2nd Segment climb gradient.
 

JAR/FAR 25.121 states (with One Engine Inop)

.......but without ground effect, the steady gradient
of climb may not be less than 2·4% for two-engined...

My question, what does "steady mean"?

Since, as airplane climbs performance decreases, does it mean the minimum acceptable gradient when minimum acceleration altitude (not less than 400 feet and can be increased by operators for their performance calculation) is reached or the minimum instantaneous value at the beginning of second segment (35 feet)?

Thanks

Interpretative material such as FAA AC 25-7 adds that the normal lapse rate of thrust with altitude does not constitute a “more critical operating condition”.

“Steady” means at constant speed V2, i.e. not accelerating or decelerating, except for the increasing TAS when climbing at constant IAS.



FAR/JAR 25.121 defines a takeoff weight limitation (a.k.a. WAT-limit) that is not directly related to the takeoff flight path used for obstacle clearance.

An interesting question.

In the old days of the Australian Regulator (DCA, pre-CASA) the local requirement imposed the minimum gradient throughout the segment .. so we lost a few kilos on RTOW for that limit to be met at the segment's end.

So the best answer is along the lines of either the design standard or the local Regulator's interpretation, if the latter is more restrictive.

Thanks for answers,

Gysbreght, in fact, my intention was to learn the effect of operator selected acceleration altitude, on second segment climb limited weight.

Let me go a little be details:

I quickly checked AC 25-7A. I did not come across a clear description of "steady climb", but I guess it implies your explanation.

So what I understand, in case of engine failure of a twin around V1 and continue to take off, for a given weight, it is enough if a 2.4% gradient is even momentarily available only at the beginning of second segment (35 feet) at V2 speed. Obviously, as maintaining this speed (=Steady Climb) the available gradient will be less and less. At the chosen acceleration altitude by the operator (e.g 800 feet), the available gradient will be less than 2.4% (e.g 1.5%) but does not matter.
If my above understanding is correct, then overall climb gradient will be less than 2.4%. In another word, when acceleration altitude is reached the actual climb gradient will be an average of 2.4% and 1.5%.

From all above, if there is no obstacle in the take off direction (i.e towards sea), changing the minimum acceleration altitude will not change second segment limited take off weight.

Any comment?

While I don't have an official reference, I seem to remember that Boeing's "Jet Transport Performance Methods" handbook (downloadable on the web) stated that 2nd segment gradient is applicable only at the beginning of climb, ie 35ft.

You still have to fulfill all applicable obstacle requirements and final segment gradient (IIRC also applicable only at the beginning of the final segment). Plus gradient at 1500 ft has to be "positive"

I thought 25.121(b)(1)(i) was clear and did not need an explanation. The minimum gradient of 2.4% is at the point where the landing gear is fully retracted, but without ground effect and in still air. At the maximum weight limited by 25.121(b), with one engine failed at V1, the height at the point where the landing gear is fully retracted is usually less than 35 ft.

Obstacle clearance must be shown with the net takeoff flight path data. The takeoff flight path takes ground effect and wind into account, as well as the variation of thrust with altitude, and the time limit for using takeoff thrust. So the flight path gradient will usually reduce with increasing altitude.