mozart
Posts: 2022
Joined: Thu Aug 14, 2003 12:21 am

How To Calculate Required Runway Length

Mon Aug 01, 2005 2:51 am

Hi,

I have a question:

I *do* know that the length of runway required for an aircraft depends upon its v1/vr speeds, the aircraf's TO weight, the performance of its engines, and son on...

What I *don't* know is how one could calculate how many feet of runway are needed for a specific flight, given weight, weather and V1/Vr speeds.

I ask the question because I could imagine that there are situations where a plane may be below MTOW, but still may not take off because the runway is too short. But how can you know which length would be "too short"?

Thanks!
 
IanatSTN
Posts: 564
Joined: Thu Dec 18, 2003 2:27 am

RE: How To Calculate Required Runway Length

Mon Aug 01, 2005 3:14 am

Hey Mozart,

Check out the following website....

http://www.dmjwilliams.co.uk/gbsep_performance.htm

It has a table showing the take off distances for the Cessna 172. As you will see, the key factors in calculating the required runway length are altitude above sea level, gross weight and headwind.

It is my understanding that each aircraft type has an individual version of this takeoff performance chart.

Cheers,
Ian.
Ian@STN ::
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: How To Calculate Required Runway Length

Mon Aug 01, 2005 4:00 am

Sort of depends on what kind of aircraft you are talking about. For the wee ones it is probably adequate to use the rudimentary charts in the back of the pilot handbook. Sad how many private pilots really don't have any idea what these charts are telling them. Every few years, for example, it seems like someone tears up a perfectly good airplane at Lake Tahoe taking off to the south because there is a tiny breeze from that direction.

For airliners there are so many things to consider that it is not likely that the average airline pilot could think of them all and work the problems correctly given the factory's charts from the AFM (as opposed to the "pilot handbook") For that reason airlines employ or contract with performance engineers to prepare runway analysis tables for each runway they are authorized to use. Runway 27L is a different runway from 09R even though they are the same strip of concrete. The slope may be different, the length may even be different with displaced thresholds etc. and obstructions in the departure area are certainly going to be different. These things will affect takeoff weight limits.

So a given chart may tell me that at 30oC on this particular runway, at flaps 5 I can take off at 137000 pounds for runway length but I am limited to 135500 pounds for second-segment climb (engine-out, gear up, flaps 5 climb) So let's say my max certificated takeoff gross weight for this airplane type is 142500 lbs, I am, in this case limited by second-segment climb. We have to run this for each takeoff, so in regular operations it comes to us over ACARS.

In the airline business the question is not "how much runway is required" but rather, since the runway is a given set of constants and variables, "how much weight can I carry off this runway today" and sometimes we do shorten up on fuel or remove cargo or even bump passengers.

Hope this helps.

Slam
- bump the non-revs
Click
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