horn; the final guard.

 

At that stage (intermittent horn), if you're unlucky enough to get to that stage, the "tea and biscuit" conversation is the least that would occur as a result, hence why is consider it a threat for briefing, and why i'd opt for SP 2.5 if the APU was available.

 

That's just me. I'm not a pilot. Your thoughts?

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Bleeds OFF is pretty much the last resort. The computer is looking to optimize the N1 hat still allows runway and climb performance.

 

For places like LIH, we're runway limited so it's a F25 takeoff. If 27k BUMP still doesn't get us the performance, then it's add BLEEDS OFF.

 

Some places might be climb limited, so F25 won't help. If we're at max power, then it's usually F5 BLEEDS OFF.

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Hmm....makes judging, as a non pilot, situations like this near impossible unless you have someone with a pilot experience to tell you.

 

As I said, Bern doesn't have a climb issue, just a short runway and right now, a high temperature. I know when it comes to 1830z Sunday, it's going to be between 30 and 35 degrees,. So maybe F. 25 isn't needed, or even Bleeds off, just as long as I can hit V.Rotate in time. But, as a non-pilot that's difficult to know.

 

Maybe that's the point. This comes out of either experience of yourself as a pilot, or airline experience. The second you will never get in the sim world, the first you can get but maybe with some dead virtual passengers in the process :)

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Stearmandriver and Spin737 are both pilots for an airline. Real 737 pilots

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I just meant there are lots of these things that come up, and it's hard to ever know what the right answer is as a non-pilot, and even then, answers vary. I just used it as an example of it being near impossible for me to know the best answer.

 

But I appreciate the responses from real pilots it's great to see and read. But, after everything that's been said all that calls out most to me is run the numbers in Topcat and see what works in my head. I'm not working in dispatch for an airline so it might not be the best answer, but what works for me is good :)

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It's worth remembering too that all this data is calculated based on worst case scenario - engine failure at V1. So realistically, just use max thrust and flaps 15/25 if you really want to be safe, and don't even mess with bleeds off. An engine is probably not going to quit. (I'm certainly not advocating this attitude in real life.) But you aren't really "missing out" on an experience by doing it this way; like I said, RW airline guys aren't figuring this out themselves, based on experience or anything else. Typically, it's computed by a computer. Possibly, it's computed by a pilot or load planner using tables... But regardless, none of us are making decisions. Those have already all been made by Boeing engineers; we just use what they tell us the day's combination of factors requires.

 

I agree, btw, with whoever said they'd regard a bleeds off takeoff as a threat and brief it accordingly. I'd consider ANY non standard takeoff config a threat. I'm not worried about forgetting to turn the bleeds back on (no way you wouldn't notice an unpressurized climbout), I'm worried about remembering to turn them off in the first place. Or about briefing a flaps 25 takeoff and then slamming the handle into the 5 gate like you've done a thousand times before. Habits are powerful things, and if you consciously develop good ones, they are valuable things as well... buy they DO mean that any required actions that run contrary to your habits automatically become threats. It's just too easy to fall back on ingrained habits. Of course, the way to trap this kind of error is to also consciously develop good checklist discipline. Don't just read/respond out of habit, but force yourself to really consider every item. I know that sounds really obvious, but on the line, doing the same things day in/out, it's easy to get complacent and sloppy if you let yourself.

 

Anyway, my two cents.

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