climb gradiant - performance theory

[downwindabeam]

Hello all,

So we all know how performance theory is based on obstacle clearance of 35' feet attained with V2 and then second segment is based on 2.4% climb gradiant , while the final segment based on 1.2% etc etc etc...

How about SIDs that require a certain climb gradiant to a certain altitude.... I've been told that we on what we call in the states 'transport category' airplanes cannot guarantee climb gradiants as they are prescribed on charts... [jepps] so my question is, how does a 747 leaving for a 13 hour flight facing a SID that asks you to notify ATC as soon as possible if you know you will not be able to make a certain altitude climb requirement knows that it will not be able to make that requirement?

and on the other side of the spectrum, how can we taking off everyday with our smaller sized planes can guarantee to ourselves that we meet climb gradients as prescribed on SIDs?

Thanks!

-downwindabeam

[Slasher]

Simply notify ATC on the AWC freq that you cant meet the
min alts on the XXX SID. Theyll ether issue a new SID or say
to expect radar vectors after TO. Or just tell them the SID
that meets with your performance.
This differs from the Engine-Out proc which doesnt necesarily
follow a SID. Mainley used when published SID min alts or
obst clearance alts cant be met.

For light ac refer to the perf graphs/charts in the AFM.

[downwindabeam]

notice that i didn't ask what to do in the above detailed case.... i asked how do you figure out you cannot meet it! thus the difference.

also, what do you do when the AFM is not an item that the airplane is certified with [meaning the company is not required to carry it in the airplane at anytime].... how can you assure yourself you can meet SID required climb gradient?

[ITCZ]

Downwindabeam, the performance requirements you mention are for one-engine-inoperative flight.

The SIDs assume normal ops, that is, all engines operating. So your 747 departing on its 13hr journey will easily make a better gradient than 2.4%, easily doing better than 3.3%, probably happily clearing 6% if required. The B717 (MD-95 ) that is my ride often makes 8% gradients at moderate weights, both engines operating.

One inoperative is a different matter though. You will then fly your company's prescribed Engine Out SID (EO SID), which may have you flying a different path over the ground to avoid obstacles, obstacle clearance based on your first- to fourth-segment limitations, one inoperative.

How to know what gradient you are making? Use this rule of thumb:

Groundspeed (kt) x Gradient (in %) = Rate of Climb/Descent (feet/min)

Example: YPPH Perth Intl, Australia. All SIDs require 4% to 2800' thence standard 3.3%. B717 initial climb V2+10 speed target at high-ish weights, 158KIAS. Call it 160kt.

160 x 4.0 = 640 feet/min

From that, 640 fpm is the minimum rate of climb to make the gradient at that speed. B717 usually achieves +1800 feet/min both engines operating.
However, suffer a total power loss on one motor after V1 and precise handling might have you going up at 400 fpm at high weights. 400 divided by 150 = 2.6%. Therefore, fly the EO SID, which has a longer upwind leg than the SID followed by a turn toward the ocean and away from the higher terrain. Alert ATC as to your performance limited situation, and advise brief tracking details. ATC then moves everyone out of your way (one hopes).

The groundspeed x gradient rule-of-thumb works for all aeroplanes. Say your light twin normally climbs out at 105KIAS and you need to make a 3.3% gradient....

105 x 3.3 = 346

So if you climb out at 350'/min your light twin will make the SID gradient. Dont forget we are referring to groundspeed, so factor that in - esp if the SID turns you downwind.