T/O (and Landing) climb limit weights

[In dis-sky's]

In the B737 FPPM graphs are given for T/O Climb Limit Weight and Landing Climb Limit Weight. What do these weights actually represent? Are these the max weights that would satisfy a minimum climb gradient after T/O (3.3%) and missed approach (2.5%) excluding any obstacles?

Thanks.

[DFC]

These limits are what limit you when there are no obstacles to think about.

Don't have the exact figures to hand but if I remember correctly for a twin like the B737,

With no obstacles you still have to acheive

Departure Climb Gradients;

1st segment - positive
2nd segment - 2.4% one engine inop or 5.2% all engines
3rd segment - 1.2% one engine inop
4th segment - 1.2% one engine inop or 4.0% all engines

Landing Climb Gradients;

1500ft above the aerodrome, a positive gradient

Baulked Landing Climb - 3.2% in the landing config with all engines operating

Approach Climb - one engine inoip, gear up - 2.1%

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These are often called the "Weight, Altitude Temperature" (WAT) limits. As altitude and temperature increase with no other limitations you will have to reduce weight to acheive these gradients.

If you have obstacles, you may have to acheive higher gradients. Similarly, the mised approach from an instrument approach procedure may also require a higher gradient - 2.5% or more.

Regards,

DFC

[john_tullamarine]

DFC ... could you hazard a reference to support the contention that there exist AEO takeoff WAT limits ?


The Type Certification requires some line-in-the-sand values for various items .. including absolute minimum climb gradients for various phases of flight.

The WAT limits (maximum (takeoff/landing) weight for (pressure) altitude and (ambient) temperature) are maximum weights which provide (at certification) demonstrated compliance with these minimum gradients. Note that we are not talking sports car performance in the OEI case .. just enough to give you some confidence that the ground might actually get further away from the aircraft than it was when you rotated ...

So, when working out, say, MTOW, we can start with the certificated MTOW (generally structure limited), check for WAT limits (which may reduce the allowable on the day), check for runway limits, check for obstacle limits .. etc., to work out the RTOW for the day...

(a) 25.117 requires that WAT conditions be satisfied in respect of

(b) 25.119 for AEO landing and

(c) 25.111 for OEI conditions,

and there are a few more requirements tucked away if you want to wade through the regs. Keep in mind that these are the current requirements .. if you want to find out more about specific requirements for a specific aircraft then you must start with the TCDS to establish the actual certification basis for the aircraft .. however, the current requirements will give you some idea of what's what.

Please don't confuse the takeoff WAT case with SID requirements .. two different animals, viz., airworthiness limits and operational limits.

[In dis-sky's]

Thanks. Very helpful.

[sparkman]

How about the requirements on a missed approach procedure? When a MAP requires a gradient in excess of the normal 2.5% it will normally give the figure somewhere on the chart. Often the vertical profile can end up many thousands of feet above the airport elevation. To what point does a MAP climb gradient have to be maintained?

[roljoe]

Usually the company determines an effra (the altitude at which you can accelerate toward the flaps retraction) having in mind that all obstacles have been cleared with a satifactory margin,

without this, start with considering the MSA sectors on the approach map,this will anyway give you an idea of an safe altitude...

DA and MDA will be however selected according to the gradient that the a/c should achieve...taking into consideration all aspects..

rgds