T/O-Perf. Climb Limit acc. to CS25

[Orthodrome]

Good morning to all of you,

during ground school the following question arised:

Besides "Field Limit" and "Obstacle Limit" (and max. breake energy etc) we need to assess the "Climb Limit" for determination of the Perf. Limited TOM prior to every T/O in commercial OPS with a Class A large transport aircraft.
Now, while EU-OPS (yes, I know we transitioned to EASA-OPS, however I do think my question is irrespective of this aspect) clearly states that we need to assess the "Obstacle Limit" and also the "Field Limit", there is NO requirement according to EU-OPS to verify we can meet the Climb Limit Gradients that are defined in CS25.

So I do wonder: Which regulations requires us to meet CERTIFICATION specifications (here: climb gradients for T/O) in day2day normal operations?

The way I understood this aspect is that the manufacturer undergoing certifications for the particular aircraft type has to prove that the aircraft can "deliver" the promulgated climb gradients (CS-25). If I would have to assure that I can guarantee that the aircraft is able to perform exactly like during certifications in normal operations by calculation, our T/O preps would take ages. As an exaggerated example to illustrate where I struggle: The aircraft needs to perform various test concerning limit load factors or buffeting behaviour during certification. But that does not mean that I would need to prove that my aircraft can still meet those requirements for a particular flight. I know my aircraft is certified, airworthy and I respect the limits my company gave me based on FCOMs/AFMS etc and that is it.

[FlyingStone]

One could argue that this statement below from CAT.POL.A.205 Takeoff also includes climb limit.

a) The take-off mass shall not exceed the maximum take-off mass specified in the AFM for the pressure altitude and the ambient temperature at the aerodrome of departure.

AFM for 737 specifically says that takeoff climb limit (2.4% gradient) has to be taken into account when determining the (performance-limited) MTOM.

Hope you don't work for those operators who think if it's VMC, you only need to look at field limit. :ugh:

[john_tullamarine]

The certification limits are embodied in the AFM ergo, if you figure out the AFM limiting weight, you have covered all that part of the work.

The operational rules may then require further calculations which may, or may not, be further limiting than the AFM limiting weight for the particular takeoff.

we need to assess the "Climb Limit" for determination of the Perf. Limited TOM prior to every T/O in commercial OPS with a Class A large transport aircraft.

There exist several climb limits in the WAT calculations - first segment (if existing), second segment, third segment (capability), and fourth segment. Some aircraft will have a fifth segment for transition to final climb. One of these will be limiting .. often, but not necessarily, the limiting case is the second segment.

As these limits are embodied in the AFM they apply across the board, not just for commercial operations.

Which regulations requires us to meet CERTIFICATION specifications

If you observe the AFM limits you meet all the certification requirements.

If I would have to assure that I can guarantee that the aircraft is able to perform exactly like during certifications

Not quite relevant for line operations .. just meet the AFM requirements and you will be doing just fine for the certification aspects.

our T/O preps would take ages

ah, yes ... for any takeoff if you use the typical AFM calculation sequence. Most operators of note promulgate General Takeoff Charts which are conservative simplification of the AFM data .. these latter are intended to provide acceptable data in a relatively short time. Depending on the aircraft, a full longhand AFM calculation can take half a day or more if the obstacle escape is complex.

I know my aircraft is certified, airworthy and I respect the limits my company gave me based on FCOMs/AFMS etc and that is it.

That sounds about reasonable but, from your other comments, perhaps your company training was not quite extensive enough ..

AFM for 737 specifically says that takeoff climb limit (2.4% gradient) has to be taken into account when determining the (performance-limited) MTOM.

Depending on the particular model AFM presentation, you will be checking all the climb WAT requirements although that may not be obvious if the AFM doesn't explicitly separate the calculations .. eg, if only one requirement is limiting, there may not be any reference to the others.

Hope you don't work for those operators who think if it's VMC, you only need to look at field limit

There have been operators which only looked at a subset of the requirements for whatever reason .. either commercial expediency or ignorance.

[FE Hoppy]

CAT.POL.A.210 Take-off obstacle clearance
(a) The net take-off flight path shall be determined in such a way that the aeroplane clears all obstacles by a vertical distance of at least 35 ft or by a horizontal distance of at least 90 m plus 0,125 × D, where D is the horizontal distance the aeroplane has travelled from the end of the take-off distance available (TODA) or the end of the take-off distance if a turn is scheduled before the end of the TODA. For aeroplanes with a wingspan of less than 60 m, a horizontal obstacle clearance of half the aeroplane wingspan plus 60 m, plus 0,125 × D may be used.

Given that the NET take-off flight path is derived from the take-off flight path which is defined by the various minimum climb gradients isn't it obvious that it must have taken them into account?

[john_tullamarine]

Perhaps not quite ..

(a) the minimum gradients (generally referred to as the WAT limits) are absolute minimum still air OEI gradients to give the chaps a fighting chance of going up rather than down ... they have naught to do with obstacles. In general, reference to "climb limits" will be to WAT limits.

(b) unless the runway is extremely benign from the point of obstacles, the required gradients for obstacle clearance generally will exceed the WAT limits with associated weight reductions compared to WAT

[FE Hoppy]

CS 25.115 Take-off flight path
(a) The take-off flight path must be
considered to begin 11 m (35 ft) above the
take-off surface at the end of the take-off
distance determined in accordance with CS
25.113 (a) or (b) as appropriate for the runway
surface condition.
(b) The net take-off flight path data must
be determined so that they represent the actual
take-off flight paths (determined in accordance
with CS25.111 and with sub-paragraph (a) of
this paragraph) reduced at each point by a
gradient of climb equal to –
(1) 0·8 % for two-engined aeroplanes;
(2) 0·9 % for three-engined
aeroplanes; and
(3) 1·0 % for four-engined
aeroplanes.
(c) The prescribed reduction in climb
gradient may be applied as an equivalent
reduction in acceleration along that part of the
take-off flight path at which the aeroplane is
accelerated in level flight.

CS 25.111 is the WAT gradients. Therefore the net take-off is de-facto already in compliance before the obstacle clearances are checked.

[john_tullamarine]

I think you miss my point but probably not worth any robust discussion ..