Do most Part 25 Jets have a 3-Segment Climb?

C150J

C150J

Well-Known Member
Hi guys,

We don't have ready access to our AFM (CL-65), so I'm just curious if most Part 25 jets have 3 takeoff path segments. I remember Polar talking about 5 with a 747, but I wanted to see what others have out there. Thanks!


J.
 
Only 3 on the 747. However, the BAe3100 had 4. It was certified under a SFAR though, due to it's (ahem) lackluster 2nd segment performance.
 
Wow, cool! I'm trying to delve into this stuff for some training. When looking through Part 25, it keeps mentioning this gross .8% climb path. Is that .8% of the obstruction clearance surface, where TERPs has a .24% path? I could be totally confusing things, but I wanted to see if you or anyone else knew... Thanks!

J.
 
It makes much more sense if you draw out all of the segments as one continuous deal.
 
Don't confuse terps with certification standards.

Also, TERPS climb requirements have nothing to do with one engine inoperative (OEI) climbs.

There is gross and net climb paths/gradients. Gross is what the airplane will do on paper (mathmatically) net is what we mere mortal pilots will get the airplane to do.

IIRC, the basic single engine climb gradient required by part 25 is 2.4% GROSS, but take off the .8 or .7 % for pilot and airplane "stuff" and you get 1.6% or so. Notice that is well below any TERPS gradient. We use an electronic weight and balance and performance calculator for the beechjet. It isn't uncommon to be weight limited well below MGTOW because the airplane can't meet the 1.6% required by certification (one of your limits to takeoff weight in the AFM) at higher elevation airports.

Don't get too wrapped around the axle on the part 25 stuff, you never need to use it or know it, other than for conversations over a beer. Part 121 and 135 operations are required to have runway analysis programs to give you OEI performance data and special DP in the event of performance loss on takeoff.
 
Dugie8 said:
Don't confuse terps with certification standards.

Also, TERPS climb requirements have nothing to do with one engine inoperative (OEI) climbs.

There is gross and net climb paths/gradients. Gross is what the airplane will do on paper (mathmatically) net is what we mere mortal pilots will get the airplane to do.

IIRC, the basic single engine climb gradient required by part 25 is 2.4% GROSS, but take off the .8 or .7 % for pilot and airplane "stuff" and you get 1.6% or so. Notice that is well below any TERPS gradient. We use an electronic weight and balance and performance calculator for the beechjet. It isn't uncommon to be weight limited well below MGTOW because the airplane can't meet the 1.6% required by certification (one of your limits to takeoff weight in the AFM) at higher elevation airports.

Don't get too wrapped around the axle on the part 25 stuff, you never need to use it or know it, other than for conversations over a beer. Part 121 and 135 operations are required to have runway analysis programs to give you OEI performance data and special DP in the event of performance loss on takeoff.
Click to expand...

Thanks! I'm well aware of the fact that EOPs and and TERPs are independent and exclusive, but an still confused about what a 2.4% gradient really is... Is that on top of some kind of obstruction plane?

Thanks to all of you for bearing with me. I realize that most of this should be transparent to a pilot (other than reading AeroData or whatever the operator uses), but the gross gradient is what confuses me.

Happy Thanksgiving!

J.
 
2.4% gradient is just that. Go forward 100 feet, go up 2.4 feet. Part 25 is simply what the FAA says the airplane must do, no obstruction planes, no obstacles, just takeoff and do this. The gross and net thing is just a buffer between manufacturing and real world ops. I'm sure you have flown two different tail numbers of the same airplane and can see how the exact same make and model can behave differently even on similiar weather days.

The definions of first, second, third, and sometimes fourth and fifth, segment climbs are a little fuzzy at times. First segment is liftoff to either, gear retraction (lever selected up) or gear in the wells, ends at 35 feet above the runway (with most airplanes this will be with lever selection to up). Second segment is from 35 feet above the runway/gear selected up, to some number, 400 feet, 1000 feet, 1500 feet, etc. This is the one everyone gets all spooled up about. It is important to note, absent a runway analysis program, what your second segment data is actually telling you in the AFM. The number you get isn't going to be a rise over run gradient, it is going to be a snapshot of some point along the second segment path, either the beginning, middle or end.

I used to have an awesome PDF from Airbus that went in to this stuff with some great graphics. It is a real eye opener as to what the airplane is supposed to be able to do at max effort takeoff with an engine out.
 
I thought maybe I had that Airbus PDF somewhere, but couldn't find it. I did come across a Boeing hand out I picked up a while back that talks about performance margins for all stages of operation. It has a section that covers V2 climb gradients.
 

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Dugie8 said:
I used to have an awesome PDF from Airbus that went in to this stuff with some great graphics. It is a real eye opener as to what the airplane is supposed to be able to do at max effort takeoff with an engine out.
Click to expand...

Google "Getting to Grips with Aircraft Performance" - thats the Airbus doc. If you are more Math Minded, you might be able to find Boeing's Jet Transport Performance Methods.

If not, I might be able to scrounge up a copy. I think SmartCockpit has them.
 
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