View Full Version : 737 NG Payload questions
28th May 2012, 20:01
Is there anyone out there to explain me how to really work out the RTOW(regulated take-off weight)?We use EFB's in my company for speeds and all performance computations.The reason i'm asking is whenever i wanna calculate my useful load i'm finding this issue.
Assuming all performance computations includes RTOW and you know ZFW and fuel required, what is the problem exactly?
28th May 2012, 20:38
The question is often when we land at some places OFP will tell me the planned ZFW LW and TOW and the guys from the dispatch come and ask me for RTOW but at that stage i still don't have the loadsheet so to obtain the RTOW using the EFB should i use the planned TOW so that it generates me the PLTOW or i should wait for the final gross weight from the load sheet?
28th May 2012, 20:55
If your that confused about this...which you clearly are then why do you continue to operate a passanger transport aircraft on a daily basis without being sure of this ???? From what you have just written in your 2 posts comes across that your very confused and you dont really know what your talking about...why have you not asked any of the Captains you have flown with on the day to guide you with this etc or to explain ????
28th May 2012, 21:00
The reason i posted it is because i wanna know,i believe that's why a forum is there for,instead of criticizing i'd prefer your explanation blablabla
28th May 2012, 21:10
If you want to know something like this then be assertive and speak up and ask the Captain your with...so you are admitting to letting this confuse you on a daily basis whilst working but havent had the sense or assertiveness to ask your colleague who works at your Airline who is sat next to you on the day to explain this to you ?????? You would rather just kinda be not sure but hope or be lucky that you kinda might have done it correctly or hopefully given the right info when asked for the purpose of the weight and balance and take-off performance of the aircraft and then wait until you get home to the safety of your Laptop and then start asking completely random people with names likes BLABLABLA on here who might not actually ever have flown a real aircraft in their life....You Sir are a Smart Man
N1 - I suggest you start by searching for a definition of RTOW as you plainly have NO idea what it is. Prove me wrong - tell me what it is, and then we might have an insight into your 'problem'.
28th May 2012, 22:29
N1 assuming you are in EASA land your company is required to carry, paper or electronic (depending on the class of EFB), versions of the perf data in table form. I would suggest you start with that. Enter with actual temp and wind component, read across, then correct for pressure, bleed, TAI, MEL/DDG. Reverse correct to find assumed TOW for R-TO assumed temp et al.
Or if your handling agents produce provisional load sheets, use that to get an idea after whacking in the numbers to get a result. Should sound any early alarm bells. If in doubt, email training, or read your part C or EFB manual. Perhaps both
28th May 2012, 23:25
RTOW, in most parlance, is the limiting takeoff weight for the occasion. Its only relevance to the loadsheet is in respect of needing to make sure that the loadsheet TOW does not exceed the RTOW.
That is to say, you should be able to determine RTOW quite independent of the LDS information. I would imagine that your EFB will have provision for you to enter the runway, ambient conditions, etc .. and it should then spit out a value for RTOW ?
Or have I missed your point ?
If your concern is only with payload, then the RTOW will let you figure out your maximum payload, considering ZFW and required fuel load. Actual payload will follow from the LDS information.
I'm sort of reading between the lines and seeing that you might be confusing RTOW with actual TOW ?
I can only imagine that your Type ground course and/or ops eng training associated with the rating training was a tad undercooked ?
Too Few Stripes
30th May 2012, 22:53
if you're flying for the airline I think you are then I know what you're getting at ! On the EFB enter the actual airfield, runway and ambient conditions and then the estimated takeoff weight from the OFP. To view the absolute max RTOW change engine rating from optimum to 26k, bleeds off, improved climb, then calculate. It will display the max RTOW for you now, enter the lower of this value and the max structural takeoff weight on the handling agents data sheet.
Hopefully a future software update will allow a max RTOW calculation without entering a guestimated takeoff weight :)
DECLARATION: I have never used an 'EFB'
Right, with that out of the closet:-
RTOW is NOT affected by estimated or actual TOW so why you have a need to enter such I cannot fathom. If you really do have to, then I assume ANY number will do to get the EFB to proceed to the next step
RTOW IS affected by fuel burn, so there MUST be somewhere that you enter this to compute?
Rarely, I suggest, would you need to 'fiddle' with engine thrust settings?
31st May 2012, 10:14
@<hidden>, the EFB tools i know start with a take off performance calculation and for that need a take off weight as entry condition. Our EFB is set up so that it uses by default a value well above MTOW (86t for the 800 and 81t for the 700) so that the max take off weight calculation is not hampered by some lower value.
Engine ratings are usually chosed as the lowest possible one for any given weight (hence Optimum), however with a weight above MTOW the EFB should revert to max rated thrust in most cases to make a departure possible.
Landing weight calculation has to be done either with another tool in our case, or even more comfortable by the centralised load control as they do know the maximum landing weight and fuel burn, no need to give them those figures.
Thrust rating is something that is different for each single departure, therefore it is of some concern, for a RTOW calculation however a well written EFB tool will try the highest possible one to get the highes load possible out of a field (remember, in the contaminated case it might well be a lower than the max one for an increased V1 margin).
Too Few Stripes
31st May 2012, 15:31
BOAC - I can't fathom why you have to enter an estimated TOM either, but in this version of EFB you do (it has no 'calculate MTOM' option). As for fiddling with the thrust settings, the EFB defaults to optimum and will calculate the minimum thrust setting for each departure so to calculate the RTOM you need to manually select the highest thrust setting, in this case 26K then when you select calculate the EFB will display the suggested derate and assumed temp for the entered TOM but it will display the RTOM for the selected options (ie. engine derate, imp climb, bleeds off etc etc ).
The software is far from perfect and is extremely basic but the answer to the original posters question is exactly as I stated (assuming I've guessed the correct airline and therefore EFB of course!).
Thanks all for the education - I am glad I never had to use an EFB! It sounds as if the programmes were not written with any pilot input (what does that remind me of............?) since one of the first questions you normally need an answer to on arrival is what is your RTOW! Denti's system seems to have sorted that by assigning TOM above structural. How tfs would cope with a tanking calculation when you might not know TOM until you know RTOW ............................
I am unclear about the landing weight 'tool' you mention, since RTOW calculations need to include planned fuel burn and to have to run another prog to get that seems arse about face! It is no good waiting for CLC to compute your tanking uplift. The bowser man wants to know now. Actually it may well be OK in a calm scheduled world, but in the flak and action...............................
I thought these things were supposed to represent progress! Considering it takes about 1 minute to ball park a useable RTOW from paper..................
31st May 2012, 18:05
I find the EFB a fantastic tool & apparently I am now a grumpy old one. I put in the ambient details, adjust for reality (increase in temp of day, fall of press etc) & execute. I have the flexability to look at differant r/way & power options. The company & I have confidence in the system & each pilot works very indepedantly until we come together for the final answer. Our EFB gives the rtow, so payload answers are easy, & speeds. However its good not to loose sight of "the feelin or experience" factor. Younger chaps dont understand Bullsh#t in, bul out. BOAC is right, paper version takes 1 min when you know it, guess this gives me confidense with EFB. Old git I have become
31st May 2012, 18:25
RTOW for us means only the performance limited take off weight to be honest. Landing weight and fuel is considered during briefing with the preliminary info on the OFP. If any calculations are needed they are done on the back of the flight plan using the good ol' parker pen, indeed the fastest way to do it, usual decision time is less than half a minute. We are rarely if ever limited by landing weight/fuel burn, even if tankering. Fuel is then ordered online and loadcontrol already gets all the infos so the loadsheet could be available once we arrive at the aircraft. The same is true later during the day for subsequent sectors, however ACARS is used instead of the internet currently, internet in the near future.
That way it is possible to get the final loadsheet for the second flight before landing the first one, if flying to a destination where the weather is stable enough to do a performance limited take off weight with the weather data available at that time.
31st May 2012, 19:06
N1 Limit, the EFB should be designed such that it will give you the maximum permissible take off weight if you don't enter an actual TOW but provide all the other parameters. If that max permissible weight result is less than the max structural, then that is your regulated TOW.
Sorry, JT. But this BOAC person goes on my nerves. Mister know it all.
2nd Jun 2012, 11:27
That, of course, is your prerogative. Provided both observe the general requirements of the forum then it remains something with which both will have to live.
Is this peculiar to a particular manufacture of EFB or is the the way they all work?
syhar. BOAC DOES know what he's talking about.
2nd Jun 2012, 16:39
N1 Limit has, I think, highlighted a widespread issue of the lack of performance understanding by many pilots in many companies. I haven't been in this game too long myself (~8 years) but sometimes I find the ideas and concepts, or lack thereof, that some of those who sit next to me have regarding performance simply breathtaking!
A basic understanding of Perf A, the performance manual or section of your aircraft's AOM/FCOM and the preamble to your company's RTOW charts (or EFB, haven't used one yet) is surely all that is required. Any more knowledge than that is a bonus, but would make sense to have IMHO.
Is it an industry wide problem? I've definately seen differences in standards of Perf training between airlines, and it's been a constant decline. Perhaps, as a lot of practical Perf teaching comes during line training, that is taken as gospel, and further reading is not undertaken? Though I have experienced more than one trainer preaching utter tripe regarding Perf.
Even with the more complex weather and airfield combination, a reasonably accurate RTOW calculation should not take more than a minute or two, and if using an EFB, does the manual not explain how to derive your RTOW?
I'm definately becoming a fully paid up member of the grumpy git club. Don't get me going on wet runways...
In the good old days, before they enclosed the cockpits and removed the top wing, we did our own loadsheets manually. Not too difficult, or even time-consuming, but it did give an understanding of the performance calculations. In fact, in the military, we didn't even have WAT limits for the runways, but calculated them from the graphs and charts. (OK, that WAS time-consuming)
"BOAC DOES know what he's talking about."
How can he, since he has never used EFB? He is from another era. The OP posted a valid and sincere question, and BOAC immediately begins to mock him, which seems to be his style.
3rd Jun 2012, 16:02
Is this peculiar to a particular manufacture of EFB or is the the way they all work?
I made an assumption based on the Boeing OPT (http://www.boeing.com/commercial/aviationservices/brochures/opt.pdf) that we use, and I presume most Boeing operators would use.
Thanks, Scio, but it is not clear from that 'short' PDF whether a TOW is required before an RTOW can be determined, which is not logical. Denti's 'default' structural + 'xx' and max thrust rating seems to be one solution - or simply a manual high TOW entry.. The system described by N1 and tfs would appear to be suitable for a 'comfortable' scheduled op, with CLC etc, but not suited to N1 who for some reason "wanna calculate my useful load" although I feel if he/she did actually understand what RTOW is the answer to post #1 would have been obvious
Are there any other links to usage of the OPT? I would appreciate an insight as my last airline muttered and mumbled about using it but never did before it went bust.:)
Like a few others, I still vote for care-worn perf sheets and a space at the bottom of the PLOG. At least you know what you are doing.
Now you are talking my language.....perhaps even standard fuel loads as well.
I remember we had 6 tons or 7 tons or ultimately full tanks on the 1-11.
That made life easy.
And we had ball park figures drummed into our brains for RTOW and V2 etc as a gross error check.
4th Jun 2012, 08:01
Back to the original question...
RTOW is the lowest of TOW encompassing limits such as MLW, MTOW and MZFW.
The limit in an EFB application can be found by calculating the takeoff/landing performance without entering the landing weight, which gives you MLW using existing conditions (those you selected such as airport/runway/temperature/qhn/...).
In essence the EFB allows you to calculate DISPATCH Landing Weight and MRTOW.
What EFB are you using?
4th Jun 2012, 09:18
BOAC,but it is not clear from that 'short' PDF whether a TOW is required before an RTOW can be determined, which is not logical.
As I mentioned earlier, this is the software we use. To determine the RTOW, all parameters (a/c, runway, intersection, wx, bleeds, thrust, flap, CG, etc) except TOW must be entered. It will then calculate the maximum TOW possible for the conditions. If an actual TOW is also provided, then it will calculate the actual performance (N1, speeds, etc) with options for assumed or TOGA. Obviously, if the actual TOW exceeds the max or RTOW it will burp at you.
Thanks to the last two who 'describe it as I would expect it' - it would appear that N1 and tfs have some sort of 'inferior' EFB.
6th Jun 2012, 21:36
Thanx svhar for being supportive,@<hidden> skyjob we use LIDO system EFB but for it to give you PLTOW it needs a Gross weight with Wind,OAT,QNH,hence i needed to know how to work that out.
14th Jun 2012, 01:05
I am not familiar with the LIDO system, so I will not comment. But this is what the forum is about. Most of us will try and help, if we can. Don't let the Oozlum bird farmer scare you.
14th Jun 2012, 15:23
Thanks very much svhr for being supportive that's the attitude i looked forward to getting.Best regards