Performance calucations

christina3hunt

New Member
What is the difference between takeoff ground roll and total takeoff distance? And landing ground roll, total landing distance??
 

sdfcvoh

This is my Custom Title
maybe "total" is referring to the inclusion of a 50' obstacle.

every single flight we do at my school requires figuring out those numbers. anyone else? ever read 91.203?

CYA.
 

Nihon_Ni

Well-Known Member
The "takeoff ground roll" is the total distance from brake release until your wheels leave the runway surface. "Total takeoff distance" is the distance from brake release until a point where every part of the plane could clear a 50 foot obstacle. Often you'll see "total takeoff distance" written as "distance over a 50' obstacle".
 

MidlifeFlyer

Well-Known Member
What is the difference between takeoff ground roll and total takeoff distance? And landing ground roll, total landing distance??
The performance chart you are looking at should tell you what "total distance" it is measuring. Usually it is, as others said, the total lateral distance you need to take off and clear a 50' obstacle.


"Ground roll" means what it sounds like - the amount of distance the airplane can be expected to cover on the ground before taking off.

SDF? Nope, we don't calculate it every time.
 

MikeFavinger

Hubschrauber Flieger
maybe "total" is referring to the inclusion of a 50' obstacle.

every single flight we do at my school requires figuring out those numbers. anyone else? ever read 91.203?

CYA.
What does 91.203 have to do with performance calculations?
 

jrh

Well-Known Member
every single flight we do at my school requires figuring out those numbers. anyone else? ever read 91.203?

CYA.
How short of a strip do you fly out of?

The shortest runways in my area are always at least 2,500 feet, and most are significantly longer, with no obstacles to worry about.

I haven't looked at the numbers recently, but I'm certain even at max gross weight with a density altitude of 6,000 feet we can get a 172 off the ground in less than 2500 feet.

I guess what I'm saying is, unless it's a really extreme circumstance, it's a little bit of overkill to calculate the TO/L distance data for *every* flight. Common sense and some base line numbers should prove it's pretty much always acceptable to fly when "regular" conditions prevail.
 

jrh

Well-Known Member
ever read 91.203?
I wanted to address this real quick, too...

91.103 requires pilots to "become familiar with" performance data for the flight. Notice that it doesn't specifically require pilots to perform exact calculations prior to each flight.

I'm sure MidlifeFlyer could explain the legal side of this better than me, but I have always interpreted that reg to mean if a pilot has a good understanding of the scenario (such as my statement about knowing a 172 can almost always get off the ground in 2500 feet) and determines the situation to be safe, it is acceptable to fly without precise calculations.
 

CoffeeIcePapers

Well-Hung Member
I wanted to address this real quick, too...

91.103 requires pilots to "become familiar with" performance data for the flight. Notice that it doesn't specifically require pilots to perform exact calculations prior to each flight.

I'm sure MidlifeFlyer could explain the legal side of this better than me, but I have always interpreted that reg to mean if a pilot has a good understanding of the scenario (such as my statement about knowing a 172 can almost always get off the ground in 2500 feet) and determines the situation to be safe, it is acceptable to fly without precise calculations.

I think in a flight school environment, it is good to have them calculate w/b, takeoff/landing distances for a few reasons, one of which is to keep them proficient doing it, so when the checkride comes, they will be familiar with it.
 

MidlifeFlyer

Well-Known Member
I think in a flight school environment, it is good to have them calculate w/b, takeoff/landing distances for a few reasons, one of which is to keep them proficient doing it, so when the checkride comes, they will be familiar with it.
Yes, but...

The problem with this, like calculating checkpoints every 10 NM on a student cross country (when it's a 45 minute flight with 4.5 hours FOB), is that, as far as I can tell, it's not explained to the student very well that this extra "make work" is "to keep them proficient doing it, so when the checkride comes, they will be familiar with it," coupled with an discussion about when it may or not be necessary to do it in the "real world". Instead, it's usually presented as , "this is the way you're supposed to do things."

The result, which I've seen during FRs, is pilots who, after the checkride, rarely do a weight and balance, rarely check performance numbers, and rarely do detailed flight planning, even when they should.

If you are explaining this to the student, then kudos on keeping them proficient for the checkride. If not, I think you're contributing to pilots who don't check these things after the checkride.

...and, jrh, I don't have a legal explanation, just a common sense one. The best I can come up with as a legal explanation is that you'll be in trouble if you run off the runway :eek:
 

sdfcvoh

This is my Custom Title
lol....

I think he meant 91.103
D'oH!!!! :D

Yep - 91.103. In the first paragraph they use three scary words, "Shall, All and Must."

Now, if I could just remember the correct reg numbers when I'm trying to be all impressive n' stuff.:drool:
 

bdhill1979

Gone West
I wanted to address this real quick, too...

91.103 requires pilots to "become familiar with" performance data for the flight. Notice that it doesn't specifically require pilots to perform exact calculations prior to each flight.

I'm sure MidlifeFlyer could explain the legal side of this better than me, but I have always interpreted that reg to mean if a pilot has a good understanding of the scenario (such as my statement about knowing a 172 can almost always get off the ground in 2500 feet) and determines the situation to be safe, it is acceptable to fly without precise calculations.
:yeahthat:

The only time I really get into it is with a runway less than 3000 feet.


Something I teach my students is to calculate the most unfavorable condition, max gross at a 7500 foot density Altitude for example, and just know that number. If they come across a runway that is 50% longer than that number it is time to get the chart out and figure it out exactly.

Example: I know my T210 needs 1775 feet at a 7500 foot density altitude at Max Gross.
 

sdfcvoh

This is my Custom Title
I won't argue about "must" have all those figures on paper. BUT.... Coming from someone who never had the influence to do it before; I've got to say that I personally enjoy looking at the figures for every landing at every intended stop.

The other thing that influenced me to grab onto this importance was reading a write up about the test flights that compiled the landing distances in the POH. After 10 landings most planes not only needed new tires, but they also had stressed the landing gear to "unusable" status. I double the distances and use that for my go/no-go decisions now. Granted, I'll never intend a stop at an airport with less than 3500ft anyway.:hiya:
 

sdfcvoh

This is my Custom Title
LINKED FULL ARTICLE

Here is a snippet from the article.
"How are landing distances calculated?
We still have a significant number of runway overrun accidents. While these accidents are
seldom fatal, we think it might be enlightening to share how the certification flight test world
generates your POH performance numbers.
First and foremost to remember, POH landing
distance numbers typically reflect the shortest
distance you will ever be able to land your airplane.
Neither 14 CFR part 23 nor part 91 require any
margins or factors in the published landing
distances that you as the pilot use. So whether you
fly a Cessna 152 or a new part 23 multiengine jet,
the landing distance calculation requirements are
the same. They are generated using skilled test
pilots in near perfect weather conditions. We
require at least 6 landings for the POH performance
charts –conducted on the same wheels, tires, and
brakes. So if you want to know just how aggressive
our landing distance tests can be… The tires, and
sometimes the brakes, are generally worn out after
just 6 landings."
 
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