Experienced Pilots: Do you always calculate takeoff distance?

Chrisgoesflying said:
If you fly out of an airport with a long runway, let's say 6,000 feet and you're flying your standard Cessna 172 (or similar), do you actually calculate your takeoff distance prior to takeoff or do you just up an go (after doing your pre-flight inspection and run-up obviously)?

To follow up on that, if you do calculate it, and let's say based on your calculation you should have a takeoff roll of about 1,500 feet, would you simply use that as your abort point, basically saying if you're not in the air by 1,500 feet down the runway, you abort the takeoff since you still have 4,500 feet remaining? Do you add some sort of padding to the number (in case the wind has changed suddenly for example)?

If you don't calculate it, what do you use as your abort point and what do you look out for to make that decision? The 50/70 rule on such a long runway really doesn't make any sense to me - I mean, if it takes you 3,000 feet to reach 70% of your Vr, something is majorly wrong, yet based on that rule, you'd still take off.

This summer, I had an issue on takeoff and I'm wondering if I could have avoided being in that situation. I fly out of a long runway with a small two seater that is usually up in the air within about 1,000 feet. One hot and humid afternoon in August, I went flying at max T/O weight (which I rarely do, but that day I took someone who is on the heavier side). I did my run-up, all seemed normal. Lined up on the runway, advanced the throttle, rpm was right about at static max rpm, I rolled down the runway, feeling a little sluggish but airspeed came alive, Vr came along further down the runway than it normally would, but I chalked it off to being hot, humid and at max weight. Anyway, once in the air, I quickly noticed climb rate is really bad, I glanced at the rpm and it was about 300 below what it should be. I managed to still climb out to about 400 feet and hold altitude with the power I had and ended up landing on one of the airport's runways without an issue.

Long story short, I had a stuck valve and couldn't make full power. How could I have avoided taking off in the first place? Now, every time I takeoff I obviously have this in mind and kind of also confirm my rpms are rising as I gain speed, basically doing: full power, confirm static rpm, confirm oil temp/pressure in green, confirm airspeed alive, confirm rpm raising, confirm Vr and rotate. What else can I do to ensure I make sound decisions while still on the ground?
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Static rpm was normal but climb was too low by 300rpm? Is that possible?
 
Grum.Man said:
Against my better judgment knowing how debates go on POA this simply is not true at least on an airplane with a fixed pitch propeller. There is a static run up allowance in the POH. The tolerance is usually about 100 rpm. If the rpm doesn’t reach that upon full power something is wrong. A 300 rpm difference from normal should have been a huge red flag and easily noticed.
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What's your static RPM for the Tiger on the ground? It won't be the top of the green arc. You'll get the top once you're moving at full speed ...

sarangan said:
Static rpm was normal but climb was too low by 300rpm? Is that possible?
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Had that twice in 152s that lost a mag after they passed in the run-up (both let go as soon as I crossed the departure threshold) ... can see that happening with a "morning sickness" cylinder like you had with a stuck valve. If you have a 4 cylinder EGT-CHT it should've shown up there
 
danhagan said:
What's your static RPM for the Tiger on the ground? It won't be the top of the green arc. You'll get the top once you're moving at full speed ...



Had that twice in 152s that lost a mag after they passed in the run-up (both let go as soon as I crossed the departure threshold) ... can see that happening with a "morning sickness" cylinder like you had with a stuck valve. If you have a 4 cylinder EGT-CHT it should've shown up there
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Ya but would an in flight mag check have revealed this before the failure?
 
Dana said:
None of my planes (all antique or experimental) have had a POH to get "book" values from either, though.
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That is true of the 2 experimental aircraft I have owned also. You just don't have a chart to refer to. The 70 50 rule helps in this situation.
 
danhagan said:
What's your static RPM for the Tiger on the ground? It won't be the top of the green arc. You'll get the top once you're moving at full speed ...



Had that twice in 152s that lost a mag after they passed in the run-up (both let go as soon as I crossed the departure threshold) ... can see that happening with a "morning sickness" cylinder like you had with a stuck valve. If you have a 4 cylinder EGT-CHT it should've shown up there
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Do not remember what it was but it’s in the POH what it should be or in the TCDS.
 
Wow, thanks for all the responses. Just to clarify some of the comments:

1. Run-up was normal. My run-up is to be done at 1,700 rpm and I had no issues getting to that setting and everything (mag check, carb heat, idle check) performed normally.
2. I should get static power at full throttle of about 2,100 - 2,200 and I confirmed that I get that when the takeoff roll started. Usually, the next time I look at the rpms is once I confirm positive climb at which point my rpm should be between 2,300 and 2,400. That day, I got (very anemic) positive climb, looked at the rpm and they were still at 2,100 at which point my pants may or may not have gotten slightly wet.
3. I don't have EGT/CHT displays in the cockpit, just tach, oil temp and oil pressure. Both oil gages were in the green.
4. Aborting when things don't feel right: I guess that I could have done but "feeling" right is so subjective. It definitely didn't "feel" like a normal takeoff but I took off from a 3,000 ft. high airport in the mountains at 35 C OAT last summer just a few weeks prior to the flight in question, and that takeoff also didn't necessarily "feel" right, climbing out at 200 ft/m, circling over the airport for 30 minutes to gain enough altitude to make it over the mountain range - yet, the plane was perfectly fine (technically) that day and I safely completed my 3 hour cross country flight.

I think I'll start roughly calculating my takeoff roll regardless of runway length going forward just to be safe, plus add one more screen to my takeoff roll, confirming that rpm is indeed higher than at the beginning of the runway, once I have picked up some speed.

Again, thank you all for so much input!
 
keen9 said:
OP said the runup was normal. Minus 300rpm is in the climb where it is already too late to not takeoff.
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That’s a very unusual failure mode for a stuck valve. Regardless the best defense is full engine monitoring which is not that expensive these days especially given how much money it can potentially save by giving early warning of potential issues.
 
You need a pressure altitude of more than 5000 and some pretty hot temps for a ground roll of 1500 ft in a 172.
 
OP asked a good question. My guess is most people do not, but they have done the numbers for most common situations. For example:

I know my standard day MTOW distance in the L8 is 625 feet (hard turf surface, no obstacle data given) and add 3% for each 1000' DA at 5000' DA this brings it up to roughly 800' with no obstacles (unless the 3% is supposed to be compounded but I don't think it is). So, having made that calculation I know I'm good on 1000' feet (25% bump) in or out - book says 500' for landing on sea level standard day. Am I comfortable with 1000' - no, but 2000' gives me no second thoughts.

So I have just set myself as 2000' min. and if it is shorter than that thought is involved.
 
I check weight, density altitude and runway length every time (altho most of the time it's just me at the airport I know and love). However, knowing the airplane and "feeling" what's going on is an excellent indication. Of course that only works if you fly that airplane all the time and learn the "quirks". I've killed the power more than once, just driving down the runway before lift off when something didn't feel right. Each time was the right thing to do.

I've also returned to the airport more than once, after takeoff, when something didn't feel right. Again, each time was the right decision. The most recent was during the eclipse ('17? ) when the take off was a bit sluggish (2 people and camping gear at 7000 DA). Got airborne but not climbing as expected. Did the pattern, landed. Re-arranged the gear (too much weight in the baggage area) and everything was fine. I had weighed my gear and believed the other person. Major mistake. There's a scale in the hangar just for this reason.

If I'm going east, the runways are usually shorter than out west, so I'll have the chart in front of me with notations. I don't care about the 70/50 rule (except at Leadville) - if I'm not airborne by the 2000 ft marker, (or 1500 ft at lower altitudes) then it's time to cancel the takeoff and see what's the problem.
 
MauleSkinner said:
And how did you teach them to apply that to the OP’s malfunction?
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This is the part of the OP message that I was responding to.

"If you fly out of an airport with a long runway, let's say 6,000 feet and you're flying your standard Cessna 172 (or similar), do you actually calculate your takeoff distance prior to takeoff or do you just up an go (after doing your pre-flight inspection and run-up obviously)?'
 
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My first plane I got my PPL in was an underpowered heavy airplane and being on the West Coast I was doing these calculations all the time, especially in the summer.

With my current airplane I do the calculations periodically but only when I think something is out of normal.

Like W&B I know what and where I can put people with what fuel and really only do calculations when it’s a new situation or I feel it’s out of whack.

Knowing your airplane is an important factor.
 
It depends on the plane I'm renting. I never fly max gross BTW. If I'm in a 182 or 172 with the 180 engine and the runway is 2500' or longer, I'm good. If I rent the Tiger or I want 4500' concrete minimum. The 172 "standard" engined I rent I fly with 2 people I want 3500'. Not exact math I'm doing here, but super conservative guidelines.
 
If I'm halfway down a 2500' runway & I'm not airborne then something is terribly wrong with me as I should have shut it down already. At gross and near sea level I'm usually up and away in 800' or so. When it's really hot it will be a bit longer but the 70/50 rule isn't for me as I want more margin than that. For higher elevations & density altitude concerns some math is required.

At home I'm flying off of a 3200' paved strip. If I'm halfway down the runway and it ain't flying ... it ain't gonna be cause I'm chopping the throttle to take it to the hangar and find out what the problem is.
 
I fly out of a 2200 ft runway with an incline and trees at both ends so I have to pay attention. I would definitely calculate for a new high altitude airport. Sounds like you doing the right things by checking static power and decisions by midpoint of the runway. The biggest factor is air temperature! My Archer feels like a six cylinder when taking off in below freezing temps and a 3 cylinder on hot days. Love the winter flying!
 
jayhawk74 said:
This is the part of the OP message that I was responding to.

"If you fly out of an airport with a long runway, let's say 6,000 feet and you're flying your standard Cessna 172 (or similar), do you actually calculate your takeoff distance prior to takeoff or do you just up an go (after doing your pre-flight inspection and run-up obviously)?'
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I would never calculate my take off distance in that scenario, unless this runway was located at 15,000' ASL.
 
Depends how close you are to the NOT having enough runway. I take off in 1000 feet at 5000 foot density altitude and the shortest runway I typically use is 3500 feet but my normal runway is 6000 foot length. Plenty of margin so no need to calc.
 
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Once a person flies a plane regularly, you get to know it, and what you can expect. The thing is that POH numbers are also based on max weight, and I find very rarely am I anywhere near gross at take off. So guess at how many lbs of fuel is left, add it to the weight of myself and if passengers their weights, guess at baggage weight, and add it to aircraft empty weight, then take a wild guess how much better it will take off, than if it were at gross, and is temp at standard, probably not, throw in airfield altitude, guess some more...then say screw it and pushes the throttles ahead and yell YEEHA really loudly...oh ya i almost forgot, if the field is high, lean the engine or engines some first, except for you rich guys who are burning Jet A...you just jam the throttles ahead and sip champagne until it feels ready to fly, then pull back on the yoke, and sip more champagne.
 
Every time. There are so many flight planning tools available now that calculating a Takeoff Distance number is trivial. I teach my students to complete a Wx brief for every flight; check notams & W&B/Performance.
Most flight schools I've been to require this as part of the dispatch process.

91.103 b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information.

I realize it may sound like a formality if you fly the same plane at the same airport, but not planning a flight properly gets people in trouble. The FAA or NTSB can come calling, and the regulations are explicit.
//
 
Remember that people lie about their weight, and people usually underestimate their baggage weight to, if you are really getting picky about the exact take off performance. So eye ball your passengers and guesstimate their real weight, and don't rely too much on the fantasy weight they tell you. A couple of years ago as a favor to an employee, I took his mom along with me on a business trip so she could visit with an old friend, at my destination. Never met her before, so day of the trip her son drops her off at my house to ride to the airport with me. Told her that i needed the weight of her bag, and herself. She told me she was 150 lbs which made me chuckle, and her suitcase was 20 lbs. Before we jumped in my Jeep, I got the bathroom scale out, weighed her bag, it was 36, then I had her get on the scale, 247 lbs without shoes or her jacket. I weigh myself in shoes, jacket unless summer, keys and knife in my pocket, and headset. Its winter time now, 174 lbs is my ready to fly weight, I will be less in the summer, as I am likely in shorts, sandals, no heavy jacket, wool socks etc. Last summer I was 169 lbs ready to go. In winter ready to go my GF is 109 lbs, summer time she will be closer to 105.
My point is a simple one, if you really are trying to do a completely accurate W&B and take off performance, get out your scales...people are full of crap. I have become very good at guessing the weight of people. That woman i spoke of, i guessed 250 lbs when she said 150 lbs. With her shoes and coat on she would likely be 250 or 251 lbs.
 
I have weighed all the standard stuff kept in the plane. Additionally, I've weighed my flightbag, toolbox, emergency bag, and camera bag. I know what I weigh, clothed and unclothed.

When just tooling around the neighborhood, depending on what I am carrying of my standard kit, I always know my takeoff weight.
 
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Domenick said:
I have weighed all the standard stuff kept in the plane. Additionally, I've weighed my flightbag, toolbox, emergency bag, and camera bag. I know what I weigh, clothed and unclothed.

When just tooling around the neighborhood, depending on what I am carrying of my standard kit, I always know my takeoff weight.
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Have you weighed your airplane?
 
neilki said:
Every time. There are so many flight planning tools available now that calculating a Takeoff Distance number is trivial. I teach my students to complete a Wx brief for every flight; check notams & W&B/Performance.
Most flight schools I've been to require this as part of the dispatch process.

91.103 b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information.

I realize it may sound like a formality if you fly the same plane at the same airport, but not planning a flight properly gets people in trouble. The FAA or NTSB can come calling, and the regulations are explicit.
//
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I've been flying the same plane for 12 years, and flown it when it's been below 0 and above 100 degrees, as close to empty weight as it gets and at full gross. I know when it's going to be off the ground or not. But, I gotta do that calculation when I'm at an air carrier ariport when I'm off the ground in under 1000' without even trying? GTFO.

Plus, the plane doesn't have that info in the 6 page AFM, so guess what, I go by b)2) which is all in my head.

Additionally it doesn't say explicitly you have to do a calculation.

You must be fun at parties.
 
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neilki said:
Every time. There are so many flight planning tools available now that calculating a Takeoff Distance number is trivial. I teach my students to complete a Wx brief for every flight; check notams & W&B/Performance.
Most flight schools I've been to require this as part of the dispatch process.

91.103 b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information.

I realize it may sound like a formality if you fly the same plane at the same airport, but not planning a flight properly gets people in trouble. The FAA or NTSB can come calling, and the regulations are explicit.
//
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The regulation is very explicit, and you cut off two of the more important parts.

on the front end, it says “familiarize”, not “calculate”.

on the back end it specifies what the takeoff and landing distance information has to be...most of the light GA fleet aren’t “aircraft for which an approved Airplane or Rotorcraft Flight Manual containing takeoff and landing distance data is required”, and therefore “other reliable information appropriate to the aircraft” is controlling.
 
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Engineers—real ones, who have a B.Eng., unlike me—talk a lot about choosing the right level of precision for the job. For example, there's no point calculating pi to 40 (or even 4) decimal places to figure out how how much stone to buy for your circular back yard patio, because you'll just give yourself false confidence in the accuracy of the result. Slide rules (including the E6B) used to take care of this automatically, but now that we can do digital calculations, we have to train our minds to ignore excessive precision.

For example, when you're looking at upper winds during flight planning, there's no point trying for anything more accurate than the nearest 10° and 5 knots (I might make a case even for 30° and 10 knot increments), and for calculating gross weight and takeoff distance in a light piston, just work in 100 lb and 500 ft increments (rounding up); otherwise, you're deluding yourself with excessive precision. e.g. your expected takeoff distance can be 1,000 ft or 1,500 ft, but not 1,217.5 ft (just round that up).
 
Domenick said:
I have weighed all the standard stuff kept in the plane. Additionally, I've weighed my flightbag, toolbox, emergency bag, and camera bag. I know what I weigh, clothed and unclothed.

When just tooling around the neighborhood, depending on what I am carrying of my standard kit, I always know my takeoff weight.
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That is great when us pilots fly alone, the problem is when we take passengers, and their bags. Lets say you take 3 passengers, each lies to you about their weight, and their bags weight, suddenly you are 400 lbs heavier than you think that you are. Like I said earlier, I use my own judgment by eye balling my passengers, and I never let them load their own bags because I want to pick them up and do my own weight guess. Usually I don't have a scale around, but looking at the woman I mentioned I would have just added 100 lbs to what she told me, and guessed her luggage at about double of her guess. I've never understood lying about weight, it seems silly. If you are fat, you know that you are, so at least be honest about it. If it bothers you, lose weight, don't lie about it. You look foolish if you're telling people a weight you made up, not your true weight, and also they won't believe anything else that you say, because you are a proven liar.
 
Here's how I've always handled this...

When I'm familiarizing myself with an aircraft I pull out the takeoff distance charts and calculate a few scenarios with full gross weight, an unusually hot day, and no wind to get the worst case takeoff distances- looking at both ground roll and over a 50' barrier. I familiarize myself with those numbers. I'm not going to calculate every takeoff but I do know where things start to get tight. For me this means if I have > 3000' of paved runway, I'm operating out of a < 1000' elevation field, it's < 100F, and I'm under gross I've got plenty of margin. Those characteristics describe 99% of my actual flights.

For W&B same deal. I've calculated it for me alone, and me with a single adult passenger in the right seat over a wide range of weights. I've also done it for me up front and my wife&kid in the back, and same passengers plus our family's typical loadout for a trip. I figure worst case scenarios and add 10lbs to everyone's stated weight, weigh the bags, and round up to the next 10#. I try putting everything in the aft cargo area and everything in the forward baggage area(even though it won't really fit). Basically I've figured out with these loads there's no way I can get outside the W&B or CG envelope for my aircraft. If I do anything outside of these typical for me situations, I do a new calculation.

But if you fly the same types of flights and same types of passenger/cargo situations in the same aircraft all the time you have a pretty good idea where your margins are. If you think it might be close, always run the numbers but when you know you're well within the limits I don't think it's necessary every time.

*I should also add know your type. I'm flying a Piper Lance... it can handle a lot of load, hence why I can say any single "typical" adult passenger is going to be fine. If you have say a Cessna 152 and your friend is 6' and 300#....uhhh.... yeah better be doing that math.
 
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cowman said:
*I should also add know your type. I'm flying a Piper Lance... it can handle a lot of load, hence why I can say any single "typical" adult passenger is going to be fine. If you have say a Cessna 152 and your friend is 6' and 300#....uhhh.... yeah better be doing that math.
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There's no math to do on that. :D
 
YKA said:
That is great when us pilots fly alone, the problem is when we take passengers, and their bags. Lets say you take 3 passengers, each lies to you about their weight, and their bags weight, suddenly you are 400 lbs heavier than you think that you are. Like I said earlier, I use my own judgment by eye balling my passengers, and I never let them load their own bags because I want to pick them up and do my own weight guess. Usually I don't have a scale around, but looking at the woman I mentioned I would have just added 100 lbs to what she told me, and guessed her luggage at about double of her guess. I've never understood lying about weight, it seems silly. If you are fat, you know that you are, so at least be honest about it. If it bothers you, lose weight, don't lie about it. You look foolish if you're telling people a weight you made up, not your true weight, and also they won't believe anything else that you say, because you are a proven liar.
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It's not a bad idea just to add 20 lb to everyone's stated weight. If they catch you, just tell them it's "to allow for clothing, purses, boots, etc". :)
 
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The day I brought my 210 home, I pulled out the back seat, never put it back in until the day I sold it. But I added some survival gear, including an axe, that was about 1.5 lbs less than the seat was, but further back. Should have done a complete new weight and balance, but never did. In my head all that I did was say to myself, its lighter but further back, meh close enough. Unless it is obvious that your CG is way too far back or forward, don't split hairs. A few lbs over gross, well taxiing, run up, and full power on the take off roll probably have you down to gross by liftoff anyway. Worrying about 10 lbs over is ridiculous, but I have seen people in a panic over it. As a 1/4 owner of a 152 way back when, the best thing to do was not calculate anything, because ignorance is bliss was what I told myself, when I know darn well at least 10% of my take offs were over gross. Camping gear in the back, GF, my German shepherd on her lap, me, full tanks, and off we went. Of course I knew we were a little heavy, I added 3 knots to my rotation speed, and gently eased her off, but I was not on 1000' runway and panicking. 5,200' of pavement made me way too complacent. I actually prefer 2,000' because it means there is no laziness allowed.
 
YKA said:
The day I brought my 210 home, I pulled out the back seat, never put it back in until the day I sold it. But I added some survival gear, including an axe, that was about 1.5 lbs less than the seat was, but further back. Should have done a complete new weight and balance, but never did. In my head all that I did was say to myself, its lighter but further back, meh close enough. Unless it is obvious that your CG is way too far back or forward, don't split hairs. A few lbs over gross, well taxiing, run up, and full power on the take off roll probably have you down to gross by liftoff anyway. Worrying about 10 lbs over is ridiculous, but I have seen people in a panic over it. As a 1/4 owner of a 152 way back when, the best thing to do was not calculate anything, because ignorance is bliss was what I told myself, when I know darn well at least 10% of my take offs were over gross. Camping gear in the back, GF, my German shepherd on her lap, me, full tanks, and off we went. Of course I knew we were a little heavy, I added 3 knots to my rotation speed, and gently eased her off, but I was not on 1000' runway and panicking. 5,200' of pavement made me way too complacent. I actually prefer 2,000' because it means there is no laziness allowed.
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I've always kept a hatchet in the pocket behind my seat. I figured it's a multi-purpose tool, good for cutting wood for fire or shelter, breaking a window for egress, or knocking an annoying passenger unconscious (using the blunt end, unless they're really annoying). So far, I haven't needed it for any of the three purposes.
 
David Megginson said:
I've always kept a hatchet in the pocket behind my seat. I figured it's a multi-purpose tool, good for cutting wood for fire or shelter, breaking a window for egress, or knocking an annoying passenger unconscious (using the blunt end, unless they're really annoying). So far, I haven't needed it for any of the three purposes.
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A hatchet within reach is a great idea. Mine was a full sized axe, but strapped down in the back, so not accessible from the front seats. If I crashed, or went camping, I like a nice fire. To this day I couldn't tell you if its even legal to pull the back seat out. Regulations likely say a professional has to weigh everything and redo the planes W&B, but I didn't. Surely not the only regulation in my life I violated. But I trained religiously with a good instructor and told her to have no mercy on me ever. I don't do drugs or drink alcohol, I stay fit, and do my best to keep maintenance done right. So I am still probably far safer than many of the people flying around.
 
YKA said:
A hatchet within reach is a great idea. Mine was a full sized axe, but strapped down in the back, so not accessible from the front seats. If I crashed, or went camping, I like a nice fire. To this day I couldn't tell you if its even legal to pull the back seat out. Regulations likely say a professional has to weigh everything and redo the planes W&B, but I didn't. Surely not the only regulation in my life I violated. But I trained religiously with a good instructor and told her to have no mercy on me ever. I don't do drugs or drink alcohol, I stay fit, and do my best to keep maintenance done right. So I am still probably far safer than many of the people flying around.
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Since I have a fixed-gear plane, I remove the wheel fairings every winter and put them back on in the spring. Strictly speaking, that probably requires an updated empty weight and CG each time they go on or off, but I don't know anyone who does that.
 
David Megginson said:
Since I have a fixed-gear plane, I remove the wheel fairings every winter and put them back on in the spring. Strictly speaking, that probably requires an updated empty weight and CG each time they go on or off, but I don't know anyone who does that.
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i have 2 sets of W&B, one with all the pants and one without. however, for the last 2 years i havent put the pants back on. it probably knocks a few knots in cruise, at least per POH, but doesnt matter a whole lot in grand scheme of things.
 
WannFly said:
i have 2 sets of W&B, one with all the pants and one without. however, for the last 2 years i havent put the pants back on. it probably knocks a few knots in cruise, at least per POH, but doesnt matter a whole lot in grand scheme of things.
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I've thought of that, but every couple of years, it seems something happens to change my base W&B (something remove or installed).
 
David Megginson said:
I've thought of that, but every couple of years, it seems something happens to change my base W&B (something remove or installed).
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i hear ya, same here, i think i am on my 5th set in 3 years

but if you do get it done once, doesnt matter what changes in your plane, the calculation will go off the ones already created. so say you remove the vacuum pump, another 2 sets of W&B will be updated based on the previous ones.
 
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