Runway limited

B

BohicaORD

New Member
Hi- long time lurker/ first time poster. I'm new to jet flying and had a question for those airline corporate gals/guys.

Can someone explain what a runway limited Vs. Non runway limited takeoff is and how to calculate it? The aircraft I'm training for has a few variances of takeoff power settings- those I can figure out just fine, but the runway limited Vs non limited is what is throwing me for a loop.

Thanks!
 
Where I work we have two take-off modes ALT-TO and TO.
If the runway limit in the mode we are using is less then MTOW then we are runway limited and will use the 80 kts abort criteria if it is greater then MTOW then we will use the V1 abort criteria.
 
BohicaORD said:
Hi- long time lurker/ first time poster. I'm new to jet flying and had a question for those airline corporate gals/guys.

Can someone explain what a runway limited Vs. Non runway limited takeoff is and how to calculate it? The aircraft I'm training for has a few variances of takeoff power settings- those I can figure out just fine, but the runway limited Vs non limited is what is throwing me for a loop.

Thanks!
Click to expand...

Are you being expected to calculate this stuff by hand?

"Runway limited" would tend to primarily refer to stop margin and brake energy in terms of a reject. Above a certain weight, you wouldn't be able to meet balanced field criteria in the event of a reject started at V1. Depending on the runway, you might be able to simply increase the thrust setting (if using a reduced thrust takeoff), use a larger flap setting (usually to the detriment of OEI climb performance), or simply find a longer runway. Runway analysis would also look at the runway available in case an engine failure occurs after V1, in which case you need to be able to have enough runway to safely get off the ground and reach 35' (and V2) by the end. Also, the runway analysis will look at a standard all-engine takeoff and determine that the runway will be long enough to meet the takeoff distance + 15% requirement ("takeoff distance" is brake release to 35') from Part 25.

If your takeoff weight makes it so one (or more) of those three requirements cannot be met, you're "runway limited."
 
dasleben said:
Runway analysis would also look at the runway available in case an engine failure occurs after V1, in which case you need to be able to have enough runway to safely get off the ground and reach 35' (and V2) by the end.
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Can you reference this? There is a TERPS requirement to reach 35' by DER, but the only 35' reference I've seen in Part 25 doesn't mention DER, just that the first segment begins at 35'. I could definitely be wrong, but I've never found anything that requires 35' by the DER when OEI.
 
C150J said:
Can you reference this? There is a TERPS requirement to reach 35' by DER, but the only 35' reference I've seen in Part 25 doesn't mention DER, just that the first segment begins at 35'. I could definitely be wrong, but I've never found anything that requires 35' by the DER when OEI.
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That comes from a Boeing takeoff performance CBT I have, but looking at Part 25.113:

Part 25.113(a) said:
(1) The horizontal distance along the takeoff path from the start of the takeoff to the point at which the airplane is 35 feet above the takeoff surface, determined under §25.111 for a dry runway;
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It doesn't specifically say anything about the DER, but the requirement does have to be met by the end of the takeoff surface. Seems to me (and the way it's presented by Boeing) that this would imply being met by the DER.
 
dasleben said:
That comes from a Boeing takeoff performance CBT I have, but looking at Part 25.113:



It doesn't specifically say anything about the DER, but the requirement does have to be met by the end of the takeoff surface. Seems to me (and the way it's presented by Boeing) that this would imply being met by the DER.
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Makes sense, I was just hoping you had "the smoking gun," as I've been looking for that reference for some time. Thanks!

I'm assuming that CBT is proprietary and password locked?
 
C150J said:
I'm assuming that CBT is proprietary and password locked?
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No password on this one, but it's on a CD I got in training. Not sure if there's a download source somewhere, but I'll look! It's simply called "Boeing Performance CBT" if you want to look for it as well. It's got everything from takeoff, enroute, and landing performance information. A little dry, but it's good info.
 
Is it that obvious I'm Asa/xjt? :(. It's kinda embarrassing- I asked twice and I'm still lost. Like for instance how can you have an ALT TO departure and yet still be runway limited? Reduced power in a limited runway? Why not just use TO and get all the power you need?
 
BohicaORD said:
Is it that obvious I'm Asa/xjt? :(. It's kinda embarrassing- I asked twice and I'm still lost. Like for instance how can you have an ALT TO departure and yet still be runway limited? Reduced power in a limited runway? Why not just use TO and get all the power you need?
Click to expand...

Can you give a more "detailed" example of what you are asking or confused about?
 
BohicaORD said:
Is it that obvious I'm Asa/xjt? :(. It's kinda embarrassing- I asked twice and I'm still lost. Like for instance how can you have an ALT TO departure and yet still be runway limited? Reduced power in a limited runway? Why not just use TO and get all the power you need?
Click to expand...

It's also partially the way you asked the question.

First of all, you should be asking your instructors this question, not us. I hate to be blunt, but I'm not very interested in giving instruction on company procedures on the internets, for both our sakes.

Talk with your instructor, they'll get you squared away. If you're not understanding it, have them explain it a different way until you get it.
 
BohicaORD said:
Is it that obvious I'm Asa/xjt? :(. It's kinda embarrassing- I asked twice and I'm still lost. Like for instance how can you have an ALT TO departure and yet still be runway limited? Reduced power in a limited runway? Why not just use TO and get all the power you need?
Click to expand...

If you are doing an ALT T/O takeoff and are still runway limited, it's probably because you don't have a full payload and don't care that you're runway limited. If you weigh 37,000 lbs but your runway limit for alt t/o is till 42,000 lbs.....who cares right? There's no reason to do a full thrust takeoff to get your runway limit up to 47,000 lbs. You already had 5,000 lbs of margin with the alt t/o, so you save the wear and tear on the engines by selecting alt t/o. Since you don't have a lot of payload to worry about, the weight penalty doesn't matter.
 
Roger That!

Smartcockpit.com or something has a wonderful amount of information regarding turbojet performance and data calculations.
 
BohicaORD said:
Is it that obvious I'm Asa/xjt? :(. It's kinda embarrassing- I asked twice and I'm still lost. Like for instance how can you have an ALT TO departure and yet still be runway limited? Reduced power in a limited runway? Why not just use TO and get all the power you need?
Click to expand...

Runway limited means you're takeoff performance, as calculated, is being limited by the length of runway. There are several factors that can limit your weight/reduction of power...such as LMTOW, climb performance, obstacle etc.. Runway length is one of them.
 
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