Hazelnuts,
The take-off flight path requirements of 25.115 and the WAT-limit requirements of 25.121 are really quite separate requirements and should not be confused.
So WAT limits are
only related to 25.121 and no other FAR?
Therefore at WAT-limit weight the average gross gradient between gear retracted and 400' will be somewhat less than 2.4%.
So the gross gradient
only needs to be 2.4% at the
point the gear is retracted, and
not a 2.4% gradient from gear retracted to 400'?
Flightpath,
I must keep trying to explain to pilots , procedure designers, and others, that departures and missed approach are designed all engine, and that engine out is NOT considered in the procedure design criteria, and as shown in the slide, that OE obstacle clearance is NOT covered in the procedures.
I think where that confusion starts, with pilots at least (myself included), is that we understand performance, in this regard, to be one item - climb gradient (climb rate and groundspeed). We will look at a departure procedure and see that it requires a climb gradient of x% which corresponds to a climb rate of say 500 fpm. If we look at our charts and see that the single engine rate of climb is >500 fpm for the conditions, why would we have to consider the departure procedure only being designed for all engine performance. In other words, if a Baron can fly the departure procedure with all engines operating and I can match the Baron's performance (climb gradient) while one engine inop, how is that any different? The procedure doesn't know if I'm performing with one engine inop or all engines - all that matters is climb performance (gradient).
Before you
I don't think that way anymore! I understand that all engine is a constant slope and OEI is a segmented procedure. OEI considers the level off to clean up, all engine doesn't. Vertical and horizontal clearance requirements are different between the two. Any other ones I'm missing?
John T,
You're mixing things up a bit here.
The minimum net second segment flight path is 1.6% which provides a limiting weight.
Note that the limiting weight for the takeoff is the most limiting weight of the various limiting weights which have to be checked. That is, second segment limits may/may not be what limits the RTOW for the particular takeoff.
So whatever the gross climb gradient the airplane will perform at that day, the net climb gradient will be reduced by 0.8%. For example, the gross gradient is 4.5%, therefore, the net gradient becomes 3.7% From a performance requirement - since the 4.5% gradient is greater than minimum required 2.4%, I can takeoff at a higher weight. From an obstacle requirement - I need to ensure the 3.7% clears the obstacles by 35'. I can decrease the net gradient to 1.6% in the second segment if that can clear the obstacles by 35', which means that I'm also at the minimum performance requirement for WAT limits (25.121). Say that a net gradient of 1.0% clears the obstacles by 35' in the second segment - I still can't use a weight higher than what would give a 2.4% gross climb gradient for the second segment.
Is that all correct?
To anyone,
Under FAR 25.115, it states that the net takeoff flight path is the actual takeoff flight path (determined in accordance with 25.111), reduced at each point by a gradient of climb equal to 0.8% for two engines.
FAR 25.111(c)(3)(i) states that at each point along the takeoff path, starting from 400', the available climb gradient must not be less than 1.2% for two engines.
Is the net climb gradient for determining obstacle clearance reduced to 0.4% then?
My understanding is that at 400', this
available climb gradient is used to accelerate the airplane to Vfto.
Thanks for your patience!
