Maximum TOW

[Driver 170]

(NOT A PILOT)

I have a said operators performance preamble and line training document. After studying the 737 800 performance reference handbook and operator performance preamble, i'm needing to know something which i can't quite grasp.

Below is a quote from the line training document...


4.8.1 EFB and Preamble data - Dispatch Planning

The dispatch landing performance data in the **** EFB OPT and Preamble are based on use of maximum manual braking and auto speedbrakes, with no thrust reverse credit. The Dry runway figures are factored by 1.67. The Wet runway figures are the Dry factored figures increased by a further 15%. The EFB OPT or Preamble tables shall be used prior to dispatch (dispatch planning stage) to satisfy the AIR OPS 1 requirement and to determine the maximum take-off weight (i.e. payload and fuel) at which the aeroplane can land at the destination or alternate airport within available landing distance in expected conditions.

I understand it all except maximum takeoff weight weight + trip fuel and payload. I know its not meaning certification MTOW but rather the lowest of the three from my dropbox link

https://www.dropbox.com/s/0kmp0szdl4aubfa/Photo%2009-05-2016%2C%2012%2017%2018.jpg?dl=0

Why is this considered as trip fuel will be burned off?

Thankyou.

[Mad (Flt) Scientist]

What they are saying is that you work out what your maximum landing weights are at destination and alternates (separately). the you add the amount of fuel to reach each. that number is the maximum you can take off at if you are going to respect the landing weight limits you just calculated. if you take off with a higher weight you may be legal at takeoff, but you're setting yourself up for a problem on landing, as you'll be too heavy.

[Driver 170]

You're finding your performance limited weight for landing, but why add trip + alternate fuel to maximum landing weight...

[MarkerInbound]

Because you can not takeoff planning to land overweight. Say your max TO weight today is 178,00 pounds but your max landing weight at your destination is 154,00. If your fuel burn is only 12,000 pounds to the destination you are limited to 166,000 even though the airplane is capable of departing at 178,000. I've never seen the case but you could in theory have a case where the alternate landing weight is further limited to say 148,000 but the burn to the alternate is only 4,000 pounds. If you departed above 164,000 you would be overweight at your alternate.

[Driver 170]

So overall you have to burn all your trip fuel if departing at max landing weight before landing?

Wouldn't the alternate landing weight be 150,000 instead of 148,000? - max landing weight 154,000 minus alternate fuel 4000...

[Chesty Morgan]

MI means you could be performance weight limited at the alternate. The 154,000 max landing weight limit is, in this hypothesis, a performance limit rather than structural as is the 148,000. Although it all depends on how much faffing around you do at the destination before you divert so probably would never be a problem.

You would have to burn more than the trip fuel to avoid landing overweight at destination because you'd need to get rid of the contingency too ;)

[Driver 170]

Performance limited weight not structural, got it !!!

So your wanting to burn all usable fuel before landing then, ie CONT, Trip fuel and alternate.

What about final reserve fuel for EASA regs or the old EU OPS thats getting replaced? Surely that can't be touched?

[Chesty Morgan]

Be careful with the term 'usable fuel'. In essence that means everything in the tanks. So not necessarily but if you're planning to land at MLW (perf. or structural) then you would need to burn the trip + cont. You can't plan to use contingency fuel and you can't always guarantee it'll be used so if you're close to the limits then you have to be careful with what you take.

Alternate fuel is accounted for in the sums - MLW + trip = MTOW. There is no need to burn the alternate fuel to ensure you meet MLW at destination. The plan is to always arrive at DA/MDA with at least ALT + FRF but if you calculate that you will arrive with less then you are allowed to continue to destination assuming the weather and traffic situation is agreeable.

FRF is there to be used if you need it, in euroland it's the final 30 minutes worth. If at any point you calculate you will land with less than FRF then you declare a mayday.

[Driver 170]

All is cleared up here. Thanks, much appreciated.

[Driver 170]

One other thing.

Do i need to find my allowable landing weight at my alternate then add my alternate fuel to that figure and also add my trip fuel to my DEST allowable landing weight?

[Chesty Morgan]

Normally just look at destination weight. If you're within limits it stands to reason that you'll be lighter if you divert.

[Driver 170]

Ok, i was just thinking about applying the alternate fuel to the max allowable landing weight at the alternate dest.

[Driver 170]

Lets say your max allowable landing weight happens to be your certified max landing weight would you have to drop some payload atleast?

[MarkerInbound]

Depends. If you are landing at your destination at your structural landing weight you will still be carrying your alternate fuel. However some airplanes have a max zero fuel weight. You have your BOW plus payload plus fuel which can not exceed your structural or performance limits. But the BOW and payload can not exceed the max ZFW. In theory you could be at at max ZFW so you couldn't add more payload.

[Driver 170]

To add something else, it says in my preamble for dispatch..

4.2.2 USE OF QRH DISPATCH LANDING PERFORMANCE DATA
To satisfy the Air OPS, prior to dispatch (planning stage) or in the event of in-flight replanning, determine the Max weight at which the airplane can land at destination or alternate airport within available landing distance in expected conditions. LDR must be equal or less than LDA.

MAX weight? I thought requirement is you use estimated landing weight to determine 60% of LDA?

Also it says LDR must be equal or less than LDA. Surely if during dispatch LDR equals LDA you'll be above 60% of LDA?


CAT.POL.A.230 Landing—dryrunways
(a) The landing mass of the aeroplane determined in accordance with CAT.POL.A.105(a) for the estimated time of landing at the destination aerodrome and at any alternate aerodrome shall allow a full stop landing from 50 ft above the threshold:
(1) for turbo-jet powered aeroplanes, within 60 % of the landing distance available (LDA); and

[Driver 170]

During dispatch with this table am i using estimated landing weight or max landing weight?

https://www.dropbox.com/s/haykw4yzwg46zoo/Photo%2013-05-2016%2C%2015%2011%2006.png?dl=0

[MarkerInbound]

As Harry Callahan said, "A man's got to know his limitations." You figure the maximum landing weight at your destination, whether it's structural, performance limited or runway limited so you have a number to work back from. As pointed out above, that could affect your TO weight if the planned fuel burn is less than the difference between today's max landing weight and your planned TO weight. Or you could have MEL items that affect the landing, anti-skid inop or ground spoilers inop. You work back your maximum allowable weight.

Actual stopping distance is the distance it takes to stop the aircraft. Required landing distance doesn't show up in the FAA regs but is usually used to describe the distance required for dispatching the aircraft. As such, it is ASD plus .666%. That number has to be
less than the landing distance available.

[Driver 170]

Ok thanks for that. So on a 737 800 what is the typical day to day performance limited weights for takeoff and landing?

[Chesty Morgan]

There aren't any typical limited performance weights.

[Driver 170]

Maybe i should say, what is the usual performance limited weights you come across?

[Chesty Morgan]

It could be any of them. There are too many variables to give you a definitive answer.

[MarkerInbound]

That's like asking what the usual temperature is or what the usual runway length is or the usual airport elevation is or the usual payload is or half a dozen other factors.

[VJW]

65317kg (the MLW)...... 99.99% of the runways allow for MLW in BA med/poor conditions..

[Driver 170]

Very true, i appreciate all the help.