What's too Much Weight?

Ron Levy said:
The number isn't random -- it's based on FAA studies of actual passenger weights, and it was kicked up a good bit a few years ago after this accident
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I suspect a great deal of airline flights have taken place with the aircraft over-gross. Based on some of my observations of the typical passengers I'm sure it still happens quite often.

In the above case - being out of CG and over-gross didn't help - but it also didn't help that the elevator was mis-rigged and they were lacking 50% of their down elevator.
 
These numbers are viable for larger aircraft, but I've been on commercial flights on small turbos & jets where some of us were asked to move for W&B reasons (actually for CG) and other times (for really small commercial puddle jumpers) I really was asked for my weight. And the bags were weighed but the pax weren't.

Don't some of the larger airports have built-in scales on the ramps? Or is this urban legend?
 
jesse said:
In the above case - being out of CG and over-gross didn't help - but it also didn't help that the elevator was mis-rigged and they were lacking 50% of their down elevator.
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I would bet that any two out of the three problems would have been fine, it was the combination of the three that caused the problem.
 
Ted DuPuis said:
I would bet that any two out of the three problems would have been fine, it was the combination of the three that caused the problem.
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Yeah. It was a bad combination of things for sure - one of the few instances where the NTSB didn't fault the pilots. They put up a pretty good fight to try and save it but they were pretty doomed the moment they took the runway.
 
lewy15 said:
There was a thread on hear earlier talking about a student pilot and his large friends trying to takeoff in an Archer and haveing a little issue due to weight so that got me thinking....... How much is to much weight to take off. I learned to fly less than a year ago and have around 55 hours total in an Archer.

Obviously you're not supposed to be over the max gross weigth and have the CG in the envelope but what if your heavy by just a few pounds... Passenger(s) lies about their weight or their baggage.... What is too much weight? What if it's 5 pounds over? 50 pounds? 100 pounds?
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lewy15 said:
Thanks for all the great posts. I'm planning a flight with some friends in a couple weeks thats about 140nm away. While doing the W&B we were about 25 pounds over weight and it got me wondering what would happen if you took off that heavy, i.e. wings fall off or never leave the ground, etc. Being that I'll be over I've already decided to drain some fuel to be under max gross weight as I won't need all 48 gallons to go 140nm.
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The second post is quite important - 25 pounds isn't much, and it'd probably be OK, but in this case you're planning a fun flight with friends where the extra 25 pounds would easily be eliminated by the removal of fuel (via de-fueling, or via going flying the day before and not refueling.) Absolutely no reason to risk it, and every reason to do things right - When you have unsuspecting passengers aboard, you have a higher duty to play by the rules because they are entrusting you with their lives.

So, in this case, the stock answer of "one pound is one pound too many" applies.
 
The really long general answer to this question is, "it depends on a lot." What's the density altitude at takeoff? What's the actual performance of this airplane (not the book performance when it was brand new) in these conditions when it's not over gross? How much over gross are you going to be? Is this airplane built to be able to handle turbulence and/or landings at the heavier weight? What kind of terrain will you be flying over?

There are MANY such questions, and people like Max Conrad who did some severely-over-gross flights had the answers before they went. Max Conrad had access to the engineers who designed the planes, and I'm sure he did plenty of calculations of his own as well.

One clue as to what to expect lies in the Cessna 182 Type Certificate Data Sheet:

C182 TCDS said:
Special Ferry Flight Authorization. Flight Standards District Offices are authorized to issue Special overweight ferry flight authorizations. These airplanes are structurally satisfactory for ferry flight if maintained within the following limits: (1) Takeoff weight must not exceed 130% of the maximum weight for Normal Category; and (2) The Never Exceed Airspeed (VNE) and Maximum Structural Cruising Speed (VC) must be reduced by 30%; and (3) Forward and aft center of gravity limits may not be exceeded; and (4)
Structural load factors of +2.5 g. to -1.0 g. may not be exceeded. Requirements for any additional engine oil should be established in accordance with Advisory Circular AC23.1011-1. Increased stall speeds and reduced climb performance should be expected for the increased weights. Flight characteristics and performance at the increased weights have not been evaluated.
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Assuming the structure of the airplane is sufficient to handle the increased weight in the conditions encountered, there are many performance issues to consider:

1) Runway length. Acceleration will be much slower. In theory, you need 70.71% of your takeoff speed before reaching the halfway point of the runway. In reality, this is not such an exact science and you probably don't want to be lifting off exactly at the end of the runway, so having 75% of Vy at the halfway point is advisable.

2) V-speeds. Speaking of Vy, it's going to go up. Vx, Vg, and all your stall speeds will go up as well, because they all depend on angle of attack, which will be increased at heavier weights at the same airspeeds. In theory Va will go up, but since you're overloaded your G-limits should be reduced, as should Vne and Vno.

3) Climb performance. This can be calculated based on the actual performance of the airplane, and you can get a reasonable guess by attempting to power-load the airplane the same as it would be when over gross. In the Max Conrad Comanche 250 example, the Comanche 250 has a gross weight of 2800 pounds and 250 horsepower. That gives you 11.2 pounds per hp. However, since he took off at 4800 pounds, he had an airplane with 19.2 pounds per hp. To get a reasonable estimate of how the plane would perform, he could have loaded it up to gross weight and set power to 58% to equal that 19.2 pounds/hp and the length of the takeoff roll and climb performance should have been roughly equal, though some difference would result from needing to accelerate to the higher Vy when heavily loaded.

I've gotta run so I can't continue right now, but there's obviously a lot of factors at work. If you don't NEED to go overgross, don't. If you NEED to (and taking your friends out is most definitely not such a need), be sure you know all of the factors involved, both engineering and legal.
 
murphey said:
Don't some of the larger airports have built-in scales on the ramps? Or is this urban legend?
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Legend. But some newer airliners can weigh themselves with sensors in their landing gear. Figures cg automatically, too. Now, can they write software into their systems which will prevent the engines from accelerating if it's overweight or out of cg with weight on wheels? OTOH, can you imagine that software failing in flight...
 
Ron Levy said:
Legend. But some newer airliners can weigh themselves with sensors in their landing gear. Figures cg automatically, too. Now, can they write software into their systems which will prevent the engines from accelerating if it's overweight or out of cg with weight on wheels? OTOH, can you imagine that software failing in flight...
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My friend has this nice (calibrated) digital scale that he has PAX step on for 15 seconds to get their weight. (it's usually just friends / family, not a business) and invariably people lie by about 10lbs+. He passes it off as:

"Well, all the stuff you wear; clothes, jewelry, and such, add to weight so let's see what we have here..."

I was the same way, but figured myself 10lbs too heavy :ihih: Guess that gym time started paying off... (the AME "suggested" a weight loss regimen was a good idea when I got my medical)
 
bbchien said:
Late to the string.
One pound over is too much.
I like living too much.
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A good safe conservative attitude, which i would expect from a CFI or examiner. However, are you just setting a good example, or do you really believe your airplane will crash if its 20 pounds over?

If people are going to break the rules anyway ( and it seems many will), lets at least provide good information about real limits versus legal limits.
 
gprellwitz said:
Wait, so you're saying that since he may already have more weight in the plane than he's accounting for that he should blithely add more?:eek: Sounds, shall we say, unwise!
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It is all about common sense and managing your risks. Flying in and of itself is inherently risky so you're already making a judgement that flying the friends is worth the added risk as compared to driving. You may fly a single, I think that is riskier then flying a twin.

Making a statement that leaving with a couple extra pounds is somehow akin to smoking pot and turning into a crazed crack addict is nonsense. Gee I left 0.6% heavy last week why not 25% this week!

To me defueling a plane, splashing blue leaded fuel on myself and the floor and subsequently leaving 25 lbs of fuel in my hangar is a much higher risk then departing 0.6% heavy and having an extra 30 minutes of gas. But hey you may look at the risk differently then I do. To each his own. Last I knew far more pilots kill themselves by running out of fuel then anything else. Give me the gas.

If you are that concerned about a couple pounds then I assume you annually weight your plane to calculate the payload and CG.
 
NotSure said:
If people are going to break the rules anyway ( and it seems many will), lets at least provide good information about real limits versus legal limits.
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The thing is that no one can provide you with a exact number beyond which the wings are going to come off and you'll fall out of the sky or come to other sorts of grief. There are too many variables. The manufacturer went to a lot of expense to design and test the airplane and applied the appropriate fudge factors for certification. Then they came up with a set of numbers which everything is based on. Of course you could say that since the FAA allows X% more weight for ferry flights that it must be safe. But how about X% + 1 pound? That must be safe too. The problem is that we are trying to apply a fixed number to a condition that isn't so black and white and people can see logically that it isn't black and white. However, there needs to be a cutoff number so why not just accept the one they came up with? Sometimes that isn't good enough, though. If you are talking about the max gross weight there are times when you might not be able to get off the runway at that weight so you need to consider that too.
 
I would also contend that there is a continuum of responsibility to consider. If you are the sole occupant, you may feel morally justified in taking off over gross, especilly if you're transporting something like emergency relief supplies to Haiti. On the other hand, if you're flying Angel Flight passengers who have an expectation that you're going to keep them safe, there's no wiggle room. Somewhere between those two extremes are scenarios like flying with another pilot who can understand the consequences (presuming you're frank about the situation) and flying with a friend or family member. I'd argue that the latter case is pretty close to the Angel Flight example. They're counting on you to keep them safe.

Let me also be clear that I'm talking about moral choices and obligations here, not legal or safe ones. Neither of those depend at all on what is filling up the airplane. The FAA may take it into consideration if they are doling out punishment after finding that you violated the regs, however. They seem to want to protect those who cannot protect themselves.

And yes, I've had an FBO defuel my plane after it was inadvertently overfueled on an Angel Flight. Was I confident that it would take off with the added weight? Certainly (it was a 10,000' runway in the plains in a 182 less than 10% over gross). Would I have taken off with another pilot aboard (e.g. my wife)? Probably, if she concurred.
 
NotSure said:
A good safe conservative attitude, which i would expect from a CFI or examiner. However, are you just setting a good example, or do you really believe your airplane will crash if its 20 pounds over?

If people are going to break the rules anyway ( and it seems many will), lets at least provide good information about real limits versus legal limits.
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WE had Lockheed tables for operation 48,000 overgross. What that did to operations was unbelievable.

No, it's not going to crash. But it's like being Virgin. You are, or you are not. Where do you draw the line?

Perhaps as Grant says, there is a continium....as in the Vietnamese Captain with his family of six in a Bird Dog landing on Oriskany......The reason better be pretty compelling.
 
dmccormack said:
What CFR (or FAR) is being broken in that scenario?
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91.107(a)(3) Except as provided in this paragraph, each person on board a U.S.-registered civil aircraft (except a free balloon that incorporates a basket or gondola or an airship type certificated before November 2, 1987) must occupy an approved seat or berth with a safety belt and, if installed, shoulder harness, properly secured about him or her during movement on the surface, takeoff, and landing. For seaplane...
 
Baron2PG said:
If you are that concerned about a couple pounds then I assume you annually weight your plane to calculate the payload and CG.
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It's been 20 years since the last time my plane was weighed and lots of new avionics plus a new engine has been installed, a new windshield etc., so I'd say my certified empty weight is +- 30 lbs. But I don't say it's okay to go 30 lbs over, instead I stay at least 30 lbs UNDER gross for all flight ops.
 
Re: Whats to Much Weight?

NotSure said:
Real world, you can expect a proportional loss of performance based on percentage over gross for climb rate (if your plane climbs at 600 fpm at gross under current conditions, you add 10% wieght, you lose approx 60-80fpm). Takeoff roll will suffer a little more than that though.
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That's a common but dangerous misconception. The effects of excessive weight are much worse than your estimate would predict. Climb rate is mathematically equal to the HP available for climb times 33000 divided by the aircraft weight (1 HP=33000 ft-lbs/min by definition). The HP available for climb is the total HP minus that required for level flight. The HP required for level flight is proportional to the cube of the airspeed and the airspeed for minimum power required is proportional to the square root of the weight. That means the min HP required for flight is proportional to weight^(3/2). Put it all together and the climb rate vs weight becomes fairly non-linear. In a typical single like a Piper Arrow, the climb rate at sea level decreases something like 70% for a 10% increase above the certified max gross weight. At 5000 DA the decrease is more than 100% since the plane won't even hold that attitude.
 
Re: Whats to Much Weight?

gismo said:
That's a common but dangerous misconception. The effects of excessive weight are much worse than your estimate would predict. Climb rate is mathematically equal to the HP available for climb times 33000 divided by the aircraft weight (1 HP=33000 ft-lbs/min by definition). The HP available for climb is the total HP minus that required for level flight. The HP required for level flight is proportional to the cube of the airspeed and the airspeed for minimum power required is proportional to the square root of the weight. That means the min HP required for flight is proportional to weight^(3/2). Put it all together and the climb rate vs weight becomes fairly non-linear. In a typical single like a Piper Arrow, the climb rate at sea level decreases something like 70% for a 10% increase above the certified max gross weight. At 5000 DA the decrease is more than 100% since the plane won't even hold that attitude.
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Bingo. Thank you for saying what I didn't have time to type earlier! :yes:

What Mari said is right on, too. There are times where even departing at your actual max gross weight is very dangerous. Departing Leadville at 300-400 pounds under gross in the 182, we still took 2000 feet of ground roll before liftoff, and that was pointing downhill! Now, Leadville has a beautiful 7,000 foot paved runway. Shorten it up, or make it grass, or uphill instead of downhill, or even just depart at max gross, and it would have ranged between "interesting" and deadly.
 
Ted DuPuis said:
Curious, what're you getting done to the 310 exactly? Only thing I've done to the one I fly is put the JPI in. We're also planning on adding some oil filters (engines have screens). Otherwise, it's a pretty nice plane as-is, but has also had a lot of work done on it prior to my first flight in it.
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Had the Generators changed to Alternators and it's currently getting a G-500, 430W and JPI 760 with fuel flows installed and 3 generations worth of disconnected avionics boxes removed. I bought the plane with "0" time Top Props on it. I will add oil filters as well when I get back, dynamically balance the props, set the fuel servos up and weigh the plane.
 
azure said:
It's been 20 years since the last time my plane was weighed and lots of new avionics plus a new engine has been installed, a new windshield etc., so I'd say my certified empty weight is +- 30 lbs. But I don't say it's okay to go 30 lbs over, instead I stay at least 30 lbs UNDER gross for all flight ops.
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A few years ago I had my aircraft weighed. The new basic empty
weight came in about 30lbs heavier. Since my airplane is a cherokee
140, this "increase" was significant.
 
I think everyone should have their airplane weighed when they buy (look in the belly, if it's filthy clean before weighing, I was amazed at the differences cleaning the belly scum out made) it so they have a "known" weight. I've weighed quite a few planes and there were only a couple that were even close after 10 years. Considering I've done over 100lbs of weight changing on a twin where a 5% difference in weight can mean the difference between flying out on one or sinking, I want accurate information to start with.
 
We ran some "weigh-ins" at Grumman fly-ins in the past, and found that the airplanes we weighed (on certified scales) had gained about 1 lb/year since their last weighing above the paperwork empty weight. Take a plane from the 70's, and that's 30-40 lb extra. Why? Probably a lot of little wiring additions, doublers, extra clamps, you name it -- all "negligible" for paperwork purposes (less than 1 lb), but much as the late, great Senator Everett McKinley Dirksen said about the budget, you add a little here, a little there, and after a while, you're talking about a lot.

So, those of you loading your legacy airplanes to MGW based on paperwork rather than a recent weighing are probably already more than 25 lb over MGW. You really want to add another 25 lb to such a plane? :no:
 
gprellwitz said:
I would also contend that there is a continuum of responsibility to consider. If you are the sole occupant, you may feel morally justified in taking off over gross, especilly if you're transporting something like emergency relief supplies to Haiti. On the other hand, if you're flying Angel Flight passengers who have an expectation that you're going to keep them safe, there's no wiggle room. Somewhere between those two extremes are scenarios like flying with another pilot who can understand the consequences (presuming you're frank about the situation) and flying with a friend or family member. I'd argue that the latter case is pretty close to the Angel Flight example. They're counting on you to keep them safe.

Let me also be clear that I'm talking about moral choices and obligations here, not legal or safe ones. Neither of those depend at all on what is filling up the airplane. The FAA may take it into consideration if they are doling out punishment after finding that you violated the regs, however. They seem to want to protect those who cannot protect themselves.

And yes, I've had an FBO defuel my plane after it was inadvertently overfueled on an Angel Flight. Was I confident that it would take off with the added weight? Certainly (it was a 10,000' runway in the plains in a 182 less than 10% over gross). Would I have taken off with another pilot aboard (e.g. my wife)? Probably, if she concurred.
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Don't get me wrong, I will defuel a plane and have done it numerous times over the years. I've pulled 300lbs or more of fuel out of my Baron before; not fun and definitely not something you plan to do but plans change. But at the same time you have to apply common sense and weigh the risks.

The conversation regarding being over Max Gross at a high altitude field is valid. When your departing out of high country you had better be looking not a MAX Gross but adjusted "acceptable" gross weight given the temperature, altitude and runway at your departure field. This is always a consideration in a twin because your plan for loss of engine during take off demands it. Down low I can climb away at max gross with one engine; up high I may not be able to.
 
I can't find it right now, but on here somewhere is the takeoff of the Free Bird from WV62. Well under gross (me Mrs. Steingar, and her stuff. No, even she can't pack THAT much) and we barely made it out of there. I turned down free beer because I was worried about that takeoff.

I can't imagine how it would have been over gross. If you haven't had your aircraft weighed (good idea) assume its heavy. Like Bruce said, one pound over is too much. He's a smart guy, that Dr. Bruce. You never know when you'll need to wring every ounce of performance out of that airplane.
 
Something must be up, because a 140 should not have used 3,000ft at 3,000ft.
 
azure said:
It's been 20 years since the last time my plane was weighed and lots of new avionics plus a new engine has been installed, a new windshield etc., so I'd say my certified empty weight is +- 30 lbs. But I don't say it's okay to go 30 lbs over, instead I stay at least 30 lbs UNDER gross for all flight ops.
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Here's one more factor to consider: how was the W&B measurement done? For at least one plane, the original factory procedure (shown in the maintenance manual) specified weighing the plane with fuel tanks empty. Later models of the plane were specified with a procedure of weighing the planes with full fuel and subtracting assumed fuel weight. The manuals for the original model were never updated with the newer procedure, but the factory used the new procedure if they weighed an older plane.

The planes hold about 5 gallons more than spec, so there is a 30 pound weight difference.
 
Keep in mind that the book fuel capacities in our planes are based on the absolute minimum amount of fuel they'd hold given assembly to the smallest capacity possible with every dimension at the diminsional tolerance minimum. That guarantees you at least the book usable fuel regardless of dimensional variances from the "nominal" values on the blueprints, and is the reason you may find you may be able to put more than the book usable fuel into an airplane, like the time we put 24.6 gallons into a 152 with a book usable fuel of 24.5 (and it was still running on taxi in after landing).

Thus, if you do the weighing by starting empty and then assuming "book" fuel, you could easily be over gross by the amount of fuel your tanks actually hold more than book usable fuel due to dimensional variances. Now, this isn't likely to be more than a gallon or two in a light single, but there's another item of hidden extra weight like those "negligibles" mentioned above. OTOH, if you fully fuel the plane for weighing and then subract book usable fuel to get your empty weight, you really know what your plane weighs with full fuel and nothing else in it, and you have better assurance that you'll really be below MGW if you load it to the computed max.
 
Ron Levy said:
Keep in mind that the book fuel capacities in our planes are based on the absolute minimum amount of fuel they'd hold given assembly to the smallest capacity possible with every dimension at the diminsional tolerance minimum. That guarantees you at least the book usable fuel regardless of dimensional variances from the "nominal" values on the blueprints, and is the reason you may find you may be able to put more than the book usable fuel into an airplane, like the time we put 24.6 gallons into a 152 with a book usable fuel of 24.5 (and it was still running on taxi in after landing).

Thus, if you do the weighing by starting empty and then assuming "book" fuel, you could easily be over gross by the amount of fuel your tanks actually hold more than book usable fuel due to dimensional variances. Now, this isn't likely to be more than a gallon or two in a light single, but there's another item of hidden extra weight like those "negligibles" mentioned above. OTOH, if you fully fuel the plane for weighing and then subract book usable fuel to get your empty weight, you really know what your plane weighs with full fuel and nothing else in it, and you have better assurance that you'll really be below MGW if you load it to the computed max.
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On the third hand, if you empty the tanks before weighing and then fill them, you know not only what the empty weight is, but, since you know how much fuel you just added, you also know the weight with full fuel and precisely how much fuel it will actually hold!
 
gprellwitz said:
On the third hand, if you empty the tanks before weighing and then fill them, you know not only what the empty weight is, but, since you know how much fuel you just added, you also know the weight with full fuel and precisely how much fuel it will actually hold!
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With the understanding that the weight of the fuel changes with temperature.
 
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